The characteristics or traits of parents are transmitted to their progeny i.e. theoffsprings through genes present on their chromosomes. This occurs during the process of sexual reproduction.In this process, the progeny inherits two genes (or a pair of genes) for each trait from its parents.The characteristic(or trait ) shown by the progeny depends on the dominant inherited gene of the two.
SEX CHROMOSOMES
It is thechromosomes which determine the sex of a person. There are two types of sex chromosomes, one is called X chromosome and the other is called Y chromosome.
SEX DETERMINATION
Two different types of sexes participate in the sexual reproduction. There are several procedures followed to determine the sex of a newborn baby. It may be based on the environmental signals while in few animal species, temperature plays a major role in sex determination. It is possible to change sex in certain animals, like snails, as they are not genetically processed. In humans, the genes which are inherited by their parents decide the sex of the child. Humans have 23 pairs of chromosomes. Out of these 23 pairs, 22 pairs are Autosomes and only one pair is the ‘Sex Chromosome’, which actively takes part in the process of sex determination.
So, the sex of an individual is genetically determined by the following way:
(a) If a sperm carrying X chromosome fertilises an ovum (or egg) which carries X chromosome, then the child born will be girls (or female). This is because the child will have XX combination of sex chromosomes.
(b) If a sperm carrying Y chromosome fertilises an ovum (or egg) which carries chromosome, then the child born will be a boy (or male). This is because the child will have XY combination of sex chromosomes.
So simplifying the statements further,
(i) A male has one X chromosome and one Y chromosome.
(ii) A female has two X chromosomes.
All children inherit an X chromosome from their mother despite whether they are boy or girl. So, the sex of the children will be determined by the type of chromosome inherited from their father. A male semen’s holds approximately 50 percent of Y sperm cells and other 50 percent of X sperm cells. Therefore, it is possible that men with three or more children of a single gender.The XY sex-determination system is found in humans, mammals, in some insects, and in few plant species.
ACQUIRED TRAITS
ACquired trait is the trait (or characteristic) of an organism which develops in response to the environment i.e. the traits are not inherited. The acquired traits of organisms cannot be passed on to their future generations. The traits can be transmitted to future generations only when there is an occurrence of change in the genes (or DNA) present in the reproductive cells (or gametes) of parent organisms.
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