1. Chapter 11 Genetics – the study of heredity Patterns of Inheritance
Copyright © 2006 Pearson Prentice Hall, Inc.

2. 11.1 What Is the Physical Basis of Inheritance?
Genes Are Sequences of Nucleotides at Specific Locations on Chromosomes
An Organism’s Two Alleles May Be the Same or Different
Figure The relationships among genes, alleles, and chromosomes (p. 168)
Copyright © 2006 Pearson Prentice Hall, Inc.

3. chromosome 1 from tomato
pair of
homologous
chromosomes
Figure: 11_01
Title:
The relationships among genes, alleles, and chromosomes
Caption:
Homologues carry the same gene loci but may have the same or different alleles at corresponding loci.
Copyright © 2006 Pearson Prentice Hall, Inc.

4. 11.2 How Were the Principles of Inheritance Discovered?
Figure Gregor Mendel (p. 168)
1860’s
Studied pea plants – parents pass to offspring the genetically heritable traits
Copyright © 2006 Pearson Prentice Hall, Inc.

5. Copyright © 2006 Pearson Prentice Hall, Inc.
Figure: 11_02
Title:
Gregor Mendel
Caption:
Copyright © 2006 Pearson Prentice Hall, Inc.

6. 11.2 How Were the Principles of Inheritance Discovered?
Doing It Right: The Secrets of Mendel’s Success
Figure Flowers of the edible pea (p. 169)
Copyright © 2006 Pearson Prentice Hall, Inc.

7. flower dissected to show reproductive structures
intact pea flower
flower dissected to show
reproductive structures
Figure: 11_03
Title:
Flowers of the edible pea
Caption:
In the intact pea flower (left), the lower petals form a container enclosing the reproductive structures. Pollen normally cannot enter the flower from outside, so peas usually self-fertilize. If the flower is opened (right), it can be cross-pollinated by hand.
Copyright © 2006 Pearson Prentice Hall, Inc.

8. Mendels Principles
Alternative forms of genes exist (more than 1 color option etc.)
2 genes, 1 from each parent, determines…thus each parent contributes 1 for a (new) combination of 2 (principle of segregation)
Dominant shows up first, what you see/expressed (recessive, unseen but there, i.e. masked)
Copyright © 2006 Pearson Prentice Hall, Inc.

9. Genetics “terms” Homozygous – same allele, “pure”
Heterozygous – diff. allele
Allele – alternatives forms of genes
Phenotype – physical characteristic (seen/expressed)
Wild Type – physical characteristic (phenotype) seen most commonly in nature
Genotype – genetic (chromosomal) make up
Copyright © 2006 Pearson Prentice Hall, Inc.

10. 11.3 How Are Single Traits Inherited?
11_UN01 Mendel's Peas: F1 Generation (p. 169)
11_UN02 Mendel's Peas: F2 Generation (p. 170)
In a mono-hybrid (X1) cross (only 1 characteristic differs at a time when crossed)
Copyright © 2006 Pearson Prentice Hall, Inc.

11. pollen Parental generation (P) pollen cross-fertilize true-breeding,
purple-flowered
plant
true-breeding,
white-flowered
plant
First-generation
offspring (F1)
Figure: 11_UN01
Title:
Mendel's Peas: F1 Generation
Caption:
all purple-flowered
plants
Copyright © 2006 Pearson Prentice Hall, Inc.

12. self-fertilize 3/4 purple 1/4 white First generation offspring (F1)
Second
generation
offspring (F2)
Figure: 11_UN02
Title:
Mendel's Peas: F2 Generation
Caption:
3/4 purple
1/4 white
Copyright © 2006 Pearson Prentice Hall, Inc.

