1. PowerLecture: Chapter 11
Observing Patterns in Inherited Traits

2. Early Ideas about Heredity
Blending theory
Problem:
Variation in traits persists

3. Gregor Mendel
Fig. 11-2, p.170

4. Genes
Fig. 12-2, p.188

5. Allele Combinations
Homozygous
Heterozygous

6. A pair of homologous chromosomes, each in the unduplicated state (most often, one from a male parent and its partner from a female parent)
A gene locus (plural, loci), the location for a specific gene on a chromosome. Alleles are at corresponding loci on a pair of homologous chromosomes
A pair of alleles may be identical or nonidentical. They are represented in the text by letters such as D or d
Three pairs of genes (at three loci on this pair of homologous chromosomes); same thing as three pairs of alleles
Fig. 11-4, p.171

7. Genotype & Phenotype
Genotype - the particular genes an individual carries
Phenotype - an individual’s observable traits

8. Probability
The chance that each outcome of a given event will occur is proportional to the number of ways that event can be reached

9. Tracking Generations Parental generation P mates to produce
First filial F1
mate to produce
Second filial F2

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

11. Monohybrid Cross Illustrated
True-breeding
homozygous recessive
parent plant
homozygous dominant
An F1 plant
self-fertilizes
and produces
gametes:
F1 PHENOTYPES
F2 PHENOTYPES aa Aa AA A a
Monohybrid Cross Illustrated
Figure 11.7 Page 173

12. 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

13. F2 Dominant-to- Recessive Ratio
Trait Studied
Dominant Form
Recessive Form
F2 Dominant-to- Recessive Ratio
SEED SHAPE
5,474 round
1,850 wrinkled
2.96:1
SEED COLOR
6,022 yellow
2,001 green
3.01:1
POD SHAPE
882 inflated
299 wrinkled
2.95:1
POD COLOR
428 green
152 yellow
2.82:1
FLOWER COLOR
705 purple
224 white
3.15:1
FLOWER POSITION
651 long stem
207 at tip
3.14:1
STEM LENGTH
787 tall
277 dwarf
2.84:1
Fig. 11-6, p.172

14. Mendel’s Theory of Segregation
An individual inherits a unit of information (allele) about a trait from each parent
During gamete formation, the alleles segregate from each other

15. Mendel’s Theory of Segregation
Homozygous dominant parent
Homozygous recessive parent
Mendel’s Theory of Segregation
(chromosomes duplicated before meiosis)
meiosis I
meiosis II
(gametes)
(gametes)
fertilization produces heterozygous offspring
Fig. 11-5, p.172

16. Test Cross dominant phenotype crossed with recessive phenotype
Examining offspring determines genotype of dominant individual

17. Punnett Squares of Test Crosses
True-breeding
homozygous recessive
parent plant
F1 PHENOTYPES aa
True-breeding
homozygous dominant
parent plant Aa Aa a a A Aa Aa AA A Aa Aa Aa Aa
Fig. 11-7b1, p.173

18. Punnett Squares of Test Crosses
An F1 plant self-fertilizes
and produces gametes:
F2 PHENOTYPES Aa AA Aa A a A AA Aa a Aa aa Aa aa
Fig. 11-7b2, p.173

19. 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

20. Dihybrid Cross: F2 Results
AaBb X
AaBb
1/4 AB
1/4 Ab
1/4 aB
1/4 ab
9/16 purple-flowered, tall
1/4 AB
1/16
AABB
1/16
AABb
1/16
AaBB
1/16
AaBb
3/16 purple-flowered, dwarf
3/16 white-flowered, tall
1/4 Ab
1/16
AABb
1/16
AAbb
1/16
AaBb
1/16
Aabb
1/16 white-flowered, dwarf
1/4 aB
1/16
AaBB
1/16
AaBb
1/16
aaBB
1/16
aaBb
1/16
AaBb
1/16
Aabb
1/16
aaBb
1/16
aabb
1/4 ab

21. Independent Assortment
Mendel concluded that “units” for one trait assorted independently of the “units” for the other trait
homologous chromosomes are sorted at random during meiosis

22. Independent Assortment
Metaphase I: OR A A a a A A a a B B b b b b B B
Metaphase II: A A a a A A a a B B b b b b B B
Gametes: B B b b b b B B A A a a A A a a
1/4 AB
1/4 ab
1/4 Ab
1/4 aB

23. (n is the number of gene loci at which the parents differ)
Tremendous Variation
Number of genotypes possible in offspring due to independent assortment and hybrid crossing is 3n
(n is the number of gene loci at which the parents differ)

24. Impact of Mendel’s Work
Mendel presented his results in 1865
Paper received little notice
Mendel discontinued his experiments in 1871
Paper rediscovered in 1900

25. Dominance Relations Complete dominance Incomplete dominance
Codominance

26. Incomplete Dominance X All F1 offspring heterozygous for flower color:
homozygous parent X
homozygous parent
All F1 offspring heterozygous for flower color:
Cross two of the F1 plants and the F2 offspring will show three phenotypes in a 1:2:1 ratio:
Fig , p.176

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

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

29. ABO and Transfusions
Recipient’s immune system attacks blood cells with unfamiliar glycolipid on surface
Type O is universal donor because it has neither type A nor type B glycolipid

30. 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

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

32. Epistasis
Fig , p.177

33. Coat Color in Retrievers (Epistasis)
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

34. Comb Shape in Poultry rose comb pea comb walnut comb single comb X
RRpp
pea
rrPP F1
all walnut
RrPp
RrPp
RrPp F2
9/16 walnut
RRPP, RRPp,RrPP, or RrPp
3/16 rose
RRpp or Rrpp
3/16 pea
rrPP or rrPp
1/16 single
rrpp
Fig , p.177

35. 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

36. Environmental Effects on Plant Phenotype
Fig a, p.179

37. Environmental Effects on Plant Phenotype
Fig b, p.179

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

39. This Siamese cat, raised in a cold environment in Moscow in the late 20s, developed a relatively dark coat. An area on his shoulder was shaved, and the cat wore a warm jacket while the fur was growing back. When the shaved hair grew back in, it was white, the same color as the cat's belly, due to the increased temperature under the jacket. This was not due to scarring, as the hair grew in normally colored later.

40. Campodactyly: Unexpected Phenotypes
Effect of allele varies:
Bent fingers on both hands
Bent fingers on one hand
No effect
Many factors affect gene expression

41. Continuous Variation
Relatively continuous range of differences in a given trait among individuals
More genes and environmental factors affect trait - more continuous variation

42. Human Variation Some human traits occur as a few discrete types
Attached or detached earlobes
Many genetic disorders
Other traits show continuous variation
Height
Weight
Eye color

43. Continuous Variation
Variation in human eye color
Fig , p.180

44. Describing Continuous Variation
Range of values for the trait
Number of individuals with
some value of the trait
Range of values for the trait
Number of individuals with
some value of the trait
(line of bell-shaped curve indicates continuous variation in population)

45. Describing Continuous Variation
Fig , p.181