Sex-Linked Punnett Square Notes

Karyotype A photograph of a cell’s chromosomes arranged in pairs according to size

Normal Karyotype: 23 pairs of chromosomes pairs 1-22 are autosomes pair 23 are sex chromosomes 24-5

Sex Chromosomes X Y

some genes are unique only to the Y chromosome X chromosome has over 1,000 genes most genes on the X chromosome do not have corresponding alleles on the Y chromosome Y chromosome has only a few dozen genes some genes are unique only to the Y chromosome

Sex-Linked Traits Those traits whose genes are found on the X chromosome but NOT on the Y chromosome

Examples of Sex-linked Traits: Red-green colorblindness Male Pattern Baldness Hemophilia (Queen Victoria was a carrier) Duchenne Muscular Dystrophy (fatal)

Color Blindness “tests”

The test below is simpler The test below is simpler. The individual with normal color vision will see a 5 revealed in the dot pattern. An individual with Red/Green (the most common) color blindness will see a 2 revealed in the dots.

Females = XX –carry 2 alleles for a sex-linked trait Males = XY – only carry 1 allele for a sex-linked trait, so it is easier for them to get sex-linked diseases

Sex-Linked Traits, cont. Males receive sex-linked traits from their mother because their mother gives them the X chromosome and their father gives them the Y chromosome

Example of Sex-Linked Trait H = Normal blood clotting h = Hemophilia

Example of Sex-Linked Trait Normal male: Male with Hemophilia: Normal female (not a carrier for hemophilia – homozygous): Normal female (carrier for hemophilia – heterozygous): Female with Hemophilia: XHY XhY XHXH XHXh XhXh

Sample Problems

1. XHXh x XHY Chances of: a. hemophiliac child? b. hemophiliac son? c. hemophiliac daughter? d. daughter who is carrier? ¼ or 25% XH Xh XH Y XHXh XHXH 25% XHY XhY 0% 25%

2. A woman who is a carrier for hemophilia marries a hemophiliac man. XHXh x XhY Chances of: a. hemophiliac child? b. hemophiliac son? c. hemophiliac daughter? XH Xh 2/4 or 50% Xh Y XhXh XHXh 25% XHY XhY 25%

3. A normal man marries a Homozygous normal woman. XHXH x XHY Chances of: a. Will any of their kids be hemophiliacs? XH XH XH Y XHXH XHXH XHY XHY 0/4 or 0%

Multiple Alleles Gene with more than two alleles Individual organism only has TWO alleles, but there are more options Ex. Rabbit Fur Color   Order of dominance: C  cch  ch  c

What happens when you cross a chinchilla (cchch) with a white (cc) rabbit? 50% chinchilla (cchc), 50% himilayan (chc) cchc chc

BLOOD TYPING There are 3 alleles of the gene that controls blood type: IA , IB , i The I stands for immunoglobin. IA and IB are Co-Dominant genes, meaning when inherited together, they are both fully expressed, not blended, as in Incomplete Dominance. “ i ” is the recessive form of the allele.

Possible genotypes are as follows: Genotypes Blood type IAIA or IAi A IBIB or IBi B IAIB AB ii O

Draw a Punnett square showing all the possible genotypes for the offspring produced by a type “O” mother and a Type “AB” father. Cross: ii x IAIB IB

A man is heterozygous for blood type A and his wife is blood type AB A man is heterozygous for blood type A and his wife is blood type AB.  What is the probability of them having a child with blood type B? IA i IA IB IAIA IAi IAIB IBi