The Transmission of Hereditary CharacteristicsBLG–5065-2Learning Guide

THE

TRANSMISSION

OF HEREDITARY

CHARACTERISTICS BLG-5065-2

Learning Guide

The Secondary V biology learning guides

are published by SOFAD

The Human Respiratory System

The Human Reproductive System and the Perinatal Period

The Transmission of Hereditary Characteristics

The learning guides in this collection have been adapted from the online courses of the same name

which were produced first. The decision to produce both an online and a printed version of the same

course was made to meet the requirements of those who do not have access to the Internet or who

prefer to work with “paper,” in accordance with the need to diversify the tools and venues for distance

learning.

The Transmission of Hereditary Characteristics

This learning guide was produced by the Société de formation à distance des commissions scolaires

du Québec (SOFAD).

Project coordinator: Jean-François Bojanowski (SOFAD)

Pedagogical design: Jean-François Bojanowski (SOFAD)

Jean-Simon Labrecque (SOFAD)

Author: Jean-Marc Robitaille (Didactica)

Illustrations: Sylvie Leduc

Pedagogical revision: Jean-François Bojanowski (SOFAD)

Diane Ménard

Translation: Claudia de Fulviis

Linguistic Revision: Barbara Chunn

Proofreading: Valérie Champoux

Claudia de Fulviis

Graphics and Layout: Daniel Rémy

First Edition: February 2010

January 2016

© Société de formation à distance des commissions scolaires du Québec

All rights for translation and adaptation, in whole or in part, reserved for all countries. Any reproduction

by mechanical or electronic means, including micro-reproduction, is forbidden without the written

permission of a duly authorized representative of the Société de formation à distance des commissions

scolaires du Québec (SOFAD).

Legal Deposit - 2010

Bibliothèque et Archives nationales du Québec

Library and Archives Canada

ISBN 978-2-89493-380-0

V© SOFAD

Table of Contents

General Introduction .................................................................................................... VII

The Biology Program ............................................................................................ VII

Using the Learning Guide ..................................................................................... VII

Evaluation ........................................................................................................ IX

Succeeding at Distance Learning .......................................................................... IX

The Transmission of Hereditary Characteristics .................................................... X

Reader’s Comments ............................................................................................. XI

Section 1 – The Mechanisms of Heredity ...................................................................... 1.0

Module 1 – Cell Basics .......................................................................................... 1.1

◆ The Cell ................................................................................................. 1.4

◆ Genes .................................................................................................... 1.16

Module 2 – Cell Division ....................................................................................... 2.1

◆ Mitosis ................................................................................................... 2.4

◆ Meiosis .................................................................................................. 2.13

Section 2 – The Laws of Heredity .................................................................................. 3.0

Module 3 – Mendel’s Experiments ........................................................................ 3.1

◆ Basic Concepts ....................................................................................... 3.4

◆ Mendel’s Laws ........................................................................................ 3.17

Module 4 – Crossbreeding .................................................................................... 4.1

◆ Monohybrid Crosses ............................................................................ 4.4

◆ Dihybrid Crosses .................................................................................... 4.19

Section 3 – Health Problems Related to Heredity ......................................................... 5.0

Module 5 – The Heredity of Blood Types ............................................................. 5.1

◆ The Antigens and Antibodies Specific to Blood Types ............................. 5.4

◆ The Transmission of Alleles Responsible for Blood Types ....................... 5.19

Module 6 – Sex Chromosomes, Mutations and Hereditary Diseases ....................... 6.1

◆ The Transmission of Sex-linked Genes ................................................... 6.4

◆ Mutations and Hereditary Diseases in Humans ....................................... 6.17

VI © SOFAD

Unit Summaries ........................................................................................................... 7.1

Module 1 – The Cell ............................................................................................. 7.3

Genes ................................................................................................ 7.4

Module 2 – Mitosis .............................................................................................. 7.5

Meiosis .............................................................................................. 7.6

Module 3 – Basic Concepts .................................................................................. 7.8

Mendel’s Laws ................................................................................... 7.9

Module 4 – Monohybrid Crosses ......................................................................... 7.11

Dihybrid Crosses ............................................................................... 7.12

Module 5 – The Antigens and Antibodies Specific to Blood Types ....................... 7.13

The Transmission of Alleles Responsible for Blood Types .................. 7.15

Module 6 – The Transmission of Sex-linked Genes ............................................... 7.16

Mutations and Hereditary Diseases in Humans .................................. 7.17

General Conclusion ............................................................................................................ 8.1

Self-evaluation Activity ...................................................................................................... 9.1

Answer Key ........................................................................................................................ 10.1

Glossary ............................................................................................................................. 11.1

VII© SOFAD

Introduction

General Introduction

◆ The Biology Program

The Société de formation à distance des commissions scolaires du Québec (SOFAD) welcomes you to

the course entitled The Transmission of Hereditary Characteristics. This course is part of the Secondary

V Biology Program for basic adult general education, which is composed of the following nine courses:

BLG-5061-1 The Human Respiratory System

BLG-5062-2 The Human Reproductive System and the Perinatal Period

BLG-5063-2 The Human Digestive System

BLG-5064-2 The Anatomy and Physiology of Cells

BLG-5065-2 The Transmission of Hereditary Characteristics

BLG-5066-1 The Human Skeletal and Muscular System

BLG-5067-1 The Human Endocrine System

BLG-5068-2 The Human Nervous System

BLG-5069-1 Ecology

Students who complete this 50-hour course can earn two Secondary V credits provided they pass

a supervised examination administered by a Québec school board. There are no prerequisites for

the courses in this program, and there is no equivalent program in the youth sector. The course’s

general objective is as follows: “By learning concepts of anatomy and physiology, adults will gain a

better understanding of the transmission of human hereditary characteristics, and the health problems

associated with it.”

