Ch. 12: Genetics and Evolution Flashcards
(133 cards)
1
Q
defn + func: genes
A
defn: DNA sequences that code for heritable traits that can be passed from one generation to the next
func: determine the physical and biochemical characteristics of every living organism
2
Q
defn + func: chromosomes
A
defn: all genes (as well as a large supply of noncoding DNA) taken together and organized
func: to ensure that genetic material is passed easily to daughter cells during mitosis and meiosis
3
Q
defn: alleles
A
alternative forms of genes
4
Q
defn: genotype
A
the genetic combination possessed by an individual
5
Q
defn: phenotype
A
the manifestation of a given genotype as an observable trait
6
Q
defn: homologues
A
two copies of each chromosome
7
Q
what is the one exception to homologus?
A
the sex chromosomes of genotypical males (one X chromosome, one Y chromosome)
8
Q
defn + func: locus
A
defn: location on a specific chromosome
func: each gene has a particular locus which is consistent among human beings (so a gene can be described by its location)
9
Q
why will a person inherit 2 alleles for all genes (except male sex chromosomes)?
A
because each chromosome is part of a homologous pair
10
Q
what are alleles categorized based on?
A
their expression
11
Q
defn + nomenclature: dominant
A
if only one copy of an allele is needed to express a given phenotype, the allele is dominant
represented with a capital letter
12
Q
defn + nomenclature: recessive
A
if two copies of an allele are needed, the allele is recessive
represented with a lowercase letter
12
Q
defn: homozygous vs. heterozygous genotype
A
if both alleles are the same for a given gene, the individual has a HOMOZYGOUS genotype
if the alleles are different for a given gene, the individual has a HETEROZYGOUS genotype
13
Q
defn: hemizygous genotype
A
only one allele is present for a given gene (as is the case for parts of the X chromosome in genotypical males)
14
Q
defn: complete dominance
A
only one dominant and one recessive allele exist for a given gene
the presence of one dominant allele will mask the recessive allele, if present
15
Q
defn: codominance
A
when more than one dominant allele exists for a given gene (so if a person has both, they will express both simultaneously)
16
Q
defn: incomplete dominance
A
occurs when a heterozygote expresses a phenotype that is intermediate between the two homozygous genotypes (i.e. red flower x white flower = pink flower)
17
Q
defn: penetrance
A
the proportion of individuals in the population carrying the allele who actually express the phenotype
other words: the probability that, given a particular genotype, a person will express the phenotype
18
Q
defn: full penetrance
A
100% of individuals with this allele will show the phenotype
19
Q
defn: high penetrance
A
most (but not all) of those with the allele show the phenotype
20
Q
what are the next 3 levels of penetrance below full and high?
A
- reduced
- low
- non
21
Q
cause: Huntingon’s disease — is a classic example used to describe what
A
caused by an expansion of a repetitive sequence in the huntingtin gene
classic example of penetrance
22
Q
defn: expressivity
A
varying phenotypes despite identical genotypes (the different manifestations of the same genotype across the population)
23
Q
defn: constant expressivity
A
all individuals with a given genotype express the same phenotype
24
defn: variable expressivity
individuals with the same genotype may have different phenotypes
25
what are the 4 basic tenets of the modern interpretation of Mendel's first law of segregation
1. Genes exist in alternative forms (alleles)
2. An organism has 2 alleles for each gene (one inherited from each parent)
3. the 2 alleles segregate during meiosis, resulting in gametes that carry only one allele for any inherited trait
4. If 2 alleles of an organism are different, only one will be fully expressed (dominant) and the other silent (recessive), unless there is codominance or incomplete dominance
26
defn: Mendel's second law of independent assortment
the inheritance of one gene does not affect the inheritance of another gene
27
defn: centromere
the daughter DNA strand is held to the parent strand at the centromere
28
defn: sister chromatids
the daughter DNA strand and parent DNA strand together
29
when + how are tetrads formed + why are they called that?
when: during prophase I of meiosis
how: homologous chromosomes pair up to form them
name: 2 chromatids in each of 2 homologous chromosomes
30
defn + func: recombination
defn: small segments of genetic material are swapped between chromatids in homologous chromosomes, resulting in novel combinations of alleles that were not present in the original chromosomes
func: allows the inheritance of one gene to be independent of the inheritance of all others
31
what 2 things increase the genetic diversity of gametes and, subsequently, the genetic diversity of offspring?
