1. Chapter 11: Introduction to Genetics
Section 11.2

2. Probability Probability is the likelihood that something will happen
Example: Flipping a coin
Example: Choosing the right question on a multiple choice test
Probability can be used to predict traits

3. Dominant vs. Recessive Alleles are represented by letters
Dominant alleles are represented by a capital letter R
Recessive traits are represented by a lower case letter r
Dominant alleles are expressed over recessive alleles
If you have to alleles together the dominant one will always be expressed or “visable”
Example: Height
Example: Brown hair

4. Key Words
Homozygous: organisms that have 2 identical alleles for a particular gene
Homozygous dominant (2 dominant alleles) RR
Homozygous recessive (2 recessive alleles) rr
Heterzgous: organisms that have 2 different alleles
Have a dominant allele (written first) and a recessive allele Rr

5. Practice Label the following as either homozygous or heterozygous EETt Zz YY Yy pp bb NN

6. Key Words
Phenotype: physical expression of alleles, the traits, “what you see”
Genotype: genetic make-up, you cannot see it, this is the letter representation of the phenotype
YY, Ff, ff

7. Example
Phenotype: Brown
Genotype Bb

8. Practice
In people, brown eyes (B) are dominant to blue (b), from the following phenotypes identify possible genotypes: bb
BB or Bb
BB or Bb bb

9. What are your traits? Curley (H) hair is dominant to straight (h)
Widow’s peak (W) is dominant to no widow’s peak (w)
Free ear lobes (F) are dominant to attached ear
lobes (f)
Hair
Widow’s Peak
Ear lobes
Phenotype
Straight
Yes
Free
Possible Genotypes hh
WW or Ww
FF or Ff

10. Punnet Squares
Punnet Squares: use probability to help predict genotypes and phenotype combinations (ratios) in genetic crosses
Monohybrid Cross: examine the inheritance of only one specific trait.

11. Completeing Punnet Squares
Start with the Parents: Find the genotype of the parents
Figure out the Gametes: Determine the alleles that each parent could pass on to their offspring
Set-up the Table: Draw the Punnet Square and place the alleles and parents on the top and the left side of the square
Complete the Punnet Square: Fill in the table with offspring’s possible genotypes
Interpret the results

12. Step 1: Start with Parents
Long fins (L) in fish are dominant to short (l). You are breeding a homozygous dominant long fin male to a homozygous recessive short fin female. What are the possible genotypes of the F1 offspring?
What are the genotypes of the parents
Male: LL
Female: ll

13. Step 2: Figure out the gametes
What alleles can the male and female possibly give to their offspring?
Male Genotype: LL
Can give an L allele or an L allele
Female Genotype: ll
Can give an l allele or an l allele LL L L ll l l

14. Step 3: Set up the Punnet Square
L L l

15. Step 4: Fill in Punnet Square

16. Step 4: Completed Punnet Square
L L l Ll Ll Ll Ll

17. Step 5: Interpret Results
What were the possible genotypes from the cross?
Ll (heterozygous dominant)
What are the possible phenotypes from the cross?
All offspring will have long fins

18. Step 5: Interpret Results
What is the probability that the genotype will be Ll?
4/4 = 100%
What is the probability that the genotype will be ll?
0/4 = 0%

19. Step 5: Interpret the Results
What is the probability that the offspring will have long fins?
4/4 = 100%
What is the probability that the offspring will have short fins
0/4=0%

20. Testcross
A testcross is a cross between an organism with an unknown genotype and an organism with the recessive phenotype
If you have an organism with the dominant phenotype and you need to determine the possible genotype you can perform a test cross.
If you cross your Dominant organism with a recessive and produce recessive offspring you know the unknown organism must be heterozygous.
If no recessive offspring are produced can you be sure of the genotype of the unknown organism? NO

21. Testcross Example Cattle are either horned or polled (no horns)
Horns are dominant to polled
Polled cattle are worth more so want genotypes that carry the polled allele
Ranchers will test cross cattle with horns to determine if they are heterozygous or homozygous dominant

22. Questions??????