More Genetics Questions Colorblindness is a sex-linked trait found on the X chromosome. Use this information to do the following problems. 1. A male who is colorblind marries and has children with a female who is not color blind. None of their offspring are colorblind. What genotype was the mother? What genotype was the father? What is the genotype of the male offspring and the female offspring? 2. A man who is colorblind marries and has children with a female who is a carrier for the colorblind gene. What percent of the males will be colorblind? What percentage of the females will be colorblind? What percentage of the females will be carriers? What percentage of the males will be carriers? Answers at the end More problems can be found at: http://biology.clc.uc.edu/courses/bio105/geneprob.htm http://www.learn4good.com/science/biology/genetics_practice_problems_single_trait_cr osses.htm http://faculty.mdc.edu/mdelcamp/BSC%202010%20Notes/Chpt_15_Genetics_Practice_P roblems.doc There are many many more problems online (I assume that your lab instructor gave you some as well. Just google genetics practice problems. Many even give you the answers. Answer #1 Xa Y XA XAXa XAY A XAXa XaY X Females both not colorblind, but are carriers Male not colorblind Male colorblind Answer #2: Xa Female not colorblind, but carrier Y XA XAXa XAY a XaXa XaY X Male not colorblind Male colorblind Female colorblind 50% of the females (1 out of 2 females) will be colorblind 50% of the females will not be colorblind and will be carriers 50% of the males will be colorblind 50% of the males will be colorblind 50% of the offspring will be colorblind 50 % of the offspring will not be colorblind ** none of the males will be carriers. Males in this case can not be carriers because they only have one X, so they don’t have another X to mask a recessive a. ** As you can see for sex-linked genes you must draw the sex chromosomes and put the alleles as small letters to the right of the chromosomes. Note there are no alleles on the Y chromosome because colorblindness is a X linked gene. It is not found on the Y chromosome only the X chromosome. If you don’t write in the chromosomes and forget that males don’t have 2 alleles in this case you will come out with a completely different, and wrong, answer. So take care when filling these out!