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MCAT Bio > Bio #12 > Flashcards

Bio #12 Flashcards

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1
Q

genes

A

DNA sequences that code for heritable traits that can be passed from one generation to the next. They determine the physical and biochemical characteristics of every living organism. All genes and noncoding DNA are organized into chromosomes

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2
Q

alleles

A

different forms of genes.

o A person will have two alleles for every gene.

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3
Q

dominant allele

A

only one copy of the allele is needed to express a given phenotype.

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4
Q

recessive allele

A

two copies of an allele are needed to express a given phenotype

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5
Q

genotype

A

genetic combination possessed by an individual

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6
Q

homozygous genotype

A

when an individual has two of the same alleles.

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7
Q

heterozygous genotype

A

when an individual has different alleles.

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8
Q

hemizygous genotype

A

only one allele is present for a given gene (which is the case for parts of the X chromosome in males). Could also be the case in a XO individual.

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9
Q

what is an example of being hemizygous?

A

the case for parts of the X chromosome in males

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10
Q

phenotype

A

manifestation of a given genotype as an observable trait

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11
Q

homologues

A

two copies of each chromosome

o Male sex chromosomes are the only non-homologous chromosomes.

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12
Q

locus

A

location of a gene on a specific chromosome. The normal locus of a particular gene is consistent among human beings.

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13
Q

complete dominance

A

when only one dominant and one recessive allele exist for a given gene. Dominant allele will mask the recessive allele if present.

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14
Q

codominance

A

when more than one dominant allele exists for a given gene. Ex: having one allele for A blood antigen and one allele for B blood antigen.

these alleles can be expressed simultaneously

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15
Q

incomplete dominance

A

no dominant alleles

when a heterozygote expresses a phenotype that is intermediate between the two homozygous genotypes.
 Ex: red, white, and pink flowers: snapdragons display incomplete dominance, in which neither allele is dominant and the heterozygous phenotype is a mixture of the two homozygous phenotypes.

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16
Q

what is this an example of: when a heterozygote expresses a phenotype that is intermediate between the two homozygous genotypes.
 Ex: red, white, and pink flowers: snapdragons display incomplete dominance, in which neither allele is dominant and the heterozygous phenotype is a mixture of the two homozygous phenotypes.

A

incomplete dominance

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17
Q

penetrance

A

a population measure defined as the proportion of individuals in the population carrying the allele who actually express the phenotype. The probability that given a particular genotype, a person will express the phenotype.

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18
Q

full penetrance

A

100% of individuals with the allele show symptoms

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19
Q

full penetrance, high penetrance, reduced penetrance, low penetrance, and nonpenetrance for Huntington’s disease

A

Huntington’s disease. people with fewer repeats have high penetrance. Fewer repeats lead to the gene having reduced penetrance, low penetrance, or nonpenetrance.

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20
Q

expressivity

A

varying phenotypes despite identical genotypes.

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21
Q

constant expressivity

A

all individuals with the same genotype express the same phenotype

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22
Q

variable expressivity

A

individuals with the same genotype express different phenotypes.
 Considered more at the individual level (penetrance is more at the population level)
 Ex: Mutation in NF2 gene  lots of clinical diagnoses of great ranges.

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23
Q

What is Mende’s first law?

A

Law of segregation

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24
Q

describe Mendel’s Law of Segregation

A

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

Key: segregation of homologous chromosomes during anaphase of meiosis I.

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25
Q

What is Mendel’s Second Law?

A

Law of Independent Assortment

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26
Q

Describe Mendel’s Law of Independent Assortment

A

Key: The inheritance of one gene does not affect the inheritance of another gene.
• Before meiosis I, spermatogonia and oogonia undergo genome replication.
• The daughter DNA strand is then held to the parent strand at the centromere.
• These DNA strands are known as sister chromatids.
• During prophase I of meiosis, homologous chromosomes pair up to form tetrads.
o Recombination: swap of genetic material resulting in novel combinations
 Inheritance of genes are independent.
 Linked genes: complicate the law

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27
Q

_____ and _____ allow for greater genetic diversity in offspring.

A

Segregation

independent assortment

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28
Q

what were the 3 experiments pointing to DNA as the genetic material?

