SvS Biology 2000 - Year 10:
Trial solutions for genetics.
4. A student with red hair wanted to map the inheritance of red hair colour. His paternal grandparents did not have red hair. They had 3 children. Two girls and a boy. Only the second girl had red hair. The student's mother did not have red hair, but her mother did. His maternal grandfather did not, and neither does his mother's only brother. The student has an older sister, who doesn't have red hair. She married a man who doesn't have red hair, and they produced two daughters, the first of whom has red hair.
(a) Construct a pedigree chart for the inheritance of red
hair in this boy's family.
(b) According to this chart, is red hair a dominant or recessive
condition? (How can you tell?)
(c) Is it possible that red hair is a sex linked trait? (How can you
tell?)
(b) Recessive condition as neither of the boy's parents had red hair, but he inherited the recessive alleles that were hidden by his parents. His parents must have both been heterozygous for the trait.
(c) Red hair can not be sex linked. If it was sex linked, all affected females would produce affected sons, as they only have the recessive allele to pass on to boys. This was not the case for the boy's maternal grandmother and his uncle.
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S. van Strien