1. segregation of homologous chromosomes
2. independent assortment of alleles
32
defn: gene pool
all of the alleles that exist within a species
33
what 2 things cause new genes to be introduced into the gene pool?
1. mutations occur
2. genetic leakage occur
34
why is genetic variability essential for the survival of a species?
it allows it to evolve to adapt to changing environmental stresses
35
defn: mutation
a change in DNA sequence
results in a mutant allele
36
defn + func: wild-type counterparts
alleles that are considered "normal" or "natural" and are ubiquitous in the study population
used to compare with mutant alleles
37
defn: mutagens
substances that can cause mutations
38
defn: transposons
elements that can insert and remove themselves from the genome
39
what happens if a transposon inserts itself in the middle of a coding sequence?
the mutation will disrupt the gene
40
defn: point mutations
occur when one nucleotide in DNA (A, C, T, or G) is swapped for another
41
what are 3 types of point mutations?
1. silent
2. missense
3. nonsense
42
defn: silent vs. missense vs. nonsense mutations
SILENT = the change in nucleotide has no effect on the final protein synthesized from the gene
MISSENSE = the change in nucleotide results in substituting one amino acid for another in the final protein
NONSENSE = the change in nucleotide results in substituting a STOP codon for an amino acid in the final protein
43
when do silent mutations most commonly occur?
when the changed nucleotide is transcribed to be the third nucleotide in a codon because there is degeneracy (wobble) in the genetic code
44
defn: frameshift mutations
occur when nucleotides are inserted into or deleted from the genome
45
why can insertion or deletion of nucleotides shift the reading frame and what is the result of this?
why? because mRNA transcribed from DNA is always read in 3-letter sequences called codons
results in: either changes in the amino acid sequence or premature truncation of the protein (bc of a nonsense mutation)
46
what are the 2 categories of frameshift mutations?
1. insertion
2. deletion
47
defn: chromosomal mutations
larger-scale mutations in which large segments of DNA are affected
48
what are the 5 types of chromosomal mutations?
1. deletion
2. duplication
3. inversion
4. insertion
5. translocation
49
defn: deletion mutations
occur when a large segment of DNA is lost from a chromosome
small deletion mutations are frameshift mutations
50
defn: duplication mutations
occur when a segment of DNA is copied multiple times in the genome
51
defn: inversion mutations
occur when a segment of DNA is reversed within the chromosome
52
defn: insertion mutations
occur when a segment of DNA is moved from one chromosome to another
small insertion mutations (including those where the inserted DNA is not from another chromosome) are frameshift mutations
53
defn: translocation mutations
occur when a segment of DNA from one chromosome is swapped with a segment of DNA from another chromosome
54
defn: advantageous (mutation) + example
confer a positive selective advantage that may allow the organism to produce fitter offspring
example: heterozygotes for sickle cell disease (have minor symptoms and have natural resistance to malaria bc the red blood cells have a shorter lifespan)
55
defn + example: deleterious (mutation)
detrimental
example: xeroderma pigmentosum (XP) = an inherited defect in the nucleotide excision repair mechanism --> DNA that has been damaged by UV radiation cannot be repaired right, so they are more likely to have cancer (esp. skin)
56
defn: inborn errors of metabolism
an important class of deleterious mutations
deficiencies in genes required for metabolism
57
what do children born with inborn errors of metabolism often need?
children need: very early intervention in order to prevent permanent damage from the buildup of metabolites in various pathways
58
what is an example of an inborn error of metabolism?
