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2.
In
humans, two genes affect the hands. One gene determines the ability to
curve the thumb,
the other
controls the presence of hair on the middle segments of the fingers. The
allele for
curved
thumb, T, is dominant to the allele for straight thumb, t. The allele for
hair on the middle
segment
of the fingers, H, is dominant to that for an absence of hair,
h. (a)
Give all
the possible genotypes of individuals who are able to curve their thumbs
but have
no hair
present on the middle segments of their fingers. (1 mark)
(b)
(i)
Complete
the table to show the possible genotypes resulting from a cross
between
two
individuals heterozygous for both of these genes.
(2 marks)
(ii) What is the probability that one of the offspring of this
cross would have hair on the middle
segments of the fingers? (1 mark)
(iii) What is the probability that the first child born to this
couple would be a girl with straight
thumbs? (1 mark)
Genotypes of female gametes
Genotypes
of
male
gametes |