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MCAT- Biology > Genetics > Flashcards

Genetics Flashcards

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1
Q

What is a gene?

A

A gene is a stretch of DNA that codes for a trait. In molecular biology- it codes for a protein, which acts to bring about a trait.

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2
Q

What is a phenotype?

A

What is observed, such as height, color

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3
Q

What is a genotype?

A

The genetic make up- such as homozygous dominant(TT), heterozygous(Tt) or homozygous recessive( tt)

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4
Q

What is a locus?

A

Location of a gene on a chromosome

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5
Q

What is an allele?

A

A variant of a gene

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6
Q

Explain the relationship between a gene and allele

A

An allele is a variant of a gene

  • a gene may have a number of alleles
  • all alleles of the same gene exist at the same locus
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7
Q

How many alleles does a cell hold?

A

A cell holds 2 alleles, one from each parent

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8
Q

What is a homozygous genotype?

A

When two alleles that an individual carries are the same.

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9
Q

What is a heterogenous genotype?

A

When the two alleles that an individual carries are different

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10
Q

What is the wild type of a genotype?

A

The normal allele or phenotype of an organism.

-Usually the most prevalent, although it doesn’t have to be

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11
Q

What is recessiveness?

A

The weak allele. Expressed only if both copies are present.

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12
Q

What is expressively?

A

The degree to which a penetrant gene is expressed

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13
Q

What is penetrance?

A

The frequency that a genotype will express the phenotype.

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14
Q

What is a leakage?

A

Gene flow from one species to another

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15
Q

Give 3 contrasts between meiosis and mitosis

A
  • no tetras in mitosis, tetras formation in meiosis leads to crossing over
  • mitosis results in diploid(2n) daughter cells while meiosis results in haploid(n) daughter cells
  • in mitosis, daughter cells are identical to parent cell while daughter cells are different to parent cell in meiosis
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16
Q

Contrast mitosis and meiosis in terms of their final products

A

Mitosis- 2 daughter cells

Meiosis- 4 sperm cells or 1 egg(with polar bodies)

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17
Q

Contrast mitosis and meiosis in terms of the number of divisions involved

A

1 division involved in mitosis.

2 divisions involved in meiosis

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18
Q

Describe the mechanism of independent assortment

A
  • In metaphase 1 of meiosis
  • Random orientation occurs between homologous chromosomes along the metaphase line( any parents chromosome can be on any side)
  • In anaphase 1 of meiosis, homologous chromosomes are pulled apart.
  • those on the left will be put into one daughter cell, those on the right will be put into another
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19
Q

What is the significance of meiosis?

A

Meiosis introduces genetic variability by genetic recombination.

Genetic recombination is the production of independent assortment and crossing-over, which introduces genetic variability

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20
Q

Put it simply, what is the overall result of independent assortment?

A

A cell has 2 copies of chromosomes, each from a parent.

Independent assortment shuffles these chromosomes and places one copy of each gamete

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21
Q

What does it mean for genes to be linked?

A

Genes are linked when they are on the same chromosome.

When genes are further apart on the same chromosome, they are less linked.

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22
Q

What is a limitation to the randomization of independent assortment?

A

Genes on the same chromosome cannot be randomized by independent assortment

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23
Q

What is the function of crossing over?

A

A mechanism that reduces linkage

Only efficient when genes are physically apart from each other on the same chromosome

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24
Q

What is the function of recombination?

A

The process that introduces genetic diversity into the gametes during meiosis

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25
Q

What are the 2 processes that makeup recombination?

A
  • Independent assortment

- Crossing over

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26
Q

When does crossing over occur?

A

In prophase 1

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27
Q

What are single crossovers?

A

Chromatids exchange alleles at a given locus resulting in genetic recombination.

Results in 2/4 recombinants

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28
Q

What is the site of crossing over?

A

Chiasma

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29
Q

How is the chiasma created?

A

Chiasma made possible because of pairing of homologous chromosomes called a tertiary

Tetrahydrofuran is formed by synapsis

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30
Q

Distinguish double crossing over scenario 1 from scenario 2 and 3

A
  • Scenario 1 does not result in genetic recombination

- Scenario 2 and 3 result in genetic recombination

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31
Q

Describe scenario 1 of double cross over

A

The chromatids involved in double cross over exchange alleles but exchanges them back.

This is the 2-strand double cross over.

