Patterns of inheritance Flashcards
Physical mutagenic agent
-X rays
-gamma rays
- UV
Chemical mutagenic agent
-mustard gas
-amines
-nitrous acid
Biological mutagenic agent
-virus
-food contaminant
3 types genetic variation
-gene mutations (point and indel)(occur during DNA replication)
-chromosome mutations
-sexual reproduction
Chromosome mutations
-Deletion- part of chromosome containing genes is lost
-Inversion- section of chromosome breaks off, rotates 180° then rejoins. Genes too far form regulatory nucleotide to be expressed
-Translocation- piece of chromosome breaks off and attaches to another chromosome
-Duplication-piece of chromosome may be duplicated meaning too many proteins are made, affecting metabolism
-Non disjunction- chromosome fails to separate so one gamete has extra chromosome, can cause down syndrome
Aneuploidy
-chromosome number isn’t an exact multiple of the haploid number
-chromosomes fail to separate during meiosis
Polyploidy
-when organisms have more than two sets of chromosomes
-found in plants
Variation in sexual reproduction
-crossing over in prophase 1
-independent assortment in metaphase and anaphase 1/2
Environmental factors that cause variation
-accent
-losing a limb
-scars
Variation caused by interaction between genes and enviro
-plants are kept in magnesium insufficient soil
-don’t develop enough chlorophyll
-leaves yellow
-can’t photosynthesise
-height
-weight
Test cross
-organism demonstrating a dominant phenotype (TT or Tt)
-crossed with homozygous recessive
-if any offspring have recessive phenotype, the dominant genotype is heterozygous
Codominant
where both alleles present in the genotype of a heterozygous individual contribute to the individuals phenotype
Dihybrid inheritance
2 different genes are inherited independently of each other and appear on different chromosomes
Autosomal linkage
-gene loci present on the same autosome that are often inherited together
Epistasis
interaction of non linked gene loci where one masks the expression of the other
Recessive epistasis
alleles at first locus are epistatic to those at the second locus which are hypostatic to those at the first locus
Complementary gene action
-where genes work to code for 2 enzymes that work in succession, catalysing sequential steps of a metabolic pathway
eg. Allele C =coloured mice
Allele A= agouti
CcAa, CCAa, CcAA= agouti
Ccaa, CCaa= black
ccAA, ccAa= albino
Epistasis ratios
-9:3:4 may suggest recessive epistasis
-12:3:1 and 13:3 suggests dominant epistasis
-9:7 and 9:3:4 and 9:3:3:1 suggest complementary gene action
Discontinuous variation
-monogenic- determined by alleles of one gene locus (sometimes 2 due to epistasis)
-phenotype classes are distinct categories
-quantitative
-alleles have a large effect on the phenotype
-unaffected by environment
eg. male female, blood group
Continuous variation
-polygenic- many genes are involved in determining the characteristic
-smooth graduation between many intermediates
-alleles of each gene may contribute a small amount to the phenotype
-can be affected by the environment
eg height, weight
2 factors effecting the evolution of species
Natural selection
Genetic drift
3 types natural selection
Stabilising selection- favours intermediate phenotypes eg. child weight favours the middle as too small and too big carry risks
Disruptive selection- favours extreme phenotypes
Directional selection- the environment changes, making one phenotype more advantageous
Genetic drift-
a change in the allele frequency within a population by chance over time
2 types genetic drift
-Genetic bottleneck- when a population shrinks and then increases again, reducing genetic diversity
-Founder effect- when a new population is established or isolated, with only a small number of people
Factors that affect allele frequency
-mutation
-migration
-natural selection
-genetic drift
-non random mating
Hardy Weinberg principle assumptions
-population is large enough so sampling errors have minimal effect
-mating is random
-there is no natural selection
-there is no mutation, migration or genetic drift
Hardy Weinberg equation
Dominant allele (A) = p
Recessive allele (a) = q
therefore p+q=1
Genotype AA =p^2
Genotype aa = q^2
Genotype Aa= 2pq
therefore
p^2 +2pq + q^2= 1
Speciation
-the process by which new species are formed
-this can only happen if the species become isolated into 2 separate populations
-in each location there’s different selective pressures causing the populations to adapt differently
-at times, the populations will be different but still able to inbreed (sub species)
2 isolating mechanisms
geographical
reproductive
Geographical isolation
-populations are separated by geographical features like lakes, mountains etc.
-isolated populations are subject to different selective pressures, and undergo different changes
-due to natural selection each population become adapted to its environment
-known as allopatric speciation
Reproductive isolation
-where biological and behavioural changes lead to isolation
-can be caused by genetic changes which can: prevent gamete fusion, make zygotes less viable or lead to infertile offspring
-can be caused by mutations which can change: courtship behaviours or animal genitalia
-known as sympatric speciation
