Why the curiosity arises together with the word “sex”? It is a question that every individual think, consider and want to understand. Basically, sex is a character which is inherited and the manner of its inheritance is somewhat akin to Mendelism.
In this living world, the body of each living organisms is made up cells. Cells are the structural and functional units of life of the living organisms. Usually, cells contain a nucleus and the nucleus serves as the commanding center of the cell. Each nucleus contains chromosomes in it.
What is chromosome?
Chromosomes are the genetic substances that help in the inheritance of characters from parents to offspring. Chromosomes are made up of one molecule of deoxyribonucleic acid (DNA). DNA contains many genes and proteins. Genes are the smallest units of DNA that control the biological characteristics of organisms.
For instance, let’s take an example of cows and maize plant. A cow resembles other cows and it’s calf. A maize plant looks like other maize plants. But the question arises as, how is it possible?
In unisexual organisms, genders or sexes are separated. Maleness or femaleness is a hereditary difference between two individuals of the same species which is determined at the moment of fertilization. There are basically two types of chromosomes in the nucleus. They are:
1. Sex Chromosomes: They’re the chromosomes that determine the sex of newly born offspring. They carry the genes for determination of sex. Only one pair of a chromosome is sex chromosome in humans.
2. Autosomes: They are the chromosomes that carry genes to determine the physical structure of the body. 22 pairs of autosomes are found in human. They regulate the growth and development of the body.
The mechanism that establishes the sex of an individual as it begins life is called sex determination.
How a baby boy or girl is born?
Humans have 23 pairs of chromosomes. One of them is somatic or autosomes which are 44 in number and the other 2 are sex chromosomes. These chromosomes are essentially needed for growth and development of body and to determine the sexes respectively. Sperm, a male gamete having (22+X) chromosome fuses with an ovum, female gamete having (22+X) chromosome to form a baby girl (44+XX) chromosomes after fertilization process and when sperm having (22+Y) chromosome fuse with ovum of female having (22+X) chromosome, a son (44+XY) is born after fertilization.
Thus, it is clear that sex chromosomes are X and Y respectively. A male has either X-Sex chromosome or Y-Sex chromosome whereas a female has either X-Sex chromosome or X-Sex chromosome.
What is a chromosomal disorder?
It is the disorder caused by the change in the number of chromosomes. If the number of chromosomes is found in proper order, it is called euploidy (in good condition). But the loss or gain of chromosomes due to the failure of proper separation of chromatids during cell division is called aneuploidy.
Types of chromosomal disorders
1. Down’s syndrome (21 chromosomal disorder): It is a genetic disorder due to the autosomal abnormality. It is caused by the presence of an additional copy of chromosome number 21. So, it is an aneuploid trisomic disease. Thus, an offspring instead of having 46 chromosomes, will have 47 chromosomes. (45+XY) in male and (45+XX) in a female.
Note: The women above 40 years are likely to produce children with Down’s syndrome as they’ve poorly developed ovum in them.
Symptoms of Down Syndrome:
- Rounded face, broad forehead
- Short stature, partially opened mouth
- Short neck, undeveloped gonads
- Small stubby fingers
2. Klinefelter’s Syndrome (Seen in Male): It is a sex chromosomal disorder and occurs by an additional copy of X chromosome in a male. This means that when an abnormal egg (22, XX) and a normal sperm (22, Y) or a normal egg (22, X) and an abnormal sperm (22, XY) come from parents, the offspring will have one extra X-sex chromosome. Thus the offspring has (44+XXY) chromosome in them. In this condition, a male will develop a lot of female characters. Dr. Harry Klinefelter first described this defect in 1942.
- Less muscular body
- Underdeveloped testes
- Enlargement of breasts
- Sparse body hair
3. Turner’s Syndrome (Seen in Female): This sex chromosomal disorder is caused in the offspring by fertilization of an abnormal egg (22,0) and a normal sperm (22, X) or a normal egg (22, X) and an abnormal sperm (22,0). Here, the female has (44+X)=45 chromosome instead of 46 chromosomes. Female will have poorly developed female characters.
- Sterile (Sterility)
- Poorly developed ovaries
- Underdeveloped breasts, small uterus
- Broad chest, no menstrual cycle.
Article Written By Pranish Lamsal. Special Thanks To Bandana Adhikari, Rupa Chhetri, Asmita Pantha, Prabina Chaudhary, Govinda Pandey, Samikshya Dhakal for their kind co-operation and assistance to write the article.