◆ Using the Learning Guide

This learning guide is the main work tool for this course and has been designed to meet the

specific needs of adult students enrolled in an individualized learning or a distance learning

program. Furthermore, a webography can be viewed at the following internet address:

http://cours1.sofad.qc.ca/ressources/fichiers/BLG_5065_webography.html

The contents of this guide are divided into three main sections, which in turn are subdivided into

modules, which are again subdivided into units. In each unit, the subject matter is presented in a

number of ways (e.g. text, tables, illustrations, exercises) in order to facilitate mastery of the program

objectives. In addition, at the end of each unit, just before the conclusion, you will be required to do

a review activity in which all the main illustrations are shown in colour. By doing these exercises, you

will be building an excellent summary of the entire course. Lastly, at the end of this guide you will

find a conclusion, a self-evaluation activity and the corresponding answer key as well as an answer

key for the exercises in the modules and a glossary.

VIII © SOFAD

Introduction

Learning Activities

This guide includes theoretical sections as well as practical activities in the form of exercises. These

exercises come with an answer key. Start by skimming through each part of this guide to familiarize

yourself with the content and the main headings. Then read the theory carefully:

◆ Highlight the important points.

◆ Make notes in the margins.

◆ Look up new words in the dictionary.

◆ Study the diagrams carefully.

◆ Write down questions relating to ideas you don’t understand.

Exercises

The exercises come with an answer key found at the end of this guide.

◆ Do all the exercises and, at the end of each modules, quizzes.

◆ Read the instructions and questions carefully before writing your answer.

◆ Do all the exercises to the best of your ability without looking at the answer key. Reread the

questions and your answers and revise your answers, if necessary. Then, check your answers

against the answer key and try to understand any mistakes you made.

◆ Complete a module before doing the corresponding review exercises. Doing these exercises

without referring to the lesson you have just completed is a better way to prepare for the final

examination.

Self-evaluation Activity

The purpose of the self-evaluation activity is to help you prepare for the final examination. Before

you tackle the self-evaluation activity, reread your notes to ensure you have covered all the material

pertaining to the learning objectives cited at the beginning of each module. Make sure you understand

the learning objectives. Then do the self-evaluation activity without referring to the main body of the

guide or the summaries. Compare your answers with those in the answer key and review any areas

you had difficulty with.

Materials

Have all the materials you need close at hand.

◆ Learning materials: this guide and a notebook in which you will summarize important concepts

relating to the learning objectives for each module.

◆ Reference materials: a dictionary.

◆ Miscellaneous materials: a calculator, a pencil for writing your answers and your notes in this

guide, a coloured pen for correcting your answers, a highlighter (or a pale-coloured felt marker)

to highlight important ideas, a ruler, an eraser, etc.

IX© SOFAD

Introduction

◆ Evaluation

In order to earn the two credits for this course and towards your Secondary School Diploma, you must

score at least 60% on a supervised examination dealing with the learning objectives outlined in this

guide and administered in an adult education centre. The two-hour written examination counts for

100% of the final course mark. The examination will consist of multiple-choice questions and short-

answer questions.

◆ Succeeding at Distance Learning

Work Pace

A few tips for organizing your time are given below:

◆ Set up a study schedule that takes into account your availability, your needs and your family and

work obligations.

◆ Try to devote a few hours a week to the course, preferably in blocks of two hours.

◆ As much as possible, stick to the schedule you have established.

Your Tutor

Your instructor is the person who will give you any help you need throughout this course. He or she is

available to answer your questions and correct and comment on your assignments. Don’t hesitate to contact

your instructor if you are having difficulty with the theory or the exercises, or if you need some words of

encouragement to help you get through this course. Information about how to contact your instructor

that is not already contained in this guide will be made available to you. Write out your questions and

get in touch with your instructor during his or her available hours. If necessary, write to him or her. Your

instructor will guide you in your work and provide you with the advice, constructive criticism and support

that will help you succeed in this course.

Homework Assignments

This guide is sold with three homework assignments designed solely for distance learning students.

The homework assignments are to be completed at the end of each of the three sections that make up

this guide. These assignments will show your tutor whether you understand the subject matter and are

ready to go on to the next part of the course. If your tutor feels you are not ready to move on, he or she

will indicate this on your homework assignments, providing comments and suggestions to help you get

back on track. It is important that you read these corrections and comments carefully. Do your homework

assignments without referring to the learning guide and take note of your tutor’s corrections so that you

can make any necessary adjustments. This is also an excellent way to prepare for the final examination.

