1. Mendel
Biology
Chapter 10.1 p

2. 10.1 Mendel’s Laws of Heredityp

3. Gregor Mendel Austrian monk Considered the “father of genetics”
The first person to succeed in predicting how traits would be transferred from one generation to another
using the garden pea plant

4. Genetics The branch of biology that studies heredity Heredity Traits
The passing on of characteristics from parents to offspring
Traits
Characteristics that are inherited
i.e. eye color, height, etc.

5. Why Mendel chose the garden pea?
Easily cultivated
Short generation time
Reproduces sexually and can be cross-pollinated
Gametes (sex cells)
Male = sperm; female = egg
Pollination
Transfer of the male pollen grains to the pistil of a flower
Fertilization
When the male gamete unites with the female gamete

6. Parts of a Flower

7. Types of Pollination
Cross-pollination
self-pollination

8. How Mendel studied the garden pea plant?
Controlled his experiments
Studied only one trait at a time
He analyzed his data mathematically
He chose true breeding garden pea plants
Offspring are identical to parents
He studied 7 traits of the garden pea

9. Pea traits that Mendel studied

10. Mendel’s Monohybrid Cross
The offspring of parents that have different forms of a trait, such as tall and short
Monohybrid cross (mono = one)
The two parent plants differed by a single trait – height
P1 – parent generation
F1 –first generation
F2 – second generation
P = parent
F = “filial” son or
daughter

11. Mendel’s Monohybrid Cross
The First Generation
Crossed 2 true breeding plants
1 tall and 1 short
All offspring of the 2 parent plants were tall P1 X F1

12. Mendel’s Monohybrid Cross
The Second Generation
Self-pollinated the plants from the first generation
¾ the offspring were as tall as the tall plants in the parent and first generation
¼ the offspring were as short as the short plant in the parent generation
3:1 ratio tall to short

13. Second Generation X

14. Mendel’s Monohybrid Cross
The rule of unit factors
Each organism has 2 factors that control each of its traits
These factors are genes
Genes exist in alternative forms called alleles
Ex. Plant height – one alleles is for tall and another is for short
One comes from the mother and one from the father

15. Mendel’s Monohybrid Cross
The rule of dominance
Each trait has an allele that will be observed more than the other
Dominant (gene)
The observed trait
Tall plant
Recessive (gene)
The trait that disappeared
Short plant
Only shows when both alleles are recessive

16. Dominate and Recessive

17. Mendel’s Monohybrid Cross
Recording the results for crosses
Dominate allele is always written first
Uppercase letter is used for dominate
T – tall
Lowercase letter is used for recessive
t – short

18. Mendel’s Monohybrid Cross
Law of segregation
During fertilization, male and female gametes randomly pair to produce 3 combinations of alleles.
Concluded that each plant in the F1 generation carried one dominate allele and one recessive allele and the F2 generation either received 2 dominate; 2 recessive; or one of each

19. Phenotypes and Genotypes
Two organisms can look alike but have different underlying gene combinations
Phenotype
The way an organism looks or behaves
What you see
Genotype
The gene combination an organism contains
The genetic makeup

20. Phenotypes and Genotypes
Homozygous
The two alleles for the trait are the same
TT or tt
Heterozygous
The two alleles for the trait are different Tt

21. Can you determine the phenotype?
White and purple garden pea flowering plants
Purple is dominate (P)
White is recessive (p)

22. Homozygous Dominate Cross
Cross = Purple X Purple P

23. Homozygous Recessive Cross
Cross = White X White p

24. Heterozygous Cross
Cross = Purple X Purple P p

25. Mendel’s Dihybrid Crosses
Cross where the peas differ in 2 traits
Ex. Seed color and Seed shape
A cross involving two traits

26. Mendel’s Dihybrid Crosses
The First Generation
Two true breeding plants (P1)
RRYY = round yellow seed (homozygous dominate)
rryy = wrinkled green seed (homozygous recessive)
When they were crossed all the plants had round yellow seeds (F1)

27. Mendel’s Dihybrid Crosses
Dihybrid Cross = round yellow X wrinkled green RY ry
RrYy
RyYy

28. Mendel’s Dihybrid Crosses
The Second Generation (F2)
Self-pollinated plants from the first generation
Resulted in 9 round yellow, 3 round green, 3 wrinkled yellow, 1 wrinkled green
A ratio of 9:3:3:1

29. Mendel’s Dihybrid Crosses
The law of independent assortment
Genes from different traits are inherited independently of each other
Ex. A pea plant that is RrYy, the alleles will separate and the traits will separate

30. Mendel’s Dihybrid Crosses
Heterozygous Cross = round yellow X round yellow RY Ry rY ry
RRYY
RRYy
RrYY
RrYy
RRyy
Rryy
rrYY
rrYy
rryy

31. Punnett Squares
Devised by an English biologist Reginald Punnett in 1905
Short hand way of finding the expected ratio of genotypes
The phenotype can also be determined by the Punnett Squares

32. Punnett Squares Monohybrid crosses
Cross between two plants but only looking at one trait
Alleles of each parent are represented in the cross
One parent is on the top the other is on the side

33. Heterozygous tall parent = Tt
Monohybrid Cross
Heterozygous tall parent = Tt
Cross = Tt X Tt T t T t TT Tt tt 

34. Punnett Squares Dihybrid crosses
Cross between two plants, and you are looking at two traits
Both traits will be represented in the cross
RrYy X RrYy (both are heterozygous)

35. Heterozygous round yellow seed parents = RrYy
Dihybrid Cross
Heterozygous round yellow seed parents = RrYy
Cross = RrYy X RrYy RY Ry rY ry RY Ry rY ry
RRYY
RRYy
RrYY
RrYy
RRyy
Rryy
rrYY
rrYy
rryy 

36. PRACTICE PUNNETT SQUARES
Probability
Genetic is like flipping a coin it can go either way
The Punnett Square is only able to show us the chance/probability that the offspring will be a certain way
All the offspring could be the same
PRACTICE PUNNETT SQUARES

37. Monohybrid Punnett Square

38. Dihybrid Punnett Square

39. Dihybrid Punnett Square