1. The Work of
Gregor Mendel

2. Gregor Mendel 1st person to trace successive generations
of living things
Augustinian Monk – Brunn, Austria
taught natural science in high school
“How did plants obtain atypical characteristics?”

3. Vocabulary Used in Genetics
phenotype: physical expression of a gene
genotype: a make of genes in a chromosome
Tall = T
short = t
T T
t t
homozygous: alleles for a trait are the same
T T
heterozygous: alleles for a trait are opposite
Tall
Short
T t

4. More Vocabulary Used in Genetics
heredity: passing characteristics from parents to offspring
genetics: study of heredity
traits: inherited characteristics

5. More Vocabulary Used in Genetics
gametes: sex cells (sperm and egg)
fertilization: uniting of male and female gametes
pollinization: plant fertilization
zygote: cell produced by fertilization
parent generation: P
filial = son or daughter: F
allele: factor that controls expression of a trait

6. Mendel’s Findings:
Hereditary factors do not combine, but are passed intact to offspring.
Each member of the parental generation transmits
only half of its hereditary factors to each offspring.
Certain factors are "dominant" over others.
Different offspring of the same parents receive
different sets of hereditary factors.
Mendel's work became, and still is, the foundation for modern genetics.

7. Mendel's work became, and still is,
the foundation for modern genetics.
However
Mendel's work became, and still is,
the foundation for modern genetics.

8. Gregor Mendel and the Laws of Genetics
I. Why Mendel succeeded:
A. used controlled experiments
B. studied only one trait at a time
C. did mathematical analysis of data

9. II. Mendel’s Monohybrid Crosses
A. First Generation Cross
1. tall pea plants = P1
2. short pea plants = P1
3. all offspring were tall = F1

10. B. Second Generation Cross
1. 2 tall offspring from first generation cross = F1
2. ¾ of these offspring = Tall = F2
3. ¼ of these offspring = Short = F2

11. C. Mendel’s conclusions: Rules
1. Rule of Unit Factors
Each organism has 2 factors for each of its traits
(alleles: gene alternatives)
2. Rule of Dominance
For each trait there exists 2 possible factors
that are expressed in physical characters,
one that may be dominant, and the other
recessive.
3. Law of Segregation
The two alleles for each trait must separate
when gametes form.

12. D. Expression of Traits
1. phenotype: physical expression of a gene
2. genotype: a make of genes on a chromosome
3. homozygous: alleles for a trait are the same
4. heterozygous: alleles for a trait are opposite

13. III. Reginald Punnett and the Punnett Squares
A. English Biologist
1905: devised a shorthand way of finding
the expected proportions of possible genotypes
in the offspring of a cross
C. Method called: Punnett Square
Takes into account that fertilization
occurs randomly
2. Agrees with Mendel’s law of segregation
If you know the genotype of the parents,
you can use a Punnett square to predict
the possible genotypes of their offspring.

14. Punnett Square
Reginald Punnett 1905

15. ♂ T T t T t T t ♀ t T t T t
V. Monohybrid Crosses

16. (cross involving two different traits)
IV. Mendel’s Dihybrid Crosses
(cross involving two different traits)
A. experimenting with plants that had two different traits that differed from each other
1. used true-breeding pea plants that had
round yellow seeds (RRYY)
2. crossed with true-breeding pea plants that
had wrinkled green seeds (rryy)
3. smooth was dominant and wrinkled was recessive
4. yellow was dominant and green was recessive

17. true-breeding pea plants that had
round yellow seeds
round seeds
yellow seeds RR YY
RRYY

18. true-breeding pea plants that had wrinkled green seeds (rryy)
wrinkled seeds
green seeds rr yy
rryy

19. true-breeding pea plants that had round yellow seeds
wrinkled green seeds +
RRYY +
(rryy)
RRYYrryy or
RRrrYYrr

20. P1 R Y R Y R Y R Y R r Y y R r Y y r y R r Y y R r Y y R r Y y R r Y y

21. Result was 100% round yellow seeded plants
true-breeding pea plants that had
round yellow seeds
true-breeding pea plants that had
wrinkled green seeds +
RRYY +
(rryy)
Result was 100% round yellow seeded plants

22. Offspring of P1 cross pea plants that had round yellow seeds
wrinkled green seeds +
RrYy
(RrYy) + ?
Result was different.

23. F1 R Y R y r Y r y R R Y Y r R Y Y R Y R R y Y r R y Y R R Y y r R Y y

24. Ratio = 9:3:3:1 9 round yellow RRYY 1/16 RrYy 4/16 9/16 RRYy 2/16 RrYY
3 round green
Ratio = 9:3:3:1
RRyy
1/16
3/16
Rryy
2/16
3 wrinkled yellow
rrYY
1/16
3/16
rrYy
2/16
1 wrinkled green
rryy
1/16
1/16
16/16

25. Genes for different traits are inherited independently of each other.
B. F1 generation produced all round yellow seeds
C. F2 generation produced
9 round yellow
3 round green
3 wrinkled yellow
1 wrinkled green
D. The Law of Independent Assortment
Genes for different traits are inherited
independently of each other.

26. Haploid n

27. Diploid 2n

28. S-phase of cell cycle
2n x 2

29. Meiosis I
2n x 2 2n 2n B A

30. n A 2n n
Meiosis II

31. 2n B n n

32. Dominant Examples Double Recessive Examples Examples
Brown Eyes over Blue Eyes
Color Vision over Color Blindness
Hairy Heads over Bald Heads
Curly Tongue over Flat Tongue
Extra Fingers over Five Fingers
Double Recessive Examples Examples
Hemophilia
Sickle-Cell Disease
Tay-Sachs Disease
Dwarfism

33. V. Probability

34. VI. Genetic Variation

35. VII. Crossing Over

36. Normal distribution of chromosomes during meiosis.
VIII. NONDISJUNCTION 46 23 23
Normal distribution of chromosomes during meiosis.

38. NONDISJUNCTION 46 24 22

39. Trisomy(21) Down Syndrome
Trisomy(13) Patau’s Syndrome
Monosomy: Turner Syndrome
Hexapoid: Wheat
Triploid: Apples
Polyploid: chrysanthamums