6.1.1 patterns of inheritance Flashcards
monohybrid inheritance
genetic cross with alleles at 1 locus
e.g. Tt x Tt
dihybrid inheritance
2 genes inherited on unlinked chromosomes so 2 characteristics at the same time
e.g. RrTt
why is each gamete equally as likely in dihybrid inheritance
independent assortment
ratio for heterozygous dihybrid cross
9:3:3:1
codominance
1 gene with multiple alleles that are both expressed
sex linkage
genes located on sex chromosomes
sex determining genes carried on non-homologous region
why are males more likely to present sex linked genes
XY only needs 1 copy of recessive allele to show characteristic, XX needs both
chi squared test
= sum of ((observed-expected)^2/expected)
degrees of freedom = no. of categories -1
less than critical value - no sig diff = accept null hypothesis
autosomal linkage
more than 1 gene on same non-sex chromosome so inherited together
causes recombinant phenotypes
what exactly causes recombinant phenotypes
crossing over in prophase 1 when bivalents form
epistasis
multiple alleles controlling phenotype, expression of one gene affects another
dominant epistasis
dominant allele masks other gene - only one copy of dom allele needed
what is the heterozygous cross ratio for dominant epistasis
12:3:1
recessive epistasis
recessive allele masks other gene - 2 copies of rec needed
what is the heterozygous cross ratio needed for recessive epistasis
9:3:4
hardy weinberg
model to calculate allele frequency of a gene in a population
hardy weinberg allele frequency
p+q=1
hardy weinberg genotype frequency
p^2 + 2pq + q^2 =1
p in hardy weinberg means
dominant
q in hardy weinberg means
recessive
what does hardy weinberg assume
no immigration/emmigration
isolated
no natural selection
no mutation
large population
random mating
heritable
can be passed down from parents
some may be caused by environment
discontinuous variation
qualitative
definite categories
monogenic
continuous variation
quantitative
wide range of variation
polygenic
phenotypic variation
phenotype determined partly genotype, partly environment
stabilising selection
selects for the norm - being average is advantageous
disruptive selection
speciation occurs as species becomes incompatible due to interbreeding
directional selection
environmental factor changes so so individuals have a selective advantage
genetic drift
change in allele frequency due to chance
founder effect
unusual genes in smaller populations that have moved away from a large population so speciation
bottleneck
catastrophic event - reduces population to a small number, recovers and only genes in survivors are passed down so variation doesn’t increases
allopatric speciation
geographical isolation of 2 populations
-variation always present
-diff conditions, diff selection pressure, diff alleles
-diff allele frequencies
-seperate gene pools so no interbreeding- 2 species
sympatric speciation
same environment
-mutations cause diff phenotypes so individuals are reproductively isolated
-no gene flow
-gene pools seperated
-diff alleles selected and passed on, can’t interbreed - 2 species
prezygotic barriers in reproductive isolation
courtship behaviour not recognised so no mating
mechanical barrier as different sized gentilia leads to incompatibility
physiological barrier as cross pollination between species happens but no fertilisation as pollen tube doesn’t grow
postzygotic barriers in reproductive isolation
hybrid not viable
hybrid is viable but sterile
