Variation and adaptation Objectives Know what is variation? Understand why it is significant? Explain how variation arise? Understand that variation leads to adaptation

Variation - the presence of variety/differences between individuals. Variation can occur within (intra) a species or between (inter) species. There are 2 main causes of variation: – Genetic – Environment There are 2 types of variation: – Continuous – Discontinuous

Genetic Variation What are alleles? Alleles are different forms of the same gene e.g. the gene for eye colour may be a blue allele or a brown allele but it is still eye colour All organisms have a different combination of alleles

Where does genetic variation come from? In sexually reproducing organisms it comes from events in meiosis Crossing over during prophase 1 Independent assortment during metaphase Random fusion of gametes It may also arise from random mutations in the DNA

Environmental Variation Not all genes are active at once Environment can effect which genes are active at any one time Food – obesity Sun – skin colour Environmental variation can not be inherited

Discontinuous variation Two or more distinct categories with no intermediate values. Members of a species may be evenly or unevenly distributed between categories. Sex – M or F Human blood groups – A, O, B, AB

Discontinuous Variation Usually categorical (has a label assigned rather than a number) Primarily due to genetic variation and very little influence of environment Usually determined by a single gene with only 2 or 3 possible alleles

Continuous variation There are two extremes and a full range of intermediates. Most individuals are close to the mean value. The number of individuals at the extremes are low. E.g. Height in humans or length of leaves on a tree.

Continuous Variation Can be due to genetics and/or environment Usually a result of the combination of many different genes and alleles and then affected by environment too Often assigned numerical values but not always, like eye colour and skin colour

Adaptations

An adaptation is a feature that enhances survival and long term reproductive success.

A well adapted organism will be able to: Find enough food or photosynthesise well Find enough water Gather enough nutrients Defend itself against predators and diseases Survive the physical conditions of its environment such as changes in temperature, light and water levels Respond to changes in its environment Have enough energy left over to reproduce successfully.

Behavioural Adaptations Physiological Adaptations Anatomical Adaptations Earthworms will retract into their burrows if you touch them – adaptation to not being eaten by birds. Saccharomyces can respire sugars aerobically or anaerobically depending on the supply of oxygen Legionella bacteria have flagella to help them move independently.

Adaptations of xerophytes Behavioural: Close stomata to reduce water loss Folding leaves to trap humid air Open stomata, leaves wilt, reduces SA exposed Physiological The mechanisms that allow for stomatal opening and closing

Marram Grass Specialists at living on sand dunes Leaf rolled up to trap air inside Thick waxy cuticle to reduce water evaporation from surface Trapped air inside with high water vapour potential Hairs on lower surface reduce movement of air Stomata in pits to trap air with moisture close to the stomata Fleshy stem or leaves Extensive roots Reduced leaf size

Summary of Xerophyte Adaptations AdaptationHow it WorksExample Smaller leaves shaped like needles. Densely packed spongy mesophyll Thicker waxy cuticle Closing of stomata Hairs on the surface of the leaf Pits containing stomata at the base Rolling of leaves Low water potential inside leaf cells.