1. Mendelian Genetics Reading: Chap. 14 I. Intro II. Mendel’s findings
A. Motivating question
B. Mendel
II. Mendel’s findings
A. Law of segregation
B. Law of independent assortment
III. Complications
IV. Examples from human genetics
As humans have altered ecosystems and caused species extinctions world-wide, a critical question is the extent to which such biotic modifications influence ecosystem-level processes.

2. Terms and Concepts - character, trait, alleles Rules of probability
- P, F1, F2
- dominant/recessive
- law of segregation
- law of independent assortment
- homozygous/heterozygous
- phenotype/genotype
- testcross
Rules of probability
Complications:
- complete, incomplete and co- dominance
- multiple alleles
- pleiotropy
- Epistasis
- quantitative characters: polygenic inheritance

3. Motivating question: Radiation of the Galápagos finches
Beak sizes
Food availability
Range overlap
Probable ancestors

4. Galápagos Islands

5. What Darwin knew (and inferred):
Patterns of distribution
Mechanism of natural selection
heritable traits
“struggle for existence”
higher fitness --> more offspring
Shift in average traits in population

6. What he didn’t know: How did heritability work?
What exactly was passed down from parents to offspring?
Blending vs. particulate?
No idea about: Genes, chromosomes, DNA, mitosis and meiosis

7. Gregor Mendel Austrian contemporary of Darwin
Darwin’s thoughts are based on many prior thinkers. We will briefly look at a few of those whose prior work made an impression on Darwin.
Austrian contemporary of Darwin
Published shortly after Darwin - but work was “buried”
Fig 22.1

8. Who was Mendel? - Austrian monk
- Background in agriculture (grew up on a farm)
- Failed his teacher’s exam
- University of Vienna: math, causes of variation in plants
- Teaching at the Brünn Modern School

9. What did he do? Pea breeding Testing mechanisms of inheritance
Used many different characters
Published results in 1865

10. Why did his experiments succeed?
Control over fertilization
Multiple generations: P, F1, F2
True breeding parents
“Either/or”
characters

11. II. What did Mendel find? A. Law of segregation (of alleles)
B. Law of independent assortment (of traits)

12. A1. Mendel’s experiments: Simple cross
P - true breeding parents with
different traits for same character.
F1 - Cross two of same
generation
F2 - evaluate resulting traits: 3 to 1

13. Mendel tested many traits
3 to 1!!!
Did Mendel fudge?

14. A2. Mendel’s interpretation
- one factor from each parent
- dominant vs. recessive
- particulate inheritance: can get pure traits back

15. Genotype vs. phenotype
homozygous vs. heterozygous

16. 3. Law of segregation
When hybrid plants produce gametes, the two parental factors segregate: half the gametes get one type, half get the other type.
All possible combinations, random combinations

17. 4. Rules of probability
- multiplicity
- additivity

18. OK, prove it! The testcross
Dominant phenotype: what genotype?
Predictions follow from particulate inheritance

19. 5. What do we know now?

20. Chromosomes, genes, and alleles
segregate on
the homologous
chromosomes P p

21. How does the law of segregation relate to meiosis?
Homologous chromosomes separate after doubling
Sister chromatids separate
Fig. 13.6

22. B. Law of independent assortment
What about two or more characters? Are they inherited together or independently?

23. 1. Two traits: an example
Together
Independent

24. Law of independent assortment (of characters)
“Independent segregation of each pair of alleles (i.e., genes coding for each character) during gamete formation.”

25. Rules of probability From YyRr x YyRr Yellow round:
YYRR YYRr YyRR YyRr
(1/4*1/4) + (1/2*1/4)+(1/2*1/4)+(1/2*1/2)
= 9/16
Green round:
yyRR yyRr
(1/4*1/4) + (1/4*1/2) = 3/16
Yellow wrinkled:
YYrr Yyrr
(1/4*1/4) + (1/2*1/4) = 3/16
Green wrinkled:
yyrr (1/4*1/4) = 1/16

26. 2. What we know now:
Mendel’s independent assortment referred to characters.
fig. 13.9
How does this relate to independent assortment of chromosomes in meiosis?

27. What if genes for two traits are on the same chromosome?
Independent or linked?
Linked, except for…?
Crossing over
Depends how close they are: genes further apart are more likely to behave as indpendent.

28. Mendel got lucky…twice
1. Genes for traits he studied were either on separate chromosomes, or
2. Far enough apart on the same chromosome that they assorted independently

29. III. Complications
A. Dominance, Incomplete dominance and Codominance

30. A1. Incomplete dominance in snapdragon
- Phenotype is intermediate
- NOT blending
Fig. 14.9

31. A2. Codominance - M, N, MN blood groupsMM MN
BOTH traits expressed NN

32. B. Complications: Multiple alleles
ABO blood groups
Dominant
Dominant
Codominant
Recessive
fig

33. C. Complications: Pleiotropy
- One gene affects many characters
- Sickling allele of hemoglobin
fig

34. D. Complications: Polygenic Inheritance and Quantitative Characters
- One trait determined by multiple genes
- Converse of pleiotropy
- e.g., skin color: at least 3 genes
fig

35. E. Complications: Epistasis
- Expression of one gene depends on another
- Mouse coat color:
B - black coat
b - brown coat
C - pigment
c - no pigment
fig

36. IV. Examples from human genetics
Several excellent examples in the book.
- Simple traits, geneologies
- Genetic disorders (Tay-Sach’s disease, Huntington’s disease, cystic fibrosis, etc.)
Understand how they work, but don’t need to memorize the details of each.
Why might mating between close offspring lead to increased incidence of genetic disorders?

37. Where do we go from here? Have: Mechanism for natural selection
Mechanism for heritability
Not yet:
Understanding of meiosis, maintenance of genetic variability
“Molecular carrier” of heritable information

38. The modern synthesis Darwin Mendel Population genetics DNA Fig 22.1
Darwin’s thoughts are based on many prior thinkers. We will briefly look at a few of those whose prior work made an impression on Darwin.
Fig 22.1