Genetics and Evolution

Question 1

Homologues

Answer 1

The two copies of each chromosome

Question 2

What is unqiue about the male sex chromosomes?

Answer 2

They are not a homologous pair. (because one is an x-chromosome and one is a y-chromosome)

Question 3

An allele in which only one copy is needed to express a given phenotype.

Answer 3

dominant allele

Question 4

An allele in which two copies are needed to express a given phenotype.

Answer 4

recessive

Question 5

Homozygous vs. Heterozygous vs. Hemizygous

Answer 5

1. Homo
   
   1. If both alleles are the same for a given gene
2. Hetero
   
   1. If the alleles are different for a given gene
3. Hemi
   
   1. When only one allele is present for a given gene (i.e. male y-chromosome)

Question 6

One dominant allele and one recessive allele

Answer 6

Complete Dominance

Question 7

More than one dominant allele

Answer 7

Codominance

Question 8

No dominant alleles. Heterozygotes have an intermediate phenotype.

Answer 8

Incomplete Dominance

Question 9

The extent to which a particular gene or set of genes is expressed in the phenotypes of individuals carrying it,

(measured by the proportion of carriers showing the characteristic phenotype.)

Answer 9

Penetrance

Question 10

Full vs. High vs. Reduced vs. Non Penetrance

Answer 10

1. Full Penetrance: 100% with allele show symptoms
2. High: Most but not all with allele show symptoms
3. Reduced/Low: Some with allele show symptoms, some don’t
4. Non-penetrance: a person carrying the allele does not express symptoms

Question 11

Different manifestations of the same genotype across a populations.

Answer 11

Expressivity

(constant vs. variable)

1. Constant: All people with specific genotype express the gene the same
2. Variable: People have same genotype, but have many phenotypes

Question 12

Mendel’s First Law of Segregation

Answer 12

Allele pairs segregate during gamete formation, and randomly unite at fertilization.

Question 13

List the four basic tenants of of Mendel’s First Law.

Answer 13

1. Genes exist in alternative forms
2. Each gene has 2 alleles (one inherited from each parent)
3. Alleles segregate during meiosis, resulting in gametes that carry only one allele for a given gene
4. If two alleles are different, one is is expressed and the other is silent (recessive vs. dominant)

Question 14

Mende’s Second Law (Law of Independant Assortment)

Answer 14

Alleles of one gene sort into gametes independently of the alleles of another gene.

(Inheritance of one gene does not affect the inheritance of a second gene)

Question 15

Advantageous vs. Deletarious Mutations

Answer 15

1. Advantageous: Positive result from mutations
2. Deletarious: Detrimental results from a mutation.

Question 16

Flow of genes between species through hybrid offspring.

Answer 16

Leakage

Question 17

Genetic Drift

Answer 17

Change in allele frequencies within a population (overtime) due to chance events.

Question 18

List and explain two types of genetic drift.

Answer 18

1. Bottleneck
   
   1. Severe decrease in population size, causing reproductive isolation
   2. Could be the result of natural barriers or catostrophic events
   3. Results in a significant decrease in one allele and increase in the other allele.
   4. May result in in-breeding with small population size
2. Founder Affect
   
   1. When a new population is formed/founded in a new location
   2. Allele frequencies can change (from reproductive isolation), resulting in a genetic pool differant than the parent population
   3. May result in in-breeding with small population size

Ultmately results in a reduction of genetic diversity and increase in certain traits/diseases within a population

Question 19

In-breeding is the mating of two genetically related indifivuals. Thus, what does inbreeding promote, in relation to alleles.

Answer 19

Promotes homozygosity (homozygous dominant and recessive genotypes)

Question 20

What are inborn errors of metabolism and why is it important to identify that early in a persons life?

Answer 20

1. Defects in genes required for metabolism
2. If not diagnosed in a timely manner, can lead to permanent damage from build up of metabolites.

Question 21

Loss of genetic variation causing reduced fitness within a population.

Answer 21

In-Breeding Depression

Question 22

Induction of unrelated individuals to a breeding group. Introduces genetic diversity and increases fitness within a population.

Answer 22

Outbreeding/Oucrossing

Question 23

Diagrams that predict the relative genotypic and phenotypic frequencies resulting from the crossing of 2 individuals.

Answer 23

Punnett Squares

Question 24

A _________ is a cross in which only one trait is being studied.

Answer 24

Monohybrid

Question 25

Explain Mendel's Monohybrid Cross with Pea plants (including results for F1 and F2 generation)

Answer 25

1. Crossing of Homozygous P Generation (w/ PP and pp) 1. 100% Pp (heterozygotes) where only dominant allele was expressed 2. Crossing of Heterozygotes of F1 Generation 1. 1:2:1 genotypic ratio 2. 3:1 Phenotypic ratio

Question 26

Crossing of heterozygotes with __________ results in a 1:2:1 genotypic ratio and 3:1 phenotypic ratio.

