6.1.2 Patterns in inheritance Flashcards
Monohybrid inheritance
one gene has 2 alleles
allele
different form of the same gene
homozygous dominant
2 dominant alleles
homozygous reccessive
2 reccessive alleles
Codominance
more than one dominant allele
when does codominance occur
when 2 different alleles for a gene are equally dominant
Multiple alleles
one gene but more than 2 alleles
example of a multiple allele
human blood group
Sex linkage
when a gene is found on the sex chromosome
genes found on X and Y chromosome
Autosomal linkage
inheritance of 2 genes on same chromosome except a sex chromosome inherited together not independently assorted
Dihybrid inheritance
2 genes on different chromosomes
no link
each gene has 2+ alleles
Epistasis
interaction of different gene loci so one gene locus masks or supresses the expression of another gene locus
changes the expected ratios
Reccessive Epistasis
reccessive alleles presence affect another locus
epistasis by complementary action
Alleles needed on both genes for correct expression
9:7 ratio
types of speciation
directional selection
stabilising selection
distruptive selection
directional selection
change in enviroment
changes the selection pressure and frequency of different alleles in gene pool change
stabalising selection
selection pressure move inwards
leads to reduction in the range of variation within population
no change in mode
disruptive selection
acts against mode favouring the extreme
produces bimodal distrubution with 2 groups of phenotypes
may produce 2 distinct forms of species
new species form over long period of time
Hardy Weinburg Principle
frequency of alleles in a population remains constant over time so long as five key conditions about the populations were met
Epectations for Hardy Weinburg principle to work
no mutations
no immigration/emigration
no selection
mating is random
population is large
why can’t there be any mutations
so no new alleles are created
why no immigration or emigration
so no new alleles are introduced or lost
why no selection
so no alleles are formed or eliminated
why must mating be random
alleles are mixed randomly
why must population be large
so theres no genetic bottlenecks
why is the Hardy Weinberg principle not very good
its an unrealistic expectation of a population
Equations for Hardy Weinburg principle
p + q = 1
p^2 + 2pq + q^2 = 1
p^2
frequency of AA
2pq
frequency of Aa
q^2
frequency of aa
p
frequency of dominant allele A
q
frequency of recessive allele a
