Reproduction in Animals

• Reproduction is essential for the continuation of species and ensures the continuation of similar individuals across generations.

Modes of Reproduction

• Animals reproduce through sexual or asexual reproduction.

Sexual Reproduction

• Sexual reproduction starts with the fusion of male and female gametes.

Male Reproductive Organs

• Male reproductive organs include testes (singular: testis), sperm ducts, and a penis.
• The testes produce male gametes called sperm, with millions produced by the testes.
• Sperm are small cells, each with a head, middle piece, and tail, containing all the usual cell components.

Female Reproductive Organs

• Female reproductive organs include ovaries, oviducts (fallopian tubes), and the uterus.
• Ovaries produce female gametes called ova (eggs).
• A single matured egg releases into the oviduct by one of the ovaries monthly in human beings.
• The uterus is where the development of the baby takes place.
• Similar to sperm, an egg is also a single cell.

Fertilisation

• Fertilisation begins with the fusion of a sperm and an ovum, where one sperm fuses with the egg.
• The nuclei of the sperm and egg fuse during fertilization, forming a single nucleus.
• This results in a fertilised egg or zygote.
• Fertilisation is the meeting of an egg cell from the mother and a sperm cell from the father.
• The new individual inherits characteristics from both parents.
• Internal fertilisation occurs inside the female body, seen in humans, cows, dogs, and hens.

Test Tube Babies

• In vitro fertilisation (IVF) involves collecting freshly released eggs and sperm, keeping them together for fertilisation outside the body.

• If fertilisation occurs, the zygote develops for about a week and is then placed in the mother's uterus.

• Babies born through this technique are called test-tube babies; babies do not grow in test tubes.

• In external fertilisation, such as in frogs and fish, the female lays eggs, and the male deposits sperm over them in the water. Sperm swim to the eggs, resulting in fertilisation.

Development of Embryo

• The zygote divides to form an embryo, a ball of cells that develops into different tissues and organs.

• The embryo embeds in the wall of the uterus for further development.

• As the embryo develops in the uterus, body parts gradually form.

• The stage where all body parts can be identified is called a foetus.

• Complete foetus development leads to the mother giving birth.

• In hens, after fertilisation, the zygote repeatedly divides and travels down the oviduct, forming protective layers, including a hard shell.

• The embryo develops inside the egg for about 3 weeks while the hen provides warmth.

• The chick develops inside the egg and eventually bursts it open.

• External fertilisation embryos develop outside the female body, growing within egg coverings until they hatch, like tadpoles in ponds.

Viviparous and Oviparous Animals

• Viviparous animals give birth to young ones, while oviparous animals lay eggs that develop into young ones.

Young Ones to Adults

• Newly born or hatched individuals grow into adults.
• Some animals' young ones look very different from the adults, like the life cycle of a frog (egg → tadpole → adult).
• Tadpoles transform into adults through metamorphosis.
• In human beings body parts are similar from birth.

Asexual Reproduction

• Hydra and amoeba reproduce asexually.
• In hydra, new individuals develop as buds, outgrowths from a single parent, called budding.
• Amoeba reproduces by binary fission, dividing its nucleus and body into two, creating two amoebae from one parent.

Cloning

• Cloning is producing an exact copy of a cell, living part, or organism.
• Dolly the sheep was the first successfully cloned mammal.
• Cloning Dolly involved taking a cell from a Finn Dorsett sheep and inserting its nucleus into an egg from a Scottish blackface ewe (with the nucleus removed).
• The resulting egg was implanted into the Scottish blackface ewe, and Dolly was born, identical to the Finn Dorsett sheep.