Ebolution - evolution PDF

Preview

Summary

evolution...

Description

PSY1003 - biological week 18 Evolution Gradual change over time in organic life from one form into another. Theory of evolution by natural selection Consists of 4 elements: - Variation - Heredity - competition - Natural election 3 main factors - Variation - individuals are similar but not identical. Minor variations in trait. - Heredity - many of the traits that vary are passed down parents to offspring. - Competition - there is competition among individuals for scarce resources. Not all have same success in reproduction. Natural selection (the consequences): - Those who are more effective competitors will leave more offspring (have greater reproductive success) than those who are less effective. - The offspring will have inherited the successful trait from the parents. - Natural selection has occurred. - Through this process the organism becomes adapted to its environment. Natural selection: - Is a slow process - Has no foresight - Does not strive for optimal design - Produces a tree not a ladder Sexual selection ‘the process whereby physical and behavioural characteristics which promote reproductive success (and the genes which code for these) are passed on to descendants.’ - Intrasexual selection - members of the same sex compete for access to members of the opposite sex. - Intersexual selection - members of one sex choose mates of the other sex to mate with. Adaptation ‘an inherited and reliably developing characteristic that came into existence as a feature of a species through natural selection because it helped to directly or indirectly facilitate reproduction during the period of its evolution.’ (Tooby and Cosmides, 1992) Deoxyribonucleic Acid (DNA) - The genetic material - Double helix (Watson and Crick 1953- and Franklin) - Consists of o The sugar deoxyribose

PSY1003 - biological week 18

-

o Phosphoric acid o 4 base pairs: adenine, thymine, guanine and cytosine Nucleotides Makes proteins

Gene - the fundamental unit of heredity. Segment of DNA that occupies a specific site on a chromosome. Allele - A variation of a gene that affects the functionality of the protein produced by the gene. “One of the possible alternatives forms a gene, usually distinguishable form other alleles by its phenotypic effects.’ (Cummings, 2003, 502) Zygosity - the degree of similarity of the alleles for a trait. - Homozygous - gene with identical alleles of a specific trait - Heterozygous - gene with two different alleles of a specific trait. Chromosomes - threadlike structures in the nucleus that carry genetic information. Humans have 46 chromosomes (23 pairs). There are two types: - Sex chromosomes (2) o XY = M o XX = F - Autosomes (44: 22 pairs) Mutations - random events/accidents in gene reproduction - Most are deleterious - Some are neutral - Occasionally a mutation may be beneficial and will therefore be selected for: o Sickle cell anaemia. - Caused by: radiation, heat, chemicals, often unknown. A Gene’s Eye View (Dawkins, 1976) - Selection occurs at the level of the gene. - Selection does not occur at the level of the species or the individual. - It is the genes that are passed on through successive generations. - The individuals act as the vehicle for the replicators....