1. Chapter 5.1 Human Inheritance

2. POINTS
Describe human traits with only 2 alleles
Describe traits with multiple alleles
Explain blood-type alleles and heredity
Describe sex determination
Explain sex-linked heredity
Define carrier and explain what it means to be a carrier

3. POINT > Describe examples of traits with 2 alleles
Some human traits are controlled by a single gene with two alleles
Dimples
Cleft in the chin
Attached/unattached ear lobes
Widow’s peak

4. Check:
What is one human trait controlled by one gene with only two alleles?

5. POINT > Describe examples of multiple alleles
Some human traits are controlled by a single genes with multiple alleles
Example: Blood type (A, B, AB, O)
Most human traits are controlled by multiple genes that act together 

6. BLOOD TYPES

7. POINT > Explain blood-type alleles and heredity
There are four types of blood – A, B, AB, and O
Three alleles control human blood type: IA , IB , i
Two of the alleles are codominant: IA and IB
One allele is recessive: i

8. POINT > Explain blood-type alleles and heredity
Genotypes: Phenotypes: IA IB = AB blood type IA i or IAIA = A blood type IB i or IBIB = B blood type i i = O blood type

9. CHECK:
What are the three alleles that control human blood type?
What are the four blood types?
Which blood type alleles are codominant?
If the genotype is ii what is the blood type?

10. IA i x IB i POINT > Explain blood-type alleles and heredity
Suppose a heterozygote with type A blood has offspring with a heterozygote with type B blood. What type blood will the children have?
IA i x IB i

11. IB i IA IAIB IA i IB i i i 25% type AB 25% type A
Type B heterozygous parent IB i IA
IAIB
IA i
IB i
i i
Type A heterozygous parent
25% type AB 25% type A
25% type B % type O

12. CHECK:
Suppose a homozygous woman with type A blood has offspring with a man with type AB blood. What are the phenotype percentages of the offspring?
IA IA x IAIB

13. POINT > Describe sex determination
Human body cells have 23 pairs of chromosomes (= 46 total)
22 pairs of “regular” chromosomes are called autosomes
1 pair of sex chromosomes = X and Y
Girls have two X chromosomes (XX)
Boys have one X and one Y chromosome (XY)

14. The Male Karyotype

15. The Female Karyotype

16. POINT > Describe sex determination
During meiosis, the sex chromosomes split apart (like the other 22 pairs) In women, all egg cells have an X chromosome In men, half of the sperm cells get an X and the other half get a Y The male sperm cell (X or Y) determines the sex of the offspring

17. The formation of egg and sperm cells: 1 sperm cell  4 sperm cells 1 egg cell  1 really good egg cell

18. CHECK:
How many autosomes do humans have?
What are the sex chromosomes in a woman?
What are the sex chromosomes in a man?

19. POINT > Explain sex-linked heredity
The genes for some human traits are carried on the sex chromosomes
They are called sex-linked genes, and the traits are sex-linked traits
Like other traits, they can have dominant and recessive alleles

20. POINT > Explain sex-linked heredity
FEMALES (XX) A dominant allele on one X will cover up a recessive allele on the other X XRXr If “r” is a recessive allele that causes a disease, this girl is not affected A girl would have to be XrXr to have the disease

21. POINT > Explain sex-linked heredity
MALES (XY)
If there is a recessive allele on the X it will be expressed
XrY
This boy will have the disease
Many recessive sex-linked traits carried on the X chromosome will show up more in males –
ex. colorblindness, hemophilia

22. POINT > Describe sex-linked traits
Ex. Red-Green Color Blindness X-linked recessive Inability to distinguish between red and green hues

23. a)XGY b) XgY c) XGXg d) XGXG e) XgXg CHECK:
If “g” is a sex-linked recessive allele that causes a disease, which people would have the disease?
a)XGY
b) XgY
c) XGXg
d) XGXG
e) XgXg

24. POINT > Define carrier and explain what it means to be a carrier
A carrier is a person who has one recessive allele for a trait and one dominant allele (heterozygous)
We usually use the term “carrier” to refer to a trait that is a recessive disease
A carrier does not have the trait, but can pass on the recessive allele to offspring
In the case of sex-linked traits, only females can be carriers

25. POINT > Define carrier and explain what it means to be a carrier
What if a female carrier for colorblindness has offspring with a colorblind man? What will the children have?
C = allele for good color vision
c = allele for colorblind
XC Xc x Xc Y

26. XC Xc Y XCXc Xc Xc XC Y Xc Y Female carrier Colorblind man
25% colorblind girls % carrier girls
25% good vision boys % colorblind boys

27. CHECK:
What is a carrier?
Does a carrier have the disease?

28. HEMOPHILIA

29. Homework Read 5.1 pages144-150 S.A. #1-3 GRAS pp. 69-71