Human Inheritance: Multiple Alleles and Sex-Linked Traits

1. Chapter 5 Human Inheritance Pages 144-150

2. So far in science class… • Chapter 4 discussed traits controlled by one, single gene. (Ex. hair line in humans, freckles, hair texture, etc.) • All of these traits only ever had TWO alleles (Ex. W and w, F and f, HC and HS)

3. Some traits are controlled by a SINGLE gene with MORE THAN TWO alleles. • Such a gene is said to have multiple alleles: • THREE or more forms of a gene (alleles) that code for a single trait. • Example: your blood type

4. Blood type in humans is an example of a trait where there are MULTIPLE ALLELES. • What is blood typing? • How many different blood types are there? • How many different phenotypes are found in the human race?

5. Blood Typing • THREE alleles • IA – dominant • IB - dominant • i – recessive • A blood can be homozygous or heterozygous • B blood can be homozygous or heterozygous • AB blood is co-dominant • O blood is recessive

6. PHENOTYPE= GENOTYPE A blood = IAIA or IAi B blood = IBIB or IBi AB blood = IAIB O blood = ii

7. Example Punnett Square • I stands for the two dominant alleles • (A and B) • i stands for the recessive alleles • (O)

8. Try this Punnett Square • Cross a mother with AB blood and a father who is heterozygous for his B blood.

9. Some traits show MANY different phenotypes. • There are some human traits that do not have just two or three phenotypes, but show MANY different phenotypes. • These traits are controlled by MANY genes that act TOGETHER to produce a single trait. • Ex. skin color or height in humans

10. Male or Female • The sex of the baby is determined by genes on chromosomes. • The 23rd pair of chromosomes are called the sex chromosomes. • The sex chromosomes are the only chromosomes that do not always match. • Male = XY • Female = XX • What are the chances of having a girl? What about a boy?

11. Sex-linked Traits • Traits carried on the X chromosome. • How many X chromosomes do males have? • How many X chromosomes do females have? • Why is it more likely for a male to have an X-linked trait than a female?

12. What is a carrier? • A person who has ONE recessive allele for a trait and one dominant allele. • If the trait is recessive , then a carrier will not have it. • It isimportant for a person to know they are a carrier because they CAN pass the trait on to their offspring. • In sex-linked traits, only FEMALES can be carriers.

13. Sex-linked traits - Alleles Sex-linked traits CAN have dominant and recessive alleles. If the trait is recessive, like colorblindness, it must be on BOTH X chromosomes for females, but only ONE X chromosome of males. • Males: Normal • XNY • Females: Normal • XNXN • Males: Colorblind • XnY • Females: Carrier • XNXn • Females: Colorblind • XnXn

14. Practice Problem XN Xn • Cross a mother who is a carrier for color blindness with a father with normal color vision. • Report all Geno/Phenotypes: XN Y XNXN

15. COLOR BLIND?LET’S TAKE THE TEST!

16. Color blindness

17. Color Blindness

18. Color Blindness

19. Color Blindness A day in the life

20. How does the Environment Effect How an Organism Look? • Factors like diet, medical care, and living conditions can also effect the way an organism looks. VS.

21. OUT: Baldness is a recessive sex-linked trait. B is not bald, b is bald Cross a Not Bald male XB Y with a Not Bald carrier female XBXb . Report all genotypes and phenotypes. XB Y XB Xb