Reproduction

Gametes are the male/female sex cells found in all organisms that reproduce sexually

They join together at fertilisation to form a zygote (containing the full number of chromosomes)

Animals- males (sperm) + female (egg cells)

Plants- males (pollen grains) + females (ovules)

Plants + Animals have 46 chromosomes in their body cells. but gametes contain 23 chromosomes.

Mammalian Gametes

Sperm cell- Lots of mitochondria provide energy for tail movement, Acrosome contains digestive enzymes to break down the egg cell's zona pellucida + and allow sperm to penetrate the egg, Flagellum allows sperm to swim towards egg cell.

Egg cell- Follicle cells form protective coating, Zona pellucida is a protective layer that sperm have to penetrate. (Much larger than sperm)

Meiosis is a type of cell division that happens in the reproductive organs to produce gametes.

Cells that are formed by meiosis have 23 chromosomes. Four new cells (gametes) that are produced are genetically different.

Crossing over of chromatids

• Each homologous pair of chromosomes pairs up, one of the chromatids from each pair cross over, one chromosome from each homologous pair ends up in each cell, each cells has a different chromatid therefore a different set of alleles,which increases genetic variation.

Independent assortment of chromosomes

• The four daughter cells formed from meiosis have different combinations of chromosomes- half from the mum (maternal) + half from the dad (paternal, when gametes are produced different combinations of each chromosome go into each cell.