phenylketonuria (PKU) = the enzyme phenylalanine hydrolase (which completes the metabolism of phenylalanine) is defective
without this enzyme, toxic metabolites of phenylalanine accumulate, causing seizures, cerebral function impairment, and learning disabilities, and a musty order
59
what happens if phenylketonuria is discovered shortly after birth?
dietary phenylalanine can be eliminated and treatments can be administered to aid in metabolizing any remaining phenylalanine
60
defn: genetic leakage
a flow of genes between species
61
who can produced hybrid offspring?
individuals from different but closely related species
62
why are many hybrid offspring not able to reproduce?
they have odd numbers of chromosomes
63
in what situation would a hybrid be able to reproduce?
with members of one species or the other
the hybrid carries genes from both parent species, so this can result in a net flow of genes from one species to the other
64
defn: genetic drift
the changes in the composition of the gene pool due to chance
65
is genetic drift more pronounced in small or large populations?
small
66
defn: the founder effect + what is a secondary possible impact?
a more 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 may occur because the breeding group is so small
67
defn: inbreeding
mating between two genetically related individuals
68
what does inbreeding encourage?
homozygosity, which increases the prevalence of both homozygous dominant and recessive genotypes
69
what do genetic drift, the founder effect, and inbreeding have in common?
a reduction in genetic diversity (and often the reason why a small population may have increased prevalence of certain traits and diseases)
70
defn: inbreeding depression
the loss of genetic variation may cause reduced fitness of the population
71
defn + aka: out-breeding
aka: outcrossing
the introduction of unrelated individuals into a breeding group
72
defn: biometric techniques
quantitative approaches to biological data
73
defn: Punnett squares
diagrams that predict the relative genotypic and phenotypic frequencies that will result from the crossing of 2 individuals
74
setup: Punnett squares
alleles of the two parents arranged on the top and side
genotypes of the progeny are the intersections of these alleles
genotypes of the progeny are the product of the two parental alleles
75
defn: homozygous vs. heterozygous
HOMO = both copies of the allele are the same
HETERO = the copies of the allele are different
76
defn: monohybrid
a cross in which only one trait is being studied
77
defn: P generation
the parent generation
the individuals being crossed
78
defn: F generation
filial
the offspring
79
how are multiple generations denoted?
F generations with numeric subscripts (i.e. grandparents are P, parents are F1, we are F2)
80
diagram: Punnett square of homozygous parents
81
diagram: Punnett square of heterozygous parents
+ what is the distribution of genotypes and phenotypes (assuming complete dominance, and in theory, it is not always perfect)
1:2:1 genotypes (homozygous dominant:heterozygous dominant:homozygous recessive)
3:1 phenotypes (dominant:recessive)
82
defn + func + aka: test cross
func: used to determine an unknown genotype
defn: the organism with an unknown genotype is crossed with an organism known to be homozygous recessive
aka: back cross
83
results: test cross
100% offspring have dominant phenotype = the unknown genotype is likely to be homozygous dominant
1:1 distribution dominant to recessive phenotypes = the unknown genotype is likely heterozygous
84
defn + func: dihybrid cross
extend a Punnett square to account for the inheritance of 2 different genes
85
phenotypic ratios: dihybrid cross between 2 heterozygotes + what law does this reflect
9:3:3:1 (9 tall purple:3 tall white: 3 dwarf purple:1 dwarf white)
note that the 3:1 ratio holds within each trait (12 tall:4 dwarf and 12 purple:4 white)
reflects Mendel's second law of independent assortment
86
how are sex-linked traits expressed genotypically in men and women? what impact does this have?