Results in 0/4 recombinants

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32
Q

What is scenario 2 of double cross overs?

A

The chromatids exchange alleles during cross over.

Then one of the crossover chromatids exchanges with a different chromatid.

This is the 3 strand cross over

Results in 2/4 crossing over

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33
Q

Describe scenario 3 of double cross over

A

The chromatids exchange

Then 2 totally different chromatids on the same chromosome exchange

This is called 4-strand double crossover.

Results in 4/4 recombinants

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34
Q

What is the synaptnemal complex?

A

The protein complex that glues the tetras complex

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35
Q

What is a tetrad?

A

The paired homologous chromosome structure

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36
Q

What are sex-linked characteristics?

A

The gene for a characteristic is on the X chromosome

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37
Q

Why are there very few genes on the Y chromosome?

A
  • The Y chromosome is very small chromosome and carries few genes of importance
  • All sex-linked alleles are carried on the X chromosome
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38
Q

What determines cytoplasmic inheritance?

A

Inheritance of other things aside from genomic DNA

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39
Q

What determines inheritance of cellular organelles?

A

Inherited from mother

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40
Q

What is a mutation?

A

Change in DNA sequence by any means other than recombination

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41
Q

List the types of mutations

A
  1. Random mutation
  2. Translation error
  3. Transcription error
  4. Base substitution
  5. Inversion
  6. Addition/insertion
  7. Deletion
  8. Translocation
  9. Mispairing
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42
Q

What is random mutation?

A

Random changes in DNA sequence, can be due to radiation, chemicals, replication error…etc

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43
Q

What is a translation error?

A

Even if the DNA for a gene is perfect, errors during translation can cause expression of a mutant phenotype

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44
Q

What is a transcription error?

A

Even if the DNA is perfect, errors during transcription can cause expression of a mutant phenotype

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45
Q

What is base substitution mutation?

A

Mutation involving a base( ATCG) turning into another base

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46
Q

What is inversion mutation?

A

A stretch of DNA breaks off(segment of a chromosome), then reattaches in the opposite orientation

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47
Q

What is the addition/insertion mutation?

A

An extra base is added/inserted into the DNA sequence

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48
Q

What is deletion mutation?

A

A base is taken out of the DNA sequence

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49
Q

What causes addition/insertion and deletion mutation?

A

Result in a frameshift mutation

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50
Q

What is translocation mutation?

A

A stretch of DNA(segment of a chromosome) breaks off, then reattaches somewhere else

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51
Q

What is mispairing mutation?

A

A not pairing with T

Or

G not pairing with C

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52
Q

What is advantageous mutation?

A

Results in a benefit to the fitness of the organism

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53
Q

Give an example of an advantageous mutation

A

Mutation that causes flies to become wingless is advantageous in an environment where it is very windy

54
Q

What is a deleterious mutation?

A

Results in a harmful effect to the fitness of the organism

55
Q

Give an example of a deleterious mutation

A

A mutation that causes an organism to be sterile

56
Q

What are inborn errors of metabolism?

A

Genetic diseases resulting in faulty metabolism

57
Q

What is Phenylketunoria(PKU)?

A

An inborn error of metabolism where people can’t metabolism phenylalanine.

58
Q

Discuss treatments and cure for Phenylketonuria(PKU)

A

No cure but treatments involve avoiding the amino acid phenylalanine

59
Q

What is a mutagen?

A

Something that leads to a mutation

60
Q

What is a carcinogen?

A

Something that causes a mutation that causes cancer

61
Q

All carcinogens are __________ . But not all mutagens are ______________

A

Mutagens

Carcinogens

62
Q

What is genetic drift?

A

Random changes in allele frequency due to chance and not due to natural selection

63
Q

What are the 5 assumptions of the Hardy-Weinberg principle?

A
  • Infinitely large population(no genetic drift)
  • No mutation
  • No migration
  • Random mating(no sexual selection)
  • No natural selection
64
Q

Give the mathematical formulas of the Hardy-Weinberg principle

A

p+q=1

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

65
Q

What is a back cross?

A

Mating between the offspring and parent- preserves parental genotype

66
Q

What is the parental generation?

A

P-generation of a parent. On a pedigree that represents this row represents the parents

67
Q

What is the Felial 1/ children on a pedigree chart?

A

F1 generation- on a pedigree, this is the row below the parents/ represents the children of the parents

68
Q

What is felial 2/ grandchildren on a pedigree chart?