Remember not to send in the next assignment until you have received the corrections for the previous

one.

X © SOFAD

Introduction

◆ The Transmission of Hereditary Characteristics

What do blond, black or brown hair, curly hair, eye colour, and the shape of the nose and ears have in

common? They are all characteristics, or traits, that are transmitted from one generation to the next.

While leafing through family photo albums, people often comment on the resemblances they see—or

don’t see—between parents and their children: “Sylvia has blond hair, yet both her mom and dad have

jet black hair!”

Although resemblances among family members have been noticed since the beginning of time, it was

the work of Gregor Mendel (1822-1884) that provided the first real insight into heredity, that is, the

transmission of biological information, or family traits, from parents to offspring. While all children

resemble their parents, in no way are they a carbon copy.

Over time, the study of heredity and the expression of hereditary characteristics in individuals gave

rise to the science of genetics.

Biology Course BLG 5065-2, The Transmission of Hereditary Characteristics, will enable you to expand

your knowledge of such topics as the mechanisms of heredity, cross-breeding, the genetics of blood

types, sex chromosomes, hereditary diseases, and the causes and effects of certain mutations.

Course Outline

General Introduction

Section 1 – The Mechanisms of Heredity

Module 1

Cell Basics

Module 2

Cell Division

Assignment 1

Section 2 – The Laws of Heredity

Module 3

Mendel’s Experiments

Module 4

Crossbreeding

Assignment 2

Section 3 – Health Problems Related to Heredity

Module 5

The Heredity of Blood Types

Module 6

Sex Chromosomes, Mutations and Hereditary Diseases

Assignment 3

General Conclusion

Self-evaluation Activity ✁

◆ Reader’s Comments

The Transmission of Hereditary Characteristics (February 2010)

SOFAD is committed to providing course materials adapted to your needs, and we value your opinion.

Please write your comments, questions or suggestions on this sheet, or contact us by phone, fax or

email. If you find any errors, ambiguities, typographical errors, etc., we would appreciate hearing

from you.

Thank you for giving us your feedback.

Alain Pednault

Project Coordinator, Sciences and Technology

Tel.: (514) 529-2193 2200, rue Sainte-Catherine Est

Fax: (514) 529-2190 Montréal (Québec) H2K 2J1

Email: pednaulta@sofad.qc.ca

Comments:

From: _________________________________________________________________________________________________________________

School Board: ______________________________________________________________________________________________________

Student: ❑ Tutor: ❑

Other: ❑ Specify: ______________________________________________________________________________________________✁

© SOFAD

Section 1

The Mechanisms of Heredity

At the end of the 19th century, Mendel conducted

conclusive experiments on the transmission of

hereditary characteristics. It was not until the

20th century, however, that understanding

of the mechanisms of heredity was

possible thanks to knowledge acquired

about cells, chromosomes and genes.

By the end of this section, you will be

able to explain the mechanisms of

heredity.

This section is divided into two modules.

The first, entitled Cell Basics, deals with the

cell, the nucleus, chromosomes, genes and

the structure of cellular proteins.

The second, entitled Cell Division, explains how genetic

material is transmitted from one cell to another during the formation and growth of sex

cells, which are essential for reproduction.

At the end of

conclusiv

hered

20t

of

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T

The

cell,

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© SOFAD

1.1© SOFAD

Module 1

CELL

BASICS

u Food for Thought

Can we select specific traits for our offspring through genetic

manipulation? Can genes be transferred from one species to

another species? If your parents could have chosen specific

traits for you, do you think your life would be any different?

What is the basis of heredity for living beings?

Start pondering these questions now, as you will be asked

to state your views at the end of this section.

The Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 .4

Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 .16

1.2 © SOFAD

Module 1 – Cell Basics

u What I Already Know

In the 21st century, basic knowledge about the transmission of hereditary characteristics is part

of general culture in industrialized countries. This knowledge allows us to understand critical

discoveries that influence our beliefs, our social values and our health.

The purpose of this exercise is to help you determine what you already know, and identify topics

with which you are less familiar. You will come back to it at the end of the module. This will allow

you to assess your progress. Answer the following questions in your own words, using one or two

sentences. Write what you know.

1. What is responsible for the transmission of hereditary characteristics?

2. Is it heredity or the environment that shapes how an organism will develop?

3. Can you give an example of one type of human cell?

4. Why has it become so important to collect DNA samples at crime scenes?

1.3© SOFAD

Lead-in

u Objectives of the Module

After completing this module, you will be familiar with the biological basis for heredity, thanks to

the activities you will be working through in the following two units: The Cell and Genes.

More specifically, you will be able to:

u associate the cell nucleus, chromosomes and DNA with the transmission of hereditary

characteristics;

u describe the structure of a chromosome and a gene.

1.4 © SOFAD

Module 1 – Cell Basics

The Cell

u Introduction

All living beings are composed of cells. Each type of cell plays a specific role. For example, the human

body uses muscle cells for movement, white blood cells to fight off microbes, and nerve cells to control

its vital functions.

