Mechanisms of Evolution (Siva-Jothy)

Question 1

Evolution

Answer 1

Any change in gene frequency

Question 2

Gene Frequency

Answer 2

Proportional representation of a gene in the population

Question 3

Pure breeding

Answer 3

Breeding back to the same genotype as the parents

Question 4

Important points on Mendelian Inheritance

Answer 4

Heredity is not blending
-Particulates (discrete) cannot blend together, e.g. not half smooth, half wrinkly - only one or the other.

Acquired characteristics are not inherited
-Changed characteristics are not passed on

It does not produce a directional change in gene frequencies
-It does not produce evolutionary change, there is no change in gene frequency, only genotype and phenotype.

Question 5

Conditions for Hardy-Weinberg

Answer 5

• Infinite population size (so no genetic drift)
• No mutation
• Mendelian Inheritance
• No selection
• Random mating

As these are requirements of the H-W equilibrium, where evolution is not occurring, they could be some of the mechanisms of evolution

Question 6

Genetic Drift

Answer 6

(Only in small populations)
GD is more likely to happen in small populations
-If population <100, drift is very important
-If population >100,000, drift is negligible

E.g. Human blood groups in Italy
-Blood group frequencies vary a lot between villages
-Blood group frequencies are similar between cities
Villages have smaller populations, so genetic drift is much more likely

Question 7

Mutation

Answer 7

Mutation: A heritable change in genetic material
Mutation might involve;
-Change in chromosome
-Change in gene

Mutation occurs at a very low rate (10-9-10-4), so is relatively unimportant as a mechanism of evolution.

Question 8

Non-Mendelian Inheritance

Answer 8

• Meiotic Drive
• Molecular Drive
• Inheritance of acquired characteristics

Question 9

Meiotic Drive

Answer 9

Meiotic drive genes distort gene segregation so that gametes that don’t carry the meiotic drive genes die.

Meiotic driveis a type ofintragenomic conflict, whereby one or morelociwithin agenomewill affect a manipulation of themeioticprocess in such a way as to favor the transmission of one or moreallelesover another, regardless of its phenotypic expression.
E.g. segregation distorter in Drosophila
-Meiotic drive is rare.

Question 10

Molecular Drive

Answer 10

Molecular drive genes are able to convert slightly different genes into identical copies of themselves.
Molecular drive is rare.

Question 11

Inheritance of acquired characteristics

Answer 11

The main problem with this theory:

• No proposed mechanism
• No detrimental characteristics passed on

Inheritance of acquired characteristics doesn’t occur.

Question 12

Selection

Answer 12

YES
Selection occurs when genotypes differ in their ability to pass genes on to the next generation
-If a genotype is successful, its genes will increase frequency
-If a genotype is unsuccessful, its genes will decrease frequency.

Question 13

Types of Selection

Answer 13

Artificial selection: Humans deciding characteristics that are beneficial to keep in the gene pool.

Natural selection: Traits that enhance survival are selected for.

• Avoiding of predators/pathogens
• Feeding and parental care (higher chance of survival).

Sexual selection: Drives non-random mating
-Sexually selected traits
-Birds courting displays and behaviours, e.g. large colourful feathers
Fighting to “guard” females, selecting for weapons.

Question 14

Random Mating

Answer 14

This does not occur due to sexual selection

Question 15

Summary

Answer 15

Mechanisms of Evolution:

• Genetic Drift YES
• Mutation NO
• Non-Mendelian Inheritance NO?
• Selection YES
• Random Mating NO