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Name ___________________________________________________ Date _____________________ Period __________ Sex Linked Inheritance Sex-linked traits are those whose genes are found on the X chromosome but not on the Y chromosome. In humans, the X chromosomes are much larger than the Y chromosome and contains thousands of more genes than the Y chromosome. Therefore, many traits are carried only on the X chromosome. Keep in mind: females have two X chromosomes (XX) while males have an X chromosome and a Y chromosome (XY). 1. In fruit flies, eye color is a sex linked trait. Red eye color is dominant to white eye color. What are the genders and eye color phenotypes for the following genotypes? Genotype XR XR XR Xr XrXr Gender Female Female Female Phenotype Red eyes Red eyes White eyes Genotype XR Y XrY Gender Male Male Phenotype Red eyes White eyes 2. Write the genotypes for the following flies. White eyed, female fly _______XrXr________ White eyed, male fly _______ XrY ________ Red eyed male ______ XRY ___________ Heterozygous red eyed female ______ XRXr ________ Homozygous red eyed female ______ XRXR _________ 3. Show the cross between a white eyed female (XrXr) with a red eyed male (XRY). a. Determine the probabilities for each of the following… Red eyed females __50___% White eyed females ___0_____% Red eyed males ___0_____% White eyed males ___50_____% XR Xr XR XRXR XRXr Y XRY Xr Y Xr Xr XR XRXr XRXr Y Xr Y Xr Y 4. Show the cross between a heterozygous red eyed female and a red eyed male. a. Determine the probabilities for each of the following… Red eyed females ____50____% White eyed females ____0____% Red eyed males ___25_____% White eyed males ____25____% 5. In the cross performed in #4, assume that 100 of the offspring flies were male and 200 of the offspring flies were female. What would be the total number of red eyed flies you would expect? ________250_______ 6. Hemophilia is a rare blood disorder in which the blood is not able to clot normally following an injury like a cut or a scrape. In humans, hemophilia is a recessive sex linked trait. Use an H to represent the normal blood clotting allele and an h to represent the hemophilia allele. a. Defend this statement…Females can be carriers of hemophilia, but males either have the disorder or they do not (males will never be carriers). Since males only have one X chromosome there is no second X chromosome to mask the trait. 7. Write the genotypes for the following individuals. Homozygous, normal female _______XHXH______ Normal Male ______ XHY __________ Normal female (carrier) _______ XHXh _______ Hemophiliac Male ______ XhY __________ Hemophiliac female ______ XhXh ___________ 8. Show the cross between a man who has hemophilia and a woman who is a carrier. a. Circle the genotypes of the children with hemophilia. What is the probability that their children will have the hemophilia blood disorder? ____50_____% XH X Y H Xh H H X X XH Y XH Xh Xh XH Xh XhXh Y XH Y XhY 9. A woman who is a carrier marries a man who does NOT have hemophilia. a. What is the probability that their children will have hemophilia? ____25____% H h X X XhY b. What is the gender of the child with hemophilia? Male 10. In some breeds, cats can be orange, black or calico (both black AND orange is expressed in splotches). Females that receive a B and an O allele are calico. Males can only be black or orange, but never calico. a. Identify the complex inheritance pattern which results in cat fur color. XB Sex-linked and codominant 11. Show the cross or a female calico cat with a black male cat. XB XO XBXB XB XO XB Y XOY a. What percentage of the kittens will be… Black and male ___25____% Black and female____25____% Y Orange and male ___25__% Orange and female ___0_____% Calico and female ____25____%