There are approximately 200 types of cells in the human body. Cells behave in the same manner as the

body as a whole; they need food to survive, they transform food into cellular structures, they develop

and communicate with one another, and they also reproduce and die. The muscle fibre, white blood

cell and brain neuron shown below are three types of cells found in the human body.

All of these activities are carried out according to a blueprint that is passed on from one generation

to the next.

In this unit, we will examine the overall structure of a cell and cell nucleus. We will also describe what

role the nucleus plays in the transmission of hereditary characteristics.

You will learn about the components of a cell, about chromosomes and about the structure of DNA.

1.5© SOFAD

The Cell

Epidermis

u The Organization of Living Organisms

Living organisms vary in their complexity. The most complex organisms have systems of organs made

of different types of tissue adapted to their specific functions. Identify the various tissues found in

different parts of the human body.

A- Cartilage

B- Epidermis

C- Muscle tissue

D- Blood

E- Nervous tissue

A- Cartilage is a flexible tissue and less rigid than bone. Like bone, cartilage contains very few cells.

The ear and the nose are good examples of cartilage. Cartilage forms the “disks” between the

vertebrae and plays a protective role in joints such as the knee.

B- The epidermis is the outermost layer of the skin. Epidermal cells are under constant “assault”

from the environment, but rapid renewal of the epidermis compensates for the loss of cells on

the skin’s surface.

C- Muscle tissue is composed of elongated cells called fibers. Their elongated shape makes it easier

for them to contract in response to a nerve impulse.

D- Blood is about 55% liquid (plasma) and 45% blood cells. The majority of cells are red blood cells

(containing hemoglobin), which carry oxygen. Blood also contains white blood cells, which

provide protection against microbes.

E- Nervous tissue is composed mainly of neurons, or nerve cells. The long, slender projections of

nerve cells are called axons. Many axons make up a nerve.

D

C

A

BE

1.6 © SOFAD

Module 1 – Cell Basics

Quick Check

1.1 Which of the following is a tissue.

q blood q the brain

q the knee q the liver

1.2 Which of the following is an organ?

q a red blood cell q a muscle fiber

q a stomach

Validate with the answer key.

Recap

In the beginning, there is only one cell. This cell divides and the thousands of cells that are produced

specialize and form different types of tissue. Organs are made of different types of tissue adapted to

their specific functions. Organs are grouped into systems that allow the organism to adapt efficiently

to its environment.

u The Components of a Cell

Every living organism is composed of cells. Each cell has several components that perform different

functions and ensure the cell’s survival. Identify the essential components of a cell and discover their

functions.

A- Cell membrane

B- Cytoplasm

C- Nucleus

D- Mitochondria

E- Ribosomes

F- Endoplasmic reticulum

G- Golgi complex

H- Centrosome

A- The semi-permeable cell membrane (also called the plasma membrane) controls the concentration

of nutrients and waste in the cytoplasm.

C

A

B

F

G

H

E

E

D

D

1.7© SOFAD

The Cell

B- The cytoplasm is essentially a thick liquid substance. It contains specialized structures, called

organelles*, that perform different functions enabling the cell to carry out vital life processes.

C- The nucleus contains most of the cell’s genome. The nucleus is referred to as the control centre

of the cell because it controls all of its activities.

D- The number of these organelles in a cell depends on what the cell needs to do. They are the

powerhouses of the cell in that they use the oxygen provided by blood circulation to create cell

energy.

E- These cellular structures are the protein builders of the cell. Proteins are the cell’s tools and are

synthesized using information contained in the genetic code.

F- A network of canals that runs through the entire cytoplasm. Proteins synthesized by ribosomes

enter the endoplasmic reticulum.

G- Proteins synthesized by the cell reach the Golgi complex through the endoplasmic reticulum.

There, they are processed, stored or sent to the required destination in order to play a specific

role.

H- Centrosomes are regions of the cell that produce the microtubules enabling chromosomes to

move to opposite ends of the nucleus during cell division.

Quick Check

1.3 To which person in a large company would you compare the cell nucleus?

q the lawyer q the big boss

q the accountant q the maintenance manager

1.4 Which of the following cell structures is involved in cell division?

q centrosome q cell membrane

q cytoplasm

Validate with the answer key.

Recap

The cell nucleus contains the genetic material responsible for the synthesis and operation of all

cell structures.

The human body has several million cells, each containing within its nucleus all the genetic

information needed to build and support the functions of the entire organism.

A single cell is all that is needed to make a completely new you!

* Words appearing in small caps are defined in the glossary at the end of this guide.

1.8 © SOFAD

Module 1 – Cell Basics

u The Cell Nucleus

The nucleus houses the cell’s genetic material. Let us examine what form this genetic material takes

in the nucleus.

Chromatin (in the nucleus)

Cell membrane

DNA

Nucleosome (bead)

Nuclear envelope

The genetic material consists of molecules of DNA packaged as chromatin or chromosomes,

depending on whether the cell is growing or in the process of dividing.

Chromatin has a “beads on a string” appearance. The beads (nucleosomes) consisting of deoxyribonucleic

acid (DNA) and proteins (histones) form a core around which the DNA molecule coils.

Early in the process of cell division, the chromatin coils, supercoils and becomes more and more

compact. This material undergoes a process of segmentation giving rise to chromosomes. Once the

cell has divided, the chromosomes decondense to become chromatin strands again.

