Chapter 12 - Mendelian Genetics & Some Microbio

Question 1

What is complete dominance?

Answer 1

It means that one allele is dominant over the other, so it determines the phenotype whenever it is present. The other allele is recessive.

Question 2

What is an allele?

Answer 2

A version of the same gene. One gene can have various alleles.

Question 3

What is a locus?

Answer 3

A physical location of a gene on a chromosme

Question 4

True or false:
In complete dominance, heterozygotes always display the dominant phenotype.

Answer 4

True

Question 5

Explain codominance

Answer 5

Codominance is an inheritance pattern in which two alleles contribute equally to an individual’s phenotype.
Example: AB blood type, a flower with red and white stripes

Question 6

Explain incomplete dominance and give an example.

Answer 6

Incomplete dominance is an inheritance pattern in which the heterozygous phenotype is a blend of the two homozygous traits.

Example: In this pattern, if RR individuals display red coloring and rr individuals are white in color, then Rr flowers would be expected to be pink.

Question 7

What is incomplete penetrance?

Answer 7

Occurs when various individuals all have identical genotypes and yet some have the disease phenotype and others do not.

Question 8

What is expressivity?

Answer 8

Expressivity refers to the extent to which an individual’s phenotype is affected by their genotype, and is often a range.
Example: Alleles can be expressed on a various range. A person with the same allele can have severe symptoms of a disorder associated w/ the allele, while another person w/ the same allele has moderate symptoms.

Question 9

What is genetic leakage?

Answer 9

The transfer of genetic information between two different species.

Question 10

Example of genetic leakage.

Answer 10

When a hybrid offspring successfully mates with one of its parent species and produces viable offspring. This causes the offspring to contain both hybrid genes and genes from parental species.

Question 11

Explain Mendel’s 2nd Law of Independent Assortment.

Answer 11

Genes that are located on different chromosomes separate independently during Anaphase.

Question 12

Explain Mendel’s 1st Law of Segregation.

Answer 12

Alleles separate independently of one another when forming gametes.

Question 13

Which process of genetic recombination occurs during prophase I of meiosis?

Answer 13

Crossing over, or the trading of DNA segments between homologous chromosomes, occurs when these chromosomes are paired together in prophase I.

Question 14

What is a mutation, and how does it arise?

Answer 14

A mutation is an alteration in DNA sequence. Mutations arise spontaneously (often from errors in DNA replication) or be induced by mutagenic substances.

Question 15

Some changes in DNA sequence, known as silent mutations, do not affect the organisms in which they occur. Describe two situations that could lead to a silent mutation.

Answer 15

A silent mutation could be caused by:

A mutation in an intron, or noncoding, sequence
A mutation that replaces one degenerate codon with another

Question 16

What is evolution?

Answer 16

Evolution is defined as any change in the allelic frequency within a given gene pool across generations.

Question 17

What are some mechanisms of evolution?

Answer 17

Natural selection
genetic drift
Mutations
Gene flow

Question 18

What is natural selection? What two things are required in order for it to occur?

Answer 18

1. Individual has a different traits that confers an advantage for survival for them.
2. Given the advantage of survival, they can reproduce & pass those traits onto future offspring.

Question 19

What is survival of the fittest?

Answer 19

Survival of the fittest is a term meaning that the individual best suited to its environment will be most likely to survive and pass on its genetic information to future generations.

Question 20

What are adaptive traits?

Answer 20

Traits that are beneficial to the organism’s evolutionary fitness and aid in survival and reproduction.

Question 21

What is genetic drift?

Answer 21

Genetic drift describes random changes in allele frequencies in populations that result from random events (natural disasters). More likely to happen in small population.

Question 22

What are the two types of genetic drift?

Answer 22

Bottleneck effect and founder effect

Question 23

What is the founder effect?

Answer 23

When a small group of individuals splits off and starts a new population with less genetic variation/diversity than the larger population they came from.

Question 24

What is the evolutionary bottleneck effect?

Answer 24

A sudden decrease in the number of individuals in a population, limiting the genetic diversity of the species.

Question 25

What is gene flow?

Answer 25

The introduction of genetic material from one species/population to another population via migration to that population and interbreeding. This causes allele frequencies of two populations to become similar.

Question 26

What is speciation?

Answer 26

The formation of new species from existing ones.

Question 27

What is convergent evolution?

Answer 27

When species from different ancestors converge because of development of analogous structures in response to similar environmental conditions.

Question 28

What is divergent evolution?

Answer 28

Divergence in two species that come from the same ancestor although they have different phenotypic traits. They diverge to produce homologous structures.

Question 29

If a species diverged from a common ancestor 80 million years ago, what does the graph look like in terms of the # of mutations she has over time?

Answer 29

The # of neutral mutations acquired over time increases.

Question 30

Name the five prerequisites for Hardy-Weinberg equilibrium.

Answer 30

Hardy-Weinberg equilibrium requires five conditions:

Large population size
No mutation
No inward or outward migration
No natural selection
Random mating

Question 31

What is pleiotropy?

Answer 31

When one single gene contributes to (more than one) various phenotypes

Question 32

Which allele in HW equilibrium denotes the dominant allele?