A

 1. Smooth and rough capsule bacteria, rough strain + heat killed strain
• Transforming principle
 2. Rockefeller Institute: purified a large quantity of heat-killed bacteria and separated into cellular components. Cellular components treated with DNA destroying enzymes and then put into nonvirulent DNA could no longer transform the nonvirulent DNA into virulent DNA.
 3. Hershey and Chase: created bacteriophages with labeled DNA and protein. Found that when bacteriophages infected nonlabelled bacteria, only labelled DNA entered the bacteria whereas no radiolabeled protein had.

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29
Q

gene pool

A

all of the alleles that exist within a species

o Mutations or genetic leakage can introduce new genes into the gene pool.

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30
Q

mutation

A

a change in DNA sequence, resulting in a mutant allele.

can occur from ionization radiation or mutagens, mistakes by DNA polymerase, transposons,

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31
Q

wild type

A

alleles that are considered normal or natural and are ubiquitous in the study population

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32
Q

mutagen

A

substances that can cause mutations

 Ex: ionizing radiation or ultraviolet rays from the sun.

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33
Q

transposons

A

can insert and remove themselves in the genome. Can insert in the middle of a coding sequence.

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34
Q

Does DNA polymerase make mistakes?

A

yes

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35
Q

point mutations

A

 Point mutations: occur when one nucleotide in DNA (A, C, T, G) is swapped for another.
• 1. Silent mutation: when the change in nucleotide has no effect on the final protein synthesized from the gene. Oftentimes the mutation is in the 3rd nucleotide of a codon and has no effect due to degeneracy (wobble effect) of the genetic code.
• 2. Missense mutation: occur when the change in nucleotide results in substituting one amino acid for another in the final protein
• 3. Nonsense mutation: occur when the change in nucleotide results in substituting a stop codon for an amino acid in the final protein.

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36
Q

silent mutation

A

point mutation
. Silent mutation: when the change in nucleotide has no effect on the final protein synthesized from the gene. Oftentimes the mutation is in the 3rd nucleotide of a codon and has no effect due to degeneracy (wobble effect) of the genetic code.

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37
Q

missense mutation

A

point mutation

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

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38
Q

nonsense mutation

A

point mutation

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

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39
Q

frameshift mutations

A

: occur when nucleotides are inserted into or deleted from the genome.
 Codons: three-letter sequences that DNA is read in
 Reading frame: a way of dividing the sequence of nucleotides in a nucleic acid (DNA or RNA) molecule into a set of consecutive, non-overlapping triplets.
• Shift in reading frame changes the amino acid sequence or results in early truncation.
• Usually results from an insertion or deletion mutation.

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40
Q

codon

A

three-letter sequences that DNA is read in

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41
Q

reading frame

A

a way of dividing the sequence of nucleotides in a nucleic acid (DNA or RNA) molecule into a set of consecutive, non-overlapping triplets.
• Shift in reading frame changes the amino acid sequence or results in early truncation.
• Usually results from an insertion or deletion mutation.

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42
Q

chromosomal mutations

A

larger-scale mutations in which large segments of DNA are affected.

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43
Q

what are the single chromosome mutations?

A

deletion
duplication
inversion

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44
Q

deletion mutation

A

singe chromosome mutation
occur when a large segment of DNA is lost from a chromosome. Small deletion mutations are considered frameshift mutations.

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45
Q

duplication mutation

A

singe chromosome mutation

a segment of DNA is copied multiple times in the genome.

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46
Q

inversion mutation

A

singe chromosome mutation

a segment of DNA is reversed within the chromosome.

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47
Q

multiple chromosome mutations?

A

insertion

translocation

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48
Q

insertion mutation

A

multiple chromosome mutation

a segment of DNA is moved from one chromosome to another. Small insertion mutations are considered frameshift mutations.

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49
Q

what are the advantages of mutations?

A

confer a positive selective advantage that may allow the organism to produce fitter offspring.
• Ex: heterozygotes for sickle cell disease actually have a selective advantage against malaria

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50
Q

what are the disadvantages of mutations?

A

detrimental mutations
• Ex: XP: defect in nucleotide excision repair
• Inborn errors of metabolism: defects in genes required for metabolism. Results in metabolite buildup in various pathways. Must be dealt with early on in child development.

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51
Q

leakage

A

flow of genes between species

results from mating of two closely linked species to form a hybrid

52
Q

hybrid offpspring

A

offspring of individuals from different (but closely related) species
 Many hybrid offspring such as the mule cannot reproduce because they have odd numbers of chromosomes. However, some of these hybrid species can reproduce with members of one one species or the other.  results in net flow of genes from one species to the other.

