Chapter 12: Genetics and Evolution Flashcards
The physical and biochemical characteristics of every living organism are determined by ____________, which are DNA sequences that code for heritable traits that can be passed from one generation to the next.
Genes
All genes (as well as a large supply of noncoding DNA) are organized into _______________ to ensure that genetic material is passed easily to daughter cells during mitosis and meiosis.
Chromosomes
Each gene may have alternative forms called ___________.
Alleles
The genetic combination possessed by an individual is known as a ______________.
Genotype
The manifestation of a given genotype as an observable trait is known as a _____________.
Phenotype
Each human being possesses two copies of each chromosome, called ______________, except for male sex chromosomes (in which there is one X chromosome and one Y chromosome).
Homologues
Each gene has a particular __________, or location on a specific chromosome.
Locus
If only one copy of an allele is needed to express a given phenotype, the allele is said to be _____________ and is usually represented with a capital letter.
Dominant
If two copies are needed, the allele is said to be _____________ and is usually represented with a lowercase letter.
Recessive
If both alleles are the same for a given gene, the individual is said to have a _______________ genotype.
Homozygous genotype
If the alleles are different, the individual has a ________________ genotype.
Heterozygous genotype
A _______________ genotype describes a situation in which only one allele is present for a given gene, as is the case for parts of the X chromosome in males.
Hemizygous
When only one dominant and one recessive allele exist for a given gene, there is said to be __________________.
Complete dominance
When more than one dominant allele exists for a given gene, there is _______________. For example, a person with one allele for the A blood antigen and one allele for the B blood antigen will express both antigens simultaneously.
Codominance
_________________ occurs when a heterozygote expresses a phenotype that is immediate between the two homozygous genotype. For example, the mating of certain flowers, in which a red flower crossed with a white flower results in pink flowers.
Incomplete dominance
______________ is a population measure defined as the proportion of individuals in the population carrying the allele who actually express the phenotype.
Penetrance
_______________ is when 100 percent of individuals with the allele show symptoms of disease.
Full penetrance
_______________ occurs when most (but not all) of those with the allele show symptoms of the disease.
High penetrance
________________ occurs when few of those with the allele show symptoms of the disease.
Reduced/low penetrance
_______________ occurs when none of the individuals with the diseased gene show symptoms.
Nonpenetrance
______________ is defined as varying phenotypes despite identical genotypes.
Expressivity
If expressivity is ___________, then all individuals with a given genotype express the same phenotype.
Constant
If expressivity is ____________, then individuals with the same genotype may have different phenotypes.
Variable
Mendel’s First Law: Law of ______________
Segregation
Four basic tenets of Mendel’s first law of segregation:
- Genes exist in alternative forms (__________).
- An organism has _________ alleles for each gene - one inherited from each parent.
- The two alleles segregate during ___________, resulting in gametes that carry only one allele for any inherited trait.
- If two alleles of an organism are different, only one will be fully expressed and the other will be silent. The expressed allele is said to be ____________, while the silent allele is ______________. (Except codominance and incomplete dominance).
- Alleles
- Two alleles
- Meiosis
- Dominant, recessive
Mendel’s second law (of ____________________) states that the inheritance of one gene does not affect the inheritance of another gene.
Independent assortment
During prophase I of meiosis, homologous chromosomes pair up to form _____________, which derive their name from four chromatids involved (two chromatids in each of two homologous chromosomes).
Tetrads
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 allows the inheritance of one gene to be independent of the inheritance of all others.
Recombination
________________ and __________________ allow for greater diversity in the offspring.
- Segregation
- Independent assortment
All of the alleles that exist within a species are known as the _______________.
Gene pool
Mutant alleles can be contrasted with their _____________ counterparts, which are alleles that are considered “normal” or “natural” and are ubiquitous in the study population.
Wild-type
Ioonizing radiation, such as ultraviolet rays from the sun, and chemical exposures can damage DNA; substances that can cause mutations are called ______________.
Mutagens
Elements known as _______________ can insert and remove themselves from the genome.
Transposons
________________ occur when one nucleotide in DNA (A, C, T or G) is swapped for another.
Point mutation
Point mutations can be subcategorized as _____________, ____________, or _____________ mutations.
- Silent mutations
- Missense mutations
- Nonsense mutations
______________ occur when the change in nucleotide has no effect on the final protein synthesized from the gene.
Silent mutations
Silent mutations most common occur when the changed nucleotide is transcribed to be the third nucleotide in a codon because there is ________________ (____________) in a the genetic code.
