6.1.2 Patterns of Inheritance Flashcards
Chi squared
Compare expected phenotype ratio (from the punnet table) with the observe phenotype ratio. Show whether differences are significant or due to chance.
How to do chi squared
-Punnet table
- Total number of offspring/ratio total x predicted ratio
- Observed is found
- Observed - Expected
- Square numbers
- Divide numbers by the Expected results
- Add both numbers (each phenotype) together
- Use 0.05 and degrees of freedom (number of phenotypes - 1)
- If the value is higher than the critical value, reject the null hypothesis
- If the value is lower than the critical value, accept null hypothesis
Continuous Variation
- Quantitative
- No distinct categories
- Polygenic
- Environmental and genetic factors
- E.g. height
Discontinuous Variation
- Qualitative
- Categories
- Monogenic
- Genetic factors
- E.g. gender
Phenotypic Variation
There is variation within a population.
Influenced by genotype, environment or both.
Genotype only
- E.g. skin colour (continuous)
- E.g. blood group (discontinuous)
Environmental only
- E.g. etiolation (plants growing spindly due to lack of sun)
- E.g. chlorosis (environmental factors cause lack of chlorosis and so yellow plants)
Both genotype and environment
- E.g. height
- E.g. body mass
Gene
Sequence of bases on dna molecule that codes for a functional protein which results in a characteristic.
Allele
A version of a gene, you have two from each of the homologous chromosomes. B or b.
Genotype
The alleles an organism has.
BB, Bb or bb.
Phenotype
The characteristics produced by the genotype.
Dominant
Appears in phenotype even if there’s only one copy. If B is for brown and b is blue eyes then BB and Bb would be brown.
Recessive
Appears in phenotype if two are present. bb would be blue.
Codominant
Alleles can both be expressed
if dominant. CR and CW can produce roan colouring in cows.
Locus
Position of gene on the chromosome.
Homozygous
Carries two of the same allele. BB or bb.
Heterozygous
Carries one of each allele. Bb.
Carrier
A person carrying an allele not expressed but present in phenotype and can be passed to offspring.
Sex linked
XA, Xa or Y.
Autosomal linkage
- 3:1
- Not sex chromosomes
- Same autosome are said to be linked as they’ll stay together through independent assortment
- Closer they are the more likely to be linked.
Monogenic
Caused by one gene.
Mono hybrid crosses
- 3:1 ratio
- One characxtaristic controlled by one gene
- NN, Nn, nn
Polygenic
Caused by more than one gene.
Dihybrid crosses
- 9:3:3:1 ratio
- Two characteristics caused by two genes
- RY, Ry, rY, ry
Epistatic gene
- 9:7
- Masks the expression of another gene
Sexual selection
Alleles make the individual more attractive to find a mate
Gene flow
Movement of alleles through migration
Gene pool
Complete range of alleles present in a population
Natural selection
- Some better adapted to section pressures due to alleles
- Increased chance of survival and reproduction
- Pass on advantageous allele
- Greater proportion of the next generation inherits allele
- Frequency of allele increases
Stabilising selection
Environment isn’t changing much, individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. Reduces the range of possible phenotypes. Selection pressures may act against extreme. E.g. babies survival is best if not over or underweight.
Directional selection
Change in the environment and the average phenotype is no longer the best adapted. Less common organisms with extreme phenotypes are selected. Allele frequency shifts towards extreme.
E.g. light moths survive best in country and dark survive best in urban so more common in each
Disruptive selection
The alleles for the extremes if the phenotype range are selected for so works against the mean.
E.g. birds attack intermediate plumage but leave threatening bright and non threatening dull.
Allopathic speciation
Populations are prevented from breeding because they’re geographically isolated. CReates two separate species
