Chapter 12: Genetics and Evolution Flashcards
Genes are organized into ____________. Each gene may have alternative forms called ________.
chromosomes; alleles
Human beings typically possess two copies of each chromosome, called ____________.
homologues
Each gene has a particular ____________, or location on a specific chromosome that is consistent across human beings - a gene can be described by its location.
locus
Because each chromosome is part of a homologous pair, a person will inherit ____ alleles for all genes.
two
If only one copy of an allele is needed to express a given phenotype, this allele is ____________.
dominant
If 2 copies of a gene are needed, it is ____________.
recessive
If both alleles are the same for a gene, the individual is said to have ________________ genotype.
homozygous
If alleles are different, this is a ____________ genotype.
heterozygous
If only one copy of an allele is needed to express a given phenotype, this allele is ____________.
dominant
A ____________ genotypes describes a situation in which only one allele is present for a given gene, e.g. X chromosome in genotypical males.
hemizygous
When only one dominant and one recessive allele exist for a given gene, there is said to be ____________ ____________.
complete dominance
In complete dominance, the presence of one dominant allele will ________ the recessive allele, if present.
mask
When more than one dominant allele
Codominance
When more than one dominant allele exists for a given gene, there is ____________.
codominance
In codominance, what can happen?
Can express both both simulatneously
____________ dominance occurs when a heterozygote expresses a phenotype that is intermediate between the two homozygous genotypes.
incomplete
____________ is 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
Penetrance
____ penetrance is when 100% of individuals with this allele express it.
full
When most (but not all) of those with the allele express it, this is ________ penetrance.
high
____________ is defined as varying phenotypes despite identical genotypes.
expressivity
If expressivity is ________, the all individuals with a given genotype express the smae phenotype.
constant
If expressivity is ________, then individuals with the same genotype may have different phenotypes.
constant
What are the 4 basic tenets of Mendel’s first law of segregation?
- Alleles exist
- 2 alleles/gene, 1 from each parent
- 2 alleles segregate during meiosis (gametes only have 1 allele for an inherited trait)
- If 2 alleles are different, only 1 will be fully expressed, other 1 is silent.
exception to #4 is codominance and incomplete dominance
What does Mendel’s second law of independent assortment state?
INheritance of one gene does not affect the inheritance of another gene
The daughter strand is held to the parent strand at the ____________.
centromere
Daughter + parent strands = ?
sister chromatids
During prophase I of meiosis, homologous chromosomes pair up to form ____________.
tetrads
What happens when tetrads come together? What is this called?
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.
This is called recombination.
Substances that cause mutations are called what?
Mutagens
Elements known as ____________ can insert and remove themselves from the genome. What can this do to genes?
transposons; if it inserts itself in the middle of a coding sequence, the mutation can disrupt the gene
________ mutations occur when one nucleotide is swapped for another. What are the 3 types?
point;
1. silent
2. missense
3. nonsense
________ mutations occur when the change in nucleotide has no effect on the final synthesized protein.
silent
Silent mutations most often occur when the changed nucleotide is transcribed to be the third nucleotide in a codon because there is ____________, or ________, in the genetic code.
degeneracy, wobble
____________ mutations occur when the change in nucleotide results in subtituting one amino acid for another in the final protein.
missense
____________ mutations occur when the change in nucleotide results in substituting a stop codon for an amino acid in the final protein.
nonsense
____________ mutations occur when nucleotides are inserted into or deleted from the genome.
frameshift
________ mutations occur when a large segment of DNA is lost from a chromosome
deletion
Small deletion mutations are considered ________ mutations.
frameshift
____________ mutations occur when a segment of DNA is copied multiple times in the genome
duplication
____________ mutations occur when a segment of DNA is reversed within the chromosome.
inversion
____________ mutations occur when a segment of DNA is moved from one chromosome to anotehr.
insertion
____________ mutations occur when a segment of DNA from one chromosome is swapped with a segment of DNA from another.
translocation
Genetic ________ is a flow of genes between species. Individuals from different but closely related species can mate to produce ____________ offpsirng.
leakage; hybrid
Many hybrid offspring cannot do what? Why?
Cannot reproduce; often have odd numbers of chromosomes, which means homologous pairing cannot occur
Genetic ________ refers to changes in the composition of the gene pool due to chance. It is more pronounced in what size populations?
drift; small
The ____________ effect is 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 ____________ that drastically and suddenly reduce the size of the population available for breeding.
founder; bottleneceks
Inbreeding encourages ____________, which increases the prevalence of both homozygous dominant and recessive genotypes.
homozygosity
The loss of genetic variation may caused reduce fitness of the population, a condition known as what?
inbreeding depression
On the opposite end of the spectrum, ____________ is the introduction of unrelated individuals into a breeding group, which could theoretically result in increased variation within a gene pool and increased fitness of the population.
outbreeding
What two genotypes are crossed in a test cross?
