Page 47 - CB1.3 Genetic Varation sciPAD

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© Silverback Academic Media 47
CB 1.3 GENETIC VARIATION
TRACKING GENES
(d) The pedigree chart below shows the inheritance of hairlessness through three
generations of cats.
(c) The sex of the cats is controlled by two chromosomes. Female cats have the
chromosomes ZZ, whereas male cats have the chromosomes ZY.
Two cats already have four male offspring.
Discuss the likelihood of their next offspring being female. In your answer you should:
• complete a Punnett square to support your answer.
• explain the relevance of the pair already having offspring.




Female gametes
Male gametes
Generation I
Generation II
A B
Generation III
Female
Normal
hair
Hairless
Male
Explain why the genotype of female A in generation II of the pedigree diagram
shown above must have the genotype Hh.










Remember the sex
of new offspring
is not affected by
the sex of previous
offspring.
State the expected
probability as
either a fraction or
a percentage.
Ensure you put
the correct
chromosomes into
the correct spaces
on the Punnett
square (i.e. ZY is
male and ZZ is
female).
Look at the parents
of female ‘A’.
her father was
hairless (hh) while
her mother was
normal (HH or Hh).
Because female
‘A’ has normal
hair, she must have
one normal hair
allele. Because her
father was hairless,
he would have
contributed an ‘h’
to her genotype.
You could draw
a Punnett square
to support your
answer.
Hints for answering
these questions
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