1. Mendelian Patterns of Inheritance
Chapter 11
Mendelian Patterns of Inheritance 1

2. Early Ideas about Heredity
People knew that sperm and eggs transmitted information about traits
Blending theory
Problem:
Would expect variation to disappear
Variation in traits persists 2

3. Gregor Mendel 1st to apply mathematics to biology Careful, delibrate
Well prepared 3

4. Garden Pea Easy to grow Self/cross pollination Many varieties
Used discrete traits, easily observed

5. Tracking Generations Parental generation P mates to produce
First-generation offspring F1
mate to produce
Second-generation offspring F2 5

6. Experimental intercross between
Monohybrid Crosses
Experimental intercross between
two F1 heterozygotes
AA X aa
Aa (F1 monohybrids)
Aa X Aa ? 6

7. Mendel’s Monohybrid Cross Results
5,474 round
1,850 wrinkled
6,022 yellow
2,001 green
882 inflated
299 wrinkled
428 green
152 yellow
F2 plants showed dominant-to-recessive ratio that averaged 3:1
705 purple
224 white
651 long stem
207 at tip
787 tall
277 dwarf
Fig. 11-6, p. 172 7

8. Genes Allele Units of information about specific traits
Passed from parents to offspring
Each has a specific location (locus) on a chromosome
Different molecular forms of a gene
Arise by mutation
Dominant allele masks a recessive allele that is paired with it 8

9. Allele Combinations Homozygous Heterozygous
having two identical alleles at a locus
AA or aa
true-breeding
Heterozygous
having two different alleles at a locus Aa
hybrids 9

10. Genotype & Phenotype
Genotype refers to particular genes an individual carries
Phenotype refers to an individual’s observable traits
Cannot always determine genotype by observing phenotype 10

11. Check Progress B = black, b= white
If a heterozygous rabbit reproduces with one of its own kind, what phenotypic ratio do you expect among the offspring?
If there are 120 rabbits, how many expected to be white?

12. 11.2 Mendel’s laws Each indv has 2 alleles for each trait
Law of Segregation
Law of Independent Assortment
Each indv has 2 alleles for each trait
Alleles separate when gametes form
Gametes have 1 allele for each trait
Fertilization gives new indv 2 alleles
Each pair of alleles assorts indepently
All possible combo of alleles can occur
Applies to alleles on diff c-somes
Expected ratio 9:3:3:1

13. Dihybrid Cross
Experimental cross between individuals that are homozygous for different versions of two traits 13

14. In fruit flies, L = long wings and l = short wings; G = gray body and g = black body. List all possible gametes for a heterozygote

15. Dihybrid Cross: F1 Results
purple
flowers, tall
white
flowers,
dwarf
TRUE-
BREEDING
PARENTS:
AABB x
aabb
GAMETES: AB AB ab ab
AaBb
F1 HYBRID
OFFSPRING:
All purple-flowered, tall 15

16. 1/4 1/4 1/4 1/4 AB Ab aB ab 1/4 AB 1/4 Ab aB 1/4 ab
meiosis,
gamete
formation AB Ab aB ab
1/4
1/16
1/16
1/16
1/16 AB
AABB
AABb
AaBB
AaBb
1/4 Ab
1/16
1/16
1/16
1/16
AABb
AAbb
AaBb
Aabb
1/16
1/16
1/16
1/16
AaBB
AaBb
aaBB
aaBb aB
1/4
1/16
1/16
1/16
1/16
AaBb
Aabb
aaBb
aabb ab
Fig. 11-9b, p.175 16

17. Laws and Meiosis
Doesn’t matter which way the homologous pair faces during metaphase I (2nd law)
Metaphase II cell has one chromosome (1st law)
Gametes can have all possible combinations of alleles (both laws) OR

18. See p. 196

19. Test Cross
Individual that shows dominant phenotype is crossed with individual with recessive phenotype
Examining offspring allows you to determine the genotype of the dominant individual 19

21. Autosomal Recessive Inheritance Patterns
If parents are both heterozygous, child will have a 25% chance of being affected
Fig b, p. 191 21

