Unit 5: Genetics, evolution & biodiversity 5H.1 & 5B.4 Genetics & evolution; variation By Mr. Wilson

Variation Variation can be thought of as the basis for evolution. Variation can be thought of as the basis for evolution. May be caused by inherited genes (heritable variation) or by the environment (non-heritable variation). May be caused by inherited genes (heritable variation) or by the environment (non-heritable variation). Heritable variation is the most significant in evolution. Heritable variation is the most significant in evolution.

Origins of variation During meiosis of gametogenesis: During meiosis of gametogenesis: Independent assortment of chromosomes (sometimes called random assortment or random segregation). Independent assortment of chromosomes (sometimes called random assortment or random segregation). Crossing over Crossing over Mutation Mutation Sexual reproduction: Sexual reproduction: Fusing of random gametes in populations. Fusing of random gametes in populations. Fusing of 1 of 2 gametes at each fertilisation (4 possible outcomes). Fusing of 1 of 2 gametes at each fertilisation (4 possible outcomes).

Discontinuous variation For a particular characteristic there are discreet/distinct groups of 2 or more types with no intermediates. For a particular characteristic there are discreet/distinct groups of 2 or more types with no intermediates. Examples – ABO blood group, sex. Examples – ABO blood group, sex. Is usually ‘MONOGENIC’, depending on one gene, but modern science suggests that this may not actually be the case in many examples. Is usually ‘MONOGENIC’, depending on one gene, but modern science suggests that this may not actually be the case in many examples. A limited number of phenotypes are possible. A limited number of phenotypes are possible.

Discontinuous variation There are no intermediate forms so data about discontinuous variation is usually shown using a SIMPLE bar chart. There are no intermediate forms so data about discontinuous variation is usually shown using a SIMPLE bar chart. Give another example. Give another example.

Continuous variation Where variation between individuals for a given characteristic varies along a range and there are many intermediate forms. Where variation between individuals for a given characteristic varies along a range and there are many intermediate forms. Examples – Height, weight, palm span. Examples – Height, weight, palm span. Caused by the combined effect of a number of genes – POLYGENIC. Caused by the combined effect of a number of genes – POLYGENIC.

Continuous variation Under normal conditions a frequency distribution graph will show a NORMAL DISTRIBUTION. Under normal conditions a frequency distribution graph will show a NORMAL DISTRIBUTION. What factors may cause a more random distribution? What factors may cause a more random distribution?

Discontinuous and continuous variation. Which of these types of variation is more strongly affected by ENVIRONMENTAL factors? Which of these types of variation is more strongly affected by ENVIRONMENTAL factors?

Phenotype variation Both genes and the environment can interact to produce phenotype variation. Both genes and the environment can interact to produce phenotype variation. Examples – Genes for being tall, but poor nutrition (environmental factor) means you don’t get that tall. Examples – Genes for being tall, but poor nutrition (environmental factor) means you don’t get that tall. Pea plants – Dwarf & tall varieties (genes & discontinuous variation), but a range of heights in each group due to nutrition, sunlight, competition etc. (environment & continuous variation). Pea plants – Dwarf & tall varieties (genes & discontinuous variation), but a range of heights in each group due to nutrition, sunlight, competition etc. (environment & continuous variation).