B1 Genes

There are two types of variation within a species: genetic variation and environmental variation.

Genetic variation occurs when genes are passed down to two parent's offsring.  Each of the sex cells (gametes) have 46 chromosomes and each gamete passes 23 single chromosomes down to their offspring to give the offspring a complete set of 23 pairs of chromosomes (46 overall).

Environmental variation occurs when an environmental factor affects an organism.

Most characteristics are determined by someone's genetic information however environmental factors can affect someone's characteristics too.

Alleles are dominant or recessive.  Dominant alleles are expressed by capital letters in genetic diagrams and only one dominant allel needs to be present to make that characteristic present.

Homozygous: when two of the same allele are present 

Hetrozygous: when two different alleles are present 

There are two types of repoduction: sexual reproduction and asexual reproduction.

Sexual reproduction: when genetic information from two gametes is combined to produce offspring which is genetically different to its parents.

23 chromosomes from each gamete are combined to give a full set of 46 to the offspring.  The mixture of genetic material causes variation.

Asexual reproduction: when an ordinary cell divides in two and the new cells are genetically identical to the parent cell (clones).

This is how animals grow and produce replacement cells; also organisms reproduce asexually like bacteria and certain plants.

Plants can be cloned from:

Cuttings are taken from good parent plants to produce genetically identical plants which can be produced quickly and cheaply.

Tissue Culture is where a few plant cells are put in a growth medium with hormones so they grow into new plants which are clones of the parents.  They can be made quickly, in little space and all year.

Animals can be cloned by:

Embryo Transplants are used when sperm cells from (for example) a prize pull and egg cells from a prize cow.  The sperm is used to artfically fertilise the egg cell; then the embryo develops and splits several times to make clones before any of the cells become speciaised.

Adult Cell Cloning is when an unfertilised egg cell has its genetic material removed (nucleus) before an adult body cell (e.g as skin cell) is inserted into the egg cell.  The egg cell is stimulated by electric shock to make it divide like a normal embryo.  When the embryo is a ball of cells it is implanted into a surrogate mother