1.9© SOFAD

The Cell

u Chromosomes

Genetic material is generally described as being carried on chromosomes. We will now examine the

structure of chromosomes.

Chromosomes become visible in the nucleus during cell division. In the illustration below, the

chromosome is composed of two strands, called chromatids. Chromatids are composed of identical

DNA and are joined in the centromere.

When the mother cell divides, each of the two daughter cells that are produced receives one of the

two identical chromatids making up each chromosome.

1.10 © SOFAD

Module 1 – Cell Basics

C G

A T

C G

A T

G C

T A

Chemical bonds

C G

A T

A T

G C

T A

u DNA Structure

The DNA molecule has a specific structure that allows it to store and transmit genetic information. It

resembles a ladder whose rungs are joined like a zipper. Identify the components of DNA.

A- Analog model

B- Schematic model

C- Simplified model

A- DNA has a spiral staircase-like structure. The sides of the ladder are composed of hundreds of

small blocks called nucleotides. The two sides are joined together like the teeth of a zipper, with

the teeth representing the four nitrogenous bases. Each nucleotide is composed of one of the

following nitrogenous bases: adenine (A), thymine (T), guanine (G), cytosine (C).

B- This model of the same molecule shows two chains of nucleotides, composed of a nitrogenous base

(A, T, G, C), a sugar (in red) and a phosphate (in green). The illustration shows how nucleotides

containing nitrogenous bases join the two open chains. The shapes of the nitrogenous bases are

complementary. Adenine can bind only with thymine (A-T) and guanine can bind only with cytosine

(G-C).

C- The simplified model shows a ladder whose rungs are formed of either an A-T pair or a G-C pair.

The sides represent the two nucleotide chains.

B

C

A

1.11© SOFAD

The Cell

Quick Check

1.5 In a DNA molecule, what joins the two sides of the ladder?

q nitrogenous bases q genes

q nucleotides q proteins

1.6 What encodes genetic information?

q the A-T and G-C pairs q the nucleotides facing each other

q the order in which the nitrogenous bases are arranged on a chain

Validate with the answer key.

Recap

The DNA molecule consists of two chains of nucleotides. Genetic information is determined by

the properties of one of the three components of a nucleotide: the nitrogenous base. There are

four nitrogenous bases: adenine, thymine, guanine, cytosine.

The order in which the nitrogenous bases are arranged encodes genetic information.

u Did You Know?

Human cells contain 46 chromosomes (23 pairs). If the

DNA from all 46 chromosomes that make up the human

genome were laid out end to end, it would stretch about

two metres, or more than six feet!

The number of chromosomes varies between species.

Fruit flies have only 4 pairs of chromosomes, horses

have 32 pairs, and dogs, 39 pairs!

2 meters

1.12 © SOFAD

Module 1 – Cell Basics

C

T

A

G

A

C

C

G

C

A

A

G

u Complementary Bases

Nitrogenous bases follow base-pairing rules. Correctly match the four nitrogenous bases below.

A- Adenine forms a complementary base pair with thymine.

G- Guanine forms a complementary base pair with cytosine.

C- Cytosine forms a complementary base pair with guanine.

T- Thymine forms a complementary base pair with adenine.

Recap

On complementary DNA strands, adenine is always paired with thymine and guanine is always

paired with cytosine.

Adenine also pairs with another nitrogenous base called uracil. In RNA, or ribonucleic acid, uracil

(instead of thymine) pairs with adenine.

Validate with the answer key.

A

G

C

T

1.13© SOFAD

The Cell

u Did You Know?

The human genome is composed of 3.2 billion base pairs. The sequence of nitrogenous bases (adenine,

thymine, guanine and cytosine) that make up the long nucleotide chains of our DNA allows for all the

variations contained in tens of thousands of genes.

Imagine the genome is a book. The information it contains would be equivalent to that in about 1000

telephone books.

As impressive as it is, the human genome is small compared with that of an organism called Amoeba

dubia. This unicellular organism has a genome containing a record 670 billion base pairs!

That is at least 200 times larger than the human genome.

1.14 © SOFAD

Module 1 – Cell Basics

u The Cell and Its Nucleus

The cell, the nucleus and the chromosomes are the basic building blocks of life. Review some related

terminology by completing the following crossword puzzle.

1 C

H

2 C R

O

M

3 A

4 C T

I

5 E N

1- Segments of condensed, tightly folded and coiled chromatin.

2- The constricted region joining the two sister chromatids that make up an X-shaped, or double,

chromosome.

3- It is part of a DNA nucleotide and pairs with thymine.

4- Each chromosome contains two, identical ones. During DNA replication, one of them serves as a

model for the other.

5- It surrounds the nucleus and controls the exchange of substances between the nucleus and the

cytoplasm.

Recap

At the beginning of the 20th century, research on the cell and the nucleus advanced by leaps and

bounds. During the 1950s, the discovery of DNA in the cell nucleus paved the way for achieving

understanding of where genetic information is stored and how this information is passed from

one cell to its progeny during the growth of an organism.

Validate with the answer key.

