1. Chapter 3 Section 1
Mendel’s Work

2. Gregor Mendel
Young priest that worked in the garden at a monastery in Vienna.
Considered the “Father of Genetics”
Observed traits in hundreds of pea plants.

3. Mendel’s Work - Vocabulary
Traits
Physical characteristics of organisims
Heredity
Passing of traits from parent to offspring
Genetics
Scientific study of heredity

4. Mendel’s Peas Why was Gregor Mendel lucky he chose peas to study?
Many traits exist only in two forms
Peas produce many offspring in one generation.

5. How did Mendel make his crosses?
Tall Plant
Short Plant

6. Mendel’s Experiments Purebred Plant
One that always produces offspring with the same form of a trait as the parent
i.e. purebred short plants will only produce short offspring.

7. Purebred pink plants will only produce pink plantsX

8. White flower would mean the parents are not purebredX

9. Mendel’s Experiments
Mendel crossed plants with opposite forms of a trait
i.e. short plants crossed with tall plants
Look at Figure 2 on page 82

10. Fig 2 page 82
What did Mendel get when he crossed purebred tall plants with pure bred short plants?
All Tall plants
What did Mendel get when he let the F1 plants self pollinate?
75% tall and 25% short.

11. Mendel’s Experiments
Mendel studied stem height followed by six other “opposite” traits.
Look at Figure 3 on page 83.
What other “opposite” traits did Mendel study?

12. Genes and Alleles Genes Alleles Factors that control traits
Different forms of a gene
One allele is inherited from each parent.
Alleles can be dominant or recessive

13. Dominant and Recessive Alleles
Dominant allele
Always seen if present
Indicated by a capitol letter (T)
Recessive allele
Masked or hidden if dominant allele is present
Indicated by a lower case letter (t)

14. Hybrid vs Purebred Hybrid Purebred
Organism has two different alleles for the trait – one dominant and one recessive.
Purebred
Organism has two identical alleles for a trait – two recessive OR two dominant.

15. Alleles are represented with capitol and lower case letters.
T = Tall allele (dominant)
t = Short allele (recessive)
Purebreds
TT – two dominant alleles – plants will be tall
tt – two recessive alleles – plants will be short
Hybrid
Tt – one dominat allele and one recessive allele – plants will be tall.

16. Phenotypes and Genotypes
Physical appearance or visible trait
Example is flower color, stem height etc.
Genotype
The genetic makeup or allele combination
Examples are TT or Tt
Genotypes determine phenotypes

17. Homozygous and Heterozygous
An organism that has two identical alleles for a trait
TT – homozygous dominant
tt – homozygous recessive
Heterozygous
An organism that has two different alleles for a trait
Tt – heterozygous – will show the dominant trait

18. What is the rabbit’s phenotype for fur color? _________
Consider a rabbit with black fur and the allele combination (Bb).
What is the rabbit’s phenotype for fur color? _________
What is the rabbit’s genotype for fur color? __________
Is the rabbit heterozygous or homozygous for the fur color trait? _______________
If black is dominant over white, what genotype would produce a white rabbit? _______
If fur color in rabbits was a codominant trait instead of dominant/recessive trait, what color fur would the (Bb) rabbit have? ________________
Black
(Bb)
heterozygous
(bb)
White and black 18

19. Probability and Genetics
Chapter 3 - Section 2

20. Probability Probability Example: coin toss
The likelihood that a particular event will occur
Example: coin toss

21. Punnett Squares Punnett Squares
chart that shows all possible combinations of alleles that can result from a genetic cross. Used to determine the probability of a particular outcome.

22. Using a punnett square Tt t T T Tt t TT Tt Tt tt Tall Tall Tall Short

23. Mendel’s Work Review Worksheet
What trait in pea plants is being studied in the cross above?
Plant height (short/tall)
What are the two alleles for this trait?
Tall (T)
Short (t)
Which allele is the dominant allele? Explain how you know.
Dominate allele is Tall (T).
Know because all offspring in F1 are tall.

24. Mendel’s Work Review Worksheet
Which allele is the recessive allele? Explain
Recessive is short (t)
Know because this trait is hidden in the F1
What alleles do the F1 offspring have? Explain which allele was inherited from which parent.
All F1 offspring are hybrids with the alleles (Tt)
(T) was inherited from the tall parent and (t) was inherited from the short parent.

25. Codominance
Codominance – alleles are neither dominant or recessive therefore both alleles are expressed in the offspring

26. Codominance
The heterozygous offspring will express (show) both phenotypes