A

F2- on a pedigreee this is below to F1 and represents the grandchildren of the parents

69
Q

What is gene mapping?

A

Physical location of genes on a chromosomes( toward the end for example)

Further apart = higher crossover frequency

70
Q

What is biometry?

A

Using statistics to analyze biological data

71
Q

What is the null hypothesis in biometry?

A

First assuming that you are wrong- there is no relationship in your data

72
Q

What is the use of t-tests in biometry?

A

Compares 2 data tests

73
Q

What is the use of ANOVA in biometry?

A

Compares 3+ data tests

74
Q

What is the p-value in stats?

A

Calculated chance that the null hypothesis is right, the chance you are wrong

75
Q

What is the significance of a p-value being less than 0.05?

A

0.05 means less than 5% chance the null hypothesis is correct(reject the null hypothesis)

76
Q

What is the Fischer exact test?

A

Compares data in a 2x2 table

77
Q

Discuss skewness

A

Skew- asymmetry in the bell curve

Skewed left- longer “tail” of the bell curve on the left

78
Q

What can be used to analyze the distribution of a single data set?

A

Standard deviation/ variation

79
Q

How is DNA converted to an mRNA transcript?

A
  1. Add hydroxyl group to the 2’ carbon of each deoxyribose. In biochemist speak, you hydroxylate the 2’ deoxyribose
  2. Snip the methyl group off of every thymine that occurs in the nucleotide strand. In biochemistry speak, you demethylate each thymine to uracil
80
Q

Give the differences in and similarities in nucleotide bases in DNA and RNA

A

DNA- Adenine, thymine, cytosine and guanine

RNA- Adenine, uracil, guanine, cytosine

81
Q

Differentiate the sugar in nucleotide in DNA and RNA

A

DNA- deoxyribose

RNA- ribose

82
Q

What is the function of DNA?

A

Information storage

83
Q

What are the type of bonds between nucleotides in DNA and RNA?

A

Phosphodiester bonds

84
Q

What is complete dominance?

A

When only one dominant gene and one recessive allele exist for a given gene

85
Q

What is codominance?

A

When more than one dominant allele exists for a gene such as AB blood type

86
Q

What is incomplete dominance?

A

Occurrence when a heterozygote expresses a phenotype intermediate between two homozygous genotypes

87
Q

Explain how penetrance effects the severity of Huntington’s disease

A

Huntington’s disease is caused by the repetitive sequence in the huntingtin gene

  • Individuals with over 40 sequence repeats have full penetrance( 100% will show symptoms)
  • fewer sequences show high penetrance, most people will show symptoms
  • even fewer repeats the gene becomes low penetrance or nonpenetrant
88
Q

Differentiate between constant expressivity and variable expressivity

A

Constant expressivity- all individuals with a given genotype express the same phenotype

Variable expressivity- individuals with the same genotype may have differing phenotype

89
Q

Differentiate penetrance and expressivity

A

Penetrance- a population parameter that examines what % of individuals with a given genotype express a phenotype

Expressivity- explores expression on an individual level

90
Q

Describe Mendel’s first law: law of segregation

A
  1. Genes exist in alternative forms ( alleles)
  2. An organism has 2 alleles form of each gene, one inherited from each parent
  3. The 2 alleles segregate, each into a gamete during meiosis
  4. If 2 alleles of an organism are different, only one will be fully expressed and the other will be silent(dominant and recessive)
91
Q

Briefly state what is Mendel’s second law (of independent assortment)

A

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

92
Q

Explain Mendel’s second law (of independent assortment)

A

Before meiosis 1, spermatogonia and oogonia undergo genome replication

In prophase 1 homologous chromosomes pair up to form tetrads and genetic material is swapped

93
Q

What is natural selection?

A

The theory that certain characteristics or traits possessed by individuals to have greater reproductive success

94
Q

Who and when did the natural selection theory develop?

A

Charles Darwin in his 1859 publication “On the Origin of Species”

95
Q

What were the basic tenets that went into making the natural selection theory?

A
  • Few offspring survive to reproductive maturity
  • variations among individuals may be heritable and variations may be favorable
  • individuals with these favorable variations have better fitness than those that dont
96
Q

How does the modern synthesis model/neo-darwanism aid Darwinism?

A

Adds knowledge of genetic inheritance and changes to the gene pool to Darwin’s theory

97
Q

What is differential reproduction?

