1. Ch. 5.1 Human Inheritance

2. Patterns of Human Inheritance
Some human traits are controlled by single genes with two alleles.
Others are by single genes with multiple alleles.
Still other traits are controlled by many genes that act together.

3. Single Genes with Two Alleles
Many human traits are controlled by a single gene with one dominant allele and one recessive allele.
They will have 2 distinctive phenotypes, meaning they are very obvious which one you have.
Can you roll your tongue?

4. Single Genes with Multiple Alleles
Some human genes are controlled by a single gene with more than 2 alleles.
This is called multiple alleles (having 3 or more different options for that trait).
Human Blood Type is an example of this. There are 4 different options:
A, B, AB, and O

5. When we talk about these kinds of genes, they are called Co-dominant.
This means that EVERY option that you end up with shows up.
So if you have a gene for blood type A from your mom and blood type B from your dad, you will be AB.
To write this out we use a superscript.

6. How to write Blood Types:IA IB
IAB
For blood type O, O is recessive, so how do you think we will write it’s allele?

7. Blood Type O
So in order to have blood type O, your genotype must be: ii

8. Traits controlled by Many Genes
Height is a great example of a trait controlled by MANY MANY MANY genes!

9. The Sex Chromosomes
The sex chromosomes are one of the 23 PAIRS of chromosomes found in each cell of the human body.
The sex chromosomes carry genes that determine whether a person is male or female.
They also carry other genes that determine other traits.

11. Girl or Boy?
The sex chromosomes are the only chromosomes that DO NOT ALWAYS match.
The two chromosomes are celled X chromosomes. Here, you do match.
If you are a boy, your sex chromosomes do not match. You are XY. They Y is much smaller than the X chromosome.

13. X and Y Chromosomes

14. Sex Chromosomes and Fertilization
Since females have only X’s (XX) they can only pass on a female gene: X.
It is then up to the guy to donate the final chromosome. He has both an X and a Y (XY).
So it will be a chance that the offspring will be a girl: XX or a boy XY.

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

16. Genes found on the X chromosome are NOT found on the Y chromosome.
Remember:
Females = XX
Males = XY
Genes found on the X chromosome are NOT found on the Y chromosome.
This means if you are XY, but you get a recessive gene on your X, you will have that recessive trait because the Y cannot offer a gene to compete!

17. This means that men are more likely to inherit rare genes found only on the sex chromosome.
Female’s can still inherit these genes, but it’s just much harder because they have the 2nd X for a backup.

18. Colorblindness
Colorblindness is a trait controlled by a recessive allele on the X chromosome.
Many more males than females have red-green colorblindness.
A carrier is a person who has one recessive allele for a trait and one dominant allele.
Meaning: they don’t show that they have the gene, but they “carry” it in hiding.

19. Let’s cross a Male with Normal Vision: XCY
And a Mother who is a Carrier: XCXc

20. Question:
1. What is the sex of a person who is a carrier for colorblindness?
2. Can a male be a carrier for colorblindness? Why or Why Not?

21. The Effect of the Environment
Many of a person’s characteristics are determined by an interaction between genes and the environment.
You have learned that several genes work together to help determine human height.

22. However, the “environment” can also have a great effect.
Meaning: If you don’t get enough vitamins and minerals from a healthy diet, you might not be able to grow as tall as your genes want you to.
Like trying to grow a giant pumpkin. If you don’t water it, it can’t grow!