Ch. 5.1 Human Ch. 5.1 Human InheritanceInheritance

Patterns of Human InheritancePatterns of Human Inheritance

Some human traits are controlled by single Some human traits are controlled by single genes with two alleles.genes with two alleles.

Others are by single genes with multiple Others are by single genes with multiple alleles.alleles.

Still other traits are controlled by many Still other traits are controlled by many genes that act together.genes that act together.

Single Genes with Two AllelesSingle Genes with Two Alleles

Many human traits are controlled by a Many human traits are controlled by a single gene with one dominant allele and single gene with one dominant allele and one recessive allele.one recessive allele.

They will have 2 distinctive phenotypes, They will have 2 distinctive phenotypes, meaning they are very obvious which one meaning they are very obvious which one you have.you have. Can you roll your tongue?Can you roll your tongue?

Single Genes with Multiple AllelesSingle Genes with Multiple Alleles

Some human genes are controlled by a Some human genes are controlled by a single gene with more than 2 alleles.single gene with more than 2 alleles.

This is called multiple alleles (having 3 or This is called multiple alleles (having 3 or more different options for that trait).more different options for that trait).

Human Blood Type is an example of this. Human Blood Type is an example of this. There are 4 different options:There are 4 different options: A, B, AB, and OA, B, AB, and O

When we talk about these kinds of genes, When we talk about these kinds of genes, they are called Co-dominant.they are called Co-dominant.

This means that EVERY option that you This means that EVERY option that you end up with shows up.end up with shows up.

So if you have a gene for blood type A So if you have a gene for blood type A from your mom and blood type B from from your mom and blood type B from your dad, you will be AB.your dad, you will be AB.

To write this out we use a superscript.To write this out we use a superscript.

How to write Blood Types:How to write Blood Types:

IIAA

IIBB

IIABAB

For blood type O, O is recessive, so how For blood type O, O is recessive, so how do you think we will write it’s allele?do you think we will write it’s allele?

Blood Type OBlood Type O

So in order to have blood type O, your So in order to have blood type O, your genotype must be: iigenotype must be: ii

Traits controlled by Many GenesTraits controlled by Many Genes

Height is a great example of a trait Height is a great example of a trait controlled by MANY MANY MANY genes!controlled by MANY MANY MANY genes!

The Sex ChromosomesThe Sex Chromosomes

The sex chromosomes are one of the 23 The sex chromosomes are one of the 23 PAIRS of chromosomes found in each cell PAIRS of chromosomes found in each cell of the human body.of the human body.

The sex chromosomes carry genes that The sex chromosomes carry genes that determine whether a person is male or determine whether a person is male or female.female.

They also carry other genes that They also carry other genes that determine other traits.determine other traits.

Girl or Boy?Girl or Boy?

The sex chromosomes are the only The sex chromosomes are the only chromosomes that DO NOT ALWAYS chromosomes that DO NOT ALWAYS match.match.

The two chromosomes are celled X The two chromosomes are celled X chromosomes. Here, you do match.chromosomes. Here, you do match.

If you are a boy, your sex chromosomes If you are a boy, your sex chromosomes do not match. You are XY. They Y is much do not match. You are XY. They Y is much smaller than the X chromosome.smaller than the X chromosome.

X and Y ChromosomesX and Y Chromosomes

Sex Chromosomes and FertilizationSex Chromosomes and Fertilization

Since females have only X’s (XX) they can Since females have only X’s (XX) they can only pass on a female gene: X.only pass on a female gene: X.

It is then up to the guy to donate the final It is then up to the guy to donate the final chromosome. He has both an X and a Y chromosome. He has both an X and a Y (XY).(XY).

So it will be a 50-50 chance that the So it will be a 50-50 chance that the offspring will be a girl: XX or a boy XY.offspring will be a girl: XX or a boy XY.

Sex-Linked GenesSex-Linked Genes

Genes that are carried on the 23Genes that are carried on the 23rdrd chromosome pair (the sex chromosomes) chromosome pair (the sex chromosomes) are called Sex-Linked because they are are called Sex-Linked because they are linked to the sex chromosome.linked to the sex chromosome.

Remember:Remember: Females = XXFemales = XX Males = XYMales = XY

Genes found on the X chromosome are Genes found on the X chromosome are NOT found on the Y chromosome.NOT found on the Y chromosome.

This means if you are XY, but you get a This means if you are XY, but you get a recessive gene on your X, you will have recessive gene on your X, you will have that recessive trait because the Y cannot that recessive trait because the Y cannot offer a gene to compete!offer a gene to compete!

This means that men are more likely to This means that men are more likely to inherit rare genes found only on the sex inherit rare genes found only on the sex chromosome.chromosome.

Female’s can still inherit these genes, but Female’s can still inherit these genes, but it’s just much harder because they have it’s just much harder because they have the 2the 2ndnd X for a backup. X for a backup.

ColorblindnessColorblindness

Colorblindness is a trait controlled by a Colorblindness is a trait controlled by a recessive allele on the X chromosome.recessive allele on the X chromosome.

Many more males than females have red-Many more males than females have red-green colorblindness.green colorblindness.

A A carriercarrier is a person who has one is a person who has one recessive allele for a trait recessive allele for a trait and one and one dominant allele.dominant allele.

Meaning: they don’t show that they have Meaning: they don’t show that they have the gene, but they “carry” it in hiding.the gene, but they “carry” it in hiding.

Let’s cross a Male with Normal Vision: XLet’s cross a Male with Normal Vision: XCCYY And a Mother who is a Carrier: XAnd a Mother who is a Carrier: XCCXXcc

Question:Question:

1. What is the sex of a person who is a 1. What is the sex of a person who is a carrier for colorblindness?carrier for colorblindness?

2. Can a male be a carrier for 2. Can a male be a carrier for colorblindness? Why or Why Not?colorblindness? Why or Why Not?

The Effect of the EnvironmentThe Effect of the Environment

Many of a person’s characteristics are Many of a person’s characteristics are determined by an interaction between determined by an interaction between genes and the environment.genes and the environment.

You have learned that several genes work You have learned that several genes work together to help determine human height.together to help determine human height.

However, the “environment” can also have However, the “environment” can also have a great effect.a great effect. Meaning: If you don’t get enough vitamins and Meaning: If you don’t get enough vitamins and

minerals from a healthy diet, you might not be minerals from a healthy diet, you might not be able to grow as tall as your genes want you able to grow as tall as your genes want you to.to.

Like trying to grow a giant pumpkin. If you Like trying to grow a giant pumpkin. If you don’t water it, it can’t grow!don’t water it, it can’t grow!