Sometimes inheritance doesn\'t always work the way Mendel predicted: A mother wi

Question

Sometimes inheritance doesn't always work the way Mendel predicted: A mother with curly hair (H) mates with a male with straight hair (h). This is a single-gene inherited trait. Their first child, Joe (F1 generation) has wavy hair. When Joe has a child with wavy haired Cindy, they have a straight haired child named Tom. 1. How can you explain this inheritance? What are the genotypes of Mom, Dad, Joe, Cindy, and Tom? What is the chance that Joe and Cindy will have a curly haired child? (draw a punnet square for help) a. b. c.

Explanation / Answer

A. This type of inheritance is called incomplete dominance. It was not observed by Mendel during his work with garden peas. According to this, some characterstics or phenotypes do not represent any of their parent phenotypes but a totally different phenotype which was not present in either of the parent. For ex. as in the given question, Joe had a phenotype for his hair which was completely novel and not found in either of the parent. Both the parents were homozygous for the trait but Joe was heterozygous for the trait(from the punnet square).

The Hh is Joe's genotype.(Heterozygous)

B. Following is the punnet square representation of a cross between Joe and Cindy,

Th last box in the punnet square is Tom's genotype(hh).

C. The chance that Joe and Cindy will have a curly haired child is 25%(from above punnet square).

h h(Joe's father) H Hh Hh H(Joe's Mother) Hh Hh

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