53
Q

genetic drift

A

o Changes in the composition of the gene pool due to chance

54
Q

genetic drift is ______ in smaller populations

A

more pronounced

55
Q

founder effect

A

an extreme case of genetic drift in which a small population of a species finds itself in reproductive isolation from other populations as a result of natural barriers, catastrophic events, or other bottlenecks that drastically and suddenly reduce the size of the population available for breeding.

 Inbreeding: mating between two genetically related individuals begins to occur.
 Increases homozygosity and causes a reduction in genetic diversity.
 Inbreeding depression: reduced fitness due to loss of genetic variation due to inbreeding.

56
Q

inbreeding

A

mating between two genetically related individuals

57
Q

inbreeding depression

A

reduced fitness due to loss of genetic variation due to inbreeding.

58
Q

outbreeding or outcrossing

A

introduction of unrelated individuals into a breeding group which could increase variation in a gene pool and increased fitness of the population. Opposite of inbreeding depression.

59
Q

biometric techniques

A

take quantitative approaches to biological data

60
Q

punnett squares

A

diagrams that predict the relative genotypic and phenotypic frequencies that will result from the crossing of two individuals.

monohybrid cross
test cross (back cross)
dihybrid cross
sex-linked cross

61
Q

On MCAT, A is ___ allele and a is ____ allele

A

dominant

recessive

62
Q

monohybrid cross

A

Only one trait is being examined

 P generation: parent generation or individuals being crossed.
 F generation or filial: offspring of the cross.
 Ex: Mendel pea plants
• PP x pp: 100% Pp genotype and 100% purple
• Pp x Pp: 1:2:1 genotype, 3:1 phenotype
• Will not always hold true, but will be more true in a larger population with complete dominance.

63
Q

test cross (back cross)

A

used to determine an unknown genotype. An organism with an unknown genotype is crossed with a homozygous recessive organism to identify the unknown genotype using the phenotypes of the resulting offspring
 If all offspring are dominant phenotype: unknown genotype is homozygous probably homozygous dominant
 If 1:1 dominant to recessive phenotypes, then the unknown phenotype is probably heterozygous.

64
Q

test cross and get all dominant phenotype what was the unknown genotype?

A

homozygous dominant

65
Q

test cross and get 1:1 dominant and recessive offspring what was unknown genotype?

A

heterozygous

66
Q

dihybrid cross

A

accounts for the inheritance of two different genes
 Unlinked genes: the inheritance of one gene is independent of the inheritance of the other (according to Mendel’s law of independent assortment)
 Ex: If P and T are dominant:
• PpTt x PpTt: phenotypic ratio of 9:3:3:1 (3:1 ratio still holds for each trait)

67
Q

unlinked genes

A

the inheritance of one gene is independent of the inheritance of the other (according to Mendel’s law of independent assortment)

68
Q

PpTt:PpTt ratios

A

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

69
Q

sex-linked crosses

A

 Sex-linked (X-linked traits): unless told otherwise, sex-linked traits are X-linked recessive
 Sex-linked traits are more common in males because they are hemizygous for many genes carried on the X-chromosome. Females can be homozygous or heterozygous.
 X: normal, Xh: defective

70
Q

Genes that are located close to each other on a chromosome are ____likely to be separated during crossing over

A

less

71
Q

chiasma

A

point of crossing over

72
Q

what is the recombination frequency?

A

the likelihood two alleles are separated from each other during crossing over, roughly proportional to the distance between the genes on the chromosome.
 0%: tightly linked genes

73
Q

genetic map

A

represents the relative distance between genes on a chromosome constructed by analyzing recombination frequencies.

 One map unit or centimorgan corresponds to a 1 percent chance of recombination occurring between these two genes.
• Ex: two genes are 25 map units apart; we would expect 25% of gametes to show recombination of the genes somewhere.
 Recombination frequencies can be added

74
Q

two genes are 25 map units apart; we would expect ______ of gametes to show recombination of the genes somewhere.

A

25%

75
Q

allele frequency

A

how often an allele appears in a population.
 Ex: 50 individuals, 100 alleles total, 75 specific alleles, allele frequency is 75%
 Evolution results from changes in the allele frequencies over time.

76
Q

if there are 50 individuals and there are 75 specific alleles, what is the allele frequency for that allele?

A

75%

77
Q

hardy-wineberg: For the gene pool to be stable, gene frequencies not to change, and evolution to not be occurring, what are the requirements:

A

 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.

