Lecture 4

Lecture 4 - Outline Introduction The Neo-Darwinian s...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Evolution II: Mechanisms Outline • Introduction – The Neo-Darwinian synthesis • Sources of Variation – Mutation – Sexual recombination • Crossing over • Independent assortment • Hardy Weinberg equilibrium – Selection – Drift – Gene Flow – Assortative mating • Maintenance of genetic variation Darwin • Did not read Mendel • Thought of inheritance as a blending of traits of parents • Blending would tend to eliminate differences among individuals, and dilute advantageous traits • Breeding experiments showed that variation could be preserved across generations and selected traits could be enhanced • This refuted the blending hypothesis but there was nothing to replace it Mendelian inheritance – Refuted the idea of blending inheritance because white and red forms could be recovered from crosses among pink flowers. – Particulate inheritance Figure 23.4 Generation 1 CRCR genotype CWCW genotype Plants mate Al CRCW (al pink flowers) 50% CR gametes 50% CW gametes Come together at random Generation 2 Generation 3 Generation 4 25% CRCR 50% CRCW 25% CWCW 50% CR gametes 50% CW gametes Come together at random 25% CRCR 50% CRCW 25% CWCW Al eles segregate, and subsequent generations also have three types of flowers in the same proportions Neo-Darwinian Synthesis • First half of twentieth century • Brought Darwin’s ideas on Natural Selection together with genetics • Provided a description of how the frequencies of genes in population change due to various forces • Dealt with both qualitative and quantitative traits • Qualitative (Discrete) traits – Can be classified on an either-or basis – Eye color, blood type, flower color in Mendel’s peas (white, pink, red) – Variation usually due to one or two loci • Quantitative traits – Vary along a continuum within a population – Height or weight of individuals, bill size in birds, seed weight – Variation due to the combined effects of many genes
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Flower color in this example is a qualitative trait with three phenotypic classes: red, pink, and white. Figure 23.4 Generation 1 CRCR genotype CWCW genotype Plants mate Al CRCW (al pink flowers) 50% CR gametes 50% CW gametes Come together at random Generation 2 Generation 3 Generation 4 25% CRCR 50% CRCW 25% CWCW 50% CR gametes 50% CW gametes Come together at random 25% CRCR 50% CRCW 25% CWCW Al eles segregate, and subsequent generations also have three types of flowers in the same proportions × AaBbCc AaBbCc aabbcc Aabbcc AaBbcc AaBbCc AABbCc AABBCcAABBCC 20/64 15/64 6/64 1/64 Fraction of progeny • Quantitative variation usually indicates polygenic inheritance Figure 14.12 A simple model for skin color Evolution occurs in populations • Individual organisms do not evolve in the Darwinian sense • Natural selection acts on genes or individuals, but populations evolve • Evolution is the change in gene frequencies in populations through time Evolution requires variation • The ultimate source of variation is mutation. A mutation alters the DNA providing
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 12/01/2010 for the course BIO BILD 3 taught by Professor Christopherwills during the Fall '10 term at UCSD.

Page1 / 14

Lecture 4 - Outline Introduction The Neo-Darwinian s...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online