Genetic Variation

Question 1

Mutation

Answer 1

Changes in DNA sequence, basis of all variation

Question 2

Types of single-gene mutations

Answer 2

Base-pair substitution, insertions and deletions, duplications, control and structural types, unusual types

Question 3

Silent mutation

Answer 3

Change in one base pair, third position, no change in the amino acid, can be detected in DNA or RNA but not in protein

Question 4

Missense mutation

Answer 4

Change in one base pair, changes codon from one amino acid to another

Question 5

Nonsense mutation

Answer 5

Change in one base pair, becomes stop codon, truncates protein

Question 6

Insertion and deletion

Answer 6

Bases added to or removed from a sequence, large ones can disrupt more than one gene, small ones can change sequence

Question 7

Frameshift mutation

Answer 7

Special insertion/deletion, number is not a multiple of 3, changes the “reading frame”, completely different amino acid sequence, premature truncation likely

Question 8

Mutations in non-coding DNA

Answer 8

Mutations can occur in any DNA sequence, may affect mRNA expression instead of protein sequence- promotors, enhancers, silencers, may affect mRNA processing and protein sequence

Question 9

Duplications

Answer 9

Large regions, whole genes are duplicated, sometimes gene function

Question 10

Transposons

Answer 10

Mobile genetic elements, can insert in or near gene and alter expression

Question 11

Expanded repeats

Answer 11

Trinucleotides, run of one amino acid, number increases, too many disrupt function

Question 12

Effects of mutation

Answer 12

Loss of function mutations- protein has no activity

Gain of function mutations- protein has new or greater activity

Question 13

Hemoglobin mutations

Answer 13

Structural- change protein (sickle cell anemia- glutamate 6 to valine)
Control of expression- thalassemias, hereditary persistence of fetal hemoglobin

Question 14

Thalassemias

Answer 14

Defect in production of alpha- or beta-globin, tetramers form due to excess of other subunit, damage to RBCs by precipitation, shorten lifespan of RBCs, cause anemia, splenomegaly

Question 15

Molecular causes of mutation

Answer 15

Ionizing radiation, nonionizing radiation, chemicals

Question 16

Ionizing radiation

Answer 16

Creates reactive radicals, react with bases, cause double-stranded breaks

Question 17

Nonionizing radiation

Answer 17

Shift electrons, cause reactions (pyrimidine dimers from UV)

Question 18

Chemicals

Answer 18

Base analogs insert, react, change, deamination reactions convert C to U

Question 19

Rate of mutation

Answer 19

Influenced by size of the gene, age at reproduction, “hot spots”

Question 20

DNA repair

Answer 20

Major role is to prevent mutation, some repairs require determining which base is changed, some mutations affect more than one base

Question 21

Xeroderma pigmentosum

Answer 21

Defect in nucleotide excision repair, cannot repair pyrimidine dimers, UV causes mutations in skin cells, several related disorders of DNA repair

Question 22

Blood groups

Answer 22

Natural variation, ABO system, A and B are antigens, O lacks antigens, co-dominant, antibodies are present to antigen not present in the cell, Rh + or -

Question 23

Hardy-Weinberg rule

Answer 23

Randomly mating population, large numbers, can estimate frequency of gene variants

Question 24

Gene frequency in population

Answer 24

Important to know risk of two carriers reproducing, high gene frequency in a population increases the chance of carriers reproducing, increases frequency of homozygotes for that gene

Question 25

Hardy-Weinberg equation

Answer 25

p^2 + 2pq + q^2 = 1
p = frequency of normal
q = frequency of mutation
q^2 = frequency of affected

Question 26

Natural selection

Answer 26

Survival and reproductive advantage, higher chance of reproduction causes higher instance of gene in population

Question 27

Genetic drift

Answer 27

Isolated population will change with time, due to different pressures and random events

Question 28

Gene flow

Answer 28

Intermixing of populations, from small numbers or large migrations

Question 29

Founder effect

Answer 29

Small numbers, large effects, very few founders, may mean gene frequencies do not reflect larger population

Question 30

Malaria and sickle cell

Answer 30

Example of selective advantage, people with sickle cell are more resistant to malaria, heterozygotes not as sffected, survive longer, reproduce more, increase gene frequency