78
Q

what are the hardy weinberg equations?

A

• Hardy-Weinberg Equilibrium population  pair of equations to predict the allelic and phenotypic frequencies
o p = frequency of T, q = frequency of t
o p + q = 1 (frequency of alleles in population)
o p2 + 2pq + q2 = 1 (frequency of genotypes and phenotypes)
 p2 = frequency of TT
 2pq = frequency of Tt
 q2 = frequency of tt
 Twice as many alleles as individuals in a population.
 Populations In HW equilibrium: cross the percentages of alleles and you will get the same percentages in the offspring.

79
Q

natural selection

A

survival of the fittest, the theory that certain characteristics or traits possessed by individuals within a species may help those individuals have greater reproductive success, thus passing on those traits to offspring. Based on Charles Darwin’s tenets:
o Organisms produce offspring but only a select few survive to be able to reproduce
o Chance variations within individuals in a population may be heritable
 Favorable variation: the variation gives the organisms a slight advantage
o Individuals with a greater percentage of the favorable traits will survive and reproduce, leading to more of these traits in future generations.
o Fitness: the level of reproductive success of an individual, it is directly related to the relative genetic contribution if an individual to the next generation

80
Q

favorable variation

A

the variation gives the organisms a slight advantage

81
Q

fitness

A

the level of reproductive success of an individual, it is directly related to the relative genetic contribution if an individual to the next generation.

82
Q

modern synthesis model (neo-Darwinism)

A

adds knowledge of genetic inheritance and changes to the gene pool to Darwin’s original theory.
 When a mutation or recombination results in a change that is favorable to the organism’s reproductive success, that change is more likely to be passed on to the next generation.
 Differential reproduction: the opposite, less favorable traits are less likely to be passed on.
 Inclusive fitness: a measure of an organism’s success in the population, based on the number of offspring, success in supporting offspring, and the ability of the offspring to then support others.
• Ex: protect offspring, altruism by relatives, improves success of the species as a whole.

83
Q

differential reproduction

A

favorable mutations are more likely to be passed on than unfavorable.

84
Q

inclusive fitness

A

a measure of an organism’s success in the population, based on the number of offspring, success in supporting offspring, and the ability of the offspring to then support others.
• Ex: protect offspring, altruism by relatives, improves success of the species as a whole rather than just one individual

85
Q

punctuated equilibrium

A

changes in some species occur in rapid bursts rather than evenly over time.
 Based on fossil record and observed explosion of evolutionary change after long periods of no evolution.

86
Q

stabilizing selection

A

keeps phenotypes within a specific range by selecting against extremes.
 Ex: birthweights of humans are kept within a narrow range.

87
Q

directional selection

A

result of adaptive pressure that leads to emergence and dominance of an initially extreme phenotype.
 Ex: plate of bacteria, only some have antibiotic resistance. After treatment with antibiotic, only the resistant ones survive and reproduce.

88
Q

disruptive selection

A

: two extreme phenotypes are selected over the norm.
 Ex: Darwin’s finches, no intermediate beaks because seeds on the island were either very large or very small, supporting the extreme beak sizes.
 Facilitated by polymorphisms: naturally occurring differences in form between members of the same population
 Adaptive radiation: the rapid rise of a number of different species from a common ancestor.
• Allows for various species to occupy different niches.
o Niche: a specific environment, including habitat, available resources, and predators, for which a species is specifically adapted.
• Favored by environmental changes or isolation of small groups of the ancestor.

89
Q

polymorphisms

A

naturally occurring differences in form between members of the same population

90
Q

adaptive radiation

A

the rapid rise of a number of different species from a common ancestor.
• Allows for various species to occupy different niches.
o Niche: a specific environment, including habitat, available resources, and predators, for which a species is specifically adapted.
• Favored by environmental changes or isolation of small groups of the ancestor.

91
Q

niche

A

a specific environment, including habitat, available resources, and predators, for which a species is specifically adapted.

92
Q

species

A

the largest group of organisms capable of breeding to form fertile offspring

93
Q

speciation

A

the formation of a new species through evolution

94
Q

isolation of species

A

two populations can no longer interbreed  now considered separate species.

95
Q

prezygotic mechanisms

A

isolation
prevent formation of the zygote completely
• Ex: breeding at different times, living in different places, not attracted to each other, incompatible reproductive anatomy, intercourse can occur but fertilization cannot.