1.15© SOFAD

The Cell

u Conclusion

The column headings in the following table are related to topics covered in this unit. Fill in the blank

spaces with the appropriate terms from the list to the right of the table.

CHROMOSOME CELL DNA

Validate with the answer key.

Recap

The cell is the basic unit of life. The human body has 200 different types of specialized cells

that make up the tissues of the various organs. The DNA in the nucleus of each cell makes up

the genome of the organism. The human genome consists of 23 pairs of chromosomes: each

chromosome consists of a DNA molecule composed of roughly 200 million pairs of nucleotides.

This genetic information ensures that hereditary characteristics are preserved and passed on.

End of unitBefore you continue, go to the “Unit Summaries” section

and complete the corresponding review activity .

Centromere

Chromatid

Ribosomes

Nucleotides

AT and GC

Nucleus

1.16 © SOFAD

Module 1 – Cell Basics

Genes

u Introduction

C G

A T

A T

G C

T A

Gene foriris colour

The DNA in the cell nucleus makes up the genetic material (i.e., genome) of all living organisms.

Hereditary characteristics, or traits, are encoded in nucleotide sequences hundreds of base pairs long.

These DNA sequences are genes.

Cells of various types carry out different functions. The cell carries out two vital tasks: it copies its

genes so that a set can be passed on to each daughter cell during cell division and it uses its genes

to synthesize proteins that are involved in the expression of hereditary traits.

In this unit, we will examine the mechanism of DNA replication in the nucleus and the mechanisms

by which the information carried by a gene is expressed.

1.17© SOFAD

Genes

u Genes

A chromosome carries thousands of genes, each of which contains a specific sequence of nucleotide

base pairs. Now we will look at the differences and similarities between genes.

A portion of gene 1 = A-C-C-G-C-A-A-G-C-A-T-G

A portion of gene 2 = A-C-C-G-C-A-A-G-C-A-T-G

A portion of gene 3 = G-G-A-G-A-A-A-G-C-C-T-T

A portion of gene 4 = G-G-A-G-A-A-A-G-C-C-T-T

A

C

C

G

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1.18 © SOFAD

Module 1 – Cell Basics

Quick Check

1.7 Why are genes 1 and 2 and genes 3 and 4 identical?

q the sister chromatids from the same chromosome come from a single parent

q the cell copied one of the chromatids from the other

q both parents passed on the same genes

1.8 Would replacing one nitrogenous base by a different base on a gene have an effect?

q such a subtle change would have no effect

q changing a single base modifies the information and so has an effect

q changing three nitrogenous bases would have an effect

1.9 Which of the following three statements do you agree with?

q each sister chromatid from the same chromosome carries its own genes

q each sister chromatid from the same chromosome carries half the genes contained in

a chromosome

q each sister chromatid from the same chromosome carries the same genes in the same

order

Validate with the answer key.

Recap

The specific order in which nucleotide base pairs are arranged encodes genetic information. A

gene is an ordered sequence of nucleotides that encodes the information needed to synthesize

a specific protein and express a particular hereditary trait. Some genes do not carry hereditary

information; they act as switches by turning gene expression on or off.

u Alleles

Humans have 23 pairs of chromosomes. One chromosome in each pair is contributed by the father

and one by the mother. For any given trait, there are two sources of information: the gene passed

on by the mother and the gene passed on by the father. These genes are the two alleles that control

specific traits, for example, eye or hair colour.

For each hereditary trait, one allele is paternally derived and the other is maternally derived.

1.19© SOFAD

Genes

u Copying a Gene

With a few exceptions, every cell in your body contains a

complete copy of your genome, or roughly 30 000 genes.

A cell generally uses only the genes it needs to function

and deactivates the rest.

In the next 60 seconds, your body will produce enough

new DNA that, if linked together, it would stretch 100 000

km, or the average distance a car travels in five years.

The cell must have the ability to keep genetic information

intact, for its own benefit and for that of its progeny. The

genes in a cell must be copied in order to preserve and

transmit information from one cell to another.

u DNA Replication

Before a cell can divide it must first make a copy of its DNA. In each box below, write the uppercase

letter representing the base that pairs with the nitrogenous base indicated.

A C C G C A A G C A T G

A C C G C A A G C A T G

Validate with the answer key.

In DNA replication, new strands of DNA are copied through complementary base pairing. This dynamic

process requires the action of proteins called enzymes. These are the cell’s tools.

1.20 © SOFAD

Module 1 – Cell Basics

u Find Out More - DNA Replication

DNA replication by complementary pairing of

nitrogenous bases is the mechanism whereby

a new DNA strand is constructed from one of

the two chains of the original DNA sequence.

This process requires the help of proteins

called enzymes. Click on the following link

to watch an animation of DNA replication:

http://cours1.sofad.qc.ca/ressources/fichiers/

BLG_5065_webography.html

u From Genes to Hereditary Characteristics

In general, it is easy to distinguish individuals by their facial features, or physiognomy. Physiognomy is the

outward expression of each person’s

specific genome, which is found in

the cell nucleus. A photograph of an

individual’s genome is equivalent to

a photograph of his or her face.

