Genetics Notes 2

Monohybrid Crosses Traits can be dominant or recessive Dominant traits are represented by a capital letter Recessive traits are represented by a lower case letter Crossing a single trait Flower color Seed shape Has a predictable outcome Can use a Punnett squares to show possible outcomes

Monohybrid Cross P P p Pp Pp Pp Pp p Cross of true breeding (homozygous) flower color Parent generation Purple – PP White – pp All the flowers will be purple Heterozygous F1 generation p Pp Pp Pp Pp p

Monohybrid Crosses P p P PP Pp p Pp pp Cross between F1 generation 3:1 phenotypic ratio Three will be purple One will be white 1:2:1 genotypic ratio One is homozygous dominant Two are heterozygous One is homozygous recessive F2 generation P PP Pp p Pp pp

Monohybrid Crosses P p p Pp pp p Pp pp Cross between F1 generation and a homozygous recessive plant 1:1 phenotypic and genotypic ratio Half will be purple Half will be white p Pp pp p Pp pp

Crosses Homozygous round seed and a heterozygous round seed Two heterozygous stem length Heterozygous green pod and homozygous yellow pod Two homozygous flower location – one axial, one terminal Two heterozygous pod shape

Probability Probability is used to predict random events Product Rule: Multiply probabilities Can only use in independent events Sum Rule: Either/Or Add probabilities

Product Rule What is the probability that you will roll a four and a five? 1/6  4 and 1/6  5 1/6 X 1/6 = 1/36

Sum Rule What’s the probability that you will roll a four or a five? 1/6  4 and 1/6  5 1/6 + 1/6 = 2/6 = 1/3

Examples What is the probability of flipping heads and tails back to back? What is the probability of rolling a 3, a 4, or a 5 at any one time? What is the probability of a couple having two girls in a row or two boys in a row?

Probability from Punnett Squares What is the probability that a pea plant will be both dominant and homozygous? Pp X Pp TT X tt Yy X yy

Probability from Punnett Squares What is the probability that a pea plant will be either homozygous or heterozygous dominant? Pp X Pp TT X tt Yy X yy