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70 Cards in this Set
- Front
- Back
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A continuous quantitative trait is often the result of
__________ and is frequently ____________. |
polygenic inheritance, multifactorial
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Meristic traits
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polygenic traits in which the
phenotype is recorded by counting whole numbers e.g. number of fingers; They are quantitative traits but do not have an infinite range of phenotypes |
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Environmental effects, incomplete penetrance and low
expressivity can lead to: |
large variation in phenotype for a
particular genotype |
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Threshold traits
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polygenic and often multifactorial
but have a small number of discrete phenotypic classes |
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multiple-factor hypothesis
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This trait is controlled by two
genes, each of which segregates independently in Mendelian fashion. Each gene has an additive allele and a nonadditive allele |
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Additive alleles
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contribute to a single quantitative character
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correlation coefficient (r) indicates
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whether:
• the two traits both increase or decrease together (r is positive), or • one increases as the other decreases (r is negative) r = covxy/sxsy |
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Heritability
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describes the proportion of total
phenotypic variation in a population due to genetic factors |
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What is the difference between broad-sense heritability
(BSH) and narrow-sense heritability (NSH)? |
NSH considers additive (not total) genotypic variance.
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identical twins, phenotypic variance equals
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environmental variance, as there is no genotypic variance.
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For fraternal twins, phenotypic differences represent
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both environmental variance and approximately half the
genotypic variance. |
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The difference in _________ for a given trait in identical versus fraternal twins suggests whether there is
a strong genetic component involved in the determination of the trait |
concordance
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A population’s gene pool
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is all of the alleles present in
that population. |
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Predictions of Hardy Weinberg Law
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- no selection
- no mutation - no migration - population infinitely large -random mating |
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The rate at which the frequency of a deleterious allele declines depends on:
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the strength of selection applied
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Directional Selection
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the genotype conferring one
phenotypic extreme is selected, resulting in a change in the population mean over time. |
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Stabilizing Selection
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intermediate types are favored,
and both extreme phenotypes are selected against |
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Disruptive Selection
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both phenotypic extremes are selected for, and the intermediates are selected against.
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Genetic Drift
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occurs when the number of reproducing individuals in a population is too small to ensure that all the alleles in the gene pool will be passed on to the next generation in their existing frequencies.
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Founder Effect
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the genetic consequences seen when a population originates from a small number of individuals
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Inbreeding Depression
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an individual will be homozygous for a recessive
deleterious allele, the significance of this fact is that inbred populations often have a lowered mean fitness, |
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Genetic Variation
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can be measured as the frequency of individuals in the population that are heterozygous at a given locus or as the number of different alleles at a locus that are present in the gene pool
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Small, isolated populations are especially vulnerable to:
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- genetic drift
- inbreeding - reduction in gene flow |
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Inbreeding coefficient
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F = (2pq – H)/2pq
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Inbreeding Depression
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may result from increased
homozygosity for deleterious alleles or from heterozygotes having a higher fitness than either of the corresponding homozygotes. |
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Ex Situ Conservation
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involves removing plants or
animals from their original habitat to an artificially maintained location to form the basis for a captive breeding program |
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Population Augmentation
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involves boosting a declining
population by transplanting individuals of the same species from elsewhere. |
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Genetic Swamping
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A potential problem with population augmentation, which occurs when the gene pool of the original population is overwhelmed from the
transplanting individuals and loses its identity |
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Outbreeding Depression
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another concern with
population augmentation as reduced fitness occurs in the progeny of matings between genetically diverse individuals |
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Autopolyploidy
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One or more sets of chromosomes identical to
the haploid complement of the same species |
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Allopolyploidy
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The combination of chromosome sets from
different species as a consequence of interspecific matings. Limitations: must be closely related; typically in the same family |
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allotetraploid
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can arise after the
hybridization of two closely related species |
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If the sterile hybrid
undergoes a natural chromosomal doubling, |
a fertile amphidiploid is
produced |
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Endopolyploidy
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is the condition in which only certain cells in an otherwise diploid organism are polyploid. In these cells, replication and segregation of chromosomes occur without nuclear division
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Duplications arise as the result of
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unequal crossing over
during meiosis or through a replication error prior to meiosis |
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paracentric inversion
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does not change the relative lengths of the two arms of a chromosome
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pericentric inversion, which includes the centromere,
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changes the relative lengths of the two arms of a chromosome
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Paracentric inversion crossover
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• one recombinant chromatid is dicentric (two centromeres)
• one is acentric (lacking a centromere) |
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In small isolated populations, gene frequencies can fluctuate considerably. The term that applies to this circumstance is
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genetic drift
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Suppose individuals with the tallest genetically based phenotypes survived and reproduced more than other genotypes. This is an example of
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directional selection
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Meristic Traits
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have phenotypes that differ in the number of some structure.
