One- and Two- Trait Inheritance Learning Outcomes Upon completion of this lecture, you should be able to 1. Understand the relationship between probability and one- and two-trait crosses. 2. Calculate the probability of a specific genotype or phenotype in an off spring of a genetic cross.

Definition In one-trait crosses (one-characteristic crosses), the inheritance of only one set of alleles is being considered. In two trait crosses (two-characteristic crosses), the inheritance of two different alleles is being considered. For both types of crosses, it will be necessary to determine the gametes of both individuals who are reproducing.

One-Trait Crosses Dominant and recessive traits Heterozygous crossing

One-Trait Crosses

Punnett square Expected results of a monohybrid cross. A Punnett square diagrams the results of a cross. When the parents are heterozygous, each child has a 75% chance of having the dominant phenotype and a 25% chance of having the recessive phenotype

Other one trail crosses This cross will determine if an individual with the dominant phenotype is homozygous or heterozygous The off spring show a 1:1 phenotypic ratio, so the individual is heterozygous All off spring show the dominant characteristic, so the individual is most likely homozygous

Two traits crosses Meiosis results in genetic diversity of gametes

The Dihybrid Cross Phenotypic Ratio 9:3:3:1 9 Widow’s peak, short fingers 3 Widow’s peak, long fingers 3 Straight hairline, short fingers 1 Straight hairline, long fingers

Phenotypic Ratios of Common Crosses GENOTYPE Monohybrid Gg × monohybrid Gg Monohybrid Gg × recessive gg) Dihybrid GgRr × dihybrid GgRr both recessive) Dihybrid GgRr × recessive ggrr PHENOTYPE 3:1 (dominant to recessive) 1:1 (dominant to recessive) 9:3:3:1 (9 both dominant: 3 one dominant: 3 other dominant: 1 1:1:1:1 (all possible combinations in equal number