Chapter: Heredity

Chapter: Heredity

Table of ContentsTable of Contents

Section 3: Biotechnology

Section 1: Genetics

Section 2: Genetics Since Mendel

Inheriting Traits

• Traits are inherited from parents

11GeneticsGenetics

• Heredity - the passing of traits from parent to offspring.

What is genetics?• Alleles - different

forms of a trait that a gene may have

• Alleles for each trait separate into different sex cells during meiosis

11GeneticsGenetics

What is genetics?• Genetics - study of how traits are inherited

11GeneticsGenetics

Mendel—The Father of Genetics• Mendel (1856) –

studied genes of pea plants

11GeneticsGenetics

• First to:

• trace one trait through several generations

• use probability to explain heredity

• Purebred - always produces the same traits generation after generation

11GeneticsGenetics

• Hybrids – receive different alleles for a trait from each parent

Dominant and Recessive Factors

• Cross-pollination - using pollen from one flower to pollinate others

11GeneticsGenetics

Dominant and Recessive Factors

• Dominant - factor expressed if there is only one allele for the trait

11GeneticsGenetics

• Recessive – factor expressed only when there are 2 alleles for the trait

Click image to view movie.

Punnett Squares 11

GeneticsGenetics

• Punnett square -tool used to predict results


• Studied > 30,000 pea plants over 8 yrs

Punnett Squares 11

GeneticsGenetics

• Uppercase - dominant allele

• Lowercase - recessive allele

• Genotype - genetic makeup11GeneticsGenetics

• Phenotype - way an organism looks and behaves

• Homozygous - two alleles that are the same

11GeneticsGenetics

• Heterozygous - two different alleles for a trait

Making a Punnett Square 11

GeneticsGenetics

11Section CheckSection Check

Question 1

How did Gregor Mendel use his knowledge of mathematics in his study of heredity in pea plants?

11Answer

Mendel was the first person to use the mathematics of probability to explain heredity. Probability is the branch of mathematics that helps you predict the chance that something will happen.

Section CheckSection Check

11Question 2

According to this diagram, if meiosis proceeds correctly, how many alleles of a particular gene can a female pass on to her offspring?


11Answer

Although she has two alleles of each gene, a mother can pass only one allele to her offspring. Meiosis separates alleles so that eggs have only one allele for each gene. The new individual then gets one allele from the mother and the other from the father.


11Question 3

Mendel crossed pea plants that were pure-bred for yellow seeds with plants that were pure-bred for green seeds. All the offspring of this cross had yellow seeds. Based on these results, which form of color was recessive and which was dominant?


11Answer

Green seed color was recessive and yellow seed color was dominant. Mendel called the form that seemed to disappear (green in this case) recessive and the form that covered up (yellow in this case) dominant.


Incomplete Dominance• Incomplete dominance – results in an

intermediate phenotype

22Genetics Since MendelGenetics Since Mendel


• Multiple alleles - trait that is controlled by more than two alleles

• Produce more than three phenotypes

Multiple Alleles 22

Genetics Since MendelGenetics Since Mendel

• Alleles for blood types

• A, B, and O.

Polygenic Inheritance• Polygenic inheritance - a group of gene

pairs acts together to produce a trait.


• Produces a wide variety of phenotypes.


Polygenic Inheritance• Examples:

• Height

• Eye color

• Skin color


Impact of the Environment

• Environment plays a role in how some genes are expressed


Human Genes and Mutations22

Genetics Since MendelGenetics Since Mendel

• Mutations – errors when DNA copies

• Can be harmful or helpful

• Chromosome Disorders - error in the number of chromosomes


Recessive Genetic Disorders - caused by recessive genes.


Sex Determination

• Egg - 1 X chromosome


• Sperm - 1 X or 1 Y chromosome

• Male XY• Female XX

Sex-Linked Disorders • Sex-linked

gene - allele inherited on a sex chromosome


• Color blindness is sex-linked

Pedigrees Trace Traits

• Pedigree - visual tool for following a trait through generations


• Males – squares

• Females – circles

Pedigrees Trace Traits

• Filled circle or square - shows trait


• Half-colored - carriers

• Empty - do not have the trait and are not carriers.


Question 1

Why is color blindness a sex-linked trait?

22Answer

This trait is sex-linked because the alleles for this trait are carried on the X-chromosome, one of the sex chromosomes. Color-blindness is caused by a recessive allele and because males get only one X-chromosome, they are more likely to be color-blind than females.


22Question 2

In Himalayan rabbits, dark-colored fur is only found on cooler parts of the rabbits’ bodies. This is an example of _______.


A. how sex-linked conditions change coat colorB. the risk of cancer in rabbits with light furC. the impact of internal environment on gene expressionD. what hybrid rabbits look like

22Answer

The correct answer is C. The alleles for dark fur color are controlled by the internal temperature of the rabbits. These alleles are expressed only at lower temperatures.


22Question 3

If an individual has three copies of chromosome 21, what condition will result?


A. color blindnessB. cystic fibrosisC. Down’s syndromeD. Hemophilia

22Answer

The correct answer is C. Down’s syndrome occurs when there are three copies of chromosome 21 instead of the usual two.


• Genetic engineering - scientists are experimenting to change the arrangement of DNA that makes up a gene.

33BiotechnologyBiotechnology

• Recombinant DNA - made by inserting a useful segment of DNA from one organism into a bacterium.

33

• Used to produce

• human insulin,

• human growth hormone

BiotechnologyBiotechnology

Gene Therapy

• Normal allele is placed in a virus.

33

• The virus then delivers the normal allele and replaces the defective one


Genetically Engineered Plants • Selective breeding - selecting plants with the

most desired traits to breed

33BiotechnologyBiotechnology

Genetically Engineered Plants 33

• Find genes that produce desired traits in one plant and then insert them into a different plant



Question 1

What is it called when scientists use biological and chemical methods to change the arrangement of DNA in a gene?


Answer

This is called genetic engineering. This process has been used to make large volumes of medicines and research is being conducted to find many other ways to use these techniques.


Question 2What does this diagram illustrate?


A. Bacteria cells can produce human insulin.B. Bacteria genes are put in human cells.


C. People with diabetes are given the gene for insulin.D. The insulin gene is inserted in people with diabetes.


The correct answer is A. Genetic engineering can be used to insert the human gene for insulin into bacterial cells. The bacterial cells then produce human insulin. This insulin can be used to treat people who have diabetes.

Answer


Using genetic engineering to replace defective alleles in people with genetic diseases is called _______.

Question 3

A. gene therapyB. Mendelian genetics C. pedigree analysisD. recombinant DNA


The correct answer is A. Often; a virus is used to deliver the normal allele to the patient. Scientists have been conducting experiments to cure many different genetic diseases, including cystic fibrosis, in this way.

Answer

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Chapter: Heredity

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