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Bio Chapter 12
Terms in this set (23)
what is complete dominance
what is incomplete dominance
what is codominance
when there is one dom and one recessive allele and the dom mask the rec
when an heterozygote expresses a genotype that is an intermediate b/t the 2 homozygote (certain flowers)
when there is more than on dom allele (ABO bloodtype)
what is penetrance
what is expressivity
Population measure defined as proportion of individuals in population carrying allele who actually express phenotype.
full penetrance is when everyone with the allele shows symptoms
high penetrance is when most but not all of those with the allele show symptoms
then there is also reduced penetrance, low penetrance and nonpenetrance
the different manifestations of the same genotype across the population (not population measure but rather on individual level)
if it is constant, everyone with given genotype expresses the same phenotype
if it is variable, everyone with given genotype expresses slightly different phenotypes
what are the four basic tenets of the modern interpretations of Mendel's First Law (of segregation)
genes exist in alternative forms (alleles)
an organism has 2 alleles for each gene (one from each parent)
the 2 alleles segregate during meiosis to produce gametes that carry only one allele for any inherited trait
if 2 alleles of an organism are different, only one will be fully expressed and the other will be silent, the expressed allele is dom and the silent is rec
Mendel's Second Law: Law of Independent Assortment
what is this law
what is the benefit of the first and second law
inheritance of gene does not affect the inheritance of another gene
so inheritance of a certain gene is independent of the other genes (this is shown in crossing over)
segregation and independent assortment increase the genetic diversity of gametes and the genetic diversity of offspring
what is a gene pool
what are wild-type alleles?
what is a mutagen + examples
how do transposons cause mutations
*rmr frameshift mutations can also be called insertion or deletion mutations
all of the alleles that exist within a species and mutation is when new genes are introduced into the pool
these are the normal or natural alleles
substances that cause mutations, ionizing radiation like UV rays from the sun and chemical exposure can damage DNA
transposon can insert and remove themselves from parts of the genome, so if they insert themselves they can disrupt the gene and cause a mutation
what are chromosomal mutations
what are deletion mutations?
what are duplication mutations?
what are inversion mutations?
what are insertion mutations?
what are translocation mutations?
more large scale in which large segments of DNA are affected
large segment of DNA is lost from a chrome (small deletions are frameshift mutations)
segment of DNA is copied multiple times in the genome
segment of DNA is reversed within the chromosome
segment of DNA is moved from one chromo to the other (small insertions are frameshift)
segment of DNA from one chromos is sapped with a segment of DNA from another chromo
consequences of mutation
what are advantageous mutations?
what are deleterious mutations?
what are inborn errors of metabolism?
advantageous: leads to OS that are stronger, ex. ppl with sickle cell disease have natural resistance to malaria because their RBC have shorter lifespan so parasite can't reproduce in them
deleterious: XP is an defect in the nucleotide excision repair mechanism, so if DNA is damaged by UV radiation, it can't be repaired and cancer can form
inborn errors of metabolism is a type of deleterious mutation, it is a defect in genes needed for metabolism which causes a buildup of metabolites in various pathways
what is genetic leakage
flow of genes b/t species
individuals from diff species can mate to form hybrid OS
many hybrids like a mule (male horse and female donkey OS) can not reproduce because they have an odd number of chromosomes and cannot undergo normal homolog pairing in meiosis to form gametes
what is genetic drift
what are its 2 types
what is inbreeding depression
what is outbreeding or outcrossing
changes in the composition of the gene pool due to chance, more pronounced in small populations
genetic drift and all of its types always lead to reduction in genetic diversity so small population have an increase prevalence of certain traits and diseases
founder effect: extreme case, small population of a species finds itself in reproductive isolation from other population due to natural barriers or catastrophic events
bottleneck: sudden and dramatic reduction in the size of a population, this leads to inbreeding which creates homozygosity which increases the prevalence of both homo dom and rec genotypes
when the loss of genetic variation causes a reduction in fitness of the population
opp of inbreeding depression, the introduction of unrelated individuals into a breeding group, can result in an increase in variation in a gene pool and increase fitness
what is a monohybrid cross
what is the parent (P) generation and the filial (F) generation?
what are the genotype and phenotype ratios that result from crossing 2 heterozygotes?
what is a test cross and what do the results tell us?
a cross where one trait is being studied
P is individuals being crossed and F is the OS (can be multiple F, F1 and F2, etc)
crossing 2 heterozygotes with complete dominance results in 1:2:1 distribution of genotypes and 3:1 ratio of phenotypes (these are theoretical and esp don't hold true in small population, more OS= closer to these ratios)
used to determine an unknown genotype, cross unknown individual with homo recessive individual,
if all OS are of dom phenotype, then unknown is likely to be homo dom
if there is 1:1 ratio of dom to rec phenotypes, then unknown is hetero
what is a dihybrid cross?
what is phenotypic ratio when doing dihybrid cross with heterozygotes?
