Slide 1
This first question asks you to think about how an X-linked
recessive trait is passed through generations.
Slide 2
The answer is B - the man's maternal grandfather.
Slide 3
To understand this answer - it is best to write out what you know
about the genotype of the man and his parents. He has red-green
colorblindness and we know his parents have normal vision - therefore his
mother must be a carrier.
Slide 4
That means we can disregard the man's father's side of the family
- the allele for colorblindness was passed to him from his mother.
The question asks which grandparent is most likely to have red-green colorblindness? We know that this condition is more common in males than females so the maternal grandfather is most likely to have the condition.
Slide 5
This question test your understanding of the role that the X and Y
chromosome play in sex determination.
Slide 6
The answer is A - male. Any individual that inherits a
functional Y chromosome will develop into a male. It is possible for
someone with a Y chromosome to develop into a phenotypic female - if there is
a problem with the Y chromosomes or key genes found on the chromosome.
Slide 7
Hopefully this was an easy question!
Slide 8
The answer is C - no! Remember, males only have one copy of
the X chromosome so they cannot be carriers. They can only be hemizygous
for X-linked traits (except in the rare case when a male has two X
chromosomes).
Slide 9
This question is best answered by creating a Punnett square
involving the two parents.
Slide 10
The answer is D - half her sons will have normal vision and half
her sons will be colorblind.
Slide 11
A Punnett square let's us visualize why option D was the untrue
statement. The female is red-green colorblind while the male is
normal. A Punnett square shows that all the sons will be
colorblind. So D was the untrue statement.
If you have any questions about these practice problems - please let me know.