96
Q

postzygotic mechanisms

A

allow for gamete fusion but yield either nonviable or sterile offspring.
• Ex: formation of a zygote that cannot develop to term, forming hybrid offspring that cannot reproduce, first gen is viable and fertile but the second gen is not (mule).

97
Q

what are the two methods of reproductive isolation?

A

prezygotic mechanisms

postzygotic mechanisms

98
Q

what are the patterns of evolution?

A

divergent, parallel, convergent

99
Q

divergent evolution

A

the independent development of dissimilar characteristics in two or more lineages sharing a common ancestor.
 Ex: Seals and cats: both mammals and Carnivora but extremely different due to environments.

100
Q

parallel evolution

A

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

101
Q

convergent evolution

A 
the independent development of similar characteristics in two or more lineages not sharing a recent common ancestor. 
	Ex: fish and dolphins: come from different class of vertebrae but have similar features from adapting to the conditions of aquatic life.
102
Q

The greater the selective pressure of the environment, the ____ the rate of evolution of the species in that environment.

A

greater

103
Q

molecular clock model

A

the more similar the genomes, the more recently the two species separated from each other.

104
Q

the genetic combination possessed by an individual is known as a ______, and the manifestation of a given ______ as an observable trait is known as a _____

A

genotype, genotype

phenotype

105
Q

what part of meiosis is Mendel’s Law of Segregation talking about?

A

anaphase I of meiosis and the separation of homologous chromosomes.

106
Q

what part of meiosis is Mendel’s Law of Indepdendent Assortment talking about?

A

prophase I, during which recombination occurs

107
Q

what 3 experiments pointed toward DNA being the genetic material?

A
  1. Frederick Griffith: transforming principle

2. Hershey and Chase:

108
Q

frederick griffith transformation principle

A

virulent virus: killed mice
nonvirulent: mice alive
killed virulent virus: mice alive
killed virulent virus + nonvirulent virus: mice alive

transformation principle (pick up material floating around).

109
Q

work done at Rockefeller to further along the Griffith experiments

A

Put one part of the killed virulent virus into the nonvirulent virus and it led to mice dying. Added DNA killing enzymes, no longer killed mice ==> DNA!

110
Q

hershey and chase

A

radiolabeled DNA entered the cell via bacteriophages

111
Q

how to label DNA vs. proteins

A

DNA: label phosphorous
Proteins: label sulfur

112
Q

translocation mutations

A

parts on two chromosomes are swapped

113
Q

describe the advantages of sickle cell disease

A

heterozygotes for sick cell disease have hemoglobin that have too short of a lifespan for malaria to do any damage. Confers resistance but being homozygous for the sickle cell allele is a threat to life.

114
Q

Inborn errors of metabolism

A

defects in genes required for metabolism. Results in metabolite buildup in various pathways. Must be dealt with early on in child development.

115
Q

why is genetic drift more common in smaller populations?

A

with a small sample size, a random mutations is more likely to sway the sample and become more common (like in data)

116
Q

what does the F generation stand for?

A

filial generation

117
Q

crossing one homozygous dominant and one homozygous recessive will result in what for gene that has one dominant and one recessive allele?

A

all dominant phenotype

all heterozygous genotype

118
Q

crossing two heterozygotes for a trait with complete dominance results in ___ ratio of genotypes and a ___ ratio of phenotypes

A

1: 2:1
3: 1

119
Q

what will be the phenotypic ratio of a dihybrid cross between two heterozygotes with complete dominance?

A

9:3:3:1

120
Q

weakly linked genes have recombination frequencies approaching ____ percent, as expected from independent assortment

A

50%

121
Q

when gene frequencies are not changing, the ___ is stable and ____ is not occurring

A

gene pool

evolution

122
Q

what do the two hardy weinberg equations tell us?

A
  1. the frequency of alleles in the population

2. frequency of genotypes and phenotypes in the population

123
Q

what does p^2 in hardy weinberg represent?

A

proportion of homozygous dominant (remember that the p is the frequency of the particular allele)
p^2 = homozygous dominant

124
Q

natural selection is a _____ for evolution

A

mechanism. allows it to take place

125
Q

fitness vs. inclusive fitness

A

inclusive: based on the number of offspring, success in supporting offspring, and the ability of the offspring to then support others.
fitness: number of viable offspring

126
Q

natural selection vs. modern synthesis model

A

natural selection: looks at traits that drive evolution

modern synthesis model: looks at alleles that drive evolution

MCAT Bio (12 decks)

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