Midphalangeal hair (hair on top of the middle segment of the fingers) is a common phenotype caused by a dominant allele m. homozygotes for the recessive allele (mm) lack hair on the middle segment of their fingers. among 1000 families in which both parents had midphalangeal hair, 1853 children showed the trait while 209 children did not. explain this result.

40% families have heterozygous genotype (Mm).

Remaining 60% of the families will have one parent with homozygous genotype (MM)

Explanation:

If both the parents are heterozygous, then the ration of children without hair to those with hair is 1:3

So, parents with genotype Mm and Mm will produce 209 kids without hair and 209 X 3 i.e 627 kids with hair.

Thus, nearly 40% families have heterozygous genotype (Mm). And the remaining 60% of the families will have one parent with homozygous genotype (MM)