concept 17 - BIO10008

describe how independent assortment relates to the segregation of alleles of different genes during meiosis

Independnet assortment is the different combinations of chromosome that occur with equal frequencies. This realtes to the segregation of alleles during meiosis as these are independently assorted to ensure different genetic combination in unlinked genes

dihybird cross

F1 hybird with heterozygous for both traits produce an F2 offsprings through self fertilisation

eg round (Rr) green (Yy) x round (Rr) green (Yy)

what is the characteristic ratio of a dihybrid cross for two genes assorting indepedently

9:3:3:1

why are there some crosses that result in a modified 9:3:3:1 ratio

due to linked genes so inheriting one trait affected the likelihood of inheriting the other

how can we determine when there are multiple genes which contribute to a trait

quantified and graphed into a bell curve (some in minimum, most in between and some in maximum)

in cases where there are two genes that interact to determine a trait how do we know if the two gene are assorting independently

when the phenotypic ratio is 9:3:3:1

describe how a single trait can be influenced by more than one gene

a single trait influenced by more than one gene is affected by the many alleles in the gene, where it can still show independent assortment ratios however it has incomplete dominance. Thus, the offsrpings (F1) of the parents generate a new phenotype distinct from the parents, and the F2 offspring will also generate one new phenotype with 9 F1, 3 of each parent of F1 and 1 new phenotype.

epistasis

the action of one gene can affect the other’s action through hiding the gene (located at another loci) or modifiying it.

may still show independent assortment at the genotypic level. In such cases, however, the phenotypic ratios may appear to deviate from those expected with independent assortment.

polygenic traits

have a bell curve distribution of phenotypes

dominant epistasis

when a presense of a dominant allele (heterozygous or homozygous) masks the trait of a gene at another loci (when inherited)

recessive epistasis

the presence of two homozygous recessive alleles at one loci masks or modifies the trait expressed from a gene in another loci (when inheritied)

two alleles have to be inherited in order for the phenotype of the second gene to be masked