- Unknown genotype
- Homozygous recessive
Tests crosses are sometimes called ________ crosses.
back
Dihybrid cross of a two plants that are heterozygous for both traits will result in what ratio?
9:3:31
____-________ traits are characteristics that are determined by genes located on the sex chromosomes
sex-linked (X-linked)
Genotypical males have only one X chromosome and are ____________ for many genes carried on the X chromosome.
hemizygous
An X chromosome carrying a defective allele is commonly given a ____________.
subscript
The further apart two genes are, the more likely it is that there will be a point of crossing over, called a ________, between them.
chiasma
The likelihood that two alleles are separated from each other during crossing over, called the ________________ ____________, is roughly proportional to the distance between the genes on the chromosome.
recominbation frequency
Tightly linked genes have recombination frequences close to 0%; weakly linked genes have recominbation frequencies approaching ____%, as expected from independent assortment.
50
A ____________ ________ representing the relative distance between genes on a chromosome can be constructed.
genetic map
One ____ ________ or ____________ corresponds to a 1% chance of recombination occurring between two genes.
map unit; centimorgan
How often an allele appears in a population is known as its ________ ____________.
allele frequency
Evolution results from what?
Changes in gene frequencies in reproducing populations over time
When gene frequencies of a population are not changing, the gene pool is stable and evolution is not occurring. What are the 5 criteria that are mandatory for this ?
- Very large population (no genetic drift)
- No mutations
- Random mating (no sexual selection)
- No migration in and out
- All genes are equally successful at being reproduced
If all 5 criteria are met to keep gene pool stable, a population is said to be in ________-____________ equilibrium, and equations can be used to predict the allelic and phenotypic frequencies.
Hardy-Weinberg
What is the Hardy-Weinberg equation?
p2 + 2pq + q2 = 1
p2 = homozygous dominant frequency
2pq = heterzygous dominant frequency
q2 = homozygous recessive frequency
The sum p2 + 2pq represents the frequency of what?
dominant phenotype
p + q =1 tells us what?
freqency of alleles
p2 + 2pq + q2 = 1 tells us what?
frequency of phenotypes
T = tall allele, t = short allele
If T is p=0.80, what are the allele frequencies of the generation?
64% TT = 64% T and 0% t
32% Tt = 16% T and 16% t
4% tt = 0% T and 4% t
Thus the allele frequencies are 80% T and 20% t
Evolution is not equivalent to natural selection, what is their relationship?
Natural selection is a mechanism for evolution
____________ ____________ is a process of favoring survival and reproduction of the fittest individuals in a population
differential reproduction
____________ ____________ is a measure of an organism’s success in the population, based on the number of offspring, success in supporting offspring, and the ability of offspring to then support otehers.
inclusive fitness
____________ selection keeps phenotypes within a specific range by selecting against extremes.
stabilizing
Adaptive pressure can lead to the emergence and dominance of an initially extreme phenotype through ____________ selection.
directional
In ____________ selection, 2 extreme phenotypes are selected over the norm.
disruptive
Disruprtive selection is facilitated by the existence of ____________ - naturally occurring differences inform between members of the same population.
polymorphisms
____________ ____________ is a related concept that describes the rapid rise of a number of different species from a common ancestor.
adaptive radiation
A ________ is defined as the largest group of organisms capable of breeding to form fertile offspring.
species
Reproductive isolation may occur in two different ways.
____________ mechanisms prevent formation of the zygote completely.
prezygotic
Reproductive isolation may occur in two different ways.
____________ mechanisms allow for gamete fusion but yield either nonviable or sterile offspring.
postzygotic
What are examples of prezygotic mechanisms?
- temporal isolation (breed at different times)
- ecological isolation (different niches)
- behavioral isolation (lack of attractino)
- reproductive isolation (incompatibility of anatomy)
- gametic isolation (fertilization can’t occur despite intercourse)
What are examples of postzygotic mechanisms?
- hybrid inviability (formation of zygote that cannot developt to term)
- hybrid sterility (forming hybrid offspring that can’t reproduce)
- hybrid breakdown (forming F1 hybrid offspring that are viable and fertile, but F2 are inviable/ infertile)
____________ evolution refers to independent development of dissimilar characteristics in 2+ lineages sharing a common ancestor, e.g. seals and cats are both Carnivora but very different.
divergent
________ evolution refers to the process whereby related species evolve in similar ways for a long period of time in resopnse to analogous environmental selection pressures
Parallel
____________ evolution refers to the indpendent development of similar characteristics in 2+ lineages not sharing a recetn common ancestor, e.g. fish and dolphins both aquatic but different classes of vertebrates
convergent
Molecular evolutions correlate the degree of genomic similarity with what?
amount of time since 2 species split off from same common ancestor
The more similar the genomes of two species are, the more recently what? What is this called?
two species separated from each other; molecular clock model
