Q. Why do all the gametes formed in human females have an X-chromosome?
Ans. The sex chromosome in human female is homomorphic i.e., they contain same chromosome XX. During meiosis process at the time of gamete formation all egg cell will get one copy of X chromosome, hence all the gametes formed in human females have an X-chromosome.
Q. How does the creation of variations in species promote survival?
Ans. Due to errors in DNA copying some variations in a species occur. Species with useful variations get adapt to the changing environment and they have better chances of survival and produce their offsprings.
Q. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?
Ans. Yes, we agree with this statement that only variations that confer an advantage to an individual organism
Q. If a trait A exists in 10% of a population of an asexually reproducing species and trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Ans. Trait B would have arisen earlier than trait A because as species are asexually reproducing, there would be very minor differences generated due to small inaccuracies in DNA copying which results in variations in trait A. But as trait B occurs in more number in the population as compared to trait A so Trait B would have arisen earlier than trait A.
Q. How do Mendel’s experiments show that traits may be dominant or recessive?
Ans. When Mendel crossed pure tall (TT) pea plants with pure dwarf (tt) pea plants, in F1 generation he found that all pea plants were tall (Tt). There were no dwarf plants produced in F1 generation. When he self-pollinated these F1 plants, in F2 generation he obtained tall and dwarf plants in the ratio 3: 1. Thus as three-fourths of the plant in F2 generation are tall and one-fourth is dwarf so tall is a dominant trait whereas dwarf is a recessive trait [which expressed itself only in homozygous condition]. So he concluded that for a particular trait [here in this example height of the plant] it may be dominant or recessive.
Q. Outline a project which aims to find the dominant coat colour in dogs.
Q. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits blood group A or O is dominant? Why or why not?
Q. How is the sex of the child determined in human beings?
During fertilisation when X carrying sperms fuse with an egg which contains X chromosome the offsprings will be a female (XX). But when Y bearing sperms fuses with an egg (X) the offspring will be male (XY). Thus the sex of a child is determined by the type of sex chromosome X or Y received by the male gamete.
Q. How is the equal genetic contribution of male and female parents ensured in the progeny?