Test: Sex Determination & Chromosomal Theory of Inheritance (November 28) - NEET MCQ

Turtles are one of the organisms which rely on environmental factors for sex determination completely. They usually depend upon temperature for this purpose.

The foundation of the chromosomal basis of sex determination was laid down by Henking in 1891. He studied a specific nuclear structure though spermatogenesis in a few insects.

When the condition of male heterogamety is present, then sperm determines the sex of the offspring because two kinds of sperms are present, one with X-chromosome and the other with Y-chromosome. Eggs of an individual are the same as both of them contain 22+ X chromosomes.

The probability of having a girl child in the sixth pregnancy, where the first five progenies were male is 50%. As humans show XY type of male heterogamety, where 50% sperms carry 22+ X chromosomes and the other 50% carry 22+Y chromosomes, therefore in each pregnancy there is 50% probability of either a male or a female child.

Mendel had published his work back in 1865. The communication methods were not well developed and for people to recognize the importance of his work took more than half a decade after it had been published.

People had performed crosses on garden pea plants before Mendel. But no one had applied a statistical and probabilistic approach to unveil the underlying phenomena. Mendel was the first to do so.

Chromosomes means colored bodies/objects. The staining procedures allowed biologists to visualize the nucleus and chromosomes during the process of cell division.

These three scientists helped in the rediscovery of Mendel’s work in the 1900s. Mendel’s work was published in 1865 and long forgotten.

A diploid cell has double the set of chromosomal content. Hence there are two copies for each chromosome present. These are called homologous chromosomes. Now, genes are fragments of DNA present on the chromosomes. Hence they also occur in pairs, with one gene present on each homologous chromosomes.

Genes occur in pairs. At the start of meiosis, there are four copies of each gene. They are segregated first during Anaphase I, where each pole receives a pair of each gene.