Ch 5 1 Human Inheritance Patterns of Human

Ch. 5. 1 Human Inheritance

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

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

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

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

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

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

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

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

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

X and Y Chromosomes

Sex Chromosomes and Fertilization Ø Since females have only X’s (XX) they can only pass on a female gene: X. Ø It is then up to the guy to donate the final chromosome. He has both an X and a Y (XY). Ø So it will be a 50 -50 chance that the offspring will be a girl: XX or a boy XY.

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

Ø Remember: l l Females = XX Males = XY Ø Genes found on the X chromosome are NOT found on the Y chromosome. Ø 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!

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

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

Ø Let’s cross a Male with Normal Vision: XCY Ø And a Mother who is a Carrier: X CX c

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

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

Ø However, the “environment” can also have a great effect. l l 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!