FEMALES: have 2 X chromosomes and so may be heterozygous (carrier) or homozygous for a X-linked condition
MALES: only have one X chromosome and are hemizygous for many X-linked genes
this is why sex-linked traits are much more common in males as having only one recessive allele is sufficient for expression of the recessive phenotype
87
mnemonic: X-linked
seX-linked is X-linked
Y-linked diseases exist, but are rare
assume sex-linked traits are recessive
88
diagram: sex-linked cross
89
for males with a sex-linked trait, what will their female offspring have? what will their male offspring have?
female offspring = carry the trait or express it
male offspring = neither express nor carry (unless the X chromosome in the egg contains the affected allele, in which case they will express it)
90
the further apart two genes are, the MORE or LESS likely it is that there will be a point of crossing over between them?
MORE
91
defn: chiasma
a point of crossing over
92
defn + char: recombination frequency
the likelihood that 2 alleles are separated from each other during crossing over
roughly proportional to the distance between the genes on the chromosome
93
relate the strength of linkage between genes to recombination frequency
TIGHTLY linked genes = close to 0 % recombo frequency
WEAKLY linked genes = close to 50% recombo frequency
94
defn: genetic map
represents the relative distance between genes on a chromosome
can be constructed by analyzing recombination frequencies
95
what does one map unit/one centimorgan correspond to on a genetic map? + example
a 1% change of recombination occurring between 2 genes
example: if 2 genes were 25 map units apart, we would expect 25% of the total gametes examined to show recombination somewhere between the 2 genes
96
diagram: genetic maps from recombination frequencies
they are roughly additive
97
defn: allele frequency
how often an allele appears in a population
98
how does evolution relate to allele frequency?
evolution results from changes in the gene frequencies in reproducing populations over time
when the gene frequencies of a population are NOT changing, the gene pool is stable and evolution is NOT occuring
99
5 mandatory criteria for the population to be at Hardy-Weinberg equilibrium
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
100
func + eqns: equations for Hardy-Weinberg equilibrium
+ meaning of the variables + meaning of the terms
used to predict the allelic and phenotypic frequencies
Let us define a particular gene as having only 2 possible alleles (T and t)
p = the frequency of the dominant allele T
q = the frequency of the recessive allele t
there are only 2 choices at the same gene locus so p + q = 1 (the combined allele frequencies of T and t must equal 100%)
p^2 = the frequency of TT (homozygous dominant genotype)
2pq = frequency of Tt (heterozygous dominant) genotype
q^2 = frequency of the tt (homozygous recessive) genotype
P^2 + 2pq = the frequency of the dominant phenotype (homozygous and heterozygous dominant genotypes)
101
what do each of the Hardy-Weinberg equilibrium equations tell us individually?
first equation: tells us about the frequency of alleles in the population
second equation: tells us about the frequency of genotypes and phenotypes in the population
102
why are there twice as many alleles as individuals in a population?
each individual has 2 autosomal copies of each gene
103
how can Hardy-Weinberg equilibrium equations be used to demonstrate that evolution is NOT occurring in a population?
assuming that the earlier conditions are met, the allele frequencies will remain constant between generations
104
defn + aka: natural selection
aka: 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
105
what are the 3 basic tenets of natural selection?
1. organisms produce offspring, few of which survive to reproductive maturity
2. chance variations within individuals in a population may be heritable. if these variations give an organism even a slight survival advantage, it is favorable
3. individuals with a greater preponderance of favorable variations are more likely to survive to reproductive age and produce offspring, which will increase these traits in future generations = this level of reproductive success = fitness
106
what is an organism's fitness directly related to?
the relative genetic contribution of this individual to the next generation
107
defn + aka: modern synthesis model
aka: neo-Darwinism
adds knowledge of genetic inheritance and changes in the gene pool to Darwin's original theory
108
defn: differential reproduction
when mutation or recombination results in a change that is favorable to the organism's reproductive success, that change is more likely to pass on to the next generation (the opposite is also true)
109
are evolution and natural selection the same thing?
natural selection is a mechanism for evolution
110
defn: 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
111
defn: theory of punctuated equilibrium
changes in some species occur in rapid bursts rather than evenly over time
112
what are the 3 types of natural selection + diagram?
