1. 9.2 Experimental genetics began in an abbey garden
Gregor Mendel
Augustinian monk who taught natural science to high school students
Mendel's brilliant performance at school as a youngster encouraged his family to support his pursuit of a higher education, but their resources were limited, so Mendel entered an Augustinian monastery
Gregor Mendel discovered principles of genetics in experiments with the garden pea
Mendel showed that parents pass heritable factors to offspring (heritable factors are now called genes)
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2. 9.2 Experimental genetics began in an abbey garden
Crosses meticulously documented
Crosses numerically/statistically analyzed
Scientists of 1860s did not understand and appreciate
Work lost in journals for 50 years
Rediscovered in 1900s independently by 3 scientists

3. Terms to know and understand
The phenotype is the appearance or expression of a trait
Genes are found in alternative versions called alleles; a genotype is the listing of alleles an individual carries for a specific gene
If the alleles differ, the dominant allele determines the organism’s appearance, and the recessive allele has no noticeable effect
Homozygous individuals have the same allele on both homologues
Heterozygous individuals have a different allele on each homologue

4. Mating of plants can be controlled
Each pea plant has sperm-producing organs (stamens) and egg-producing organs (carpels)
Cross-pollination (fertilization between different plants) can be achieved by dusting one plant with pollen from another
Figure14.2 Crossing pea plants

5. The true-breeding parents are the P generation
In a typical experiment, Mendel mated two contrasting, true-breeding varieties
The true-breeding parents are the P generation
The hybrid offspring of the P generation are called the F1 generation
When F1 individuals self-pollinate, the F2 generation is produced
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6. Parents (P) Offspring (F1)
White 1
Removed
stamens from
purple flower
Stamens
Carpel 2
Transferred
pollen from stamens of white
flower to carpel of purple flower
Parents
(P)
Purple 3
Pollinated carpel
matured into pod 4
Planted seeds
from pod
Offspring
(F1)

7. Mendel’s crosses led to questions
When Mendel crossed contrasting, true-breeding white and purple flowered pea plants, all of the F1 hybrids were purple
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8. EXPERIMENT P Generation (true-breeding parents) Purple flowers White
Fig
EXPERIMENT
P Generation
(true-breeding
parents) 
Purple
flowers
White
flowers
Figure 14.3 When F1 hybrid pea plants are allowed to self-pollinate, which traits appear in the F2 generation?

9. EXPERIMENT P Generation (true-breeding parents) Purple flowers White
Fig
EXPERIMENT
P Generation
(true-breeding
parents) 
Purple
flowers
White
flowers
F1 Generation
(hybrids)
All plants had
purple flowers
Figure 14.3 When F1 hybrid pea plants are allowed to self-pollinate, which traits appear in the F2 generation?

10. Mendel’s crosses led to questions
When Mendel crossed contrasting, true-breeding white and purple flowered pea plants, all of the F1 hybrids were purple
When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers, but some had white
Mendel discovered a ratio of about three to one, purple to white flowers, in the F2 generation
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11. EXPERIMENT P Generation (true-breeding parents) Purple flowers White
Fig
EXPERIMENT
P Generation
(true-breeding
parents) 
Purple
flowers
White
flowers
F1 Generation
(hybrids)
All plants had
purple flowers
Figure 14.3 When F1 hybrid pea plants are allowed to self-pollinate, which traits appear in the F2 generation?
F2 Generation
705 purple-flowered
plants
224 white-flowered
plants

12. Questions are . . . Questions that arise Answers?
Questions that arise
Why does one trait seemed to disappear in the F1 generation?
Why does that trait reappear in one quarter of the F2 offspring?
Answers?

13. These inherited factors are what we now call a genes
Mendel reasoned that only the purple flower factor was affecting flower color in the F1 hybrids
Mendel called the purple flower color a dominant trait and the white flower color a recessive trait
These inherited factors are what we now call a genes
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14. Table 14-1

15. Four related concepts make up this model
Mendel’s Model
Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring
Four related concepts make up this model
These concepts can be related to what we now know about genes and chromosomes
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16. The first concept is that alternative versions of genes account for variations in inherited characters
For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers
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17. 2. The second concept is that for each character an organism inherits two alleles, one from each parent
Mendel made this deduction without knowing about the role of chromosomes
The two alleles at a locus on a chromosome may be identical, as in the true-breeding plants of Mendel’s P generation - homozygous
Alternatively, the two alleles at a locus may differ, as in the F1 hybrids - heterozygous
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18. 3. The third concept is that if the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance
In the flower-color example, the F1 plants had purple flowers because the allele for that trait is dominant
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19. 4. The fourth concept, now known as the law of segregation, states that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes
Thus, an egg or a sperm gets only one of the two alleles that are present in the somatic cells of an organism
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20. Let’s look at this example again
Before we were only looking at phenotype just like Gregor Mendel
Let’s apply his hypotheses and look at genotype as well
Draw a Punnett square that would represent true breeding purple flowers crossed with true breeding white flowers

