Question

The following crosses were performed between parental lines with indicated genotypes.
(i) $BB\times Bb$
(ii) $AAbb\times aaBB$
(iii) $BB\times bb$
(iv) $Bb\times Bb$
(v) $AA\times AA$
(vi) $bb\times Bb$
The above crosses that are expected to produce only $50$% homozygotes among the F${}_1$ progeny are

• A. (ii), (iii) and (v)
• B. (i), (iv) and (vi)
• C. (i), (ii) and (v)
• D. (i), (ii), (iii) and (vi)

Answer 1

The correct option is B (i), (iv) and (vi)

In a cross made between BB and Bb, the first parent will have one type of gamete, B and the other parent will have two types of gametes, B and b. Hence, the F${}_1$ generation will have 50% homozygotes (BB) and 50% heterozygotes (Bb). Similarly, a cross is made between AAbb and aaBB. In this, the first parent will have gamete Ab and the other parent will have gaemete aB. Hence, the F${}_1$ generation will have 100% heterozygotes (AaBb). A cross is made between BB and bb. In this, only one type of gamete is formed by both the parents, that is B and b. The F${}_1$ generation will be 100% heterozygotes (Bb). Similarly, cross between AA and AA will produce F${}_1$ progeny with homozygous genotype (AA). When a cross is made between Bb and Bb, both the parents will have two types of gametes, B and b. Hence, the F${}_1$ generation will have 50% homozygotes (BB and bb) and 50% heterozygotes (Bb). In a cross made between bb and Bb, the first parent will have only one type of gamete, b and other parent will have two types of gametes, B and b. Hence, the F${}_1$ generation will have 50% homozygotes (bb) and 50% heterozygotes (Bb).

Thus, the correct answer is 'i, iv and vi.'