when we study the inheritance of 2 traits or genes
for unlinked genes, Mendels laaw of independent assortment holds true
if we cross 2 heterozygotes, OS have pheno ratio of 9331 (rmr its still 3:1 for each gene)
how do we write genotype for sex-linked traits
use X and Y
X chromo with defective allele is usually given a subscript (letter at bottom) like Xb
unless under-wise stated, assume all sex-linked traits on the MCAT are X linked recessive
what is a chiasma and what is recombination freq?
further the genes, the more likely they are to be separated during CO
point of crossing over is called a chiasma which is b/t 2 genes
likelihood that 2 genes are separated from each other during CO, is called the recombination freq and this is roughly proportional to the distance b/t the genes
strength of linkage is also given by recombination freq
tightly linked genes have recombination freq closer to 0 percent
weakly linked genes have recombination freq closer to 50 percent
how do we get a genetic map and what are the units on it?
recombination freq can give us a genetic map that shows the distance b/t genes on a chromosome
one map unit= 1% chance of recombination
if recombination freq are known we can find the order of genes on the chromosome because map units are roughly additive
what is an allele freq
what 5 criteria are need for a populations allele/gene freqs to not change, its the gene pool to be stable and evolution to not occur?
what is it called when these 5 criteria are met?
allele freq is how often the allele appears in the population and changes in allele or gene freq leads to evolution
the population is very large (no genetic drift)
there are no mutations that affect the gene pool
mating b/t individuals in the population is random (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
the population is in hardy-weinberg equilibrium and we can use the hardy-weinberg equations now
what are the 2 equations we need to know?
what does each equation tell us?
p is freq of dom allele, q is freq of recessive
the second one tells us abt the freq of alleles in the population and the first one tells us about the freq of genotypes and phenotypes in the population
what is natural selection
what are the 3 basic tenets of this theory?
certain traits give an individual greater reproductive success, so traits are passed to OS
because the gene pool changes over time, it is important to note that populations evolve, not individuals
organism produce OS, few of which survive to reproductive maturity
chances variation within individuals in a population may be heritable, if these variations give an organism even a slight survival advantage, the variation is favourable
individuals with greater preponderance of these favourable variations are more likely to survive to reproductive age and produce OS, this increases the presence of these traits in the future, this level of reproductive success is called fitness
when we discovered that inheritance occurs through the passing of genes, how was Darwin's theory updated?
what is differential reproduction?
what is inclusive fitness?
what is punctuated equilibrium?
when mutation or recombination results in a change that is favourable to the organisms reproductive success, that change is more likely to pass on to the next generation
traits passed on by the more successful organisms will become ubiquitous in the gene pool
opposite of natural selection, this is true also (so weaker don't reproduce and wont pass traits)
a measure of an organism's success in the population, based on the number of OS, success in supporting OS, and the ability of the OS to then support others
another theory that said changes in some species occurs in rapid burst rather then evenly over time
evolution: modes of natural selection
what is stabilizing selection
what is directional selection
what is disruptive selection
keeps phenotypes within a certain range by selecting against extremes (ex. birth weights, smaller and larger babies may not survive)
adaptive pressure can lead to the romance of one extreme phenotype (ex. bacteria colonies with antibiotic resistance survive)
2 extremes are selected over the norm (ex. Darwin's finches, none had med size beaks because the seeds on the island were very large or very small)
this type of selection is facilitated by the existence of polymorphism, naturally occurring differences in for b/t members of the same population
what is adaptive radiation?
what is a niche
rapid rise in number of different species from a common ancestor
allows for various species to occupy different niches
niche is a specific environment (habitat, resources and predators) for which a species is specifically adapted
What is speciation?
formation of new species through evolution
if we took 2 populations of the same species and separated them geographically, evolutionary pressures would lead to different adaptive changes
if enough time passed, the changes would be sufficient to lead to isolation, which means the progeny of these populations could no longer freely interbreed, groups are now separate species
what are 2 ways reproductive isolation can occur
prezygotic mechanisms which prevents formation of the zygote completely
ex. temporal isolation (diff breeding times), ecological isolation (living in diff niches in same territory), behavioural isolation (lack of attraction b/t members of the 2 species due to differences in pheromones, courtship displays, etc), reproductive isolation (reproductive anatomy is not compatible), or gametic isolation (intercourse can happen but fertilization can't)
postzygotic mechanisms allows for gamete fusion but yields sterile or nonviable OS
ex. hybrid inviability (formation of a zygote that can't develop), hybrid sterility (forming hybrid OS that cannot reproduce), and hybrid breakdown (forming first-gen hybrid OS that are viable and fertile, but second gen hybrid OS that are inviable or infertile)
patterns of evolution
what are the 3 patterns of evolution
divergent evolution: independent development of dissimilar characteristics in 2 or more lineages sharing a common ancestor
parallel evolution: related species evolve in similar ways for long periods of time due to similar environmental selection pressures
convergent evolution: independent development of similar characteristics in 2 or more lineages not sharing a recent common ancestor
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