1. Fig. 14-1

2. Fig. 14-2a
TECHNIQUE 1 2
Parental
generation
(P)
Stamens
Carpel 3 4

3. Monohybrid Cross for Flower Color
Parents differ for one trait
Parents are true breeding
Analyze parents for two generations, F1 and F2
Examine large number of progeny
Parentals X
Purple White X
F1 Generation
100% Purple
F2 Generation
Purple and White Flowered Plants
705 purple and 224 white
3:1 Ratio

5. Mendel’s Postulates (based on monohybrid crosses)
Alternative versions of genes (alleles) account for variation in characteristics
Each individual has two alleles for each gene, one inherited from each parent
If the individual has two different alleles, one allele is dominant to the other which is recessive
The two alleles randomly segregate during gamete formation with 50% of the gametes having one allele and 50% having the other allele.

6. Important Terminology
Genotype – the list of alleles an individual possesses.
Phenotype – a measurable characteristic displayed by an individual
Homozygote – an individual possessing two identical alleles for a gene
Heterozygote – an individual possessing two different alleles for a gene

7. Allele for purple flowers
Fig. 14-4
Allele for purple flowers
Homologous
pair of
chromosomes
Locus for flower-color gene
Figure 14.4 Alleles, alternative versions of a gene
Allele for white flowers

8. Example testcross

9. Independent Assortment vs Linkage
Parental Combination of
Alleles F1
Genotype of
F1Gametes YR yr YR yr Yr yR
Parental Only % Parental 50% Recombinant

10. Linked Independent AssortYR yr YR yr Yr yR
Law of Independent Assortment: Each pair of alleles segregates independently of other pairs of alleles during gamete formation

11. Dihybrid Testcross to Detect Independent Assort
YYRR X yyrr
YrRr X yyrr YR Yr yR yr
Dihybrid
yyRf
Yyrr
yyrr
YyRr
Eggs
Sperm yr YR Yr yR
Phenotypic ratio
1:1:1:1
Ratio of parental:Recombinant
1:1

12. Independent Assortment and Meiosis

13. What is Mendel’s Law of independent assortment?
Take home message:
What is Mendel’s Law of independent assortment?
A gene is distributed into gametes independently
of how other genes are distributed.

14. Frequency of Dominant Alleles
Dominant alleles are not necessarily more common in populations than recessive alleles
For example, one baby out of 400 in the United States is born with extra fingers or toes
The allele for this unusual trait is dominant to the allele for the more common trait of five digits per appendage
In this example, the recessive allele is far more prevalent than the population’s dominant allele
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

15. Variations on Mendel Allelic Interactions Sex Linkage
Mendel focused on traits based clearly on dominant and recessive alleles.
However , the expression pattern of genes for some traits are not so straight forward.
Allelic Interactions
Sex Linkage
Complete/Partial Linkage
Organellular Genes

16. Allelic Interactions Complete Dominance Partial Dominance Codominance
Multiple Alleles
Pleiotropy
Multigenic traits
Environmental Interactions

17. Complete Dominance – the heterozygote is indistinguishable from one of the two homozygotes.
Rh factor – a protein found on the surface of the blood cells in some people.
Two Alleles
Rh+ - possess the Rh factor
Rh- - lacks the Rh factor
Heterozygote
Rh+,Rh- - possess the Rh factor and has positive type blood.

18. Partial Dominance
Hypercholesterolemia – defect in LDL receptor mediated endocytosis.
Two alleles
Hc+ - functional LDL receptor
Hc- defective LDL receptor
Homozygotes
Hc-,Hc- super high serum cholesterol early onset of heart disease.
Hc+,Hc+ normal serum cholesterol- typical risk of heart disease.
Hc+,Hc- high serum cholesterol – high risks of heart disease.

