❌ Dihybrid Crosses

Dihybrid Crosses

• Looks at 2 different traits/genes on 2 different chromosomes (e.g. hair length on one chromosome, eye color on another chromosome)

  • Must be two different chromosomes since they assort independently (hair length doesn’t cross with eye color)

Gametes

• Gametes are still haploid because they only have one allele from each gene (e.g. in the RY gamete, there is the round allele and yellow allele)

• e.g. the RrYy genotype is heterozygous at both loci

  • Gametes from RrYy: RY, Ry, rY, ry

• For het x het, phenotypic ratio is 9:3:3:1 (9 dom dom, 3 dom rec, 3 rec dom, 1 rec rec)

Independent Assortment

• Alleles on different chromosomes assort independently from each other (e.g. A doesn’t affect B)

• Occurs during anaphase I in meiosis I

Segregation

• Alleles for a given gene segregate into separate gametes (e.g. A separates from a)

• Also occurs during anaphase I in meiosis I

Probabilities

• To find probabilities of phenotypes/genotypes occurring, use two separate punnett squares

  • Multiply or add probabilities