13. 11.3 How Are Single Traits Inherited?
The Pattern of Inheritance of Single Traits Can Be Explained by the Inheritance of Alleles of a Single Gene
11_UN03 Mendel's Peas: Gametes from a homozygous parent (p. 170)
11_UN04 Mendel's Peas: Gametes from a heterozygous parent (p. 171)
11_UN05 Mendel's Peas: Allele production (p. 171)
11_UN06 Mendel's Peas: Heterozygote offspring from dominant and recessive parents (p. 171)
11_UN07 Mendel's Peas: F1 alleles to F2 generation (p. 171)
Copyright © 2006 Pearson Prentice Hall, Inc.

14. More terms
Hybrid cross – offspring of 2 diff. varieties crossed. 1 = mono, 2= di
P1 generation= parents
F1 generation = offspring of P1 generation; next = F2
Copyright © 2006 Pearson Prentice Hall, Inc.

15. homozygous parent gametes A A A A
Figure: 11_UN03
Title:
Mendel's Peas: Gametes from a homozygous parent
Caption:
Copyright © 2006 Pearson Prentice Hall, Inc.

16. heterozygous parent gametes A a A a
Figure: 11_UN04
Title:
Mendel's Peas: Gametes from a heterozygous parent
Caption:
Copyright © 2006 Pearson Prentice Hall, Inc.

17. purple parent PP P P all P sperm and eggs white parent pp p p
Figure: 11_UN05
Title:
Mendel's Peas: Allele production
Caption: pp p p
all p sperm and eggs
Copyright © 2006 Pearson Prentice Hall, Inc.

18. F1 offspring sperm eggs P p Pp or p P Pp
Figure: 11_UN06
Title:
Mendel's Peas: Heterozygote offspring from dominant and recessive parents
Caption: p P Pp
Copyright © 2006 Pearson Prentice Hall, Inc.

19. Copyright © 2006 Pearson Prentice Hall, Inc.
gametes from
F1 plants F2
offspring
sperm
eggs PP P P p Pp P
Figure: 11_UN07
Title:
Mendel's Peas: F1 alleles to F2 generation
Caption: p P Pp p p pp
Copyright © 2006 Pearson Prentice Hall, Inc.

20. 11.3 How Are Single Traits Inherited?
Simple “Genetic Bookkeeping” Can Predict Genotypes and Phenotypes of Offspring
Figure The Punnett square method (p. 172)
Copyright © 2006 Pearson Prentice Hall, Inc.

21. Copyright © 2006 Pearson Prentice Hall, Inc.Pp
self-fertilize 1 — 2 1 — 2 p
eggs p 1 — 2 P
Figure: 11_04
Title:
The Punnett square method
Caption:
The Punnett square method allows you to predict both genotypes and phenotypes of specific crosses. Here we use it for a cross between plants that are heterozygous for a single trait, flower color. (1) Assign letters to the different alleles. Use uppercase for dominant and lowercase for recessive. (2) Determine all the types of genetically different gametes that can be produced by the male and female parents. (3) Draw the Punnett square, with the columns labeled with the egg genotypes and the rows labeled with the sperm genotypes. (We have included the fractions of these genotypes with each label.) (4) Fill in the genotype of the offspring in each box by combining the genotype of sperm in its row with the genotype of the egg in its column. (We have placed the fractions in each box.) (5) Count the number of offspring with each genotype. (Note that Pp is the same as pP.) (6) Convert the number of offspring of each genotype to a fraction of the total number of offspring. In this example, out of four fertilizations, only one is predicted to produce the pp genotype, so 1/4 of the total number of offspring produced by this cross is predicted to be white. To determine phenotypic fractions, add the fractions of genotypes that would produce a given phenotype. For example, purple flowers are produced by ¼ PP + ¼ Pp + ¼ pP, for a total of 3/4 of the offspring. 1 — 4 1 — 4 PP Pp
sperm 1 — 2 p 1 — 4 1 — 4 pP pp
Copyright © 2006 Pearson Prentice Hall, Inc.

