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Genetic diagrams???

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could somebody please walk me through this step by step. It makes no sense to me and i cant work it out :frown:

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Reply 1

Elyxeia

Hi. I'm doing biology a level this year. So hopefully I will get this right...
The questions says you breed a chocolate male and a black female. Since they produce cinnamon kittens which is the most recessive gene and therefore needs a bi allele from both the mother and father. This tells you the father is b,bi because he is chocolate coloured but has a recessive bi cinnamon trait to produce cinnamon fur offspring with the mother who also must have a cinnamon trait because recessive needs two of its alleles to be expressed. The mother is black so therefore needs B,bi. This means the father has gametes bi and b and the mother has B and bi. If you draw a table with bi and b along one side and B and bi in the other, you will know the offspring genotype. You know you only have one B from the mother so the black phenotype must only have one because you only have one. And since you have b and bi from he father which are both recessive to B, the black genotype scan be B,b or B,bi. For cinnamon you must have bi,bi because it is the most recessive and will not be expressed otherwise. And finally for chocolate you have one b chocolate allele from the father and can't have the B allele from the mother otherwise it'll be black so it must be b,bi.
I rambled a bit. Sorry. Hopefully it made sense.

Reply 2

username2396569

Original post by Ismail786

could somebody please walk me through this step by step. It makes no sense to me and i cant work it out :frown:

Yh so this is pretty logical, you know that if the parents are making cinnamon offspring, then they must both have the cinnamon allele (bi). So this makes the parent genotypes nice and easy to work out, father must be bbi, and mother must be Bbi. The reason that both parents must have bi alleles is because the bi allele is the most recessive, so the offspring must receive a bi allele from both parents.

Now, for the "gametes" part, all you have to do is draw 4 circles and write the individual alleles in each circle, so for the father it will be a "b" in a circle and a "bi" in a separate circle, and for the mother it will be a "B" in a circle and a "bi" in a separate circle. That is how you denote gametes when asked in a question like this.

And then for the offspring genotypes you need to draw a punnet square. The punnet square will show that the 4 possible combinations of offspring genotypes will be Bb, Bbi, bbi and bibi. So the genotypes for the black offspring are Bb and Bbi, the genotype for the chocolate offspring is bbi and the genotype for the cinnamon offspring is bibi.

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