1. Chapter 4 Genetics
4.1 Mendel’s Work

2. POINT > Describe who Gregor Mendel was
POINT > Define heredity, trait, and genetics
POINT > Explain why pea plants were so useful
POINT > Describe Mendel’s experiments
POINT > Define genes and alleles
POINT > Define dominant and recessive

3. POINT > Describe who Gregor Mendel was
Gregor Mendel ( ) was an Austrian monk and botanist He discovered rules that control how characteristics get passed from parents to offspring He did his work using pea plants in his garden He is known as “The Father of Genetics”

4. POINT > Define trait, heredity and genetics
A trait is a physical characteristic (hair color, eye color, height, leaf size, etc) Heredity is the passing of traits from parents to offspring Genetics is the study of heredity

5. CHECK:
What kind of plant did Mendel use? What is genetics? What is heredity? What is a trait?

6. POINT > Explain why pea plants were so useful
1) Mendel noticed that some pea plants have different traits

7. POINT > Explain why pea plants were so useful
2) Mendel noticed that the offspring always had the same traits as the parent plant

8. POINT > Explain why pea plants were so useful
The offspring pea plants always had the same traits as the parent plant = purebred
3) Pea plants are self-pollinating: the plant fertilizes itself

9. POINT > Explain why pea plants were so useful
4) Pea plant traits are dichotomous: traits were one way or the other, not in between

10. CHECK:
What does dichotomous mean? Pea plants are self-pollinating. What does that mean? What does purebred mean? What are the 3 parts of a nucleotide? What part of the cell cycle includes DNA replication? What are the 3 parts of the cell cycle? What are the 4 phases of mitosis?

11. POINT > Describe Mendel’s experiments
Mendel decided to cross-breed: fertilize plants that had different traits
For example, cross a purple flower plant with a white flower plant

12. POINT > Describe Mendel’s experiments
When Mendel did this cross, purple x white, all of the offspring had purple flowers
The same result occurred with other traits

13. POINT > Describe Mendel’s experiments
Purple x White = P generation (P=parent)
The offspring (all purple) = F1 generation (F=filial)

14. POINT > Describe Mendel’s experiments
Mendel decided to let the F1 generation self-pollinate (F1 x F1)
Remember, all these plants had purple flowers

15. POINT > Describe Mendel’s experiments
25% of the F2 generation were white!
The same was true of the other traits 75% -25%

16. POINT > Describe Mendel’s experiments
In the F1 generation 100% showed one trait
In the F2 generation there was always a 3:1 ratio

17. POINT > Describe Mendel’s experiments
This was a mystery, but Mendel solved it
He found that the factors that control traits come in pairs (2 factors for each trait)
One of the factors comes from each parent
One of the factors can cover up the other one

18. POINT > Define genes and alleles
The factors that control traits come in pairs (2)
We now call these factors genes. Genes control what traits appear in an individual
Different forms of a gene for one trait are called alleles
For example, there is an allele for purple flowers and an allele for white flowers

19. CHECK:
What do genes do? What are alleles? What is a prokaryote?

20. POINT > Define genes and alleles
For example, there is an allele for purple flowers and an allele for white flowers
Ex. One allele for tall plants and one allele for short plants
When two different alleles are in one plant, one of the alleles is dominant over the other allele

21. POINT > Define dominant and recessive
One allele is dominant and the other allele is recessive
Ex. The allele for purple flowers is dominant and the allele for white flowers is recessive
A plant with one purple allele and one white allele will have all purple flowers

22. POINT > Define dominant and recessive
We identify the dominant allele with capital letters: ex. P for purple flowers
We identify the recessive allele by using small letters: ex. p for white flowers
T = tall plant allele
t = short plant allele

23. POINT > Define dominant and recessive
Each individual has two alleles for a trait
PP - plant has two dominant alleles (purple flowers)
pp - plant has two recessive alleles (white flowers)
Pp - plant has one dominant and one recessive allele (purple flowers)

24. CHECK:
How many alleles are there for one trait? Which is the dominant allele: “R” or “r”? P is the dominant allele and gives purple flowers. p is the recessive allele and gives white flowers. If a plant has one P allele and one p allele, what color are the flowers? What are the alleles of a plant with white flowers?

25. Homework:
Complete Study Guide
Read pages
S.A. page 115 #1-2
GRAS pages 55-57