22. Examples
Methemoglobinemia
Cystic Fibrous
Niemann-Pick

23. Autosomal Dominant Inheritance
Trait typically appears in every generation
Fig a, p. 190 23

24. Achondroplasia Autosomal dominant allele
In homozygous form usually leads to stillbirth
Heterozygotes display a type of dwarfism
Have short arms and legs relative to other body parts 24

25. Huntington Disorder Autosomal dominant allele
Causes involuntary movements, nervous system deterioration, death
Symptoms don’t usually show up until person is past age 30
People often pass allele on before they know they have it 25

26. ABO Blood Type Range of genotypes: IAIA IBIB or or IAi IAIB IBi ii
Fig a, p.176 26

27. Codominance: ABO Blood Types
Gene that controls ABO type codes for enzyme that dictates structure of a glycolipid on blood cells
Two alleles (IA and IB) are codominant when paired
Third allele (i) is recessive to others
Also known as Multiple Alleles 27

28. Incomplete Dominance Incomplete Dominance X Homozygous parent
Intermediate phenotype
Familial hypercholesterolemia
CF heterozygous
Incomplete pentrance
polydactyly
All F1 are
heterozygous X
F2 shows three phenotypes in 1:2:1 ratio 28

29. The allele for albinism (c) is recessive to allele for normal pignmentation (C). A normally pigmented woman whose father is an albino marries a man whose parents are normal. They have 3 children, 2 normal and 1 albino. Give the genotypes for each person.

30. In garden peas, one pair of alleles controls the height of the plant and a second pair of alleles controls flower. The allele for tall (D) is dominant to allele for dwarf (d), and the allele for purple (P) is dominant to the allele for white (p). A homozygous tall purple plant is crossed with a dwarf white plant.
What is the appearance of F1 and F2?

31. Epistasis Interaction between the products of gene pairs
Common among genes for hair color in mammals 31

32. Examples Antocyanin pigments Lab coat color Eye color humans
Start molecule colorless Intermediate colorless  Purple
Lab coat color
Start molecule melanin  deposition
Eye color humans
Blue 1  Blue 2  Green  Brown

33. Coat Color in Retrievers
BBEE X
bbee
F1 puppies
are all BbEe
F2 puppies BE Be bE be BE
BBEE
BBEe
BbEE
BbEe
black Be
BBEe
BBee
BbEe
Bbee
brown bE
BbEE
BbEe
bbEE
bbEe
yellow be
BbEe
Bbee
bbEe
bbee 33

34. Pleiotropy
Alleles at a single locus may have effects on two or more traits
Marfan syndrome - Mutation in gene for fibrillin affects skeleton, cardiovascular system, lungs, eyes, and skin 34

35. Polygenic
A more or less continuous range of small differences in a given trait among individuals
The greater the number of genes and environmental factors that affect a trait, the more continuous the variation in versions of that trait 35

36. Continuous Variation Variation in human eye color Eye color Calculator
Fig , p.180 36

37. Temperature Effects on Phenotype
Rabbit is homozygous for an allele that specifies a heat- sensitive version of an enzyme in melanin-producing pathway
Melanin is produced in cooler areas of body
Figure Page 179 37

38. Environmental Effects on Plant Phenotype
Hydrangea macrophylla
Action of gene responsible for floral color is influenced by soil acidity
Flower color ranges from pink to blue 38

39. Elevation and the yarrow
Fig b, p.179 39

40. X-Linked Recessive Inheritance
Males show disorder more than females
Son cannot inherit disorder from his father
Fig , p.194 40 40

41. Thomas Morgan 1900’s Red female x white male = all red
F2 = 3 red: 1 white male
Supported chromosome theory of inheritance
Males = hemizygous 41 41

42. Fig. 12-9, p.193 42 42

43. Examples of X-Linked Traits
Color blindness
Hemophilia
Menkes syndrome
Muscular Dystrophy
Adrenoleukodystrohy (ALD) 43 43

44. Color Blindness
Fig , p.195 44 44

45. Color Blindness
Fig , p.195 45 45

46. 1 XrXr
2 XRY
3 XRY
4 XRXr
5XrY
6 XRXr
7 XrY
8 XrXr
9 XrY
10XRX
11 XRY
12 XRX
13 XrY
14 XrXr
15 XrY

47. Hemophilia
Fig , p.194 47