Reproduction

Sexual and asexual reproduction

meiosis leads to 4 non-identical cells being formed

mitosis leads to 2 identical cells being formed from 1


Sexual reproduction involves the fusion of male and female gametes (fertilisation)

There is therefore a mix in genetic information as every gamete is different.

This leads to a variety in offspring.

  • Gametes are where there are only one type of cell where the chromosomes are not paired.

  • Gamete cell are made through the process of meiosis.

Human gamete cells: Sperm(23) ,egg(23)

Flower cells: Pollen, egg


Asexual reproduction involves only one parent

No fusion off gametes.

Happens using mitosis where two identical cells are formed from one.

There is no mixing of genetic information.

This leads to genetically identical offspring (clones).

Meiosis

Meiosis is the formation of four non-identical cells from one cell.

Cells in reproductive organs divide by meiosis to form gametes.

  1. Chromosomes are copied(doubled information)

  2. The cell divides into 2 each with half chromosomes

  3. Each cell divide again producing 4 cells each with a quarter amount of chromosomes forming gametes.


Each gamete are genetically different from each other as the chromosomes are shuffled during the process which results in random chromosomes ending up in each of the 4 cells.


  • The gametes with 23 chromosomes join to produce a cell with 46 chromosomes(fertilisation).

This restores the full number of chromosomes.

  • The new cells now divide by mitosis and the number of cells increases.

  • As the embryo develops, the cells differentiate.

Advantages and disadvantages of sexual and asexual reproduction


Sexual Reproduction

Asexual Reproduction

Advantages

Produces variation in offspring:

  • If environment changes the organism will have a characteristic to survive

Selective breeding:

  • Allows for a mixing in genetic information

  • Speeds up natural selection

  • 1 parent so more efficient in time and energy.

  • Because it’s fast many clones can be produced rapidly.


Disadvantages

Slower, takes more time and energy to find a mate.

Since genetically identical, there is a risk they could all die if conditions become unfavourable.

Organisms that can use both to reproduce:

Malarial parasites

  • Reproduces sexually in mosquitos

  • Reproduce asexually in in human hosts

Fungi

  • Reproduce sexually to produce variation in offspring

  • Reproduce asexually by spores

Flowering plants

  • Reproduce sexually to produce seeds

  • Reproduce asexually by runners(strawberry plants) bulb division(daffodils)

DNA and the genome