Reproduction and Meiosis

Reproduction

• Sexual reproduction is where genetic information from two organisms is combined to produce offspring that are genetically different to either parent.
• In sexual reproduction, the mother and father produce gametes by meiosis.
• In humans, each gamete contains 23 chromosomes- half the number of chromosomes in a normal cell.
• The egg and the sperm cell then fuse together to form a cell with the full number of chromosomes.
• Sexual reproduction involves the fusion of male and female gametes and because there are two parents, the offspring contain a mixture of their parents' genes.
• This is why the offspring inherits features from both parents- it's received a mixture of chromosomes from its mother and its father.
• This mixture of genetic information produces variation on the offspring.
• Flowering plants can reproduce in this way too. They also have egg cells, but their version of sperm is pollen.
• In asexual reproduction there's only one parent so the offspring are genetically identical to that parent.
• Asexual reproduction happens by mitosis- an ordinary cell makes a new cell by dividing in two.
• The new cell has exactly the same genetic information as the parent cell- it's called a clone.
• In asexual reproduction there's only one parent. There's no fusion of gametes, no mixing of chromosomes and no genetic variation between parent and offspring. The offspring are genetically identical to the parent- they're clones.
• Bacteria, some plants and some animals reproduce asexually.

Meiosis

• Gametes only have one copy of each chromosome, so that when gamete fusion takes place, you get the right amount of chromosomes again.
• To make gametes which have half the original number of chromosomes, cells divide by meiosis. This process involve two cell divisions. In humans, it only happens in the reproductive organs.
• Before the cell starts to divide, it duplicates its genetic information, forming two armed chromosomes- one arm of each chromosome is an exact copy of the other arm. After replication, the chromosomes arrange themselves into pairs.
• In the first division in meiosis, the chromosome pairs line up in the middle of the cell.
• The pairs are then pulled apart so each new cell only has one copy of each chromosome. Some of the father's chromosomes and some of the mother's chromosome go into…