2. Hair and Eye Color In Scandinavia, people who do not have blond hair and blue

Question

2. Hair and Eye Color

In Scandinavia, people who do not have blond hair and blue eyes stand out. A study considered hair and eye color in families from Copenhagen, Denmark. In each of 50 families, one partner has the common blond hair and blue eyes, while the other partner has brown hair and brown eyes (parents). For the brown-haired, brown-eyed partners, each has a parent that looks like them and a parent that is blue-eyed and blond-haired (grandparents). In total, the 50 families have 260 children with the following phenotype frequencies (children):


Phenotype # of children
Brown hair, blue eyes 4
Blond hair, brown eyes 6
Brown hair, brown eyes 120
Blond hair, blue eyes 130

Brown hair (H) is dominant to blond hair (h), and brown eyes (B) are dominant to blue eyes (b).


A. What is the genotype or genotypes of the blond-haired, blue eyed parents?


B. Are the genes for these traits linked or unlinked? Justify your answer?





C. Explain or diagram how the brown-haired, blue-eyed and blond-haired, brown-eyed children arose.

Explanation / Answer

Brown hair=H Blond hair=h Brown eyes=B Blue eyes=b A. Genotype of blond hair, blue eyed parents = hhbb (both traits are recessive) B. LINKED. The combination of brown eyes and brown hair & the combination of blue eyes with blond hair occur much more frequently than brown eyes with blond hair or blue eyes with brown hair. This suggests that the gene for eye color and the gene for hair color are located close to each other (less than 50 map units apart) on the SAME chromosome. C. In order to have a child with brown hair and blue eyes, or a child with blond hair and brown eyes, crossing over of the chromosome must occur BETWEEN the gene for hair color and eye color during meiosis. This does not happen frequently, which is why the number of crossovers is much less than the number of children born with brown eyes & brown hair or blue eyes & blond hair. Diagram: B------H (from 1 parent) x b------h (from other parent) Cross over between, would result in child getting B----h or b---H instead of B---H or b----h. Hope that helps. :)

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