T7: Genetics, Populations, Evolution + Ecosystems Flashcards
allele
one of the different forms of a gene
genotype
the genetic makeup of an organism
homologous chromsomes (pair)
a pair of chromosomes (maternal+paternal) that have the same loci in diploid organisms
gene
a length of DNA that normally codes for a polypeptide
pedigree charts
diagram representations of family trees that show patterns of inheritance
male - square + female - circle , shading means characteristic present in phenotype
epistasis
when the allele of one gene affects or masks the expression of another in the organism, two genes interact together to affect the phenotype
e:g agouti mice
linked genes / autosomal linkage
two or more genes carried on the same non-sex chromosome, explains why characteristics are often inherited together
homozygous
two or more of the same alleles present on both homologous chromosomes
loci
the position of a gene on a particular chromosome
phenotype
the observable or biochemical characteristics of an organism
recessive
an allele only expressed when present with an identical allele
Mendel’s law of independent assortment
law that states that each member of a pair of alleles may combine randomly with either of another pair
dihybrid crosses
inheritance patterns of two genes
dominant
an allele always expressed in the phenotype that masks the expression of other alleles
multiple alleles
a gene with more than two allelic forms
chi squared
stats test that compares observed data with expected ratios
null hypothesis
there is no significant difference between observed and expected values
if Mendel’s law applies then
sex linked
a gene that is carried on both the X or Y chromosome
co-dominant
two alleles are both expressed in the phenotype
what do genetic diagrams look like?
must contain (F1 ) parent phenotype, parent genotype, gametes and punnet square
4 conditions of Hardy weinberg?
Large population
No immigration or emigration
No mutations
No natural selection
Formula for Hardy weinberg
P2+2pq+q2
P = homozygous dominant
2pq = heterozygous
Q = homozygous recessive
Explain how natural selection occurs
Variation occurs due to mutations giving rise to new alleles
Selection pressure = struggle for survival
Some organisms have alleles that provide are advantageous so are more likely to survive and reproduce
They pass on their advantageous alleles to their offspring
The allele frequency in population increases over time
Directional selection
Selective pressures favour individuals with a favourable combination of alleles one direction from the mean
Mean shifts in direction of phenotype
Stabilising selection
Selective pressures favour the mean
Individuals with extreme phenotypes less likely to survive so SD gets smaller over time
Disruptive selection
Selection against the mean
Favours both extremes of phenotypes
Could result in 2 separate species
Speciation
Formation of a new species from an existing species
Reproductive separation of 2 populations can result in the accumulation of differences in their gene pools, new species arise when these 2 populations cant interbreed to produce fertile offspring
Allopatric speciation
Geographical isolation separates the gene pools, no gene flow
Then evolution by natural selection occurs resulting in 2 species that can’t interbreed to produce fertile offspring
Sympatric speciation
Populations in the same area
Genetic drift
Allele frequencies change in a population due to chance factors
Stronger in small populations due to chance having a larger effect