Answer 32

p

Question 33

Which allele in HW equilibrium denotes the recessive allele?

Answer 33

q

Question 34

What is the HW equilibrium equation which denotes the fraction of individuals which have a certain genotype?

Answer 34

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

Question 35

What is the HW equilibrium equation which denotes the frequency of each allele (p and q)?

Answer 35

p + q = 1

Question 36

Define what it means for our genetic code to be “degenerate”.

Answer 36

It means that for each amino acid, there can be multiple codons which code for that amino acid. This occurs due to the 3 position in the codon called the wobble position.

Question 37

True or false:
Mutations aren’t evolutionarily favorable.

Answer 37

False, they do favor evolution and provide genetic variation.

Question 38

What is the difference between a substitution mutation and a missense mutation?

Answer 38

A substitution mutation simply changes the DNA sequence (substitutes one base to another), but CAN change the amino acid sequence.
A missense mutation requires a change in the amino acid sequence.

Question 39

What is extranuclear inheritance?

Answer 39

The transfer of DNA that is not located in the nucleus. In eukaryotes, this is associated with mitochondria, which contain their own genes

Question 40

How many chromosomes does a haploid cell have?

Answer 40

23

Question 41

What are linked genes? When do they occur?

Answer 41

Genes which are linked together and cross over together.
Linkage occurs, however,
when two genes are very, very close to each other on the same chromosome because at certain
proximity it becomes unlikely that a crossing over event will occur exactly between them.

Question 42

What is mosaicism? Why is it rare?

Answer 42

Mosaicism is the case in which different somatic cells within the same individual contain non-identical genotypes.
It is rate because all the somatic cells in your body should contain the same set of alleles/genes.

Question 43

Can females and males both be carriers for an X-linked condition?

Answer 43

No, only females can be carriers. Males have 1 X chromosome which means they will be affected by the disease if they have the bad allele.

Question 44

What aspect of crossing over violates Mendel’s Law of Independent Assortment?

Answer 44

Linked genes which are more likely to assort into gametes together.

Question 45

What is a test cross used to determine?

Answer 45

A test cross is used to find the unknown genotype of an individual with a dominant phenotype.
The unknown individual is crossed w/ a homozygous recessive individual and based on the offspring, the parental genotype can be determined.

Question 46

What are imprinted genes?

Answer 46

Genes that are passed down from parents, which are epigenetically modified (that is methylated) to silence those specific genes on the chromosome. There are about 80 known mammal genes that function in this “imprinted” manner. For a gene coding for insulin growth factor, the maternal copy is expressed while the paternal copy is imprinted, so its inactive.

Question 47

What did Mendel’s dihybrid cross (two traits) show?

Answer 47

True breeding (homozygous parents) produced all heterozygous offspring.
F2 generation had a 9:3:3:1 phenotypic ratio.

Question 48

For an imprinted gene, what happens if both the maternal and paternal copy are expressed?

Answer 48

This can lead to serious life-altering conditions, developmental conditions, etc.

Question 49

What are the different types of prezygotic reproductive isolation (no fertilization occurs)?

Answer 49

Temporal, habitat, behavioral, mechanical, gametic

Question 50

Temporal isolation

Answer 50

Two species breed at different times

Question 51

Habitat isolation

Answer 51

Two species live in different habitats

Question 52

Behavioral isolation

Answer 52

Two species have completely different mating behaviors

Question 53

Mechanical isolation

Answer 53

Two species have structural differences in reproductive organs

Question 54

Gametic isolation

Answer 54

The gametes are incompatible with one another, sperm can’t fertilize th egg

Question 55

What are the forms of postzygotic reproductive isolation (after fertilization)?

Answer 55

hybrid inviability, hybrid sterility, and hybrid breakdown

Question 56

Hybrid inviability

Answer 56

When the offspring die during development in the womb

Question 57

Hybrid sterility

Answer 57

When the offspring that is born is sterile and unable to produce future offspring

Question 58

Hybrid breakdown

Answer 58

When offspring produced in later generations is either sterile or inviable

Question 59

How do you figure out the genotype frequency when observing two traits?

Answer 59

You draw two monohybrid crosses for the two different genes. Than you multiply 1 frequency from one cross with the other frequency from 2nd cross.

Question 60

How to answer this type of question:
How many different types of gametes could be produced by an individual with the arbitrary genotype of AAbbCCDdEe?

Answer 60

You take 2^n
n is equal to the # of heterozygote genotypes which is only 2 in this case
so 2^2 = 4 different gametes

Question 61

AAMC SB Bio #24

Question 62

AAMC FL4 #58
Use rule for non-mutually exclusive events for calculating probability

Answer 62

1. Recognize that genes are unlinked –> meaning events are INDEPENDENT of one another and recognize that the 2 events CAN OCCUR simultaneously, that is the person can have both alleles for deafness –> use special rule
2. Rule: probability of (Event A + Event B) - (Event A x Event B)
3. Application to problem: (1/2 + 1/4) - 1/8 = 5/8

Question 63

Rule for mutually exclusive events: Events that CAN’T occur at the same time

Answer 63

Probability of A or B occuring: probability A x probability B