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Flashcards in Modern Synthesis Deck (17)
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1

Mendel

(1822-1884) - Answered Darwin's questions on method of inheritence
-1858 conducted experiments on inheritance in peas
-Published 1866

2

Particulate inheritance (Genetic inheritance)

Characteristics of organisms are determined jointly by particles inherited one from the mother, one from the father

3

Independent segregation

each of these two particles (from the mother and the father) is equally likely to be transmitted when gametes are formed

4

Mendel's Three Principles

1. Principle of particulate heredity

-Large no. of independent irreducible particles

-Retain distinctive identity

-Disproved ‘blending’
2. Principle of segregation (1st law)
-Hereditary particles come in pairs

-1 of each pair from each parent
3. Principle of independent assortment (2nd law)
-Particles for different traits inherited independently of one another

-Meiosis -genes on separate chromosomes sorted independently

5

Fisher, Haldane, Wright

Three biometricians were important in unifying Mendelism and Darwinism by the early 1930s

6

Polygenic inheritance

Variation in continuously varying traits is based on several or many discrete, particulate genes, each of which affects the trait slightly

7

Origin of Mutation

-New genetic variation arises due to random mutation
• Mutations occur during DNA replication.
• Genes mutate, usually at a fairly low rate that a mutation will have any beneficial effect (most will be neutral or deleterious).
• The phenotypic effect of such mutations can range from undetectable to very great.
• The variation that arises by mutation is amplified by recombination among alleles at different loci.

8

Recombination

-Occurs at Meiosis
-In sexually reproducing species, recombination allows for the number, type and combination of alleles on each chromosome in each gamete to change each generation

9

The Modern Synthesis

Term coined by Julian Huxley in 1942, the unification of Darwinism, Mendelian genetics and mutation theory

10

Disruptive selection

Selection for small and large individuals - two extremes

11

Stabilizing selection

Selection for midsized individuals - middle of normal distribution curve
-Selection against both homozygotes
• Only heterozygotes (Aa) survive and reproduce
• Balanced polymorphism (frequency of two alleles (A and a) can remain at 50%)
e.g Sickle cell trait in African malarial zones

12

Directional selection

Selection for one extreme - e.g large or small individuals.
Selection against one of the homozygotes e.g aa not selected.
Linked to European diseases:
• small pox
• the bubonic plagues from 14Cth?

13

Culture and natural selection

Modern humans have been able to alter the selective pressure for or against certain genes
e.g. modern medicine and retinoblastoma
e.g. introduction of farming and lactose tolerance

14

Reprogenetics

Parental control over genes of their offspring

15

Gene-culture

Dual inheritance theory (DIT), also known as gene–culture coevolution or biocultural evolution, was developed in the 1960s through early 1980s to explain how human behavior is a product of two different and interacting evolutionary processes: genetic evolution and cultural evolution

16

Co-evolution

The influence of closely associated species on each other in their evolution.

17

Genetic Drift

Evolution, or change in gene pool frequencies, resulting from random chance. Genetic drift occurs most rapidly in small populations. In large populations, random deviations in allele frequencies in one direction are more likely to be cancelled out by random changes in the opposite direction.