SBI3U – Unit 2: Genetics
Date: ____________________
5.2 Studying Genetic Crosses
What is a Punnett Square?

In a in monohybrid crosses, a _______ punnett square is used.
The possible gametes produced by the parents are written at the top and along the side:
Mother: Bb
Father: bb
The gametes are combined to produce all of the possible F1 genotypes:
Example 1:
Find the genotypes and phenotypes of the F1 and F2 generations when a homozygous tall (T) pea
plant is crossed with a homozygous short (t) plant.
What information is given?
What are the Gametes from the above information?
F1 Genotypes:
F1 Phenotypes:
SBI3U – Unit 2: Genetics
Date: ____________________
Example 1 Continued…..
To find the F2 generation, you cross the offspring produced in the F1 generation.
Given:
Gametes:
F2 Genotypes:
F2 Phenotypes:
Homozygous Parents Cross:
- in the case of a cross that involves parents that are homozygous for a particular trait.
F1 will always have:
•
Genotypes that are ______________________________________
•
Phenotypes that resemble the
______________________________________________
F2 will always have:
• Genotypic ratio of ________________
(1 homozygous dominant: 2 heterozygous: 1 homozygous recessive)
•
Phenotypic ratio of ____________
(3 dominant 1 recessive)
Test Cross
Cross an unknown parent (BB or Bb) with a known parent (bb)

Case #1 – unknown parent = BB
•
If all F1 show the dominant trait, then the unknown parent was BB
SBI3U – Unit 2: Genetics
Date: ____________________

Case #2 – unknown parent = Bb

If even one F1 shows the recessive trait, then the unknown parent was Bb
TO DO:
Section 5.2 (Part 1)
 Practice Problems p. 212 #1-10 (practice problems)
 Learning Check p. 212 #7-12