Ch 12 - Genetics and Evolution

Question 1

What do chromosomes contain?

Answer 1

genes in a linear sequence

Question 2

What are alleles?

Answer 2

alternative forms of genes

Question 3

What is the difference between dominant and recessive alleles?

Answer 3

• dom require only one copy to be expressed

- rec require 2 copies

Question 4

What is genotype?

Answer 4

the combination of alleles one has at a given genetic locus

Question 5

What are homozygous, heterozygous, and hemizygous ?

Answer 5

• homo have 2 of the same allele
• hetero have 2 different alleles
• hemi have only 1 allele (male sex chromosomes)

Question 6

What is a phenotype?

Answer 6

the observable manifestation of a genotype

Question 7

What is complete/incomplete dominance and codominance?

Answer 7

• complete: when the effect of 1 allele completely masks the effect of another
• codominance ahs more than one dominant allele
• incomplete: has no dominant alleles; heterozygotes have intermediate phenotypes

Question 8

What is penetrance?

Answer 8

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

Question 9

What is expressivity?

Answer 9

the varying phenotypic manifestations of a given genotype

Question 10

How do the modern interpretations of Mendel’s laws help explain the inheritance of genes from parent to offspring?

Answer 10

• 1st law (segregation): an organism has 2 alleles for each gene, which segregate during meiosis, resulting in gametes carrying only 1 allele for a trait
• 2nd law (independent assortment): the inheritance of 1 allele does not influence the probability of inheriting an allele for a different trait

Question 11

What did Griffith’s experiment show?

Answer 11

the transforming principle, converting non virulent bacteria into virulent bacteria by exposure to heat killed virulent bacteria

Question 12

What did Avery-McLeod-McCarty’s experiment show?

Answer 12

DNA is the genetic material because degradation of DNA led to cessation of bacterial transformation

Question 13

What did Hershey-Chase’s experiment show?

Answer 13

DNA is the genetic material because only radiolabeled DNA could be found in bacteriophage infected bacteria

Question 14

What is a gene pool?

Answer 14

all of the alleles in a given population

Question 15

What are mutations?

Answer 15

changes in DNA sequence

Question 16

What are point and frameshift mutations?

Answer 16

• point: substituting of one nucleotide for another

- frameshift: moving the 3 letter transcriptional reading frame

Question 17

What is the silent mutation?

Answer 17

has no effect on the protein

Question 18

What is the missense mutation?

Answer 18

substitution of one amino acid for another

Question 19

What is the nonsence mutation?

Answer 19

substitution of a stop codon for another amino acid

Question 20

What are insertions and deletions?

Answer 20

result in a shift in the reading frame, leading to changes for all downstream amino acids

Question 21

What are deletion mutations?

Answer 21

occur when a large segment of DNA is lost

Question 22

WHat are duplication mutations?

Answer 22

occur when a segment of DNA is copied multiple times

Question 23

What are inversion mutations?

Answer 23

occur when a segment of DNA is reversed

Question 24

What are insertion mutations?

Answer 24

occur when a segment of DNA is moved from one chromosome to another

Question 25

What are translocation mutaitons?

Answer 25

occur when a segment of DNA is swapped with a segment of DNA from another chromosome

Question 26

Why would genetic leakage in animals be rare prior to the last century?

Answer 26

- genetic leakage requires the formation of a hybrid organism that can then mate with members of one or the other parent species - while hybrids existed historically, fertile hybrids were certainly rare before a more modern understanding of genetics

Question 27

What is a genetic drift?

Answer 27

occurs when the composition of the gene pool changes as a result of chance

Question 28

What does the founder effect come from?

Answer 28

results from bottlenecks that suddenly isolate a small population, leading to inbreeding and increased prevalence of certain homozygous genotypes

Question 29

What are punnett squares?

Answer 29

visually represent the crossing of gametes from parents to show relative genotypic and phenotypic frequencies

Question 30

How are generations represented in punnett squares?