19. Codominance – Heterozygote expresses both alleles (with no blending as in partial dominance)
Two non-identical alleles of a gene are both expressed in heterozygotes, so neither is dominant or recessive. Co-dominance may occur in multiple allele systems.
Multiple Alleles – More than two alleles in the population, although any individual still has only two alleles.
ABO Blood type – carbohydrate attached to surface protein of blood cells.
Three Alleles
IA – A type blood
IB – B type blood
IO – O type blood
Six genotypes
Homozygotes Heterozygotes
IA,IA IA,IB
IB,IB IA,IO
IO,IO IB,IO
A type
B type
AB type
O type

20. Pleiotropy – one gene may influence multiple traits.
Cystic Fibrosis
Two Alleles
CF – healthy allele –functional Cl transporter (dominant)
cf – cystic fibrosis allele – non functional Cl transporter (recessive)
Homozygotes for cf exhibit several symptoms
- mucus filled lungs
- kidney failure
- digestive problems
- salty sweat

21. Genes encoding products used throughout the body are the ones most likely to be pleiotropic.
Sergei Rachmaninoff
Mutations in the fibrillin gene cause a disorder called Marfan syndrome.
Fibrillin (long fibers) impart elasticity to the heart skin, blood vessels, tendons and other parts of the body. In Marfan syndrome the fibrillin are defective or not present.
The aorta is particularly affected, can rupture during exercise.
Hard to diagnose, affected people are typically, tall, thin , loose jointed. 1 in 5000

22. Marfan Syndrome. Become Aware Haris Charalambous, a 6’10’’ Centre, died during a light training session at Toledo University on 9 October He was 21 years of age. He began his basketball career at Manchester Magic at age 13 and left the club at 18 to take up his scholarship at Toledo. He was later diagnosed with Marfan Syndrome, which is a genetic disease associated with abnormally tall people. At the time, neither the club nor Toledo knew of this situation
Syndrome are a tall thin physique, disproportionately long limbs,
fingers and toes, flat feet, spinal curvature and abnormally shaped
narrow chest.

23. Multigenic Traits – traits influenced by more than one gene.
Epistasis – Alleles at one gene mask the expression of alleles at a second gene.
Example – black/ brown gene of mice - albino gene
B – black is dominant C – allows pigment (dominant)
b – brown is recessive c – prevents pigment (recessive)

24. 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4  BbCc BbCc Sperm Eggs BBCC BbCC BBCc
Fig 
BbCc
BbCc
Sperm
1/4
1/4
1/4
1/4 BC bC Bc bc
Eggs
1/4 BC
BBCC
BbCC
BBCc
BbCc
1/4 bC
BbCC
bbCC
BbCc
bbCc
1/4 Bc
Figure An example of epistasis
BBCc
BbCc
BBcc
Bbcc
1/4 bc
BbCc
bbCc
Bbcc
bbcc 9
: 3
: 4

25. Polygenic Inheritance – many genes influencing a single trait
Results in a continuum of variation (height in humans, skin pigmentation in humans,
Fat content of milk cows, yield of kernels in corn)
# dark alleles
1/ / / / /64 6/64 1/64

27. Multifactoral traits – traits influenced by both the genetic and environment.
Examples Flower color in hydrangea Skin pigmentation in humans Milk yield in cows

28. Sex-linked genes follow specific patterns of inheritance
For a recessive sex-linked trait to be expressed
A female needs two copies of the allele
A male needs only one copy of the allele
Sex-linked recessive disorders are much more common in males than in females
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

29. Sex-linked genes follow specific patterns of inheritance
For a recessive sex-linked trait to be expressed
A female needs two copies of the allele
A male needs only one copy of the allele
Sex-linked recessive disorders are much more common in males than in females
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

30. EXPERIMENT RESULTS CONCLUSION Fig. 15-4 + w w + w w + +
Generation F1
All offspring had red eyes
Generation
RESULTS F2
Generation
CONCLUSION P + X w X w
Generation X  Y + w w
Sperm
Eggs F1 + +
Figure 15.4 In a cross between a wild-type female fruit fly and a mutant white-eyed male, what color eyes will the F1 and F2 offspring have? + w w
Generation w w + w
Sperm
Eggs + + + w w F2 w
Generation + w w w w + w

32. Reciprocal Crosses ♂ ♀ ♂ ♀ Fruit flies use XY sex chromosomes
X-linked white eye gene
R – normal red eyes (dominant)
r - white eyes (recessive)
White eye X Red eye Red eye X White eye
♂ ♀ ♂ ♀
Assume flies came from true breeding cultures