A hereditary characteristic can be

observed only at the level of tissues

or organs, but genes express

themselves only at the cellular level.

How is a gene expressed at the

cellular level?

Gene expression occurs through

the synthesis of different proteins.

Each protein within the body has a

specific function. Some proteins

serve as construction materials

(structural proteins), while others

act as catalysts (enzymes). Hormones

and antibodies are also proteins.

The human body needs 20 amino

acids to synthesize the thousands of proteins it uses.

amylase in the saliva breaks down sugar like starch in bread

renin controls blood pressure

the main component of hair fibre is keratin

myosin is responsible for contraction

hemoglobin carries oxygen

Red blood cells

Salivary glands Hair

Kidneys

Muscles

CCTT

AA

GG CC

AA TT

CC GG

GG

This material is not covered in the course.

1.21© SOFAD

Genes

u Find Out More - Protein Construction

DNA strand

A C C C G A A G C A T G

U G G G C U U C G U A C

Transcription

Translation

Amino acids

Genons

Codons

mRNA

Protein

DNA molecule

Tryptophan Arginine Serine Tyrosine

How do cells go about building proteins?

Proteins are synthesized on the ribosomes found in the cell cytoplasm.

1. DNA carries genetic information on segments called genes and is enclosed in the cell nucleus.

2. The cell transcribes, or transfers, the genetic information to a strand of messenger RNA (mRNA).

This process is called transcription. The mRNA carries the genetic information out of the nucleus

to the ribosomes.

3. The amino acids encoded in the mRNA are transported to the ribosomes. Transfer RNA, or tRNA

(not shown), are molecules that bind to and carry specific amino acids, of which there are 20, to

the ribosomes and places them opposite a mRNA codon.

4. The amino acids must be assembled in the order determined by the mRNA. Each tRNA molecule

carries an anticodon that is complentary to a specific codon of mRNA on the ribosome. When a

given codon and anticodon pair up, the ribosome removes the amino acid from the tRNA. This

process is called translation.

A protein can consist of between 100 and 300 amino acids.

Visit http://cours1.sofad.qc.ca/ressources/fichiers/BLG_5065_webography.html to see an animation

of cell protein construction.

This material is not covered in the course.

1.22 © SOFAD

Module 1 – Cell Basics

u DNA, Genes, Alleles and Chromosomes

The four terms in the table below are related. Match each description in the right-hand column with

the corresponding term in the left-hand column by drawing a line between them.

Validate with the answer key.

Recap

Each chromosome is composed of DNA, specific segments of which serve to synthesize cell proteins.

These segments of DNA are genes. Genes can either carry or control inherited characteristics. In

living organisms that reproduce sexually, like humans, chromosomes exist in pairs. Each inherited

characteristic, such as eye colour, is determined by two variants of a specific gene, one from the

father’s chromosome and the other from the mother’s chromosome. Thus, a pair of chromosomes

contains a paternal allele and a maternal allele, the two versions of the gene that controls a given

hereditary trait.

A giant molecule composed of two chains of nucleotides.

There are four different nucleotides, each of which has a different nitrogenous base.

GENE

A sequence of DNA nucleotides that occupies a

specific site on a chromosome. This sequence serves as a

template for the synthesis of a specific protein.

ALLELE

Made up of DNA and histone proteins, it carries several

genes.

DNA

One of two alternative forms of a gene (one from the father

and one from the mother) specifying an inherited

characteristic.

CHROMOSOME

1.23© SOFAD

Genes

3

1

u Did You Know?

We have more in common with other

living beings than we could ever imagine!

In their genome, individuals have traces of

ancient genes stemming from the beginning

of time that they share with every living organism.

What do you have in common with a

MONKEY or a MOUSE? Find out more at:

http://cours1.sofad.qc.ca/ressources/fichiers/

BLG_5065_webography.html

u Example: Chromosome 7

Several genes located on human chromosomes have been mapped. Identify some of the genes on

chromosome 7.

1- NUMBER OF GENES

2- GENES AND DISEASES

3- GENE FOR COLOUR BLINDNESS

1- Genes occupy specific spots, or loci, on a chromosome. To date, 1443 genes have been identified

on chromosome 7.

2- Although genes work together in complex ways to keep our bodies functioning properly, some

alleles have defects that can result in disease. Several genes on chromosome 7 predispose to

disease. Osteoporosis and colon cancer are two examples.

3- Many colour blind people have a defective perception of red and green. This deficiency is caused

by an abnormality in the structure of the retina. The gene that codes for blue pigment is located

on chromosome 7. The other two genes involved in colour blindness, those coding for red and

green pigments, are located on the X chromosome.

2

Colon cancer

Osteoporosis

1443 genes

Colour blindness

1.24 © SOFAD

Module 1 – Cell Basics

u A Silk Goat!

What is a GMO? A genetically modified organism (GMO) is a

plant, animal or microorganism whose genetic code has been

altered in order to give it characteristics that it does not have

naturally.

Scientists can now transfer genes between species

that otherwise would be incapable of mating, for

example, a goat and a spider. Find out more at:

http://cours1.sofad.qc.ca/ressources/fichiers/BLG_5065_

webography.html

u DNA and Genes

Genes are located on chromosomes. What concepts are used to define a gene and its role in the

transmission of inherited characteristics? Review these concepts by completing the following crossword

puzzle.

