1. Chapter 16: perpetuation
06 Many organisms reproduce by asexual means

2. 06.1 Understand that, in eukaryotes, asexual reproduction involves mitosis
Survival of a species involves reproduction
Two methods: sexual and asexual
Many plants and animals can do both – not mutually exclusive
SEXUAL REPRODUCTION- is when at any time tow cells fuse together or fertilise each other
The cells are gametes and half the chromosome number-haploid number
When gametes combine- chromosome number restored- diploid number
Gametes are produced by meiosis- in the gonads

3. Asexual reproduction;
No fertilisation or fusion
Offspring just grow from a part of the adult
In eukaryotes this is by mitosis (C8.4)
QUICK AND EFFICIENT
TWO MAIN METHODS IN ANIMALS:
Budding:
Hydra produce buds that can break off and grow into a new identical organism- mitosis is the process then involved in producing the new cells for the growing hydra

4. Fragmentation: The plant Kingdom: Asexual reproduction common
Some animals can fragment
The adult body breaks into several pieces and each bit grows into another adult
Sea corals, sponges,, flat worms, some insects, starfish and reptiles
The plant Kingdom:
Asexual reproduction common
Rhizomes- underground fleshy structures-iris’
Fleshy tubers- potatoes
Runners- couch grass and strawberries

5. Vegetative propagation:
Process where part of an adult plant is broken off and can be grown into a separate supporting plant body
New tissue is grown by mitosis form the existing cells
These can be modified-stems, roots or leaves
Carried away by wind/water to another place where they will grow
Important to humans we can grow what we need and be specific
Seedless watermelons, navel oranges, sultana grapes- all propagated this way
Can have desirable characteristics

6. 06.2 Explain why the offspring of asexual reproduction are genetically identical to their parent. In asexual reproduction genetic variation only occurs through mutation
Asexual reproduction- identical offspring to parents
Not always in looks, but in genetic makeup- environment can alter things- discolour, break things off etc.
**** mitosis produces identical copies of cells/therefore offspring produced are identical to the parent
****** mutations in the DNA are the only way that variation is introduced into the offspring of parents that reproduce asexually
Mutations-
random
caused by mutagens- chemicals, radiation, uv light
Asexual reproduction does mean that less variation means less ability to survive changing environments: therefore more susceptible to death/extinction

7. Germ line mutations:
If a mutation occurs in a gamete – fertilisation occurs in sexual reproduction- the zygote and all cells of the body that develop from the zygote will be affected- a germ line mutation
If the mutation only occurs in the zygote a large proportion of body cells affected but not all.

8. 07 sexual life cycle involves meiosis and fertilisation
Somatic or tissue cells- all cells not gametes (egg or sperm)
Diploid- pairs of homologous chromosomes
A set of human chromosomes- karyotype
Homologous chromosomes- similar shaped pair, similar banding, and structure
At one gene locus- each chromosome has a gene that codes for the same characteristic- one of the pair is from dad/one from mum
Humans have 23 pairs/ or 46 chromosomes
Each chromosomes has about 1000 genes on it
Genes on the same chromosomes are inherited together
If a copy of the gene is the same or different in each parent the effects/outcomes will vary- the different copies of the same gene are called alleles

9. 07.2 Explain why the products of meiosis are haploid cells and contain a single set of chromosomes
Sexual reproduction involves production of gametes with half the number of chromosomes Fertilisation involves them coming together and restoring the chromosome number MEIOSIS- name given to process by which gametes are made (Should know this from year 11)

10. 07.3 Explain the importance of crossing over and independent assortment in meiosis
In prophase homologous chromosomes/two identical chromatids, lie adjacent to each other
The four chromatids are called a tetrad
The chromosomes appear to be in contact with one another at a number of points- chiasmata
Certain enzymes apparently snip bits (identical sites on ach non sister chromatid and “swap” the genes over
This is crossing over
Two or three crossing over events occur for each pair of chromosomes during meiosis
Result is different combinations of genes- greater variety in the offspring- crossing over results in recombinant genes
ITS RANDOM
CAN CROSS BACK OVER
( WORK SHEET AND MEIOSIS SQAURE DANCE ANIMATION)

11. Independent Assortment
This means that each pair of homologous chromosomes separates independently of the others
Accounts for lots of the diversity in sexually reproduced organisms
Occasionally are mutations too
Total number of genes is the gene pool- compared to a pack of cards a mutation is like a new card, whereas assortment and random combination is like shuffling the pack
Diagram next slide

13. 07.4 Know that fertilisation restores the diploid number
In most animals and some plants an organism is either male or female and only produces male or female gametes
In some animals and MOST plants one organism may produce both male and female gametes
Fertilisation is the beginning of a new genotype- occurs in different places but always in a watery medium
In humans and most animals its in the oviduct and in flowering plants the ovary of a flower
Frogs and fish its external- as the eggs and sperm are mixed