genetic inheritance and evolution Flashcards
mendelian genetics
pea plant experiements to track phenotypic variation and established dominant and recessive traits
genotype
combination of genes responsible for phenotype
phenotype
physical manifestation of a genotype
- multiple genotypes can show same phenotype
gene
sequence of dna that codes for a given trait
allele
variations of a gene
homologues
copies of the same chromosome
- same set of genes but different alleles
locus
region of a chromosome where a gene resides
descriptions of alleles
dominant and recessive
dominant allele
1 copy is needed to show phenotype
recessive
2 copies needed to show phenotype
do loss of function mutations tend to be dominant or recessive
recessive
do gain of function mutations tend to be dominant or recessive
dominant
example of fatal gain of function disease
huntingtons
punnett square
common technique to illustrate genetic cross over where parental genomes are aligned on each axis, with 4 or more outcomes
homozygus
2 copies of the same allele
heterozygus
1 copy of 2 different alleles
hemizygous
one copy of an allele is present
- nondisjunction
test cross
an individual with a DOMINANT phenotype is crossed with an individual of the recessive phenotype , if the dominant is homozygous , the f1 generation wont have any of recessive phenotype
back crossing
hybrid cross with a parent organism to obtain offspring similar to parent
wild type
default genotype or phenotype
w+ means no mutation
w (experiment group)
has mutation
w+
does not have mutation // wild type
complete dominance
medelian genetics where one dominant phenotype is always expressed over recessive
codominance
2 dominant alleles are expressed at the same time
what kind of dominance does the ABO blood type exhibit
co dominance
incomplete dominance
heterozygote blend of phenotypes
a red and white flower make pink
penetrance
likelyhood that a carrier of a genotype will manifest the corresponding phenotype
- how often a mutation is phenotypically expressed
what factors determine penetrance
gene expression and epigenetic modification
expressivity
intensity or extent of variation in a phenotype
example of expressivity of a mutation
severity of a disease
dihybrid cross
punnette square for two traits
distribution of a dihybrid cross for two traits that are both heterozygous
9:3:3:1
law of independent assortment
there is no link of inheritance between alleles of different genes
- applies to genes on different chromosomes AND genes on the same chromosome at different loci
why does law of independent assortment apply to genes on the same chromosome
because of crossing over at the chiasmata point
when does corssing over occur
prophase 1 of meiosis
recombination frequency
describes how often a single cross over event will occur between two genes on the same chromosome
- if recombination frequency is 50% then the genes in question obey law of independent assortment
centrimorgan (cM)
linkage
recombination is a distance between genes and 1% is linkage
pedigree analysis
individuals arranged in generations
circles are female and squares are male
what kind of autosomal mutations like to skip generations
recessive
T/F: dominant mutations can skip generations
false
sex-linked inheritance
genes located on the x chromosome
- males much more suseptible because they only have 1 x
- can be dominant or recessive
evolution requires
- variation in population
- mechanism for those variations to be reproduced
- envirnmental constraints that favor some variations over others
differential reproduction
envirnmental conditions that allow favorable variations to be more readily reproduced
natural selection
tendency of certain phenotypes to be favored for reproduction
- not same thing as evolution!
fitness
chance of reproduction associated with phenotype compared to a baseline
- must be determined in terms of specific envirnmental constrains
group selection
natural selection acted on level of group
inclusive fitness
expanded evolutionary definition of fitness to account for individuals and their relatives that share same alleles
altruistic behavior
it is advantagous for an individual to engage in altruistic behavior or even self sacrifice to ensure the survival of more copies of the gene
gene pool
combined set of all genes and alleles in a population
hardy-weinberg equillibrium criteria
model of stable gene pools
1. diploid individuals reproduce sexually
2. mating is random
3. population is large
4. alleles are randomly distributed by sex
5. no mutations occur
6. there is no migration into or out of the population
hardy-weinberg eqn
p + q = 1
P^2 + 2pq + q ^2 = 1
what do p^2 and q^2 represent
homozygous genotypes
2pq
frequency of heterozygotes
a population has a 9% homozygous recessive trait, what % have the homozygous dominant?
P + q =1
sqr (.09) = .3 so 1-.3 =.7 so .7^2 = 49%
polygenic
many genes go into a phenotype
example: height
stabilizing selection
the median phenotype is selected for
disruptive selection
selection against the average phenotype, favors both extremes
directional selection
1 extreme is favored
genetic drift
role of chance in determining reproductive fitness
evolutionary bottleneck
external event dramatically decreases population size in a way that is essentially random
speciation
new species evolves from evolution
species
a group that can reproduce together and produce fertile offspring
prezygotic barriers
prevent speciation from occuring before the formation of a zygote
ecological niches
incompatible anatomy
temporal/seasonal mating differences
inability to fertalize after intercourse
postzygotic barriers
after the formation of a zygote
nonviable zygote
hybrid breakdown
hybrid breakdown
hybrid is fertile but not in second generation
leakage
genes travel between species
