Question

In a certain species of animals, black fur ($B$) is dominant over brown fur ($b$). Predict a genotype and phenotype of the offsprings when both parents have heterozygous black fur.

Answer 1

According to Mendel, a trait that is inherited is controlled by a single gene with two alleles where one is dominant over another. The other allele is called the recessive gene and the expression of it is suppressed when the dominant allele is present.

Complete answer:
We can see that the dominant allele is the allele for black fur which is $B$and the recessive allele is $b$
First let us understand what homozygous and heterozygous conditions are. Homozygous is a condition where both the alleles are the same. It can either be homozygous dominant ($BB$) or it can be homozygous recessive ($bb$). Heterozygous ($Bb$) is a condition where one recessive and one dominant allele is present in an individual for a particular trait.
Let us work out a cross to understand the question better.
Parental generation $\to$ ${P_1}$ $\to$ $Bb$ x $Bb$
Gametes of parental generation $\to$ $B,b$and $B,b$
${F_1}$ or first filial generation $\to$ $BB$, $Bb$, $Bb$ and $bb$
As we can see, the genotype of the offsprings when both parents have heterozygous black fur is in the ratio as given below:
$BB$: $Bb$: $bb$ $\to$ $1:2:1$
And the phenotype of the offsprings are in the ratio:
Black: brown $\to$ $3:1$

Note: This is a typical monohybrid cross and it can be noted that the ratio of genotype for a monohybrid cross that follows Mendelian genetics will always be the same for a cross between two heterozygous individuals, that is $1:2:1$ for genotype and $3:1$ for phenotype. When there is a deviation seen from the original ratio it can be a case of deviation from Mendelian inheritance like incomplete dominance, codominance etc.