Lecture 11

Question 1

What are 4 key evolutionary mechanisms?

Answer 1

1. Natural selection (positive or negative)
2. Genetic drift (random changes)
3. Gene flow (migration)
4. Mutation (source of new alleles; mostly random

Question 2

What are the 3 modes of selection?

Answer 2

• directional, stabilizing and disruptive selection

Question 3

explain directional selection

Answer 3

• favours one extreme phenotype, causing the average phenotype in the population to change in one direction

Question 4

explain stabilizing selection

Answer 4

• favours phenotypes near the middle fo the range of phenotypic variation, maintaining average phenotype

Question 5

explain disruptive selection

Answer 5

• favours extreme phenotypes at both ends of the range of phenotypic variation
• may initiate speciation

Question 6

Who had discoveries of particulate inheritance (genes) using pea plants

Answer 6

gregor mendel

Question 7

What is the Mendelian Inheritance

Answer 7

• classic experiment with pea plants

Question 8

explain mendelian inheritance

Answer 8

• inheritance in sexual species does not operate by “blending” characters of parents
• inheritance is “particulate,” controlled by segments of DNA we now call genes
• some traits are dominant to other recessive ones (he coined the terms)
• the type of gamete (male or female) does not affect the inheritance of traits
• pea traits chosen segregated independently of each other in meiosis (lucky choice: different genes located on the same chromosome do not segregate independently)

Question 9

Why did Mendel choose garden peas and what did he do with them?

Answer 9

• 2n =14
• easy to grow and polymorphic (many forms) for flower color and other easily visible traits of pods and seeds
• pea flowers normally self-pollinate. Therefore, Mendale artificially made crosses by removing anthers from one flower and transferring pollen from another with an artist’s brush

Question 10

What is the principle of independent assortment

Answer 10

• the genes for seed shape and seed colour assort independently, because they are located on different chromosomes and these chromosomes have 2 equally likely ways of lining up before they are segregated

Question 11

Review Mendel’s model to explain the results of a monohybrid cross

Answer 11

1. peas have 2 copies of each gene and thus many have 2 different alleles of the gene. This is true for many other organisms
2. Genes are particles of inheritance that do not blend together. Genes do not change when being transmitted between generations
3. Each gamete contains one copy of each gene (one allele). This is due to the principle of segregation - the members of each gene pair segregate during the formation of gametes
4. Males and females contribute equally to the genotype of their offspring. When gametes fuse, offspring acquire a total of 2 of each gene - one from each parent
5. some alleles are dominant to other alleles. When a dominant and a recessive allele for a gene are paired in a heterozygote, that individual has the dominant phenotype

Question 12

What are the 3 misconceptions about dominant & recessive alleles and what are their clarifications?

Answer 12

1. dominant traits are more likely to be inherited : dominant and recessive alleles are equally likely to be passed on after meiosis (50:50)
2. recessive alleles are not expressed : both can be expressed (recessives mostly if homozygous)
3. dominant alleles are more common than recessive alleles : the frequency of an allele is independent of whether it is dominant or recessive