Correct option (c) A is true but R is false
Explanation :
In most animal species, chromosomes can be categorised as two types: autosomes and sex chromosomes. Autosomes are non-sex chromosomes that are of the same number and kind between sexes. Sex chromosomes determine if the individual is male or female. Sex chromosomes in the human female are XX; those of the male are XY.
During the very early stages of this gestation period the development of the embryo is predisposed in certain directions by the possession of the sex chromosomes which are composed of two elements. one contributed by the mother and the other by the father. The mother can contribute only what is termed as an X chromosome which predisposes towards the development of female structural, functional and temperamental characteristics, but the father can contribute either an X or a Y chromosome predisposing in the first instance to female, of in the second to male structural and functional and temperamentaI characteristics. In short. the sex of the child to be born is initially governed by the chromosomal contribution of the lather. All chromosomes are paired. and they is dominant over the X chromosome when combined with it. A child conceived will therefore be subject during development thereafter to a predisposition towards femaleness if receiving an X chromosome from the mother and an X chromosome from the father (XX). or towards maleness if receiving an X chromosome from the mother but a Y chromosome from the father (XY). Therefore, sex in human is a monogenic not polygenic.
Polygenic traits or continuous traits are those traits that ale determined by the combined effect of more than one pair of genes. An example of this is human stature. The combined size of all of the body parts from head to foot determines the height of an individual. There is an additive effect. The sizes of all of these body parts are, in turn, determined by numerous genes. Human skin, hair, and eye colour are also polygenic traits because they are influenced by more than one allele at different loci. The result is the perception of continuous gradation in the expression of these traits.
