Lecture 4: Evolutionary Significance of Genetic Variation

Question 1

Where does heritable variation come from?

Answer 1

Mutation, independent assortment, recombination.

Question 2

What is mutation

Answer 2

• a stable change in the DNA sequence
• occurs at a low but variable rate
• not directed by organism or environment

Question 3

Mutations can be…

Answer 3

neutral, deleterious, lethal, or beneficial

Question 4

What can affect rate of mutation?

Answer 4

Environmental factors like high temperature, mutagens.

Question 5

Point mutation

Answer 5

Mutation affecting only one nucleotide in gene sequence. Involved substitution of one nucleotide.
ATGCAGT –> ATCCAGT

Question 6

Frameshift mutation

Answer 6

Insertion/deletion. Extra nucleotide inserted in sequence affects all codons after insertion or deletion
ATGCAGT –> ATGGCAGT

Question 7

Silent mutation

Answer 7

Type of point mutation. Because of the redundancy of genetic code, there is no change in the amino acid.

Question 8

Missense mutation

Answer 8

Type of point mutation. The substitution changes the amino acid.

Question 9

Nonsense mutation

Answer 9

Type of point mutation. Occurs when nucleotide substitution results in an amino acid codon changing to a stop codon (makes polypeptide too short and thus non functional)

Question 10

Duplication Mutation (changes in repeat number)

Answer 10

codon is abnormally copied

Question 11

Translocation mutation

Answer 11

Chromosomal level mutation where there is a translocation of groups of base pairs from one part of chromosome to the other

Question 12

Inversion mutation

Answer 12

Chromosomal level mutation which occurs when a segment on the chromosome is cut out, turned around and reinserted backwards.

Question 13

What is the rate of new mutation in humans?

Answer 13

• per base pair per generation -> 1.2 x 10^-9
• 72 new mutations per individual
• in entire human pop. EACH base pair is being mutated on average 92 times every generation

Question 14

At which letter in a codon does a mutation have the greatest effect?

Answer 14

First letter. Mutation of third letter is most likely to end up as a silent mutation.

Question 15

Number of fitness-affecting mutations per diploid genome each generation of humans?

Answer 15

1.6 - 3 (greater than fruit fly, worm, plant, and rat)

Question 16

What is G6PD?

Answer 16

Glucose-6-Phosphate Dehydrogenase is an enzyme involved in the function of red-blood cells. Deficiency of this enzyme is the most common deficiency in humans and causes severe anemia but protects against malaria.

Question 17

What is G6PD deficiency caused by?

Answer 17

The deficiency allele is associated with 2 amino acid replacement mutations in coding sequence of G6PD.
A-allele that has reduced enzyme activity has the sequence Met Asp Leu while the wild type has Val Asn Leu .

Question 18

How does Independent Assortment affect diversity?

Answer 18

Independent assortment of parent chromosomes during meiosis allows different combos. Shuffling of chromosomes makes millions of different combos.

Question 19

What other than independent assortment generates diversity?

Answer 19

recombination.

Question 20

What did spermists/ovists believe in the 1700s? What is blending theory?

Answer 20

They believed only one parent contributed to inheritance. Blending theory in 1800s suggested parents genes mixed together irreversibly.

Question 21

What is Gregor Mendel known for?

Answer 21

Experiments with pea plants. He discovered fundamental laws of inheritance—that genes come in pairs and we inherit two distinct units, one from each parent.

Question 22

What were Mendel’s conclusions from pea experiments (4)?

Answer 22

1. Inheritance determined by discrete particles (genes)
2. Each organism carries two copies (alleles) of each gene
3. Organisms form gametes (pollen/sperm, eggs/ovules) containing only one allele
4. Offspring inherit one allele from each parent at random.

Question 23

Genotype

Answer 23

Genetic constitution of an organism—used in relation to a particular gene or gene combo ex. Aa, AaBB

Question 24

Phenotype

Answer 24

The organism as observed—used when discussing a trait or feature of an organism that varies.

Question 25

Genome

Answer 25

The organism’s DNA including both genes and non-coding regions.

Question 26

Discrete trait

Answer 26

Simple, mendelian genetics, One phenotype or the other is apparent. You have it or you don’t (tongue rolling).

Question 27

Continuous trait

Answer 27

complex inheritence, multiple genes factor into the corresponding phenotype (height)

Question 28

R. A. Fisher, J. B. S Haldane, and S. Wright

Answer 28

Initiated theoretical population genetics in the 30s. Showed that continuous variation and darwinian natural selection were consistent with mendel’s laws. Also demonstrated evolutionary significance of genetic variation.

Question 29

What is the relationship between gene number and phenotypic variability?

Answer 29

The more genes involved in creating the phenotype the more variation we see. If aa codes for blue and AA/Aa codes for yellow (two phenotypes), in another case Aa (heterozygote) might code for green. Two genes involved would give 5 different phenotypes.

Question 30

What are quantitative traits affected by?

Answer 30

Genes and environment. It is very difficult to make simple connections between genotype and phenotype as it’s hard to control for environmental differences in humans.

Question 31

Discontinuous variation

Answer 31

genes of major effect, dominance and recessiveness, spread of alleles. You can deduce phenotype from genotype.

Question 32

Continuous variation

Answer 32

many genes of minor effect, important environmental effects, selection response.