Transcript Gene Linkage

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• If the genes are closer to one another, what happens to their
recombination grequency?
• If Gene A recombines 12% of the time with gene B, but 16% of
the time with gene C, which gene is closer to gene A?
• If gene B and C recombine with one another 28% of the time,
what is the order of genes A, B C along the chromosome?
• Answer the Interactive Question 15.4 on p. 113 in the study
guide and then answer the genetics questions on p. 116.
• Why is crossing-over not as common with sex chromosomes?
• What types of genes are on the sex chromosomes?
• If there is a gene on the top portion of the X chromosomes and
the males have an X and a Y, how many alleles do the have for
that one locus?
• Because of the lack of homology in the sex chromosomes, male
only have one allele for some traits. What do we call a male
genotype for these genes since he is neither homozygous or
heterozygous?
• Make a pedigree for the following family:
• 3 generations, some members have the recessive trait of color blindness
• Genotypes are written as XBXB – for female with normal vision, XBXb for
a female who is normal but is a carrier for colorblind, and XbXb for a
female who is colorblind; XBY for a male with normal vision and XbY for
a male who is colorblind.
• There are two sets of grandparents in the 1st generation
• The 2nd generation has at least 8 people half are male and half are
female
• 2 people are married to each other in the 2nd generation.
• The 3rd generation has at least 6 people, half are male and half are
female.
• The sex-linked trait of male color blindness is present through a
heterozygous genotype (XBXb) in the grandmother of one side of the
family and in the grandfather (XbY) of the other side of the family.
• All phenotypes and genotypes should be depicted for all family
members.