22. 2 results w/ a monohybrid cross
3:1 ratio phenotype
1:2:1 ratio genotype
Look the same!
Copyright © 2006 Pearson Prentice Hall, Inc.

23. 11.3 How Are Single Traits Inherited?
Mendel’s Hypothesis Can Predict the Outcome of New Types of Single-Trait Crosses
Copyright © 2006 Pearson Prentice Hall, Inc.

24. Copyright © 2006 Pearson Prentice Hall, Inc.
Seed
shape
smooth
wrinkled
Seed
color
yellow
green
Pod
shape
inflated
constricted
Pod
color
green
yellow
Flower
color
purple
white
Figure: 11_05
Title:
Traits of pea plants that Mendel studied
Caption:
Flower
location
at leaf
junctions
at tips of
branches
Plant
size
tall
(1.8 to
2 meters)
dwarf
(0.2 to 0.4
meters)
Copyright © 2006 Pearson Prentice Hall, Inc.

25. 11.4 How Are Multiple Traits Inherited?
Mendel Concluded That Multiple Traits Are Inherited Independently
Figure Predicting genotypes and phenotypes for a cross between parents that are heterozygous for two traits (p. 173)
Figure Independent assortment of alleles (p. 174)
Copyright © 2006 Pearson Prentice Hall, Inc.

26. What if 2 characteristics are different?
Di-hybrid cross
2 characteristics differ simultaneously…
You get independent assortment – separate out individually during gamete formation, do not effect each other
Result: 9:3:3:1 genotype
Copyright © 2006 Pearson Prentice Hall, Inc.

27. SsYy
self-fertilize
eggs 1 — 4 1 — 4 1 — 4 1 — 4 SY Sy sY sy 1 — 4 SY 1 — 16 1 — 16 1 — 16 1 — 16
SSYY
SSYy
SsYY
SsYy 1 — 4
Figure: 11_06
Title:
Predicting genotypes and phenotypes for a cross between parents that are heterozygous for two traits
Caption:
In pea seeds, yellow color (Y) is dominant to green (y) and smooth shape (S) is dominant to wrinkled (s). In this cross, both parents are heterozygous for each trait (or a single individual heterozygous for both traits self-fertilizes). There are now 16 boxes in the Punnett square. In addition to predicting all the genotypic combinations and the 9:3:3:1 overall phenotypic ratio, the Punnett square predicts 3/4 yellow seeds, 1/4 green seeds, 3/4 smooth seeds, and 1/4 wrinkled seeds, just as we would expect from crosses made of each trait separately. Sy 1 — 16 1 — 16 1 — 16 1 — 16
SSyY
SSyy
SsyY
Ssyy
sperm 1 — 4 sY 1 — 16 1 — 16 1 — 16 1 — 16
sSYY
sSYy
ssYY
ssYy 1 — 4 sy 1 — 16 1 — 16 1 — 16 1 — 16
sSyY
sSyy
ssyY
ssyy
Copyright © 2006 Pearson Prentice Hall, Inc.

28. Copyright © 2006 Pearson Prentice Hall, Inc.
pairs of alleles on homologous
chromosomes in diploid cells
chromosomes replicate
replicate homologous
pair during metaphase
of meiosis I,
orienting like this
or like this
meiosis I
Figure: 11_07
Title:
Independent assortment of alleles
Caption:
Chromosome movements during meiosis produce independent assortment of alleles, as shown here for two genes. Each possible combination is equally likely, producing gametes in the proportions ¼ SY, ¼ sy, and ¼ Sy.
meiosis II SY sy Sy sY
independent assortment produces four equally
likely allele combinations during meiosis
Copyright © 2006 Pearson Prentice Hall, Inc.

29. 11.5 How Are Genes Located on the Same Chromosome Inherited?
Genes on the Same Chromosome Tend to Be Inherited Together
11_UN08 Pair of homologous chromosomes (p. 175)
Copyright © 2006 Pearson Prentice Hall, Inc.

