Question

“The sex of the children is determined by what they inherit from their father and not their mother”. Justify.

Answer 1

The establishment of male and female individuals or male or female organs of an individual is called sex determination. It is of three types- environmental, genetic and chromosomal.

Complete answer:
In most animals and some plants, sex is determined by sex chromosomes or allosomes. In mammals including human beings and many insects, XY method of sex determination is followed. It is also called male heterogamety.The females in such organisms are homomorphic having the XX chromosomes while the males are heteromorphic and possess the XY chromosomes. Y chromosome is shorter than the X chromosome. So females form only one type of gametes (i.e. the gametes have only X chromosome) while the males form two types of gametes called angiosperms (22 + X) and gymnosperms (22 + Y). So the sex of the children is determined by what they inherit from their father and not their mother.XY chromosome synapse during zygotene. They have two parts, homologous and differential. Homologous regions of the two take part in synapsis and they carry similar genes called the X-Y linked genes. The differential or non-homologous region of the Y-chromosome is mostly heterochromatic.
The euchromatic part of the differential region of the Y-chromosome has holandric genes that are directly transferred from father to son.
Genes present on the differential region of the X-chromosome also find expression in males whether they are recessive or dominant because males are hemizygous for these genes.

Note: XY determination is found in many bryophytes like Sphaerocarpus and angiosperms like Melandrium, Coccinia, Salix, Elodea , etc. Sex in this case is determined at the time of fertilization and it is known as syngametic sex determination.