Railway Science (Biology-Reproduction in Animals)

It is called temperature dependent sex determination (TSD). In most species, gender is determined during fertilization. However, the sex of most turtles, alligators, and crocodiles is determined after fertilization. The chromosomes which are responsible for the determination of sex are known as Allosomes.

Obesity is a complex disease involving an excessive amount of body fat. Growth of nails also does not constitute a part of pubertal development. Puberty - Process of physical changes (happens between ages 10 and 14 for girls and ages 12 and 16 for boys) through which a child's body matures into an adult body capable of sexual reproduction.
It is initiated by hormonal signals from the brain to the gonads - the ovaries in a female, the testes in a male, associated with emotional and hormonal changes as well as physical changes such as breast development in females (thelarche), genital changes in males, voice changes, an increase in height, and the onset of menstruation (menarche).

Different species use different strategies to determine sex of a newborn individual. It can be environmental cues or genetically determined. Environmental Cue:- In some animals, the temperature at which fertilized eggs are kept determines whether the developing animal in the egg is male or female. Ex- lizard. In some animals like the snail, an individual can change sex under different stress and environmental conditions.
Genetically :- In humans a child who inherits an X chromosome from her father will be a girl and one who inherits a Y chromosome from the father will be a boy, because in the case of humans the males determine the gender of the child.

When a cell divides, each daughter cell receives an identical copy of the DNA. This is accomplished by the process of DNA replication. It helps in the transfer of information or characters from parents to offspring.
This process involves several enzymes and other proteins. During RNA replication, the gene-start and gene-end signals are ignored and an exact complementary copy of the genome (antigenome) is synthesized.

Two types of reproduction in animals : Sexual Reproduction - When two parents (opposite sex) participate in the reproductive process and Asexual Reproduction - When offspring is produced by a single parent. Different types of asexual reproduction that occur in animals are Regeneration, Budding, Fragmentation. A basic event in reproduction is the creation of a DNA copy.

Two factors that cause variations during reproduction are errors in DNA copying and sexual reproduction. Figure would represent the situation if a single individual reproduces, as happens in asexual reproduction.
If one bacterium divides, and then the resultant two bacteria divide again, the four individual bacteria generated would be very similar. There would be only very minor differences between them, generated due to small inaccuracies in DNA copying.

A baby's sex is determined at time of fertilization. Out of the 46 chromosomes that make up a baby's genetic material, only 2 (1 from the sperm and 1 from the egg) determine the baby's sex.
These are known as the sex chromosomes. Every egg has an X sex chromosome; a sperm can have either an X or a Y sex chromosome. If the sperm that fertilizes an egg has an X chromosome, the baby is female; if it has a Y chromosome, the baby will be a boy, so male is responsible for human sex determination.

Epididymis is the tube which moves the sperm from the testicles. Vas deferens - A tube in which the sperm is stored and it carries the sperm out of the scrotal sac. The vas deferens is between the epididymis and the urethra and connects these together.

Humans have 23 pairs of chromosomes; 22 pairs are Autosomes and only one pair is the ‘Sex Chromosome’, which actively takes part in the process of sex determination.
Male has one X and one Y (XY, X-chromosome is larger while Y-chromosome is smaller) sex chromosome (both active). Female has both X (XX) sex chromosomes (one is active). All children will inherit an X chromosome from their mother.
Thus, the sex of the children will be determined by the type of chromosome inherited from their father. A child who inherits Y chromosome will be a boy and who inherits X chromosome will be a girl.

Chromatin material - Genetic material consisting of DNA, Whenever the cell is about to divide, the chromatin gets condensed to form the chromosomes. Chromosome - Thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA).
Gene - The basic physical and functional unit of heredity. Genes are made up of DNA. Nucleoplasm - A semi-fluid which contains a number of enzymes which help in the synthesis and functioning of DNA and RNA.