Answer 26

Complete Dominance

Question 27

Used to determine and unknown genotype.

Answer 27

Test Cross

Question 28

How is a test cross used to determine an unknown genotype. What are the results?

Answer 28

1. Unknown genotype is crossed with homozygous recessive alleles 2. If unknown genotype is heterozygote 1. Genotype is 50:50 (1:1 ratio) 1. 50% Heterozygous (dominant phenotype) 2. 50% Homozygous Recessive 3. If unknown is homozygous 1. 100% heterozygotes for a trait with complete dominance

Question 29

This type of punnett square results accounts for the inheritance of 2 different genes.

Answer 29

Dihybrid Punnet Square

Question 30

Genes on different chromosomes that segregate independantly into gametes

Answer 30

Unlinked Genes

Question 31

Linked genes thay are on the same chromosome and are often inherited together (due to close proximity).

Answer 31

Linked Genes

Question 33

What does a dihybrid cross for 2 heterozygotes with complete dominance result in in?

Answer 33

9:3:3:1 Ratio (3:1 phenotypic ratio holds for each trait)

Question 34

Sex linked diseases are \_\_\_\_-linked.

Answer 34

X-Linked ## Footnote *(This is due to the fact that men only get one X chromosome, which they inheret from their mother. Even if the trait is recessive, the male will still express the gene due to that fact they are hemizygous for that gene. In contrast, women get two XX chromosone, thus, if they inheret a recessive chromosone for a specific gene, they will only show it if the are homozygous for that gene. If they are heterozygous, the dominant gene will only be fully expressed)*

Question 35

Unless otherwise stated on MCAT, always assume that sex-linked traits or x-linked and ________ \_\_\_\_\_\_\_\_\_.

Answer 35

Recessive

Question 36

Likelihood of two alleles being separated during crossing over in meiosis.

Answer 36

Recombination Frequency ## Footnote *(Greater recombination frequency is often directy proprotional to the distance between these genes on the chromosome. Two alleles with a smaller distance between them will have a lower recombination frequency and will be less likely to separate during meiosis)*

Question 37

\_\_\_\_\_\_\_\_\_ _________ can be made using the recombination frequency and use centimorgans as a scale.

Answer 37

Genetic Map 1. Measures the distance between two genes on a chromosome. 2. Measured using centimorgans (represent the percentage to which recombination will occur between to two alleles 1. i.e.: 15 centimorgan units = 15% change of recombination

Question 38

Asserts tthat if the population meets specified criteria, the allele frequencies will remain constant.

Answer 38

Hardi-Weinberg Equilibrium

Question 39

What are the criteria for Hardi-Weinberg Equilibrium?

Answer 39

1. A large breeding population. 2. Random mating. 3. No mutation (or significant changes in allelic frequencies) 4. No immigration or emigration. 5. No natural selection.

Question 40

What are the two Hardy-Weinberg Equilibrium Equations? What do each of them tell?

Answer 40

1. p + q = 1 1. Tells each allelic frequency 2. p² + 2pq + q² = 1 1. Tells about genotypes and phenotypes

Question 41

What can the Hardy-Weinberg equations tell, in addition to the allelic/genotypic/phenotypic frequencies of the current population?

Answer 41

Can be used to demonstrate that evolution is NOT occuring by showing that allele frequencies of following generation are unchanged from parent generation

Question 42

Variations within a population that increase an individual's fitness (for the environement), will have a greater opportunity of reproductive success.

Answer 42

Natural Selection

Question 43

What is differential Reproduction?

Answer 43

The idea that those organisms best adapted to a given environment will be most likely to survive to reproductive age and have offspring of their own. (Neo-darwinism)

Question 44

Theory that the genetic success of individual organisms is often dependent upon the cooperative success of the group.

Answer 44

Inclusive Fitness

Question 45

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

Answer 45

Punctuated equilibria

Question 46

Naturally occuring differences in form between members of the same population (species)

Answer 46

Polymorphism

Question 47

Rapid emergence of species from a common ancestor, each of which occupies it own niche. (not punctuated equilibrium)

Answer 47

Adaptive radiation

Question 48

Evolution in which dissimilar species gradually become more similiar.

Answer 48

Convergent

Question 49

Type of evolution in which closely related species gradually become very different.

Answer 49

Divergent Evolution

Question 50

When a population splits in two, yet they continue to evolve similarly.

Answer 50

Parallel Evolution