Variation and Evolution, Lecture notes of Biology

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VARIATION

Dr. Foster Kyei Senior lecturer

LEARNING OUTCOMES

 Define the term “variation”.  Discuss the fact that variation occurs within, as well as between, species.  Describe the differences between continuous and discontinuous variation, using examples of a range of characteristics found in plants, animals and other organisms.  Explain both the genetic and the environmental causes of variation.

Are individuals in a population of a species

the same?

 No – all members of a species share the common characteristics of that species, but there are still differences  Variation – differences between individuals of the same species  eg. All dogs have hair, but not all dogs have the same color hair

Dog Variation

**What causes variation?

Recombination** – The creation of a new set of DNA in offspring during sexual reproduction  Since each parent passes down only ½ of their DNA, the DNA in the offspring is a unique combination of DNA from both parents

Variation

Variation can be within species (Think of all the differences between individual humans) These are different varieties of the same species

Variation can be CONTINUOUS , ie have any value between two extremes. Eg: Height of human, Body mass of cats, Trumpet length of daffodils, Leaf width of shrub, Length of bacteria All these features show normal distribution (see graph)

Types of Variation

 Variation can be DISCONTINUOUS , in this case there are only a few possible categories that the characteristic can fall into.  Eg: Flower colour in a single species, Human blood group or ear lobe type, Bacteria that are or are not resistant to an antibiotic

Types of Variation

Genetic Environmental Differences that are due to the DNA inside the cells of the organism rather than the effect that its surroundings have on it. Differences that are due to the external environment. For example availability of water, nutrients, light, prevailing winds.

Sources of Variation

How does variation lead to evolution?

 Sometimes mutations or recombination results in a trait that improves an organism’s chances for survival (increases fitness)  Adaptation – a trait that helps an organism to survive and/or reproduce  There are 2 types of adaptations:

1. Structural Adaptation
2. Behavioral Adaptation

How does variation lead to evolution?

2. Behavioral Adaptation – a behavioral trait that helps an organism to survive (EX. plover birds faking injury to lure predators away from nest)

How does variation lead to evolution?

 Adaptations are traits which means they are caused by genes  Organisms with the best adaptations have the “best” genes and highest fitness  These organisms survive and reproduce more, passing on their genes, and changing the relative frequency of genes in the gene pool of the next generation (“good” genes appear more frequently)

Variation and Evolution

 Many of the differences between species are present because they help the individuals to survive.  We call these differences ADAPTATIONS. You should understand that there are Adaptations to: ANATOMY or body FORM, PHYSIOLOGY or body FUNCTION, BEHAVIOUR

 SAGUARO CACTUS  Accordion folded stem is fleshy to store water  Roots mostly less than 15cm deep but cover huge area  (^) 1 deep tap root  (^) Can absorb 750 litres water in a single storm  (^) Leaves reduced to spines to reduce transpiration rate  (^) Waxy cuticle reduces transpiration  (^) Stomata only open at night

Variation and Evolution