21. To make a Punnett Square . . .
The possible combinations of sperm and egg can be shown using a Punnett square, a diagram for predicting the results of a genetic cross between individuals of known genetic makeup
A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele
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22. Let’s look at this example again
Before we were only looking at phenotype just like Gregor Mendel
Let’s apply his hypotheses and look at genotype as well PP pp Pp P P p Pp Pp Pp Pp p
Flowers will all be purple because of dominance

23. Let’s look at this example again
Before we were only looking at phenotype just like Gregor Mendel
Let’s apply his hypotheses and look at genotype as well
Draw the Punnett square that would represent two of the F1 generation breedingt PP pp Pp
This cross gives us the F1 generation P P p Pp Pp Pp Pp p

24. Let’s look at this example again
Allow F1 generation to self-pollinate and fill out the next Punnett square PP pp Pp P p P PP Pp Pp pp p

25. Let’s look at this example again
Allow F1 generation to self-pollinate and fill out the next Punnett square PP pp Pp P p P PP Pp PP Pp Pp pp Pp pp p
¾ of flowers will all be purple because of dominance. ¼ will be white.

26. Let’s look at this example againPP pp Pp P p P PP Pp PP Pp Pp pp Pp pp p
Phenotypic ratio
3 purple : 1 white
Genotypic ratio
1 PP : 2 Pp : 1 pp
Single trait cross

27. 9.3 Mendel’s law of segregation describes the inheritance of a single character
Four Hypotheses
Genes are found in alternative versions called alleles; a genotype is the listing of alleles an individual carries for a specific gene
For each characteristic, an organism inherits two alleles, one from each parent; the alleles can be the same or different
A homozygous genotype has identical alleles
A heterozygous genotype has two different alleles
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28. 9.3 Mendel’s law of segregation describes the inheritance of a single character
Four Hypotheses
If the alleles differ, the dominant allele determines the organism’s appearance, and the recessive allele has no noticeable effect
The phenotype is the appearance or expression of a trait
The same phenotype may be determined by more than one genotype
Law of segregation: Allele pairs separate (segregate) from each other during the production of gametes so that a sperm or egg carries only one allele for each gene
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29. Humans show dominant and recessive traits
Three traits that are determined by single genes with alternate alleles
Dominant Traits
Recessive Traits
The dominant allele determines the phenotype when at least one copy is present
Freckles
No freckles
PTC taste strips
Widow’s peak
Straight hairline
Attached earlobe
Free earlobe

30. Some Genetic Disorders/Anomalies
Polydactyly - dominant
Tay Sachs - recessive
Cystic Fibrosis - recessive
Huntington’s Disease - dominant
Sickle Cell Anemia - recessive
Cause?
Single substitution of an amino acid in hemoglobin

31. Polydactyly
Alfredo Alfonseca "The Six Shooter", former Chicago Cubs relief pitcher
Six fingers and toes on each hand, all functional

32. 9.8 Genetic traits in humans can be tracked through family pedigrees
A pedigree
Shows the inheritance of a trait in a family through multiple generations
Demonstrates dominant or recessive inheritance
Can also be used to deduce genotypes of family members
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33. First generation (grandparents) Ff Ff ff Ff Second generationFf Ff ff Ff
Second generation
(parents, aunts,
and uncles) FF ff ff Ff Ff ff or Ff
Third generation
(two sisters) ff FF
Figure 9.8B Pedigree showing inheritance of attached versus free earlobe in a hypothetical family. or
Female
Male Ff
Affected
Marriage
Unaffected
Siblings
Pedigree for a family inheritance of a recessive trait such as deafness

34. Recessive disease Rr rr ? rr rr

35. Dominant disease

36. Dominant disease dd dd dd Dd dd

37. Huntington’s Disease - handout

38. Huntington’s Disease Questions
Questions
What are the chances of a parent with HD passing with HD passing the gene on to any one of his or her children?
Thinking of all the ways in which the number of repeats may be passed on to children, discuss the possibility that John may get an HD gene
from his mother
from his father
From which parent did Dink get the gene for HD? Explain how you can tell.
Do you expect John's mother to show symptoms of HD? Why or why not.

39. Huntington’s Disease Questions
Questions
John's Aunt Barbara refused to have the test for HD.
Discuss some reasons that she may have had for coming to that decision.
When she applied for a job as an airline pilot, the company, knowing of the occurrence of HD in the family, insisted that she be tested. Does the company have the right to require the test? Explain why or why not.
When John reaches the age of 18, he may make the decision of whether or not to be tested for the HD gene. Consider this question from the perspective of John, John's future children, John's future wife, John's employer, John's medical insurer.
Explain to John why he should have the test done.
Explain to John why he should not have the test done.

