Genetics and Evolution

Question 1

Homologues

Answer 1

Each human being possesses 2 copies of each chromosome, except for male sex chromosomes

Question 2

locus

Answer 2

Location on a specific chromosome, where a gene is located –> locus of a particular gene is consistent among human beings.

Question 3

Hemizygous

Answer 3

Describes a situation in which only one allele is present for a given gene, as is the case for parts of the X chromosome in males.

Question 4

Complete dominance

Answer 4

When only one recessive and one dominant allele are present, the presence of one dominant allele will mask the recessive allele, if present.

Question 5

Incomplete dominance

Answer 5

Occurs when a heterozygote expresses a phenotype that is intermediate between the 2 homozygous genotypes

Question 6

Penetrance

Answer 6

The proportion of the population with a given genotype who actually express the phenotype

Question 7

Expressivity

Answer 7

The different manifestations of the same genotype across the population

Question 8

Constant expressivity

Answer 8

All individuals with a given genotype express the same phenotype.

Question 9

Variable expressivity

Answer 9

Individuals with the same genotype may have different phenotypes

Question 10

4 basic tenets of Mendel’s first law (of segregation)

Answer 10

1) Genes exist in alternative forms (alleles)
2) An organism has 2 alleles for each gene – one inherited from each parent
3) The 2 alleles segregate during meiosis, resulting in gametes that carry only one allele for any inherited trait
4) If 2 alleles of an organism are different, only one will be fully expressed and the other will be silent (codominance and incomplete dominance are exceptions to this rule).

Question 11

Mendel’s second law (of independent assortment)

Answer 11

States that the inheritance of one gene does not affect the inheritance of another gene

Question 12

Gene pool

Answer 12

All of the alleles that exist within a species.

Question 13

Transposons

Answer 13

Can insert and remove themselves from the genome

Question 14

Point mutations

Answer 14

Occur when one nucleotide in DNA is swapped for another

Question 15

Silent mutations

Answer 15

Occur when the change in nucleotide has no effect on the final protein synthesized from the gene

Question 16

Missense mutations

Answer 16

Occurs when the change in nucleotide results in substituting one amino acid for another in the final protein

Question 17

Nonsense mutations

Answer 17

Occurs when the change in nucleotide results in substituting a stop codon for an amino acid in the final protein.

Question 18

Frameshift mutations

Answer 18

Occur when nucleotides are inserted into or deleted from the genome

Question 19

Chromosomal mutations

Answer 19

Larger-scale mutations in which large segments of DNA are affected

Question 20

Inborn errors of metabolism

Answer 20

Defects in genes required for metabolism

Question 21

Leakage

Answer 21

A flow of genes between species, e.g. when individuals from different (but closely related) species can mate to produce hybrid offspring.

Question 22

Genetic drift

Answer 22

Refers to changes in the composition of the gene pool due to chance

Question 23

Inbreeding depression

Answer 23

The loss of genetic variation may cause reduced fitness of the population

Question 24

Outbreeding or outcrossing

Answer 24

The introduction of unrelated individuals into a breeding group

Question 25

Punnett squares

Answer 25

Diagrams that predict the relative genotypic and phenotypic frequencies that will result from crossing 2 individuals.

Question 26

Monohybrid

Answer 26

A cross in which only one trait is being studied

Question 27

Crossing 2 heterozygotes for a trait with complete dominance results in what type of ratio of genotypes and of phenotypes

Answer 27

1:2:1 ratio of genotypes (homozygous dominant: heterozygous dominant: homozygous recessive)
AND
a 3:1 distribution of phenotypes (dominant:recessive)

Question 28

Test cross/back cross

Answer 28

Used to determine an unknown genotype

Question 29

Dihybrid cross: ratio in offspring for crossing 2 things that are heterozygous for 2 different traits

Answer 29

9:3:3:1

Question 30

Recombination freqency

Answer 30

The likelihood that 2 alleles are separated from each other during crossing over

Question 31

map unit or centimorgan

Answer 31

Corresponds to a 1 percent chance of recombination occurring between 2 genes

Question 32

5 conditions required for a population to be in Hardy-Weinberg equilibrium

Answer 32

1) the population is very large (no genetic drift)
2) There are no mutations that affect the gene pool
3) Mating between individuals in the population is random (no sexual selection)
4) There is no migration of individuals into or out of the population
5) The genes in the population are all equally successful at being reproduced`

Question 33

2 key Hardy-Weinberg equations

Answer 33

p + q = 1
p^2 + 2pq + q^2 = 1

p is the frequency of the dominant allele
q is the frequency of the recessive allele

Question 34

Neo-darwinism

Answer 34

Adds knowledge of genetic inheritance and changes in gene pool to Darwin’s original theory: when mutation or recombination results in a change that is favorable to the organism’s reproductive succes, that change is more likely to pass on to the next generation

Question 35

Natural selection

Answer 35

The theory that certain characteristics or traits possessed by individuals within a species may help those individuals have greater reproductive success.

Question 36

Punctuated equilibrium

Answer 36

Theory that little evolution would occur within a lineage of related lifeforms for long periods of time, followed by an explosion in evolutionary change.

Question 37

Adaptive radiation

Answer 37

A related concept that describes the rapid rise of a number of different species from a common ancestor.

Question 38

Prezygotic mechanisms

Answer 38

Prevent formation of the zygote completely –> can cause speciation

Question 39

Postzygotic mechanisms

Answer 39

Allows for gamete fusion but yield either nonviable or sterile offspring –> can cause speciation

Question 40

Divergent evolution

Answer 40

Refers to the independent development of dissimialr characteristics in 2 or more lineages sharing a common ancestor

Question 41

Parallel evolution

Answer 41

Refers to the process whereby related species evolve in similar ways for a long period of time in response to analagous environmental selection pressures

Question 42

Convergent evolution

Answer 42

Refers to the independent development of similar characteristics in 2 or more lineages not sharing a recent common ancestor

Question 43

Molecular clock model

Answer 43

The more similar the genomes, the more recently the 2 species separated from each other.
Molecular evolutionists correlate the degree of genomic similarity with the amount of time since 2 species split off from the same common ancestor.