REPRODUCTION IN ANIMALS
IMPORTANT TERMS
Reproduction Reproduction may be defined as the process by which living things produce offspring of their own kind.
Asexual Reproduction In asexual reproduction, a new individual is formed from the cell(s) of a single parent. For example- Amoeba, Hydra, Yeast, Starfish etc.
Sexual Reproduction In sexual reproduction, two parents are required to produce new individual. For example- Most plants and mammals including human being.
Fertilization The Fusion of male and female gametes to produce a new organism is known as fertilization.
Internal Fertilization In this type of fertilization, the fusion of male and female gametes occurs inside the female’s body. For example- Mammals such as cow, horse, dog, cat and human being.
External Fertilization In this type of fertilization, the fusion of male and female gametes occurs outside the female’s body. For example- Fish, frog and starfish.
Viviparous Animals Animals that give birth to live offspring are known as viviparous animals. For example- Mammals such as cow, dog, horse, cat including human being etc.
Oviparous Animals Animals that lay eggs, which hatch into offspring are called as oviparous animals. For example- Birds, snakes, frogs etc.
Metamorphosis The transformation of larva into adult through a series of drastic changes is called metamorphosis.
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Reproduction
Reproduction is defined as the process by which living things produce offspring of their own kind.
Modes of Reproduction
There are two types of modes for reproduction.
Asexual reproduction- In this type of reproduction, a new individual is formed from the cell(s) of a single parent. Amoeba, Hydra, Yeast, Starfish, Sponges and worms reproduce asexually. Examples of asexual reproduction are Budding and Binary Fission
In binary fission of Amoeba, Nucleus first divides into two nucleus and then body divides into two parts, each part receiving one nucleus. Hence two daughter Amoeba are formed.
Cells exist in different shapes. They can be disc-shaped, polygon, rectangular, branched or even irregular. The shape of cell depends on the specific function it performs.
In hydra, a bulge known as bud, is formed.
The Bud grows to form a baby Hydra.
Then the baby Hydra separates from the parent.
Sexual reproduction- In this type of reproduction, two parents are required to produce a new organism. All plants and mammals, including human beings, reproduce sexually. Example of sexual reproduction is reproduction in Human Beings.
Both Males and Females have special reproductive cells called as gametes. The female gamete is known as ovum and the male gamete is known as sperm. Two gametes join or fuse during a process called fertilization. This initiates the formation of a baby.
The Zygote gradually develops into an Embryo. The zygote divides repeatedly to give rise to a ball of cells. The cells then begin to form groups that develop into different tissues and organs of the body. The developing structure is called an Embryo. The Embryo gets embedded in the wall of the uterus. The development continues and the stage of an embryo in which all the body parts can be identified is called a foetus. When the development of the foetus is complete, the mother gives birth to the baby. It takes 40 weeks for the child to be born.
Male Reproductive Organs
The male reproductive organs include a pair of Testes, Urethra, Two sperm duct and Penis.
Female Reproductive Organs
Female reproductive organs includes Ovary, Oviducts, Uterus and Vagina
Fertilization
The fusion of male and female gametes to produce new organisms is called fertilization. The main stages of fertilization in human being are as follows.
Types of Fertilization
There are two types of fertilization- Internal fertilization and External fertilization
Internal Fertilization- In this type of fertilization, the fusion of male and female gametes occurs inside the female’s body. Mammals such as cow, horse, dog, cat buffalo and human beings etc. reproduce by internal fertilization.
External Fertilization- In this type of fertilization, the fusion of male and female gametes occurs outside the body. Fish, frog, starfish etc. are the examples of external fertilization.
During spring or rainy season the female lays hundreds of eggs. Males deposits sperms over them. Each sperm swims randomly in water with the help of its long tail. The sperm comes in contact with the eggs. This results in fertilization known as External fertilization.
Viviparous and Oviparous Animals
Viviparous Animals- Animals that give birth to the live offspring i.e. baby, are called as Viviparous animals. Mammals such as cow, dog, cat and human being all are the examples of viviparous animals.
Oviparous Animals- Animals that lay eggs, which hatch into the offspring, are called as Oviparous animals. Birds, snakes, frogs, fish etc. are the examples of Oviparous animals.
Determination of the Sex of the Baby
The thread like structures found inside the nucleus is called chromosomes, which carry information in the form of genes.
Each cell contains 23 pairs of chromosomes, in which 22 pairs are called autosomes which are similar in males and females and one pair of chromosomes is sex chromosome. There are two types of sex chromosomes X and Y chromosomes. Female cell contains the XX pair and the male contains XY pair.
The gametes contain only one set of chromosomes consisting of one member of each pair. Ovum consists of one chromosome X while sperm may contain X or Y.
When the ovum containing X gets fertilized with sperm containing X, then the pair of sex chromosome will be XX and the baby will be a girl. If the ovum gets fertilized by a sperm containing Y chromosome, then the sex chromosomes pair will be XY and the baby will be boy.
Metamorphosis
The transformation of larva into adult through series of drastic changes is called Metamorphosis.
Metamorphosis occurs in Frogs and Butterflies
There are three main stages in the life cycle of the frog
Egg- Larva- Adult. These changes are controlled by the hormone Thyroxine.
Similarly, there are four main stages in the life cycle of Butterfly.
Egg- Larva- Pupa- Adult. These changes are controlled by two hormones- Juvenile hormone and Ecdysone.
Gender Issues and Myths
Techniques such as ultrasound, which enable doctors to determine the sex of the unborn child, were being misused by the people for killing the girl foetus inside the mother womb, which is called Abortion.
To put a stop to female infanticide (killing of girl foetus), the government has made it illegal to find out the sex of the foetus.
Many people blame the mother for the birth of a girl child. Such thinking is scientifically baseless, as the sex of the child is determined by the sperm of the father.
Cloning- It is the production of the exact copy of a cell, any other living part, or a complete organism. Cloning of an animal is done successfully for the first time by Ian Wilmut and his colleagues. They successfully cloned a sheep named Dolly. Dolly was born on 5th july1996 and died on 14th February due to lung disease.
Some Interesting Facts