33. ♂ ♀ ♂ ♀ White eye X Red eye Red eye X White eye R Y r Y r Rr rY R Rr
♂ ♀ ♂ ♀
rY RR RY rr
Sperm
Sperm
R Y
r Y r Rr rY R Rr RY
Eggs
Eggs
50%
Red
female
50%
White
male
50%
Red
female
50%
Red
male

34. Pedigree Analysis
A pedigree is a family tree that describes the interrelationships of parents and children across generations
Inheritance patterns of particular traits can be traced and described using pedigrees
Key
Male
Female
Affected
male
female
Mating
Offspring, in
birth order
(first-born on left)
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

35. (a) Is a widow’s peak a dominant or recessive trait?
Fig b
1st generation
(grandparents) Ww ww ww Ww
2nd generation
(parents, aunts,
and uncles) Ww ww ww Ww Ww ww
3rd generation
(two sisters) WW ww
Figure 14.15a Pedigree analysis or Ww
Widow’s peak
No widow’s peak
(a) Is a widow’s peak a dominant or recessive trait?

36. Pedigrees can also be used to make predictions about future offspring
We can use the multiplication and addition rules to predict the probability of specific phenotypes
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

37. The Behavior of Recessive Alleles
Recessively inherited disorders show up only in individuals homozygous for the allele
Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal (i.e., pigmented)
Albinism is a recessive condition characterized by a lack of pigmentation in skin and hair
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

38. Parents Normal Normal Aa Sperm A a Eggs Aa AA A Normal (carrier)
Fig
Parents
Normal
Normal Aa  Aa
Sperm A a
Eggs Aa AA A
Normal
(carrier)
Normal
Figure Albinism: a recessive trait Aa aa a
Normal
(carrier)
Albino

39. If a recessive allele that causes a disease is rare, then the chance of two carriers meeting and mating is low
Consanguineous matings (i.e., matings between close relatives) increase the chance of mating between two carriers of the same rare allele
Most societies and cultures have laws or taboos against marriages between close relatives
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

40. Cystic Fibrosis
Cystic fibrosis is the most common lethal genetic disease in the United States,striking one out of every 2,500 people of European descent
The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes
Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

41. Sickle-Cell Disease
Sickle-cell disease affects one out of 400 African-Americans
The disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells
Symptoms include physical weakness, pain, organ damage, and even paralysis
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

42. Dominantly Inherited Disorders
Some human disorders are caused by dominant alleles
Dominant alleles that cause a lethal disease are rare and arise by mutation
Achondroplasia is a form of dwarfism caused by a rare dominant allele
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

43. Parents Dwarf Normal Sperm Eggs Dwarf Normal Dwarf Normal Dd dd D d Dd
Fig
Parents
Dwarf
Normal Dd  dd
Sperm D d
Eggs Dd dd
Figure Achondroplasia: a dominant trait d
Dwarf
Normal Dd dd d
Dwarf
Normal

44. Huntington’s Disease
Huntington’s disease is a degenerative disease of the nervous system
The disease has no obvious phenotypic effects until the individual is about 35 to 40 years of age
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

45. Multifactorial Disorders
Many diseases, such as heart disease and cancer, have both genetic and environmental components
Little is understood about the genetic contribution to most multifactorial diseases
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

46. Genetic Testing and Counseling
Genetic counselors can provide information to prospective parents concerned about a family history for a specific disease
Tests for Identifying Carriers
For a growing number of diseases, tests are available that identify carriers and help define the odds more accurately
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

47. (b) Chorionic villus sampling (CVS)
Fig
Amniotic fluid
withdrawn
Centrifugation
Fetus
Fetus
Suction tube
inserted
through
cervix
Placenta
Placenta
Chorionic
villi
Uterus
Cervix
Fluid
Bio-
chemical
tests
Fetal
cells
Several
hours
Fetal
cells
Several
hours
Several
weeks
Figure Testing a fetus for genetic disorders
Several
weeks
Several
hours
Karyotyping
(a) Amniocentesis
(b) Chorionic villus sampling (CVS)

48. Newborn Screening
Some genetic disorders can be detected at birth by simple tests that are now routinely performed in most hospitals in the United States
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings