Chapter 12: Genetics and Evolution

Question 1

Mosaicism

Answer 1

Presence of cells with two different genotypes within a single organism, which can occur because of mutations during mitosis or errors during meiosis. A rabbit displaying mosaicism would likely look spotted or blotchy, but probably not solid gray.

Question 2

Complete Dominance

Answer 2

Describes traits in which only one allele can be expressed as a phenotype, either the dominant allele or the recessive allele.

Question 3

Codominance

Answer 3

Refers to traits that are both expressed at the same time in heterozygotes (individuals with one copy of each allele)

Question 4

Chimerism

Answer 4

Presence of multiple distinct genomes within one organism, caused by the merging of two fertilized eggs.

Question 5

Dihybrid Cross

AaBb * AaBb

Answer 5

Genotype Ratio -> 9:3:3:1

• 9 -> Dominant for both genes
• 3 -> Dominant for Gene 1 and Recessive for Gene 2
• 3 -> Recessive for Gene 1 and Dominant for Gene 2
• 1 -> Recessive for both genes

Question 6

Monohybrid Cross

Aa * Aa

Answer 6

*Genotype Ratio -> 1:2:1
(Homozygous Dominant: Heterozygous: Homozygous Recessive)
*Phenotypic Ratio -> 3: 1
(Dominant: Recessive)

Question 7

Autosomal Dominant Disease

Answer 7

Only needs 1 dominant allele for disease to be expressed

Question 8

Penetrance

Answer 8

Measures the fraction of people with the genotype who express the corresponding phenotype.

Question 9

Expressivity

Answer 9

Measures the range of expression of a certain genotype

Question 10

Constant expressivity

Answer 10

Genotype is expressed exactly the same way each time.

Question 11

What does recombination frequency tell indicate about chromosomal location?

Answer 11

The higher the recombination frequency , the farther apart the alleles are.

Question 12

When is Hardy Weinberg Equilibrium only achieved?

Answer 12

When natural selection is not occurring

Question 13

Which type of lethal allele can persist through a population?

Answer 13

Recessive

It can persist through carriers.

Question 14

Bottleneck effect

Answer 14

• Is a severe reduction in population size. Can be caused by natural disasters.
• It increases the effect of genetic drift

Question 15

Fecundity

Answer 15

Ability to produce an abundance of offspring or new growth

OR

Fertility

Question 16

Genetic Drift

Answer 16

Random changes in allele frequencies due to chance

Question 17

Pre-zygotic isolation

Answer 17

Refers to barriers that prevent 2 organisms from mating and occur before a zygote is successfully formed by the combination of a sperm and an egg.

i.e. gametic isolation and temporal isolation

Question 18

Hybrid inviability

Answer 18

Occurs when a hybrid is born, but can not live to a reproductive age.

Question 19

Gametic isolation

Answer 19

Inability of 2 gametes (i.e. sperm and egg) to join

Question 20

Zygote mortality

Answer 20

Refers to the inability of a zygote to survive embryonic development

Question 21

Temporal Isolation

Answer 21

Refers to when organisms are separated by a factor of time, such as day and night or summer and winter, and therefore can not reproduce.

Question 22

Assortive mating

Answer 22

Mates are not chosen randomly, but instead certain individuals are selected over others possibly because of phenotype or location.

Question 23

Directional selection

Answer 23

Occurs when one extreme of a trait is favored over another and the population starts to express that extreme phenotype more often.

Question 24

Gene flow

Answer 24

Refers to alterations in the composition of a gene pool due to migration of individuals between different populations.

Question 25

Disruptive selection

Answer 25

Occurs when 2 extreme phenotypes on a continuum are selected for

i.e. Heterozygous pink flowers selected against while homozygous red and homozygous white flowers are selected for.

Question 26

Stabilizing selection

Answer 26

Opposite of disruptive selection

i.e. Oak trees with medium-sized leaves being evolutionarily favored over those with large or small leaves

Question 27

Ways to show relationship between species

Answer 27

1. A fossil that shared traits with both species
2. Similar embryonic stages
3. The most commonly sequenced genes for testing evolutionary relationships are ones that are essential to almost all organisms, such as the genes for ribosomes.

Question 28

Analogous structures

Answer 28

Structures that serve the same function, but come from a different evolutionary origin.

Question 29

Group Selection

Answer 29

Idea that traits that benefit the population as a whole will still be selected for even if they don’t directly help the individual expressing that trait to survive and reproduce. The trait of alarming other monkeys persists in Vervet monkeys because of this concept of group selection.

Question 30

Differential reproduction

Answer 30

the idea that certain individuals are more likely to reproduce than others, and will therefore have their genetic traits expressed at a higher rate in future generations.

Question 31

Coevolution

Answer 31

Occurs when two species evolve alongside each other and exert evolutionary pressures on one another.

Question 32

Convergent Evolution

Answer 32

Occurs when two populations that don’t share a recent common ancestor start to resemble each other as they adapt to the same or similar environments (e.g. a dolphin and a fish).

Question 33

Parallel Evolution

Answer 33

Occurs when two related populations evolve similarly for a long period of time as they experience similar environmental conditions.

Question 34

Adaptive radiation

Answer 34

Is when one lineage diverges into many others as isolated populations occupy different niches. This fits with the example of humans and skin color.