40. VARIATIONS ON MENDEL’S LAWS
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41. 9.11 Incomplete dominance results in intermediate phenotypes
Incomplete dominance
Neither allele is dominant over the other
Expression of both alleles is observed as an intermediate phenotype in the heterozygous individual
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42. P generation Red RR White rr Gametes R r F1 generation Pink Rr Gametes
Red RR
White rr
Gametes R r
F1 generation
Pink Rr
Gametes 1 – 2 R 1 – 2 r
Sperm 1 – 2 R 1 – 2 r
F2 generation RR rR 1 – 2 R
Eggs Rr rr 1 – 2 r

43. Genotypes: HH
Homozygous
for ability to make
LDL receptors Hh
Heterozygous hh
Homozygous
for inability to make
LDL receptors
Phenotypes:
LDL
LDL
receptor
Cell
Normal
Mild disease
Severe disease

44. 9.12 Many genes have more than two alleles in the population
Multiple alleles
More than two alleles are found in the population
A diploid individual can carry any two of these alleles
The ABO blood group has three alleles, leading to four phenotypes: type A, type B, type AB, and type O blood
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45. 9.12 Many genes have more than two alleles in the population
Codominance
Neither allele is dominant over the other
Expression of both alleles is observed as a distinct phenotype in the heterozygous individual
Observed for type AB blood
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46. Blood
Group
(Phenotype)
Genotypes
Red Blood Cells O ii
IAIA or
IAi A
Carbohydrate A
IBIB or
IBi B
Carbohydrate B AB
IAIB

47. Phenotype Genotype A IA IA , IA i B IB IB , IB i AB IA IB O i i
Blood Type
Phenotype
Genotype A
IA IA , IA i B
IB IB , IB i AB
IA IB O
i i

48. Blood Genetics
IA i
IA IB
IB i
IA i
i i IB i

49. Blood Typing Questions
Given a mom with blood type AB and child with blood type A, what are the possible blood types of the father?
IA IB
IAIA
IA i IA
? ____ i
IAIA
? ____ IA

50. Dominance Worksheet
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51. 9.13 A single gene may affect many phenotypic characters
Pleiotropy
One gene influencing many characteristics
The gene for sickle cell disease
Affects the type of hemoglobin produced
Affects the shape of red blood cells
Causes anemia
Causes organ damage
Is related to susceptibility to malaria
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52. Individual homozygous for sickle-cell allele
Sickle-cell (abnormal) hemoglobin
Abnormal hemoglobin crystallizes,
causing red blood cells to become sickle-shaped
Sickle cells
Clumping of cells
and clogging of
small blood vessels
Breakdown of
red blood cells
Accumulation of
sickled cells in spleen Fi
Physical
weakness
Heart
failure
Pain and
fever
Brain
damage
Damage to
other organs
Spleen
damage
Anemia
Impaired
mental
function
Pneumonia
and other
infections
Kidney
failure
Paralysis
Rheumatism

53. 9.14 A single character may be influenced by many genes
Polygenic inheritance
Many genes influence one trait
Skin color is affected by at least three genes
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54. aabbcc (very light) AABBCC (very dark) AaBbCc AaBbCc
P generation
aabbcc
(very light)
AABBCC
(very dark)
F1 generation
AaBbCc
AaBbCc
Sperm 8 – 1 8 – 1 8 – 1 8 – 1 8 – 1 8 – 1 8 – 1 8 – 1
F2 generation 8 – 1 8 – 1 8 – 1 64 –– 20 8 – 1
Eggs 8 – 1 64 –– 15 8 – 1 8 – 1
Fraction of population 8 – 1 64 –– 6 64 –– 1 64 –– 1 64 –– 6 64 –– 15 64 –– 20 64 –– 15 64 –– 6 64 –– 1
Skin color

55. 9.15 The environment affects many characters
Phenotypic variations are influenced by the environment
Skin color is affected by exposure to sunlight
Susceptibility to diseases, such as cancer, has hereditary and environmental components
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56. Environment—It can fool you

57. Environment—It can fool you !
The hydrangea flower color is controlled first by flower color genes similar to those in the pea.
Purple vs. white
has complete
dominance. But,
pink vs. blue is
controlled by the
acidity of the soil

58. Environment—It can fool you !
The hydrangea flower color is controlled first by flower color genes similar to those in the pea.
Purple vs. white
has complete
dominance. But,
pink vs. blue is
controlled by the
acidity of the soil