[Spud93]

Figure 1 A family tree showing the pattern of inheritance of colour vision
deficiency.

(a) Explain what is meant by saying an individual is heterozygous for the colour
vision gene, and why females can be heterozygous for colour deficiency in
this family but males cannot. (About 80 words)

(b) Study Figure 1 and then using the symbol 'XB' for the allele coding for
normal colour vision and 'Xb' for the allele coding for colour vision
deficiency, write down the genotypes for the colour vision gene for the
following three grandparents in the family. In each case briefly state how you
reached your conclusion (a few sentences). (Hint: you will have to consider
the phenotypes of all three generations to answer this question.)

• Alfred
• Diane
• Fiona

__________________________________________________ _______________

(c) Matthew and Paul are both baby boys, and it is too early to determine
whether they have normal colour vision. Given the knowledge that they are
male, calculate the statistical probability that:

(I) Matthew will have colour vision deficiency

(ii) Paul will have colour vision deficiency
In calculating your answers, you should include two genetic cross diagrams
for the parents of Matthew and Paul showing the genotypes and phenotypes
of the parents and of all the possible offspring with respect to colour vision.

[Unknown008]

Same thing here... what do you think would be the answer to your questions?

Show your attempt!

[Spud93]

As for this question I have no idea this is a topic that I have never covered before. :(our tutor told us that we would be covering genetics next month.
Then our monthly project arrived with this question, and I don't have a clue we get our study material on a monthly basis so I don't even have the correct books yet.
Any advice would be greatly appreciated thanks :(

[Unknown008]

(a) Explain what is meant by saying an individual is heterozygous for the colour
vision gene.

(I can only help you with that, for the I can't see how the next part is true, that is, in the family tree, I see Graham, Ivan and Edward potential heterozygous males for the colour vision gene.)

Heterozygous (as opposed to homozygous) formed by the prefix hetero (different) means that one individual will have different alleles coding for the same gene. Here, this particular gene is the colour vision gene. Now, you express that into your own words. Don't talk about the etymology of the word. I added those to help you understand. Explain also what the resultant character of the individual will be.

(b) I hope that you know such things a little

XBXB - Homozygous dominant genotype
XBXb - Heterozygous dominant genotype
XbXb - Homozygous recessive genotype

Since only 1 of those 3 can be identified, you immediately know that Alfred, Colin, Holly, Keith and Nathan have the XbXb genotype.

The others might be XBXB or XBXb. Can you try to solve this problem now?

Hint: Then crossing, one parent will pass on 1 allele to the child.

(c) Get first the genotypes of the parents of Matthew and Paul. You can either work it out from their parents, or take a good guess by looking at their children.