Patterns Of Inheritance 2 Flashcards
Evolution
The change in inherited characteristics of a group of organisms over time
Occurs due to change in frequency of different alleles within population
Gene pool
Sum of all genes in a population at any given time
Allele frequency
The relative frequency of a particular allele in a population
Allele frequency
P + q = 1
P^2 + 2pq + q^2 =1
P^2= frequency of homo dominant
Q^2= frequency of homo recessive
2PQ= frequency of heterozygous
Factors affecting evolution
Mutation
Sexual selection
Gene flow- movement of alleles between populations
Genetic drift- change in allele frequency due to random mutation ( greater in smaller pop)
Natural selection
Limiting factors
Density dependent- dependent on population size eg disease predation etc
Density independent- affect all sizes of pop eg climate change and natural disasters
Bottlenecks
Large reduction in population size
Gene pool greatly reduced
Founder effect
Establishment of new colonies by a few isolated individuals
Small populations have a far smaller gene pool
If carried to new population freq of alleles that were rare in original pop will be much higher in the new - much bigger impact during natural selection
Stabilising selection
The norm or average is selected for and the extremes are selected against
Increase in frequency of average alleles
Directional selection
Change in the environment and the less common extreme phenotypes are positive selected - allele frequency of this increases
Disruptive selection
Extremes are selected for and the norm selected against
Eg blue lazuli birds
Brown non threatening not compete pop increase
Blue too threatening not compete pop increases
Mix compete pop fall
Speciation
Formation of a new species through the process of evolution
Not able to interbreed to produce fertile offspring
Events that lead to speciation
Members become isolated and no longer interbreed resulting in no gene flow
Alleles within the groups undergo random mutations
Accumulation of mutations and changes in allele frequencies over many generations lead to large changes in phenotype - no longer able to interbreed
Allopatric speciation
When members of population separated from main by a physical barrier eg sea
Different selection pressures thus different adaptions - founder effect/ generic drift
Sympatric speciation
Within population that shares the same habitat
When members of 2 different species interbreed and form fertile offspring
Different No of chromo to parents and may longer not be able to breed w parental population
Artificial selection/selective breeding
Selection of plants or animals with desirable characteristics by farmers or breeders
Inbreeding and it’s problems
Breeding closely related individuals
-decreases genetic diversity and adaptability
- recessive genetic disorders more common
- less biologically fit - less likely to survive and produce offspring
Seed banks
Alleles are used to increase genetic diversity by outbreeding
Reduces homozygous recessive and increase potential to adapt
Chlorosis
Plants have a lack of chlorophyll
Not a genetic disorder which alters phenotype - environmental factors
- lack of light
- mineral deficiency
- virus infections
Animal body mass
Controlled by genetics and environment
Obesity= environment
However can be genetic eg mice mutation on chromo 7 fat deposition is different
Continuous variation
Polygenic
Take any value within a range
Genetic and environmental
Eg skin colour
Discontinuous variation
Only appear in specific discrete values/ catergories
Monogenetic
Eg blood group
Monogenic inheritance
Inheritance of a single gene
Eg parents Gg and Gg for green pods
Form GG Ggx2 and gg (yellow pod)
Codominance
When two alleles of the same gene are equally dominant
Both are expressed
Eg snap dragons white x red = pink
Upper and lower case not used
Multiple alleles
Eg blood group Ia and Ib are codominant however Io is recessive
Sex linkage
Genes carried on sex chrosomomes- sex linked
As the Y is much smaller than X doesn’t hold all copies from X
If X holds recessive allele characteristic is more commonly shown in men eg colour blindness and haemophilia
Haemophilia
Sex linked genetic disorder
V slow blood clotting due to the absence of a protein blood clotting factor
Dihybrid inheritance
Show the inheritance of 2 genes
Heterozygous = 9:3:3:1
Linkage
Ratios in dihybrid crosses differ significantly from those expected. - due to linkage genes on same chromo
Autosomal linkage
When the genes that are linked are found on the same chromosome
Linked genes are inherited as one unit - no independent assortment
3:1 if not this ratio crossing over would have occurred
Recombinant offspring
Different combinations of alleles than either parent
Proximity of genes effect
Closer the genes on a chromosome the less likely they are to be separated during crossing over and fewer recombinant
Recombinant frequency
Amount of crossing over
No of recombinant offspring/ total No of offspring
50% indicates no linkage
Less than 50% there is linkage and independent assortment has been hindered
Chi squared
Sum of((observed-expected)^2/expected)
If greater than critical value reject null hypothesis sig diff vice versa
Epistasis
Interaction of genes at different loci
Dominant or recessive epistasis
Dominant epistasis
If dominant allele has an effect on the expression of another gene masking it
Recessive epistasis
If both alleles recessive blocks the expression of another gene
