6.2.3 dihybrid inheritance Flashcards
define dihybrid
involving 2 gene loci
what are dihybrid crosses
investigations which examine simultaneous inheritance of 2 characteristics
what did mendel examine the inheritance of using dihybrid crosses
seed shape & colour in pea plants
how did mendel examine inheritance of seed shape & colour in pea plants
crossed true-breeding pea plants with yellow/round seeds with pea plants with green/wrinkled seeds
what was the F1 generation
- hybrids, having phenotype for yellow-rounded seeds
- each plant is heterozygous for both genes (seed colour/shape)
- yellow & round = dominant traits
what did mendel conclude from the results of the dihybrid cross
◦ the alleles of the 2 genes are inherited independently, so each gamete has 1 allele for each gene locus
◦ during fertilisation, any 1 of an allele pair can combine with any 1 of another allele pair
how can the ratios be predicted for trait in the F2 generation (assuming seed colour/shape are 2 separate monogenic characteristics)
◦ for colour characteristic: in F2 generation we would predict 3/4 are yellow & 1/4 green (3:1 ratio)
◦ for shape characteristic: we’d predict 3/4 would be round & 1/4 wrinkled (3:1 ratio)
◦ taken from punnet square:
‣ 12/16 possible gamete combinations
produce phenotype yellow (3/4) & 4/16
(1/4) produce phenotype green = 3:1
‣ 12/16 (3/4) produce round seeds & 4/16 produce wrinkled seeds = 3:1 ratio\
how the ratios of traits in the F2 generation be predicted when 2 independent events occur simultaneously
◦ product of individual probabilities = combined probability of occurrence
◦ use equation to calculate probabilities of all other phenotypes in F2 generation
eg. yellow & round = 3/4 x 3/4 = 9/16
eg. green & round = 1/4 x 3/4 = 3/16
what ratio did mendel get when he counted his pea plants in the F2 generation of the dihybrid cross
9:3:3:1
