Sex Determination

Genetic information is transferred to the offspring from their parents by the means of asexual or sexual reproduction. Transferring traits from parents to their offspring is called heredity and it is also known as biological inheritance or inheritance. Natural selection is the way in which the species evolve and through heredity, many variations can evolve in species which finally leads to evolution. Genetics is known as the study of heredity in biology. Genotype is the complete set of genes present in an individual. Genes are the ones that control all inherited trait in an organism.

Evolution

Over successive generations change in heritable characters in population is called evolution. Genes are passed from parents to offspring through reproduction and through genes, these characteristics are expressed. When the processes like natural selection and genetic drift occur in a population then evolution takes place. Heritable characters constantly over generations as the characters which are common or rare in a population are decided by evolutionary pressure which changes constantly. Variations that are seen at all levels i.e., at the level of species, biological organization, organisms, molecules, etc. are the result of evolution. 

Natural selection has three ways to determine whether the organism is fit for survival or not i.e., behavior and structural traits vary among populations, the Rate of reproduction and survival differs among individuals, and fit traits can pass from generation to generation. Through the evolution of this method, we can determine which offspring are more able to survive in a population. So, to survive in the respective scenario the fit traits are passed on to the next generation which leads to variations in the characters of the individual which ultimately leads to evolution. Through the evolution of the species i.e., by passing on the useful characters and leaving behind the useless characters, we can able to see the present biodiversity around us which is the result of the same process. 

Sex Determination

 

The process of determining of the sexual characteristics of an individual is known as sex determination. Usually, there are two sexes when an offspring is born through sexual reproduction. Hermaphrodite character is seen in some species in which both male and female organs are present in one individual. When a female reproduces without fertilization i.e., through parthenogenesis then it gives birth to offspring of one sex only. Sexual characters or sexual morphology can be determined by different genes or different alleles. Usually, the process of sex determination is a genetic process. Due to the different combinations of chromosomes, different sexes originate like XY, ZW, XO, etc. The Domino effect is followed as there is one main gene called a sex locus which differentiates the sex of an organism and the other genes follow it. Through variations in environment sex of the fetus can be determined. Nowadays, there is no such system that can determine the sex of the fetus accurately but in the future to be 100 % sure about the sex of the child in a worm they are developing such systems which can analyze initialized signals of reproduction through which they can tell the sex of the offspring in worm accurately. These systems will also clarify hermaphrodite individuals who have fully or partially male and female reproductive organs. In ancient times this technique was developed to cure genetic and hormonal diseases in fetuses. As there are many hormonal and genetic diseases that can not be cured after birth but through the technologies, those diseases can be cured inside the worm. In this technique cells from the worm are taken and tests are carried out through which the sex of the fetus is determined along with any diseases that it carries. But later on, people start misusing this technique by abording the girl child. As the misuse of this increased the government banned this technique and now the tests are done but the sex of the fetus is not revealed.

 

XY/XX Sex Chromosomes

It is usually found in humans and also in mammals and in some insects. Males have XY chromosomes in this system whereas the female has the same set of chromosomes i.e., XX. The size and shape of these chromosomes are different. In fruit flies, the sex is determined as the egg gets fertilized while in humans the sex is determined lately.

XO/XX Sex Chromosomes

Male only carry one chromosome i.e., XO while the female carries the XX chromosome in this system of sex determination. The absence of a chromosome is determined by O. Across the two chromosomes, the number of genes that get expressed will tell us about the sex of the offspring. Usually, this system is observed in crickets of Orthoptera order, cockroaches from Blattodea, insects, grasshoppers, etc.

ZZ/ZW Sex Chromosomes

This system is seen in some reptiles, some insects, birds, etc. In this system, the male is identified as having two same sets of chromosomes i.e., ZZ while the female carries a ZW set of chromosomes. DMRT1 in chickens is found to be responsible for the expression of these genes. The chromosome which is smaller means it carries important characters while the other one that is large carries less important characters.

Frequently Asked Questions

Question 1: Give the importance of evolution and heredity?

Answer:

Heredity determines the traits which passes on to the next generation. It is responsible for passing the new and fit traits to the next generation while evolution is important for the change in population. Variation is very important part of population as the environmental conditions changes rapidly so for the species to survive in respective changing environment it is very important for them to evolve accordingly.

Question 2: Is heredity important to humans. If yes, then why?

Answer:

Yes, heredity is very important for humans because the fundamental and structural unit of our genome is gene and gene is carried through the process of heredity. Moreover, our whole genetic makeup, our behavioral activities are the results of the genes that are carried by heredity from our parents. So, it won’t be wrong if we say that all the characters and the whole personality of an individual is the result of heredity.

Question 3: Explain a method by which the sex of human offspring can be determined.

Answer: 

Each parent gives one chromosome to the offspring. From the mother, one X chromosome is received as the mother carry a set of the same XX chromosome whereas from the father either X or Y can be received as the father carry a set of different chromosome i.e., XY. It is not wrong to say that the sex of offspring can be determined by the chromosome that the offspring received from his father. If the offspring is having XX set of chromosome then it’s a baby girl and if the offspring carry XY then it will be a baby boy.

Question 4: Explain the sex chromosome and tell us the pair of sex chromosomes present in human beings.

Answer: 

Chromosome that differs from other chromosomes in shape, size, and behavior which is heterotypical chromosome, allosome, and idiochromosomes known as sex chromosomes. In human, only one pair of sex chromosomes are present which are typically mammal allosomes. There is a difference between autosomes and allosomes i.e., allosomes are different from one another due to which they determine sex like XY is a set of chromosome which are different from each other due to which they determine the sex whereas autosomes are same pair of chromosomes which are same in both male and female.  

Question 5: Give the difference between the homogametic and heterogametic sex determination systems.

Answer: 

Usually, there are two types of systems by which we can determine the sex of offspring i.e., the homogametic sex determination system which has similar gametes, and the heterogametic sex determination system which carries different gametes. Both systems can be seen in all living organisms. The organisms in which have homogametic system is seen in female i.e., seen in human beings, insects, true bugs, grasshoppers, cockroaches, roundworm (XX), produces one type of eggs (A+X) whereas in organisms where females shows heterogametic system like in reptiles, birds, moths, butterflies produces two different types of eggs (A+W), (A+Z). Same goes for males where they show homogametic system produces one type of sperms (A+Y) i.e., in human beings and where they show heterogametic system in cockroaches there produces two types of sperms (A+X), (A+Y).