Degeneracy (wobble)
________________ occur when the change in nucleotide results in substituting 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
Because mRNA transcribed from DNA is always read in three-letter sequences called ___________, insertion or deletion of nucleotides can shift the reading frame, usually resulting in either changes in the amino acid sequence or premature truncation of the protein (due to the generation of a nonsense mutation).
Codons
Framshift mutations can be subcategorized as _____________ or _____________.
- Insertion mutations
- Deletion mutations
_______________ are larger-scale mutations in which large segments of DNA are affected.
Chromosomal mutations
_________________ occur when a large segment of DNA is lost from a chromosome.
Chromosomal/Large deletion mutations
________________ occur when a segment of DNA is copied multiple times in the genome
Duplication mutations
_________________ occur when a segment oof DNA is reversed within the chromosome.
Inversion mutations
__________________ occur when a segment of DNA is moved from one chromosome to another.
Chromosomal/Large insertion mutations
_________________ occur when a segment of DNA from one chromosome is swapped with a segment of dNA from another chromosome.
Translocation mutations
Some mutations can be ______________, conferring a positive selective advantage that may allow the organism to produce fitter offspring.
Advantageous
Some mutations can be detrimental or _______________.
Deleterious
One important class of deleterious mutations is known as _____________________. These are defects in genes required for metabolism.
Inborn errors of metabolism
Genetic ____________ is a flow of genes between species.
Leakage
In some cases, individuals from different (but closely related) species can mate to produce ____________ offspring.
Hybrid
______________ refers to changes in the composition of the gene pool due to chance.
Genetic drift
The ______________ is 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.
Founder effect
_______________ are drastic and sudden events that reduce the size of the population available for breeding.
Bottlenecks
______________ is the mating between two genetically related individuals.
Inbreeding
The loss of genetic variation caused by genetic drift, the founder effect, and inbreeding may cause reduced fitness of the population, a condition known as ____________________.
Inbreeding depression
Genetics is a field in which a number of __________________, or quantitative approaches to biological data, have been developed.
Biometric techniques
_______________ are diagrams that predict the relative genotypic and phenotypic frequencies that will result from the crossing of two individuals.
Punnett squares
A cross in which only one trait is being studied is said to be ______________.
Monohybrid
The ___________ or ______________ generation refers to the individuals being crossed.
- Parent
- P generation
The offspring in the Punnett squares are the _____________ or ____________ generation.
- Filial
- F generation
Crossing two heterozygotes (monohybrid) for a trait with complete dominance results in a ___________ ratio of genotypes and a ___________ ratio of phenotypes.
- 1:2:1
- 3:1
A _____________ is used to determine an unknown genotype.
Test cross
Because a test cross is used to determine the genotype of parent based on the phenotypes of its offspring, test crosses are sometimes called ______________.
Back crosses
We can extend a Punnett square to account for the inheritance of two different genes using a _______________.
Dihybrid cross
According to Mendel’s second law (of independent assortment) the inheritance of one gene is independent of the inheritance of the other. This will hold true for ___________________.
Unlinked genes
Crossing four heterozygotes (dihybrid cross) for a trait with complete dominance results in a ___________ ratio of genotypes and a ___________ ratio of phenotypes.
- 9:3:3:1
- 3:1
When considering ____________ (____________) traits, a slightly different system is used to symbolize the various alleles because females have two X chromosomes and thus may be homozygous or heterozygous for a condition carried on the X chromosome.
Sex-linked (X-linked) traits
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.
Recombination frequency
Tightly linked genes have recombination frequencies close to _________ percent.
0 percent
Weakly linked genes have recombination frequencies approaching _______ percent, as expected from independent assortment.
50 percent
By analyzing recombination frequencies, a ________________ representing the relative distance genes on a chromosome can be constructed.
Genetic map
By convention, one ____________ or _____________ corresponds to a 1 percent chance of recombination occurring between two genes.
- Map unit
- Centimorgan
How often an allele appears in a population is known as its ________________.
Allele frequency
Hardy-Weinberg equilibrium population conditions:
- The population is very large (no ______________)
- There are no mutations that affect the ______________.
- Mating between individuals in the population is ____________ (no sexual selection)
- There is no migration of individuals into or out of the population.
- The genes in the population are all equally successful at being reproduced.
- Genetic drift
- Gene pool
- Random
Hardy-Weinberg equations:
_____________
_____________
_______________, sometimes called survival of the fittest, is 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.
Natural selection
Charles Darwin’s basic tenet(s):
Chance variations within individuals in a population may be heritable. If these variations give an organism even a slight survival advantage, the variation is termed _______________.
