DNA & CHROMOSOMES

Mrs. StewartHonors BiologyCentral Magnet

School

Standards

• CLE 3210.4.1 Investigate how genetic information is encoded in nucleic acids.

• CLE 3210.4.2 Describe the relationships among genes, chromosomes, proteins, and hereditary traits.

Objectives

• Evaluate the structure of a chromosome

• Differentiate between prokaryotic and eukaryotic chromosomes

• Infer the complexity of an organism based on chromosome number

• Identify gender based on chromosomes

How big is the unseen world of cellular biology?

• Cell Sizes – Scale

• Scale of the universe

What is DNA?

• DNA – contains all the genetic (hereditary) information necessary to build and maintain an organism

DNA and Genes

• Genes – specific sections of DNA that code for a trait

How much DNA is in most of the cells in a human body?

• Approx. 2 meters in every diploid cell

• 2 meters = ___6.5___ Feet

• Approx 6 billion base pairs of DNA per cell

• Each of us has enough DNA in our bodies to reach from here to the sun and back -more than 300 times

• How is all of that DNA packaged so tightly and squeezed into a tiny nucleus?

Activity• Materials needed:

– Yarn = DNA– Easter Egg = Nucleus

• Question: What do the differently colored sections of yarn relate to in DNA?

• Mission: Make all the DNA fit into the nucleus in a way that it would still be “organized”

ChromatinDefinition:

Histones:

DNA that is tightly wrapped around proteinsfound in the nucleus of Eukaryotic cells

A sphere-shaped protein that DNA wraps aroundoNot found in Eubacteria

Chromosome Vs. Chromatin

• Chromosomes are only present during cell division.

• In between cell divisions, chromosomes are unraveled and called Chromatin

Chromosome Vs. Chromatin

• Chromosome:

• Chromatin:

Tightly coiled DNA & proteins during cell division; DNA cannot be “read” while in this form.

Loosely coiled DNA & proteins during the cell’s life other than cell division. DNA can be “read” to direct activities of the cell.

Chromosomes• Definition:

– Rod-shaped or X-shaped structures made of tightly coiled chromatin in preparation for the cell to divide

CH

RO

MO

SO

ME

S

Chromosomes

What do they look like?

• How many do humans have?

•They look like an “X” after the DNA has been duplicated (just before the cell divides)

•They look like an “I” after they divide and between cell divisions

23 Pairs of chromosomes (23 from mom, 23 from dad)

= 46 chromosomes

What does a chromosome look like?

Chromosomes

Centromere

Chromatids

Chromosome Terminology

• Centromere- Connecting point between two chromatids - holds the chromatids together

• Chromatids- identical strands of a duplicated chromosome – become visible at the beginning of

Mitosis or Meiosis– Contains same genetic information

on both

Prokaryotic vs. Eukaryotic Chromosomes

Prokaryotic• Circular• Only one• No histones (except

Archaebacteria)• Not in a nucleus

Eukaryotic

• Rod or X shaped• Many• Histones• In nucleus

Chromosome

Think – Pair – ShareWhich is more complex in

terms of DNA?

Think – Pair – ShareWhich is more complex in

terms of DNA?Adders Tongue Fern

OR

Human

Think – Pair – ShareWhich is more complex in

terms of DNA?

Potato

OR

Sand Dollar

Chromosome NumbersOrganism # of chromosome

Fruit Fly 8

Carrots & Lettuce 18

Cat 32

Earthworm 36

Human 46

Gorilla / Chimpanzee 48

Potatoes / Plums 48

Sand Dollar 52

Horse 64

Adder’s Tongue Fern 1262

Two Types of Chromosomes

• SEX– Determine the gender of the individual – Carry a few other traits– 2 out of our 46 chromosomes

• AUTOSOMES– Carry most of the traits that we inherit– 44 of the 46 chromosomes

SEX Chromosomes

• XX =

• XY =

HOMOLOGOUS CHROMOSOMES

• A pair of autosomes that are the same size and shape and code for the same genes

• One comes from ____________• One comes from ____________

• Humans have 44 autosomes, so they have 22 pairs of homologous autosomes

MomDad

KARYOTYPE

• A picture taken from a microscope of all the chromosomes within a cell. The chromosomes are then arranged in homologous pairs and given a set of numbers

Diploid vs Haploid Cells

Diploid Haploid

Description Both sets of homologous

chromosomes present

Only one of each homologous chromosome

present

Type of Cell All cells but sex cells (egg or

sperm)

Only sex cells- Egg or Sperm

Abbreviation 2n 1n

Standards

• CLE 3210.4.1 Investigate how genetic information is encoded in nucleic acids.

• CLE 3210.4.2 Describe the relationships among genes, chromosomes, proteins, and hereditary traits.

Objectives

• Evaluate the structure of a chromosome

• Differentiate between prokaryotic and eukaryotic chromosomes

• Infer the complexity of an organism based on chromosome number

• Identify gender based on chromosomes

Exit Ticket

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• Room Number: Stewart348