GENETIC NOTES Mrs. Callan 2017

GENOTYPE Genotype – an organism’s genetic makeup. The letters used in a Punnett Square Three types: 1. Homozygous Dominant – two dominant alleles. Example: BB 2. Homozygous Recessive – two recessive alleles. Example: bb 3. Heterozygous – One dominant and one recessive allele. Example: Bb *Always write the capital (dominant) trait first!

PHENOTYPE Phenotype – an organism’s physical appearance. The traits you CAN SEE. Example: Flower color, plant height, eye color

Punnett Square A way to find the expected proportion of possible genotypes/phenotypes in the offspring of a cross. Monohybrid Cross – a cross in which only one characteristic is tracked.

Example 1: Homozygous x Homozygous Cross a homozygous dominant flower with a homozygous recessive flower. P P P = Purple (Dominant Trait) p = White (Recessive Trait) Pp Pp p Pp Pp p

Example 1: Homozygous x Homozygous Cross a homozygous dominant flower with a homozygous recessive flower. P P Genotype: 4/4 or 100% Pp Phenotype: 4/4 or 100% Purple Pp Pp p Pp Pp p RATIO: 1:0 for both Genotype and Phenotype

Example 2: Homozygous Dominant x Heterozygous Cross a person homozygous dominant for brown eyes with a person heterozygous for brown eyes. B B B = Brown (Dominant Trait) b = Blue (Recessive Trait) BB BB B Bb Bb b

Example 2: Homozygous Dominant x Heterozygous Cross a person homozygous dominant for brown eyes with a person heterozygous for brown eyes. B B Genotype: 2/4 or 50% BB 2/4 or 50% Bb Phenotype: 4/4 or 100% Brown BB BB B Bb Bb b Genotype Ratio: 2:2 Phenotype Ratio: 1:0

Example 3: Homozygous Recessive x Heterozygous Cross a person homozygous recessive for blue eyes with a heterozygous for brown eyes. b b Genotype: 2/4 or 50% Bb 2/4 or 50% bb Phenotype: 2/4 or 50% Brown 2/4 or 50% Blue Bb Bb B bb bb b Genotype Ratio: 2:2 Phenotype Ratio: 2:2

Example 4: Heterozygous x Heterozygous Cross a heterozygous purple flower with another heterozygous purple flower. P p Genotype: ¼ or 25% PP 2/4 or 50% Pp ¼ or 25% pp Phenotype: ¾ or 75% Purple ¼ or 25% White PP Pp P Pp pp p Genotype Ratio: 1:2:1 Phenotype Ratio: 3:1