Question

What are chromosomes XX and XY and what is their work in reproduction?

Answer 1

Chromosome is present inside the nucleus of the cell. It is made up of long chains of genes that carry hereditary information. Chromosome is formed from the dense chromatin. Chromatin is made up of DNA and proteins which are tightly packed together. There are twenty-three pairs of chromosomes present in each cell. Chromosomes are replicated and distributed evenly to daughter cells during cell division.

Complete explanation:
Each cell in the human body has twenty-three pairs of chromosomes. The first $22$ pairs are called autosomes Both males and females have the same autosomes. The twenty third pair is called allosome or the sex chromosome which differ between males and females. Females have two copies of the X chromosome and males have one X and one Y chromosome as sex chromosomes.
In organisms with XY sex determination system, XX and XY are two types of sex chromosome combinations. This type of sex determination occurs in humans, mammals, some plants, snakes and insects. The X and Y chromosomes also show mendelian inheritance.
During fertilization, when the X chromosome of the mother combines with the X chromosome of the father, then the baby is male. When the X chromosome of the mother combines with the Y chromosome of the father, the baby is female. In this way the XY chromosome or sex chromosome plays an important role in reproduction.

Note:
The sex of the baby can be determined through ultrasound test or blood test. At around the sixth week of pregnancy the baby will develop a small bud called genital tuber at the site of the genitals. It looks the same for both the male and female babies. Around 9th week the sex organs begin to form from the genital tuber and by the end of ${20^{th}}$ week, the external sex organs are fully formed for both male and female babies. During the ultrasound the sex organs are visible through which the doctors can confirm the sex of the baby.