A

When mutation or recombination results in a favorable change, it is more likely to pass to the next generation

The opposite is true

98
Q

What is inclusive fitness?

A

A measure of an organisms success in the population

Based on number of offspring, success in supporting offspring and ability of offspring to support others

99
Q

What idea/theory does inclusive fitness promote?

A

Promotes the idea that altruistic behavior can improve the fitness and success of a species

100
Q

Describe the origins of punctuated equilibrium

A

Examination of the fossil records showed little evolution occurred within a lineage of life forms followed by quick bursts of evolutionary change

Niles Elridge and Stephen Jay Gould proposed punctuated equilibrium in 1972 to contented with Darwin’s theory

101
Q

What are the modes of natural selection?

A

Stabilizing selection

Directional selection

Disruptive selection

102
Q

What is stabilizing selection ?

A

Selection that keeps phenotype in a specific range by selecting against extremes(human birth weight)

103
Q

Why is it advantageous to keep the fetus birth weight to a narrow range?

A

Too little birth weight may not be healthy enough to survive

Too much can cause trauma when traveling through the birth canal and reqyiring more resources from the mother

104
Q

What is directional pressure?

A

Adaptive pressure can lead to the emergence and dominance of an initially extreme phenotype

105
Q

How can antibiotics cause directional selection in bacteria?

A

Giving antibiotics to bacteria will cause a new standard phenotype to emerge as a result of differential survivorship

106
Q

What is disruptive selection?

A

When 2 extreme phenotypes are selected over the norm

107
Q

Give an example of disruptive selection

A

Finches in the Galápagos Islands.

Beaks were either small or big with few medium sized due to the size of the seeds

108
Q

What are polymorphisms?

A

Naturally occurring differences between members of the same population

This facilitates disruptive selection

109
Q

What is adaptive radiation?

A

Concept of a rapid rise of a number of different species from a common ancestor

110
Q

What is the benefit of adaptive radiation?

A

Allows various species to occupy different niches decreasing competition for resources

111
Q

What is a niche?

A

A specific way of life including habitat location, utilization of resources

112
Q

What is a species?

A

The largest group of organism capable if breeding to form fertile offspring

113
Q

What is speciation?

A

The formation of a new species

114
Q

Reproductive isolation may occur either ____________ or ___________

A

Prezygotically

Postsygotically

115
Q

What are prezygotic mechanisms?

A

Prevent formation of the zygote completely

116
Q

What are postzygotic mechanisms?

A

Allow for gamete fusion but yield either non viable or sterile offspring

117
Q

What are examples of prezygotic mechanisms?

A
  1. Temporal isolation
  2. Ecological isolation
  3. Behavioral isolation
  4. Reproductive isolation
  5. Gametic isolation
118
Q

What is temporal isolation?

A

Breeding at different times

119
Q

What is ecological isolation?

A

Living in different niches within territories

120
Q

What is behavioral isolation?

A

A lack of attraction between members of the two species due to differences in pheromones,courtship…

121
Q

What is reproductive isolation?

A

Incompatibility of reproductive anatomy

122
Q

What is gametic isolation?

A

Intercourse can occur but not fertillization

123
Q

Give examples of postzygotic mechanisms

A

Hybrid inviability

Hybrid breakdown

Hybrid sterility

124
Q

What is hybrid inviability?

A

Formation of zygote that cannot develop to term

125
Q

What is hybrid breakdown?

A

Forming first generation hybrid offspring that are visible and fertile but second generation are infertile and inviable

126
Q

Mules are an example of__________

A

Hybrid sterility

127
Q

What are the 3 patterns of evolution?

A
  1. divergent evolution
  2. Convergent evolution
  3. Parallel evolution
128
Q

What is parallel evolution?

A

Refers to the process whereby related species evolve in a similar way for a long time because of response of analogous environmental species

129
Q

What is divergent evolution?

A

The independent development of dissimilar characteristics in 2 or more lineages sharing a common ancestor

130
Q

What is convergent evolution?

A

Refers to the independent development of similar characteristics in two or more lineages sharing a common ancestor

131
Q

How is the rate of evolution measured?

A

The rate of change of a genotype over a period of time

132
Q

What is the molecular clock model?

A

The correlation of degree of genomic similarity with the amount of time since two species split off from the same common ancestor

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

MCAT- Biology (2 decks)

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