30. flower color gene pollen shape gene purple allele, P long allele, L
Figure: 11_UN08
Title:
Pair of homologous chromosomes
Caption:
red
allele, p
round
allele, I
Copyright © 2006 Pearson Prentice Hall, Inc.

31. 11.5 How Are Genes Located on the Same Chromosome Inherited?
Crossing Over Can Create New Combinations of Linked Alleles
Copyright © 2006 Pearson Prentice Hall, Inc.

32. 11.6 How Is Sex Determined?
Figure Photomicrograph of human sex chromosomes (p. 175)
Figure Sex determination in mammals (p. 176)
Copyright © 2006 Pearson Prentice Hall, Inc.

33. Copyright © 2006 Pearson Prentice Hall, Inc.
Figure: 11_08
Title:
Photomicrograph of human sex chromosomes
Caption:
Notice the small size of the Y chromosome, which carries relatively few genes.
Y chromosome
X chromosome
Copyright © 2006 Pearson Prentice Hall, Inc.

34. Copyright © 2006 Pearson Prentice Hall, Inc.
female parent
eggs
Figure: 11_09
Title:
Sex determination in mammals
Caption:
Male offspring receive their Y chromosome from the father. Female offspring receive the father’s X chromosome (labeled Xm). Both male and female offspring receive an X chromosome (either X1 or X2) from the mother.
male parent
female offspring
sperm
male offspring
Copyright © 2006 Pearson Prentice Hall, Inc.

35. 11.8 Do the Mendelian Rules of Inheritance Apply to All Traits?
No!
Incomplete Dominance Produces Intermediate Phenotypes
Figure Incomplete dominance (p. 177)
Copyright © 2006 Pearson Prentice Hall, Inc.

36. Incomplete dominance = Pink flowers, a combo of Red and white.
Thus heterozygous alleles are
both dominant
and effect equally.
Phenotype +
Genotype =
1:2:1 RR
R´R´
F1:
RR´
RR´
F2: 1 — 2 1 — 2 R
eggs R´
Figure: 11_10
Title:
Incomplete dominance
Caption:
The inheritance of flower color in snapdragons is an example of incomplete dominance. (In such cases, we use capital letters for both alleles, here R and R’) Heterozygotes (RR’) have pink flowers, whereas the homozygotes are red (RR) or white (R’R’). 1 — 2 R 1 — 4 1 — 4 RR
RR´
sperm 1 — 2 R´ 1 — 4 1 — 4
RR´
R´R´
Copyright © 2006 Pearson Prentice Hall, Inc.

37. 11.8 Do the Mendelian Rules of Inheritance Apply to All Traits?
A Single Gene May Have Multiple Alleles
Figure E11.1 Cystic fibrosis (p. 179)
Table Human Blood Group Characteristics (p. 178)
Copyright © 2006 Pearson Prentice Hall, Inc.

38. 2 alleles effect 1 trait – codominance, both phenotypes expresseed
Figure: 11_T01
Title:
Human Blood Group Characteristics
Caption:
2 alleles effect 1 trait – codominance, both phenotypes expresseed
In heterozygous cross
Copyright © 2006 Pearson Prentice Hall, Inc.

39. 11.8 Do the Mendelian Rules of Inheritance Apply to All Traits?
Other exceptions…
The Environment Influences the Expression of Genes
Figure Environmental influence on phenotype (p. 178)
NATURE vs. NURTURE debates
Copyright © 2006 Pearson Prentice Hall, Inc.

40. Others…
Pleiotropy – 1 gene effects lots of characteristics (sickle cell anemia)
Polygenic inheritance – additive effect of 2+ genes = continuum, skin color
Sex linked genes – (law of independent assortment is not ALWAYS the case) i.e. color blindness example (men)
What can we do – amniocentisis, pedigree charts…
Copyright © 2006 Pearson Prentice Hall, Inc.