1. stabilizing
2. directional
3. disruptive
113
defn + example: stabilizing selection
keeps phenotypes within a specific range by selecting against extremes
example: human birth weight
- those who way too little may not survive
- those who way too much can have trauma during delivery + the more maternal resources it requires
114
defn + example: directional selection
adaptive pressure can lead to the emergence and dominance of an initially extreme phenotype
example: if we have a heterogenous plate of bacteria, very few may have resistance to antibiotics
if the plate is treated with ampicillin, only those colonies that exhibit resistance to this antibiotic will survive
a new standard phenotype emerges as a result of differential survivorship
natural selection is the history of differential survivorship over time
115
defn + example: disruptive selection
2 extreme phenotypes are selected over the norm
example: Galapagos finches all have either large or small beaks
116
defn + func: polymorphisms
defn: naturally occurring differences in form between members of the same population (like light and dark coloration in the same species of butterfly)
func: facilitates disruptive selection
117
defn + benefit + what favors this: adaptive radiation
describes the rapid rise of a number of different species from a common ancestor
benefit: allows for various species to occupy different niches
favored by: environmental changes or isolation of small groups of the ancestral species
118
defn: niche
a specific environment, including habitat, available resources, and predators for which a species is specifically adaptive
119
defn: species
the largest group of organisms capable of breeding to form fertile offspring
120
defn: speciation
the formation of a new species through evolution
121
what would happen if we took two populations from the same species and separated them geographically for a long period of time? what would happen if enough time passed?
different evolutionary pressures would lead to different adaptive changes
if enough time passes, the changes would be sufficient to lead to isolation
122
impact: isolation
the progeny of the 2 populations can no longer freely interbreed and the two groups are now considered separate species
123
what are the 2 ways that reproductive isolation can occur?
1. prezygotically
2. postzygotically
124
defn: prezygotic vs. postzygotic mechanisms (of reproductive isolation)
PREZYGOTIC = prevent formation of the zygote completely
POSTZYGOTIC = allow for gamete fusion but yield nonviable or sterile offspring
125
what are 5 examples of prezygotic mechanisms (of reproductive isolation)?
1. TEMPORAL isolation (breed at different time)
2. ECOLOGICAL isolation (live in different niches within the same territory)
3. BEHAVIORAL isolation (a lack of attraction between members of 2 species due to differences in pheromones, courtship displays, etc.)
4. REPRODUCTIVE isolation (incompatibility of reproductive anatomy)
5. GAMETIC isolation (intercourse can occur, but fertilization cannot)
126
what are 3 examples of postzygotic mechanisms (of reproductive isolation)?
1. hybrid INVIABILITY (formation of a zygote that cannot develop to term)
2. hybrid STERILITY (forming hybrid offspring that cannot reproduce)
3. hybrid BREAKDOWN (form first-gen hybrid offspring that are viable and fertile, but second-gen hybrid offspring that are inviable or infertile)
127
what are the 3 patterns of evolution + diagram
1. divergent
2. parallel
3. convergent
128
defn: divergent evolution
the independent development of dissimilar characteristics in two or more lineages sharing a common ancestor
they live in very different environments and adapted to different selection pressures while evolving
129
defn: parallel evolution
the process whereby related species evolve in similar ways for a long period of time in response to analogous environmental selection pressures
130
defn: convergent evolution
the independent development of similar characteristics in two or more lineages not sharing a recent common ancestor
131
what is the rate of evolution measured by and related to?
measured by: the rate of change of a genotype over a period of time
related to: the severity of the evolutionary pressures on the species
132
defn: molecular clock model
by comparing DNA sequences between different species, scientists can quantify the degree of similarity between two organisms
as species become more taxonomically distant, the proportion of the shared genome will decrease
the more similar the genomes, the more recently the two species separated from each other
correlate the degree of genomic similarity with the amount of time since 2 species split off from the same common ancestor
