1. Introduction to Mendelian Genetics

2. The Work of Gregor Mendel
A. Genetics is the scientific study of heredity.
Every living thing has a set of characteristics inherited from its parent or parents!

3. B. Gregor Mendel What: Who & Where: Austrian monk, “Father of
Genetics”, born 1822
What:
His work was important to the
understanding of heredity. In
charge of monastery’s garden;
studied traits of pea plants

4. C. So Why Peas? Pea plant flowers are closed Self-fertilizing
True-breeding
Have 7 easily visible traits called phenotypes

6. Every time Mendel crossed 2 different traits, only ONE was seen in the offspring!

7. C. Mendel’s Principles Principle of Dominance Principle of Segregation
Principle of Independent Assortment

8. Back to Mendel’s Experiments…

9. If these hybrids self-pollinate..
The Next Generation
If these hybrids self-pollinate..
The hidden trait returns!
F1 generation: Tt x Tt Result?

10. What happened to Recessive Allele?
Plants with different genotypes
(TT and Tt)
can have the same phenotype (“tall”).

11. Genotype: genetic makeup of organism
Phenotype: physical characteristics of an organism
Genotype
Phenotype
C c
T T
P p

12. D. Principle of Dominance
Definition:
some alleles are dominant and others are recessive. The dominant gene shows up in the phenotype when present.
Example: Smooth peas S
wrinkled peas s

13. E. Principle of Segregation
During sex cell formation, alleles separates from each other
Each gamete has one allele for each trait

14. Each trait is controlled by a gene that is in two contrasting forms
The different forms of a gene are called alleles.

15. Homozygous: two identical alleles
Example: TT or tt or SS or ss
Heterozygous: two different alleles
for the same trait
Example: Tt or Ss

16. II. Probability and Punnett Squares
Why used?
Punnett squares used to predict and compare genetic variations that will result from a cross
The Rules:
Dominant traits are
the 1st letter and
CAPITAL
Recessive are the 2nd
letter and lowercase

17. B. Practice T T t T t T t t T t T t Tall= T short= t
1) If a homozygous tall person was crossed with a homozygous short person, what are probably offspring? T T
Tall= T
short= t t T t T t t T t T t

18. Punnett Square T t T T T T t 1 TT: 2 Tt: 1 tt T t t t t
2) Cross two heterozygous tall parents.
Tall= T
short= t T t
What is the
genotype ratio? T T T T t
1 TT: 2 Tt: 1 tt
What is the
phenotype ratio? T t t t t
3 Tall: 1 short

19. Punnett Square 3) The long-eared allele (L) is dominant
to the short-eared allele (l). Cross a
homozygous long ear with a
homozygous short-ear.
Cross the F1 generation and give the F2 results.

20. III. Independent Assortment
Mendel discovered that genes for different traits segregate independently during gamete formation
Ex. Wrinkled/Smooth and Yellow/Green peas

21. Here is a heterozygous tall, heterozygous purple plant:
B. Dihybrid Cross:
two traits being crossed at the same time
Here is a heterozygous tall, heterozygous purple plant:
T t P p

22. TP Tp tP tp F O I L First Outer Inner Last
How can we figure out the alleles present in the gametes?
F O I L
First Outer Inner Last
Using F.O.I.L., list the possible gametes:
TP Tp tP tp

23. Tall and Purple are dominant to short and white. Example:
Cross two heterozygous tall,
heterozygous purple pea plants.
T t P p x T t P p
There are four possible gametes each parent can make..

24. MOTHER t T P T p P t p
TTPp
TtPP T P
TTPP
TtPp
TtPp
TTPp
TTpp
Ttpp T p
FATHER t P
TtPP
TtPp
ttPP
ttPp
TtPp
Ttpp
ttPp
ttpp t p

25. Results in fractions? Phenotypes: Tall, Purple? Tall, White?
Short, Purple?
Short, White?
Ratio from heterozygous
dihybrid cross is
ALWAYS
9: 3: 3: 1
Alleles assort independently.
9/16
3/16
3/16
1/16

26. Use FOIL to set up these examples:
FfPp:
SSTt:
DdRR: FP Fp fP fp ST ST St St DR DR dR dR

27. IV. Beyond Pure Dominance….
Some alleles are not simply dominant or
recessive..
A. Incomplete dominance:
Alleles are expressed as a blend.
Each allele has a capital letter.
Red= R Yellow= Y

28. Red=R White=W R R R W W R W R W R W W Genotype: 100% RW
1. Cross a red flower with a white flower, showing incomplete dominance.
Red=R
White=W R R R W W R W R W R W W
Genotype: 100% RW
Phenotype: PINK!

