Warm ups: 1.How many chromosomes do humans have? 2.How many X chromosomes do males have? 3.How many X chromosomes do females have?

Sex linked traits in Genetics

Genetics gets more complex! There are certain genes that are only on the sex chromosomes… X and Y X chromosome has about 1,100 genes Y chromosome has about 200 genes Remember: - if you are a female, you have two X chromosomes (XX) - if you are a male, you have one X and one Y chromosomes (XY)

Sex Linked Disorders 1.Some conditions are closely linked to the X and Y chromosomes (although most sex linked disorders are on the X chromosome) 2.An allele inherited on a sex chromosome is a sex-linked gene 3.Color Blindness and hemophilia – on x chromosome 4.If a man inherits an X with the gene on it, he will have the disease 5.A female has to have two X with the gene (recessive)

Hemophilia – a sex-linked disorder that affects the ability to clot your blood. That means if you get a little cut or a scratch, you would bleed to death

Color blindness– a sex-linked inability or decreased ability to see color, or perceive color differences, under lighting conditions when color vision is not normally impaired. - on the “X” chromosome

COLOR BLINDNESS TESTs The color blindness test consists of a set of five charts. Each chart shows a number in one color on a different backgound color. People with normal color vision will have no problem seeing the numbers on the charts, but people with color blindness will see only random colored dots. Seventy-five percent of color blind people have poor green perception. Of the remaining, 24% have poor red perception, and one percent are affected by a rare tritan type

Color blindness test 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.

1. A mother carries the gene for hemophilia on one of her X chromosomes. She marries a man with no gene for this disease. Complete a punnett square to see how this will affect their offspring. ( X = normal, x’ = hemophilia) Father = _____ Mother = ____ XY X’X Y X XX’ Y XX X Y ____ % carrier ____ % have hemophilia ____ % no gene for disease 25 75

2. A mother carries the gene for color blindness and her husband is color blind. Complete a punnett square to see how this will affect their offspring. ( X = normal, x c = color blind gene) Father = _____ Mother = ____ XcYXcY XX c XXcXXc Y XcXc XcXc X X Y XcXc XcXc XcXc Y ____ % carrier ____ % have color blindness ____ % no gene for disease 25 50

QUESTIONS! 1. A man has one “X” chromosome with the gene for hemophilia on it. Does he have the disease? _________ 2. A woman has one “X” chromosome with the gene for baldness. Does she have the disease? ____________. She is called a ____________ because even though she does not have the disease, she carries it and can pass it on to her offspring. 3. A woman has to have ______ “X” genes with the disease gene in order for her to have the disease.