patterns of inheritance Flashcards
what is a locus
specific position of a gene on a chromosome
what is co-dominance
pairs of alleles which are both expressed when present red flower + white flower = pink flower
what 2 processes cause genetic mutation?
- random mutation
- meiosis/sexual reproduction
what are physical agents of creating mutagens
ionising radiation e.g. X-rays
what is polyploidy
cell has extra set of chromosome
what is non-disjunction in cell division?
separation fails to occur causing both sister chromatids to be pulled to one side of the cell
environmental variation examples
hair length, accent
environmental and genetic variation examples
skin colour, height, weight
what is chlorosis and why is it an example of variation?
less chlorophyll = causing yellow leaves - it is an example of variation as the plant all have correct genes, chlorosis is affected by lack of light, and mineral deficiencies.
which form of data has a higher range of intermediates?
continuous
what do F2 ratios tell us?
if recessive allele is found in F2, both F1 parents must be heterozygous.
what are the steps of working out a Punnett square / dihybrid cross?
- find parent genotype
- use foil to work out gamete genotype
- set out 4 x 4 Punnett square
- combine possible gametes
- determine phenotype ratio
why are males described as hemizygous?
because they are haploid for X-linked gene.
features of haemophilia
- unable to clot blot fast
- gene found on non-homologous region of X-chromosome.
why can males never be a carrier?
if they inherit the faulty gene on chromosome X then they are bound to have the disease.
what is the relevance of “inactivation of X chromosomes in females?’
to avoid females expressing double number of genes from X chromosome, one is inactivated in every nucleus.
Happens randomly during embryonic development.
what is an autosome?
non sex chromosome
what is autosomal linkage?
two genes on the same non sex chromosome
which type of autosome can undergo independent assortment?
non linked because each one can move to one side where as linked can’t split
what is meant by autosomal ‘linkage’
genes are on the same chromosome so likely to be inherited together and do not undergo independent assortment.
what is recombinant gamete
combination of alleles
hypostatic gene
the second gene loci that is masked by the epistatic gene
what is epistasis?
the interaction of non-linked gene (independent assortment) loci where one masks the expression of the other gene.
what is meant by complimentary gene action?
genes work together to code for two enzymes that work in succession e.g. catalysing sub sequential steps of the metabolic pathway.
describe what is meant by recessive antagonistic epistasis
homozygous presence of a recessive allele at the first locus that prevents the expression of another allele at a second locus.
describe what is meant by dominant antagonistic epistasis
if the epistatic allele is dominant, then having at least one copy of it will mask the expression of other gene = working antagonistically.
what are the three types of selection
- stabilising
- directional
- disruptive selection
what ratio does recessive epistasis suggest?
9:3:4
what ratio does dominant epistasis suggest?
12:3:1
list the key words of natural selection
random mutation
migration
variation
selection pressures
selective advantage
beneficial allele
allele frequencies
when does directional selection occur?
when there is a change in environment, and species with alleles form an extreme phenotype are more likely to survive + reproduction. Over many generations there is a gradual shift in the optimum value for trait.
what is genetic drift
change in allele frequency in a population due to chance
when does disruptive selection occur?
a type of natural selection where the extreme values are selected over the intermediate.
what is a genetic bottle neck
when former population shrinks then new population rises again with advantageous alleles.
how can gene pool be narrowed?
- bottle neck
- founder effect
similarities between founder effect and genetic bottle neck
- involve inbreeding
- result in new population that carries alleles that are different from original group.
what is the founder effect?
new population is established from a very small number of individuals who originate from a larger population.
This new population is likely to be less genetically varied.
difference between founder effect and genetic bottle neck
bottle neck populations are killed, whereas founder effect occurs when populations are geographically separated.
give three impacts of a small populations
- loss of genetic diversity
- inbreeding
- rise in genetic disorders
what factors affect the genetic diversity within a gene pool
- population size
- mutation rate
- migration
- natural selection
- genetic drift
- isolation of species (founder)
what is allopatric speciation? (geographical)
formation of two different species from one original species due to geographical isolation.
what is sympatric speciation? (reproductive)
formation of two different species from one original species, due to reproductive isolation, while the populations inhabit the same location.
what is artificial selection?
selective breeding of organism involving humans choosing desired characteristics
how can genetic diversity be increased in a population (by what process?)
hybrid vigour -> crossing over 2 varieties who are likely to reproduce heterozygous individuals, lowering the chance of recessive disorders.
what are the ethical issues of artificial selection?
- unfamiliar environment for species can lead to both psychological and physical distress
- violation of animal rights
what are the counter points to the unethical nature of artificial selection?
- increases crop yield = boosts economy
- greater breeding in plants and animals to allow their groups to survive which helps endangered species
- quicker and efficient, get desirable characteristics e.g. size, milk yield.