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According to the phylogenetic species concept, the major criterion for determining if two population are part of the same species is
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sharing uniquely acquired characteristics
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Inbreeding depression refers to:
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a decrease in population fitness due to deleterious recessive alleles being expressed.
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What is the term applied to a form of speciation in which one species gives rise to two distinct daughter species?
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cladogenesis
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Name the two individuals who provided the foundation for the modern interpretation of evolution.
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Darwin and Wallace
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There are a number of mechanisms that operate to maintain genetic diversity in a population. Why?
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Diversity may better adapt a population to inevitable changes in the environment.
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Assume that a cross is made between tall and dwarf tobacco plants. The F1 generation showed intermediate height, while the F2 generation showed a distribution of height ranging from tall to dwarf, like the original parents, and many heights between the extremes. These data are consistent with the following mode of inheritance:
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multiple factor inheritance
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What is the difference between broad-sense heritability (BSH) and narrow-sense heritability (NSH)?
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NSH considers additive (not total) genotypic variance.
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Why might you expect natural populations to have little genetic variation?
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Well-adapted populations would have lost variation due to selection.
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Which of the following is a measure of intraspecific diversity
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Percent nucleotide difference for one gene between two populations of guppies.
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Which statement is consistent with the neutral theory of molecular evolution?
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Genetic drift is responsible for the fate of many alleles.
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The number of deleterious alleles present in the gene pool of a population is referred to as the ________.
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Genetic load
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What explanation is generally given for lethality of monosomic individuals?
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Recessive lethal alleles are unmasked with monosomic chromosomes (hemizygous condition).
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In Drosophila, mutations in segment polarity genes cause:
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defects at homologous sections of each segment
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Immediately after fertilization of a Drosophila egg, the zygote nucleus undergoes a serious of divisions. Subsequent nuclear migration generates a:
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synctial blastoderm
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Mutations that eliminate contiguous region in the Drosophila embryo's segmentation patter are called:
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gap genes
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In functional genomics, identifying a gene in a different species thought to be descended from a gene in a common ancestor is a:
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ortholog
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Chromatin Remodeling
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changes in DNA/chromosome structure can influence overall gene output
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Promoters
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recognize transcription machinery and bind proteins that regulate transcription initiation.
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Enhancers
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necessary for achieving the maximum level of transcription. They are responsible for time and tissue gene expression.
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Transcription Factors
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have various structural motifs which bind DNA and influence transcription.
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Activators
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increase transcription
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Repressors
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reduce transcription
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Alternative Splicing
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can generate different forms of mRNA from a pre-mRNA, giving rise to a number of proteins from one gene.
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RNA Silencing
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gene silencing by RNA interference uses a protein called Dicer to cleave dsRNA into small interfering RNA's that bind to RNA induced silencing complex for unwinding. RNAi allows silencing of single genes to allow rapid analysis of gene function.
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expected allele frequency after x generations formula
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(qg = q0/(1 + gq0))
q0 is original frequency g is # of generations |
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What is the main reason that a species with a population size of 100 or less would become extinct?
a) The number of individuals available for mating at the same time is very low. b) reduction in genetic variability and the problems associated with it c) genetic drift d) All of the above statements are true. |
All of the above
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Isozymes are used to
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predict genetic variation in a population
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Small RNAs silence genes via 3 different mechanisms. Briefly describe how each one works.
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the antisense strand is maintained in the RiSC complex. when the sense strand is encountered:
1. if perfectly complementary, sense binds to antisense, RISC cleaves the double-stranded RNA and it is degraded by ribonucleases
2. if complementation is less than perfect, RISC complex doesn't release RNA and thus interferes with translation
3. alternatively, single antisense strand can be packaged into RITS complex and directed to the nucleus where it binds to a specific gene and recruits histone methyltransferases to methylate DNA
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In eukaryotes, what basal transcription factors assist in the loading of RNA Polymerase onto a gene? Explain the function of the ones that were discuessed in class.
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TFIID (composed of TBP subunit and several TAFs) binds TATAA box in the promoter. This complex attracts other TFs to the promoter (TFIIA,B,F,H,J). Importantly, TFIIF chaperones RNA polymerase II to this initiator complex leading to initiation of transcription.
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