31. D. Co-dominance Both traits dominate, seen separately!
Red Horse White Horse

32. Give you ROAN!

33. 1. Example of Codominant Problem
Red feathers are codominant to white feathers in chickens.
CR= red
CW= white
Cross a homozygous Red with a homozygous white feathered chicken. CR CR
GENOTYPE:
100% CW CR CW CR CW CR CW
PHENOTYPE:
100%
Red and white mixed feathers CW CR CW CR CW

34. C. Multiple Alleles One trait, many allele options!
But remember: an individual cannot inherit more than two actual alleles, even if more than two possible alleles exist.
Example: Blood type
A, B, AB, O!

35. Blood Type Problem I IA IA IB IA IB IA i i
Cross a homozygous Type A with a heterozygous Type B. What are the possible phenotypes of offspring? IA IA IB IA IB
Phenotypes:
50% Type AB
50% Type A IA i i

36. Blood Type Problem II i IA IB IA IB IB i IA i i i i
Cross a heterozygous Type A man with a heterozygous Type B woman. Is it possible for them to have an O child? i IA
Phenotypes:
25% Type AB
25% Type A
25% Type B
25% Type O IB IA IB IB i IA i i i i

37. Blood Type Problem III Rh- Rh+ Rh- Rh+ Rh- Rh- Rh- Rh+ Rh- Rh- Rh- Rh-
Cross a heterozygous Rh+ man with a Rh- woman. What are the possible phenotypes of offspring?
Rh-
Rh+
Phenotypes:
50% Type +
50% Type -
Rh-
Rh+
Rh-
Rh-
Rh-
Rh+
Rh-
Rh-
Rh-
Rh-

38. Rabbits have 4 basic colors (alleles!)
brown
chinchilla or grey
It is recessive to brown.
himalayan or white with black tips.
It is recessive to both brown and chinchilla.
albino
It is recessive to all.

39. Chinchilla
Full color
AIbino
Himalayan

40. D. Polygenic Traits Traits produced by many genes with many alleles
Most human traits are polygenic
Most variety of expression
There are 3 genes that contribute to skin color.. And many alleles for each gene!

42. More examples:
Height
Weight
Intelligence
Eye color

43. V. Sex Determination
In humans, the X and Y chromosomes control the sex of offspring.
Outcome is always 50% chance of a male, and 50% chance of a female

44. Sex-linked traits XR XR Xr y
Traits controlled by genes on the sex chromosomes are called sex-linked.
Alleles for sex-linked traits are written as superscripts on the X chromosomes only.
Example: Red eyes in fruit flies found in females
Males tend to have white eyes, which is recessive. XR XR Xr y

45. X and Y sex chromosomes are non-homologous
Any allele on the X chromosome will NOT be masked by a matching allele on the Y chromosome.

46. Why are sex-linked disorders more common in males than in females?
Males have just one X chromosome containing an allele. So all X-linked alleles are automatically expressed in males, even if they are recessive.

47. C. Examples of Sex-Linked
Color blindness
Duchenne Muscular Dystrophy
Hemophilia

48. Frank and Awilda at Breakfast
Frank: Are you sure you want to wear that new shirt to work today? A green and red shirt like that would be better for Christmas, not for St. Patrick's Day.
Awilda: Oh no! Not again! I hate being color blind! I really thought this shirt was just different shades of green. Where's the red?
At Dinner That Night
Awilda: We should try to find a way to make sure we only have sons, no daughters. I don't want to have any daughters who might be color blind and have so many problems like I do. Color blindness wouldn't matter so much for a boy.

49. Frank: Remember, the doctor said that, since I'm not color blind, none of our daughters would be color blind, only our sons.
Awilda: That doesn't make any sense. Our daughters should be color blind like me and our sons should be normal like you.
Frank: No, the doctor said the gene for color blindness is on the X chromosome, so only our sons will inherit your colorblindness.
Awilda: I don't agree. Girls have more X chromosomes than boys, so girls should be more likely to be color blind.

50. Help Frank to explain to Awilda why the doctor was right by answering the following questions.
1. What are the genotypes of Awilda and Frank? (Since the allele for color blindness is recessive and located on the X chromosome, use the symbol Xc for an X chromosome with the allele for color blindness and XC for an X chromosome with the normal allele.)
Awilda: Frank:
Xc Xc
XC y

51. X X X XC Xc XC Xc Xc y Xc y y C = normal vision c = colorblind
2. Draw the Punnett square for this couple and their children. In this Punnett Square, circle each daughter and use arrows to indicate any colorblind offspring. c c X X C X
XC Xc
XC Xc
Xc y
Xc y y
C = normal vision
c = colorblind

52. 3. Write an explanation to help Awilda understand why their daughters will not be colorblind like their mother. 4. Explain why their sons will be colorblind even though their father has normal vision. 5. Explain why having two X chromosomes decreases a person’s risk of color blindness, instead of increasing their risk, as Awilda fears.