1 C

H

2 P R

O

M

O

3 A S

O

M

4 G E

5 G S

1- A function of genes that are not carriers of hereditary characteristics.

2- Each carrier gene expresses itself by synthesizing these.

3- A pair of genes that determine the same characteristic and that are provided by each parent.

4- Each chromosome contains hundreds of these.

5- Small segments of a DNA molecule that express hereditary characteristics.

Validate with the answer key.

1.25© SOFAD

Genes

Recap

Cell activities are regulated by the expression of the genes located on the chromosomes, i.e., the

alleles received from both parents. Genes express themselves by synthesizing proteins on the

cell’s ribosomes. Not all genes are carriers of inherited characteristics; some control cell activities.

Depending on its needs, the cell can switch genes on or off.

u Conclusion

The column headings in the following table are related to topics covered in this unit. Fill in the blank

spaces with the appropriate terms from the list to the right of the table.

GENE CHROMOSOME PROTEINS

Validate with the answer key.

Recap

Cells carry out two vital tasks related to genes. First, they accurately copy the genes prior to cell

division. Second, they translate the information encoded in the genes by making thousands of

proteins.

End of unitBefore you continue, go to the “Unit Summaries” section

and complete the corresponding review activity .

Chromatids

Insulin

Sequence of nucleotides

Alleles

Centromere

Amino acid

1.26 © SOFAD

Module 1 – Cell Basics

u What I Know Now

At the beginning of this module, you answered four questions about the learning content of each

of the two units to the best of your knowledge. Here are the same questions. Answer them again,

then compare your answers to your previous ones.

1. What is responsible for the transmission of hereditary characteristics?

2. Is it heredity or the environment that determines how an organism will develop?

3. Can you give an example of one type of human cell?

4. Why has it become so important to collect DNA samples at crime scenes?

1.27© SOFAD

Wrap-up

u Share Your Opinion

Given what you have learned about the cell and genes, you should now be able to understand the

social issues related to genetically modified organisms.

If it were possible to alter the human genome, would you want to select hereditary characteristics

that could be passed on to your children?

q Yes q No q I don’t know

Recap

More and more people are turning to plastic surgery (e.g., facelifts), a wide range of medications,

hormones and nutritional supplements to enhance their appearance or their performance, or to

simply improve their quality of life. Now that researchers have identified the location of certain

defective genes on human chromosomes, work is under way on approaches for inserting new,

functional genes or for repairing defective ones. This is called gene therapy. Although the

technology is still in its infancy, it holds considerable promise.

u Quiz

1. Living organisms vary in their complexity. The most complex are composed of systems of

organs consisting of different types of tissue adapted to the function of each organ. Which of

the following is a type of tissue?

A. cartilage

B. the liver

C. the knee

D. the brain

2. What am I? In the cell, I contain specialized structures called organelles, which carry out the

various tasks that ensure proper functioning of the cell.

A. the nucleus

B. mitochondria

C. cytoplasm

D. a ribosome

3. What am I? In the cell, I serve as the assembly site for cellular proteins, which are synthesized

from the information in the genome.

A. the endoplasmic reticulum

B. the Golgi complex

C. a ribosome

D. the centrosome

1.28 © SOFAD

Module 1 – Cell Basics

4. The genome is contained in the cell nucleus. The form in which the genome exists in the cell

can be described in different ways. Which of the following statements is true?

A. Chromatin is composed of chromatids.

B. A chromosome is composed of one chromatid and two centromeres.

C. A chromatid is composed of 46 strands of chromatin.

D. A chromosome consists of a DNA molecule and proteins called histones.

5. DNA and the cell. Which of the following statements is false?

A. DNA is contained in the nucleus and cannot leave it.

B. Only chromosomes (not chromatin), once formed, are made up of DNA.

C. There are 46 DNA molecules in a cell.

D. DNA consists of two chains of nucleotides.

6. How is a gene represented in a cell?

A. by each DNA base pair

B. by a nitrogenous base pair, A-T or G-C

C. by a sequence of DNA base pairs

D. by a group of three base pairs out of four

7. How is a gene expressed in a cell?

A. by protein synthesis

B. by the synthesis of alleles

C. by DNA replication

D. by the transformation of chromatin into a chromosome

8. What roles do genes play?

A. They transform chromatin into chromosomes.

B. They carry genetic information or control the activity of other genes.

C. They form the ribosomes.

D. They join the chromatids together.

9. Which of the following statements is true?

A. A chromosome contains hundreds of different genes.

B. A hereditary characteristic is determined by an allele from one parent.

C. The cell nucleus contains only the DNA necessary for the activities of a single cell.

D. It is impossible to add genes to or to alter the genome of a living being.

1.29© SOFAD

Wrap-up

10. All living organisms are composed of cells. How many types of cells are there in the human

body?

A. The human body has only one type of cells: human cells.

B. There are 200 types of cells grouped into tissues.

C. There are 2000 types of cells grouped into different organs.

D. Each organ in the human body has its own type of cells.

Validate with the answer key.