Genes and inheritance

Help! I am finding it difficult to answer this question. A student crossed Tom (black mouse) with Sharon (white mouse). The results showed that the offspring were four black mice and 5 white. I have to use a genetic diagram to explain why some of the baby mice had white fur.

Really stuck, so any help gratefully received!

(edited 7 years ago)

Reply 1

S.G.

22

Original post by BethanyVJ

Help! I am finding it difficult to answer this question. A student crossed Tom (black mouse) with Sharon (white mouse). The results showed that the offspring were four black mice and 5 white. I have to use a genetic diagram to explain why some of the baby mice had white fur.

Really stuck, so any help gratefully received!

What are the genotypes for each phenotype?

Use those to make a generic cross

Reply 2

BethanyVJ

OP

8

Original post by SGHD26716

What are the genotypes for each phenotype?

Use those to make a generic cross

The colour of the fur is controlled by one gene which has two alleles B and b

Reply 3

OxFossil

19

Some principles to work from:

*By definition, if one allele is dominant over the other, then all mice which carry that allele will be that colour - but they could be either homozygous or heterozygous.

* Any animals which are the recessive colour must be homozygous for the recessive allele

* If you have a mix of colours in offspring, then the parent of the dominant colour must be a heterozygote (because if it was homozygous, all its offspring will inherit the dominant allele, and so they will all be the dominant colour)

Reply 4

Asad_2015

12

Original post by BethanyVJ

Help! I am finding it difficult to answer this question. A student crossed Tom (black mouse) with Sharon (white mouse). The results showed that the offspring were four black mice and 5 white. I have to use a genetic diagram to explain why some of the baby mice had white fur.

Really stuck, so any help gratefully received!

Approximately equal numbers of both, so we assume that phenotypic ratio of black:white will be 1:1.

If tom was homozygous black (BB), and Sharon was (bb), than all f1 offspring will be heterozygous (Bb) (black).

However, if tow was heterozygous black (Bb), and Sharon was (bb), than the f1 offspring will be half white and half black, ratio 1:1 - white:black. The genotype of these offspring will be (bb - white) and (Bb - black). Hence we have solved the problem :smile:

Genes and inheritance

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