Question

A black mouse mates with a brown mouse and all of the offspring are black. Explain.

Answer 1

Hint: Organism's genes mostly determine an organism's character.Genetic makeup is involved in developing the organism which in turn is affected by environmental factors.

Complete Answer:
Certain species of animals like rat Black(B) is dominant over brown(b). The genotype and phenotype of a species can be determined using punnett square.

	B	b
B	BB	Bb
b	Bb	bb

Genotype : 25% homozygous black fur(BB)
                     25% homozygous brown fur(bb)
                     50% heterozygous balck fur(Bb)
Phenotypes: 75% black fur
                       25% brown fur.

When the black mouse mates with the brown mouse to send all black offspring, it means that the skin colour black allele is dominant over the skin colour brown allele. The black allele can manifest itself in a heterozygous state, thereby giving the mouse a black coloured phenotype. The colour of the skin is a trait that has two alleles-the dominant black allele and the recessive brown allele, and the skin colour of the mouse will be determined by its selective expression.

A number of experiments were conducted during the first years after the rediscovery of Mendel 's laws that gave results that did not coincide with the laws at first glance. A cross between a yellow-coated mouse and a mouse with a grey coat was made in 1904. The grey-coated mouse was widely inbred and was thus deemed strictly bred.
The grey mouse, we know, is homozygous (because it is a pure line). If the grey coat were dominant, then we'd see the grey mouse all over. Since both yellow and grey mice are made, yellow must be dominant over grey.

Note: Lethal gene-a gene contributing to the death of an individual; in nature, these can be either dominant or recessive. Perhaps the allele causes the coat to yellow in a single dose, but when expressed in two doses, the gene product destroys the animal. This gene, therefore, actually has an effect on two phenotypes. Pleiotropic gene-a gene affecting more than one phenotype