(1)

If father has blood group 'B', mother has blood group 'A' and the child with blood group 'O' appear in progeny, this means that the parents are heterozygous.
The genotype of the father, mother and child will be $I^{B}i,$ $I^{A}i$ and $ii$ respectively.

(2)

When a pink flowered (Rr) snapdragon plant was crossed with a red flowered (RR) snapdragon plant then red flowered as well as pink flowered phenotypes are expected in the progeny.

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(2)

Test-cross is performed to determine the genotype of black seed colour (BB/Bb) plant. In a typical test-cross, plant showing dominant phenotype (BB/Bb) is crossed with the homozygous recessive parent (bb).

(2)

Violet is dominant over white. So, heterozygous violet flowers will have the genotype of (Vv) and white flowers will have genotype of (vv). When these two plants are crossed, the ${\mathrm{F}}_1$ generation will have the ratio of violet : white as 1 : 1. It is shown as:

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Thus, 20 violet and 20 white flowers are produced among 40 progenies.

(3)

Alleles are the two or more different forms of the same gene. In a typical test cross, an organism showing a dominant phenotype (and whose genotype is to be determined) is crossed with the recessive parent. The cross of an ${\mathrm{F}}_1$ hybrid with one of the two parents is called backcross. Ploidy is the number of complete sets of chromosomes in a cell.

(4)

The production of gametes by the parents, formation of the zygotes, the ${\mathrm{F}}_1$ and ${\mathrm{F}}_2$ plants can be understood from a diagram called Punnett square developed by a British geneticist, Reginald C. Punnett.

(4)

Sickle cell anaemia is an autosomal recessive disorder.

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(3)

ABO blood groups are controlled by the gene $I$. The gene $\left(I\right)$ has three alleles $I^A,I^B$ and $i$. The alleles $I^A$ and $I^B$ produce a slightly different form of the sugar while allele $i$ does not produce any sugar. Because humans are diploid organisms, each person possesses any two of the three $I$ gene alleles. When $I^A$ and $I^B$ are present together they both express their own types of sugars, because of co-dominance.

(1)

Law of segregation applies in this case as when pink flowers obtained in ${\mathrm{F}}_1$ are selfed then red and white flowers are obtained in ${\mathrm{F}}_2$ which indicates that there is no mixing of gametes.

(2)

If the genotypes of husband and wife are $I^A{I}^B$ and $I^{A}i$ respectively, then the probabilities of genotypes and phenotypes among their children can be worked out as:

[IMAGE 17]

Genotype:         $I^A{I}^A$          $I^{A}i$           $I^A{I}^B$           $I^{B}i$

Phenotype:         A                A               AB              B

Thus, there are four possible genotypes, viz., $I^A{I}^A,I^{A}i,I^A{I}^B$ and $I^{B}i$ and three possible phenotypes, viz., A, AB and B among the children.