The person A has only B chromosomes in all its gametes. On the other hand, another person C has chromosome D in half of gametes and chromosome E in the other half of gametes. When chromosomes B and D combine during fertilization, a female zygote results. On the other hand, combination of B and E chromosomes produces a male zygote.
(a) What are chromosomes?
(i) B
(ii) D, and
(iii) E ?
(b) Out of B, D and E, which two chromosomes are of the same type?
(c) Which chromosome is smaller in size?
(d) What is the general name of chromosomes such as B and E?
(e) Out of the two persons A and C, which one is
(i) male, and
(ii) female ?
(a) (i) The chromosome B are X chromosomes because if person A is entirely madeup of B chromosomes it means the person is a female an has all X chromosomes.
(ii) The chromosome D is X chromosome again because when B and D combine a female offspring is produced. A female zygote can only be produced when both of the chromosomes in the gamete are ‘X’. Chromosome B is X as already said above; now chromosome D is also X. Thus only then when B and D chromosome i.e. X and X chromosome combine, a female zygote is produced.
(iii) The chromosome E is a Y chromosome because when B and E combine a male zygote is produced. B is a X chromosome as discussed above and when E i.e. Y chromosome combine , a male zygote is produced(XY)
(b) Chromosome B and D are of the same type, i.e. X chromosome.
(c) Chromosome E is smaller in size since it is a Y chromosome.
(d) Chromosome B (X) and chromosome E (Y) are known as Sex Chromosomes
(e) (i) C is male since it has half genes from D and half genes from E.
D is a X chromosome and E is a Y chromosome so when they combine a male zygote is formed.
(ii) A is female since it has all B chromosomes in it i.e. X chromosome which is only possible in female.