Notes #9
Calculating Probabilities of Monohybrid (Single Trait) Crosses
Principles of Probability
What is it?
ANS:
How to Determine the Sex of the baby?
Human cells have a total of ___________ somatic (body) chromosomes.
Each human cell has a total of __________ sex chromosomes.
Total # of Chromosomes in a single typical human cells is: _________
What makes girls different from guys, besides the obvious?
ANS:
Female Sex Chromosomes
vs.
Male Sex Chromosomes
Story 1 (Starting a family.)
What is the probability that the newlyweds, Kevin and Connie will have a boy as their first born
child?
P
Kevin
x
____ ____
Connie
_____ _____
Meiosis I & II
Gamete Cells
Punnett Square:
(Dad’s Sex Cells)
Total Possible Outcomes:___
Total Possible Boys: ____
(Mom’s Sex Cells)
XY probability: _____
ANS: The chance that Kevin & Connie will have a boy is: ________
TRIVIA Q: Which parent determines the sex of the baby?
ANS:
Story 2 (The expected Couple.)
Congratulations! Kevin and Connie are expecting their first child. Both parents have brown eyes,
and they are curious about what color eyes their son will have.
Your Prediction: ___________
Kevin Jr’s Eye Color: _____________
The Dominant Eye Color is: ________________
Dominant Allele Symbol : ______
The Recessive Eye color is: ________________
Recessive Allele Symbol: ______
Phenotype vs. Genotype
1. Phenotype:
2. Genotype:
Homozygous vs. Heterozygous
1. Homozygous:
Ex.
2. Heterozygous:
Ex.
Trait Analyzed: Eye Color (Brown Eyes vs. Blue Eyes)
1. List the possible Genotype(s) for brown eyes: ______________
2. List possible Genotype(s) for blue eyes: _____________
Fill out the chart below with the information we already know about the family.
Kevin
Connie
Kevin Jr.
Q1: Is Kevin Jr. considered a Heterozygous or Homozygous individual? __________________
Q2. Since we know the genotypes of the Kevin & Connie, using the information,
What is the probability that their second child will have brown eyes?
(Show work with a Punnett Square)
Phenotype Ratio: ____ Brown : _____Blue
Genotypic Ratio: _____ : _____ : _____