Biology - Lethal Example
If a pair of yellow-haired mice is mated, the ratio of particular coat
colours in the offspring are always the same. 2/3 are yellow, 1/3 is grey,
that is, a ratio of 2:1. Why not 3:1?
The phenotype yellow is dominant to grey.
_Let Y denote allele for yellow coat_
_Let y denote allele for grey coat_
* When the female parent was examined 1/4 of the offspring were found
dead in the uterus.
* In repeated crossings of yellow with yellow, grey and yellow offspring
are always produced. This must mean that the yellow mice are heterozygous
 for the allele.
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