Sex-Linked Punnett

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

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 to the left 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.The test to the left 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. 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  GenotypesPhenotypes HHNormal HhNormal/Carrier hhHemophilia

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: XHYXHY XhYXhY XHXHXHXH XhXhXhXh XHXhXHXh

Sample Problems

1. X H X h x X H Y  Chances of:  a. hemophiliac child?  b. hemophiliac son?  c. hemophiliac daughter?  d. daughter who is carrier? XHXHXHXH XHYXHY XhYXhY XHXhXHXh XHYXHY X H X h ¼ or 25% ½ or 50% 0% ½ or 50%

2. A woman who is a carrier for hemophilia marries a hemophiliac man.  Chances of:  a. hemophiliac child?  b. hemophiliac son?  c. hemophiliac daughter? XHXhXHXh XHYXHY XhYXhY XhXhXhXh XhYXhY X H X h 2/4 or 50% ½ or 50% X H X h x X h Y

3. A normal man marries a Homozygous normal woman.  Chances of:  a. Will any of their kids be hemophiliacs? XHXHXHXH XHYXHY XHYXHY XHXHXHXH XHYXHY X H X H 0/4 or 0% X H X H x X H Y

A normal woman (whose father is a hemophiliac) marries a hemophiliac man.  What are their genotypes? XHX?XHX? XhYXhY Her dad - X h Y X H X h and X h Y