Favourable
Charles Darwin’s basic tenet(s):
Individuals with a greater preponderance of these favourable variations are more likely to survive to reproductive age and produce offspring; the overall result will be an increase in these traits in future generations. This level of reproductive success is termed _____________, and an organism’s fitness is directly related to the relative genetic contribution of this individual to the next generation.
Fitness
The __________________ model, sometimes called _________________, adds knowledge of genetic inheritance and changes in the gene pool to Darwin’s original theory.
- Modern synthesis model
- Neo-Darwinism
________________ 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 the offspring to then support others.
Inclusive fitness
Updated Darwin’s theory: when mutation or recombination results in a change that is favourable to the organism’s reproductive success, that change is more likely to pass on to the next generation. The opposite is also true. This process is termed ____________________.
Differential reproduction
In contrast to Darwin’s theory, _________________ suggests that changes in some species occur in rapid bursts rather than evenly over time.
Punctuated equilibrium
Natural selection may occur as ___________________, __________________, or ___________________.
- Stabilizing selection
- Directional selection
- Disruptive selection
_________________ keeps phenotypes within a specific range by selecting against extremes. An example is human birth weight.
Stabilizing selection
Adaptive pressure can lead to the emergence and dominance of an initially extreme phenotype through ________________. An example is antibiotic resistant bacteria.
Directional selection
In _______________, two extreme phenotypes are selected over the norm. An example is the finches’ beak size on the Galápagos Islands.
Disruptive selection
Disruptive selection is facilitated by the existence of ________________ - naturally occurring differences in form between members of the same population, such as light and dark coloration in the same species of butterfly.
Polymorphisms
________________ is a related concept that describes the rapid rise of a number of different species from a common ancestor.
Adaptive radiation
The benefit of _______________ is that it allows for various species to occupy different niches.
Adaptive radiation
A ____________ is a specific environment, including habitat, available resources, and predators, for which a species is specifically adapted.
Niche
A ___________ is defined as the largest group of organisms capable of breeding to form fertile offspring.
Species
The formation of a new species through evolution is called ______________.
Speciation
If enough time passed, the adaptive changes from different evolutionary pressures would be sufficient to lead to ______________, which means the progeny of these populations could no longer freely interbreed.
Isolation
_________________ may occur either prezygotically or postzygotically.
Reproductive isolation
_______________ mechanisms prevent formation of the zygote completely.
Prezygotic mechanisms
_______________ mechanisms allow for gamete fusion but yield either nonviable or sterile offspring.
Postzygotic mechanisms
Examples of prezygotic mechanisms include:
- ______________ isolation (breeding at different times)
- ______________ isolation (living in different niches within the same territory)
- ______________ isolation (a lack of attraction between members of the two species due to differences in pheromones, courtship displays, and so on)
- ______________ isolation (incompatibility of reproductive anatomy)
- ______________ isolation (intercourse can occur, but fertilization cannot)
- Temporal isolation
- Ecological isolation
- Behavioural isolation
- Reproductive isolation
- Gametic isolation
Examples of postzygotic mechanisms include:
- __________________ (formation of a zygote that cannot develop to term)
- __________________ (forming hybrid offspring that cannot reproduce). Example is a viable mule.
- __________________ (forming first-generation hybrid offspring that are viable and fertile, but second-generation hybrid offspring inviable or infertile)
- Hybrid inviability
- Hybrid sterility
- Hybrid breakdown
Three patterns of evolution emerge: _____________ evolution, ______________ evolution, and _______________ evolution.
- Divergent evolution
- Parallel evolution
- Convergent evolution
_________________ refers to the independent development of dissimilar characteristics in two or more lineages sharing a common ancestor. An example is seals and cats are mammals in the order of Carnivora, yet they differ markedly in general appearance.
Divergent evolution
________________ refers to the process whereby related species evolve in similar ways for a long period of time in response to analogous environmental selection pressures.
Parallel evolution
__________________ refers to the independent development of similar characteristics in two or more lineages not sharing a recent common ancestor. An example is fish and dolphins have come to resemble one another physically, though they belong to different classes of vertebrates.
Convergent evolution
______________ is a slow process, featuring changes in the environment and subsequent changes in genotypes and phenotypes of a population over time.
Evolution
As species become more taxonomically distant, the proportion of the shared genome will (increase?/decrease?)_______________.
Decrease
The more similar the genomes, the more recently the two species separated from each other. This is sometimes called the ___________________.
Molecular clock model