Answer 30

- parent (P) | - offspring (filial) F1, F2, and so on

Question 31

What are mono/dihybrid crosses?

Answer 31

- mono accounts for 1 gene (3:1 phenotypic ratio) | - di accounts for 2 (9:3:3:1 phenotypic ratio)

Question 32

What are sex-linked crosses?

Answer 32

sex chromosomes are usually used to indicate sex as well as genotypes - X lined on MCAT (Y linked rare)

Question 33

What is the recombinant frequency?

Answer 33

the likelihood of 2 alleles being separated during crossing over in meiosis

Question 34

How are genetic maps made?

Answer 34

can be made using recombination frequency as the scale of centimorgans

Question 35

What is the Hardy-Weinberg principle?

Answer 35

states that if a population meets certain criteria (aimed at a lack of evolution), then the allele frequencies will remain constant

Question 36

What is natural selection?

Answer 36

states that chance variations exist between individuals and that advantageous variations - those that increase an individual's fitness for survival or adaptation to the environment - afford the most opportunities for reproductive success

Question 37

What does the modern synthesis model (neo-Darwinism) account for?

Answer 37

mutation and recombination as mechanisms of variation and considers differential reproduction to be the mechanism for reproductive success

Question 38

What does inclusive fitness consider?

Answer 38

an organism's success to be based on the number of offspring, success in supporting offspring, and the ability of the offspring to then support others - survival of offspring or relatives ensures appearances of genes in subsequent generations

Question 39

What does punctuated equilibrium consider?

Answer 39

evolution to be a very slow process with intermittent rapid bursts of evolutionary activity

Question 40

What is the difference between stabilizing, direction, and disruption selection in regards to changes in phenotypes?

Answer 40

- stabilizing: keeps phenotypes in a narrow range, excluding extremes - directional: moves the average phenotype toward one extreme - disruptive: moves the population toward 2 different phenotypes at the extremes and can lead to speciation

Question 41

What is adaptive radiation?

Answer 41

the rapid emergence of multiple species from a common ancestor, each of which occupies its own ecological niche

Question 42

What are species?

Answer 42

- the largest group of organisms capable of breeding to form fertile offspring - reproductively isolated from each other by pre- or postzygotic mechanisms

Question 43

What is the difference between divergent, parallel, and convergent evolution?

Answer 43

- div: occurs when 2 species sharing a common ancestor become more different - par: occurs when 2 species sharing a common ancestor evolve in similar ways du eto analogous selection pressures - con: occurs when 2 species not sharing a recent ancestor evolve to become more similar due to analogous selection pressures

Question 44

What does the molecular clock model show?

Answer 44

the degree of difference in the genome between 2 species is related to the amount of time since the species broke off from a common ancestor

Question 45

What is a testcross?

Answer 45

used to determine an unknown genotype - unknown genotype is crossed with homozygous recessive - if all offspring are dominant phenotype, unknown is homozygous dominant - if 1:1 distribution of dominant to recessive, unknown heterozygous dominant

Question 46

What are the criteria for Hardy-Weinberg principle?

Answer 46

- the population is very large (no genetic drift) - no mutations that affect the gene pool - mating between individuals in the population is random (no sexual selection) - no migration of individuals into or out of the population - genes in the population are all equally successful at being reproduced

Question 47

What are Hardy-Weinberg equations?

Answer 47

p + q = 1 (frequency of alleles) p^2 + 2pq + q^2 = 1 (frequency of genotypes and phenotypes) p is dominant allele and q is recessive allele

Question 48

At what point to 2 populations descended from the same ancestral stock considered to be separate species?

Answer 48

when they can no longer produce viable, fertile offspring

Question 49

What was Darwin's main argument?

Answer 49

- natural selection was the driving force of evolution - argues that change variations between organisms can help certain organisms survive to reproductive age and produce many offsprings, transmitting their variations to the next generation