Biology [Module6:Inheritance]

monohybrid inheritance

-single gene inheritance

-inheritance of a pair of contrasting characteristics

cross of a pure breed

cross of f1 generation

dominant characteristics

multiple allele

3 or more alleles of a gene e.g blood group

co dominance

both alleles of a gene contribute to a phenotype

dihybrid cross

the inheritance of 2 pairs of contrasting characters

son&daughter inheritance

artificial selection

-humans select organisms with desirable phenotypes an interbreed from these

-monoculture:plants have been selected for high yield ,pest and disease resistance

-in live stocks:animals have been selected for high yield,obedience and ability to be trained

disadvantages of artificial selection

-reduces genetic diversity as selected commercial varieties are genetically similar so could be susceptible to the same pathogen

-in breeding depression can occur if 2 related individuals are crossed(the chance of inheriting 2 copies or harmful recessive alleles

to prevent in breeding depression

-hybrid vigour:

-a cross between individuals of different alleles to obtains individuals that are heterozygous at many gene loci

-increases genetic diversity

-increased probability that an allele that is resistant to the parishes is present within gene pool so survives

ethical considerations of artificial selection

-domesticated animals are friendly an docile so less able to defend themselves,so they become easy prey and not able to survive in the wild

-live stock animals e.g pigs are selected for means and fa might succumb to low temp during winter if not housed

-some breeds of dogs are more susceptible to disease

-some coat colours selected by humans because of their looks could fail to camouflage the animals

gene banks

-gene banks :store of th genomes of living organisms e.g seed banks,botanical gardens

natural selection

-the process by which organisms which are better adapted to their environment will survive and breed while those that are less adapted fail to do so(environment selectes)

process of natural selection

-genetic variation arises due to mutations

-gives rise to different alleles,genotype and phenotype

-there is selective pressure

-advantageous alleles survive,inbreed and produce offspring

-over time the frequency of the advantageous alleles increase,change in population

stabilising selection

-selects against both extremes

-factoring the mean characteristics

-preserving the characteristics of the population

directional selection

-select one extreme

-favouring one extreme phenotype

-change in characteristics of population

disruptive selection

-selects against the mean

-results in a distinct populations

-could lead to speciation=2 diff species evolve

species

organisms that can interbreed to prices fertile offspring an are similar morphologically

specification

formation of a new species from

a previous species

geographical isolation

allopatric specification

sexual isolation

the formation of a new species due to sympatric specification

the founder effect

few individuals with fewer alleles colonise new habitats

-low genetic diversity

generic bottle neck

-disaster occurring causing a drop in population

-few alleles survive

-reducing the genetic diversity

genetic drift

-disaster causes a drop in population

-change in the allelic frequency and phenotype of population,lost during genetic diversity

epistasis

different genes interacting on different chromosomes with one gene masking(epistatic gene)the phenotypic expression of another gene (hypostatic gene)

autosomal linkage

-autosome=non sex chromosome

-2 or more gene loci are present on the same autosome

-genes are transmitted in a single unit,no independent assortment

sex linkage

hardy weinberg principle

-predicts that the allelic frequency of dominant and recessive alleles increase a population remains the same form one generation to the next provided that:

-no mutation arises

-no migration

-no selection

-population is large

chi squared test