53. Practice Problems
Hemophilia is an X-linked recessive disease. Cross a heterozygous female with a normal male.
Duchenne Muscular Dystrophy is an X-linked recessive disease. Cross a heterozygous female with a normal male.

54. Examples of Sex-linked Diseases
Colorblindness

55. D. Sex-Limited Traits
A few traits are not caused by genes on the X or the Y chromosome but still occur in only one sex of animals
Examples
Antlers in deer- only bucks have antlers
Milk yield in bovines is a trait expressed
by only cows (females)
Eggs in chickens

56. E. Sex-Influenced
Some traits are sex-influenced because of genes that interact with a substance (like hormones) that is not produced equally in males and females
Example: early pattern baldness

57. Baldness Sample Problem
Baldness is a dominant trait. Heterozygous men are bald, BUT heterozygous women have all hair.
Cross a Heterozygous woman with a normal hair male. Bb x bb
Genotype - Phenotype
If all girls?
If all boys? B b
B b b
b b b
B b
b b

58. Human Genetic Disorders

59. Down Syndrome Symptoms:
learning difficulties, mental retardation, a characteristic facial appearance, and poor muscle tone
Detection/
Frequency?
1 in 1000 live born infants
Mode of Inheritance/Chromosome
Chromosome 21, nondisjunction
Treatment
Physical therapy for muscle weakness, heart is checked regularly for problems, educational therapy
Prognosis
May have shortened life span

61. Marfan Syndrome Symptoms:
Myopia, retinal detachment, bone overgrowth and loose joints, may have long thin arms and legs, bent chest inwards or outwards
Detection/
Frequency?
occurring 1 in 10,000 to 20,000 individuals
Mode of Inheritance/
Chromosome
Autosomal dominant, Chromosome 15
Treatment
Surgery to correct skeletal problems, sight issues fixed with glasses, must avoid contact sports

63. Red-Green Colorblindness
Symptoms:
Detection/
Frequency?
Mode of Inheritance/Chromosome
Treatment
Prognosis

65. Retinoblastoma Symptoms: Detection/ Frequency?
Mode of Inheritance/Chromosome
Treatment
Prognosis

67. Albinism Symptoms: Detection/ Frequency?
Mode of Inheritance/Chromosome
Treatment
Prognosis

69. Duchenne Muscular Dystrophy
Symptoms:
Detection/
Frequency?
Mode of Inheritance/Chromosome
Treatment
Prognosis

71. Turner Syndrome Symptoms: Detection/ Frequency?
Mode of Inheritance/Chromosome
Treatment
Prognosis

73. Dwarfism (Achondroplasia)
Symptoms:
Detection/
Frequency?
Mode of Inheritance/
Chromosome
Treatment
Prognosis

75. Hemophilia Symptoms: Detection/ Frequency? Mode of Inheritance/
Chromosome
Treatment
Prognosis

77. Huntington’s Disease Symptoms: Detection/ Frequency?
Mode of Inheritance/Chromosome
Treatment
Prognosis

79. Tay-Sach’s Symptoms: Detection/ Frequency?
Mode of Inheritance/Chromosome
Treatment
Prognosis

81. Klinefelter’s Symptoms: Detection/ Frequency?
Mode of Inheritance/Chromosome
Treatment
Prognosis

83. Cystic Fibrosis Symptoms: Detection/ Frequency?
Mode of Inheritance/Chromosome
Treatment
Prognosis

85. Sickle Cell Anemia Symptoms: Detection/ Frequency?
Mode of Inheritance/Chromosome
Treatment
Prognosis

87. Phenylketonuria (PKU)
Symptoms:
causes increase of phenylalanine in blood - results in mental retardation, heart problems, small head size (microcephaly) and developmental delay
Detection/
Frequency?
1 in 10,000 to 1 in 15,000 newborn babies
Mode of Inheritance/Chromosome
Treatment
Limiting dietary intake of phenylalanine
Prognosis

89. Symptoms:
Detection/
Frequency?
Mode of Inheritance/Chromosome
Treatment
Prognosis

91. Symptoms:
Detection/
Frequency?
Mode of Inheritance/Chromosome
Treatment
Prognosis

95. 11.5 Linkage & Gene Maps Thomas Hunt Morgan, 1910
Research fruit flies
Found 50+ Drosophilia genes
Many of them “linked” together
All the genes from one group were inherited together
Chromosomes assort independently, not the genes

97. How did Mendel miss this linkage?
By pure luck, the 6 genes he looked at were on different chromosomes
Gene Maps
Crossing-over sometimes separates genes on the same chromosomes onto homologous chromosomes.
Occasionally separate and exchange linked genes and produce new combinations

98. The farther apart two genes are, the more likely they are to be separated by a crossover in meiosis.
Alfred Sturtevant created a gene map showing the locations of each known gene on one of the Drosophila chromosomes