1. The Scientific Study of Inheritance
Genetics
The Scientific Study of Inheritance

3. Terms Allele Barr body Codominance Dihybrid cross Dominant Epistasis
Genotype
Heterozygous
Homozygous

4. Inbreeding
Incomplete dominance
Linkage
Locus
Multi-allelic
Phenotype
Pleiotropy
Polygenic
Recessive
Sex-linked

5. Gregor Mendel Monk Austria; Czech republic
1st to analyze inheritance in a scientific manner
Scientific method
Careful record-keeping

6. Gregor Mendel Studied garden peas Easy to grow
Produce lots of offspring
Easily distinguished characteristics
Fruit flies - today

7. Gregor Mendel
“Parents pass ‘factors’ to their offspring that are responsible for traits”
‘Factors’ = genes
Garden peas self-pollinate
True-breeding = parents produce offspring identical to themselves

8. Gregor Mendel Control cross-pollination
Cross-pollination produced hybrids
Called a ‘cross’
Hybrids = offspring with mixed traits
Traits = inherited characteristic

9. Crossed pure-breeding and got one trait
Crossed pure-breeding and got one trait. What happened to the white trait?

10. Gregor Mendel Allowed F1’s to self-pollinate Produced F2 generation
F2’s; 705 purple; 224 white
3:1 ratio
The heritable ‘factor’ for white was ‘masked’ but was not destroyed

11. Gregor Mendel - 4 Hypotheses:
There are alternate forms for ‘factors’ that control heredity
For each characteristic, there are 2 factors inherited; one from each parent
3. A gamete carries only one form for each factor’; during fertilization, the 2 ‘factors’ unite
4. One form of the factor is fully expressed (visible) and the other has no effect

12. Law Of Dominance

13. Modern Genetics ‘Factors’ = genes Alternate ‘forms’ = alleles
Genes = sections of DNA; code for making proteins
Expression of proteins determines trait
Dominant Allele= allele that IS expressed; protein is expressed (made)
Recessive Allele = allele that is NOT expressed (made); or masked; protein is not made

14. Structure Of A Chromosome
Chromosomes are homologous pairs
Same size, banding, centromere location and genes
Made of DNA
Sections of chromosomes are genes

15. Two alleles to a gene; alleles may be dominant or recessive
Chromosome 1
Homologue
Gene
Allele
Allele
Two alleles to a gene; alleles may be dominant or recessive
From dad
From mom

17. Modern Genetics Genotype = an organism’s genetic makeup PP
Phenotype = an organism’s expressed or physical traits
Purple

18. Mendel’s Principle of Segregation: Law of Segregation

19. Principle of Segregation
All organisms have 2 sets of homologous chromosomes; one from each parent;
Diploid
One allele located on each chromosome; one from mom, one from dad
2 alleles = 1 gene

20. Principle of Segregation
Pairs of alleles separate (segregate) during gamete formation
1 form of a ‘factor’ goes into 1 gamete while the other form separates and goes into another gamete (handout)
Locus = location of a gene on a chromosome; loci (pl.)
Alleles are at the same locus on each homologous chromosome

21. Principle of Segregation
Homozygous = both alleles for the trait are the same (homo)
PP, pp = homozygous
Heterozygous = the two alleles are different
Pp = heterozygous

22. Fertilization During fertilization, the sperm unites with the egg
1 haploid sperm + 1 haploid egg = 1 diploid zygote
Which sperm unites with which egg is by random chance
Flipping a coin

23. This is too hard to do!!!!

24. Use The Laws of Probability
Probability = chance that something will occur
How can we predict what will happen easier?
Punnett Square
How does it work, you say?
I’m so glad you asked ……

25. Punnett Square Use letters to represent each allele
a. Use the CAPITAL for dominant and small case for recessive
b. Ex. P = purple; p = white
T = tall; t = short
Y – yellow; y - green

26. 2. Draw a square
PURPLE x white

27. c. Every gene has 2 alleles so use 2 letters
Determine what letters to use to represent the alleles
Example:
a. Cross a PURPLE with a white flower
b. PURPLE is dominant over white in pea plants so use P = PURPLE and p = white
c. Every gene has 2 alleles so use 2 letters

28. pp PP
Crossing a homozygous purple flower with a homozygous recessive white flower pp X PP

29. BE CAREFUL HOW YOU MAKE YOUR LETTERS!!
Separate letters (alleles) around the square – this represents segregation PP
BE CAREFUL HOW YOU MAKE YOUR LETTERS!! P P p pp p

30. P P P p P p P p P p p p PURPLE PP x white pp
5. Combine the letters (alleles) into each box of the square
PURPLE PP x white pp P P p P p P p p P p P p

31. P P Pp Pp Pp Pp p p PP x pp = 4 Pp; and 4 PURPLE
6. Determine the results
PP x pp = 4 Pp; and 4 PURPLE P P 2 Pp 1 Pp
Genotype = 4 Pp
Phenotype = 4 PURPLE p
Purple
Purple 3 4 Pp Pp p
Purple
Purple

32. Results: Genotype – combination of letters (alleles); Pp
Phenotype – appearance (what do they LOOK like?
Purple

33. Pp x Pp What If You Crossed heterozygous
purple with heterozygous purple? Pp Pp
Pp x Pp

34. Separate letters (alleles) around the squarePp P p P Pp p

35. Combine the letters (alleles) in the squaresP p P P P p P
Purple
Purple P p p p p
Purple
white

36. p P P PP P p pp Pp p Pp x Pp Genotypes – 1 - PP 2 - Pp 1- pp
Purple
Purple
Phenotypes – pp Pp
3 - PURPLE p
Purple
white
1 - white

37. Practice Problems Tall is dominant to short
What genotypic and phenotypic results would be expected if you crossed a HOMOZYGOUS tall with a HOMOZYGOUS short?

38. Practice Problems T T What genotypic and phenotypic results would
be expected if you crossed a HOMOZYGOUS tall
with a HOMOZYGOUS short? T T t t

39. T T Tt Tt t Tt Tt t Genotypes - 4 - Tt Phenotypes - 4 - tall 100% tall

40. Practice:
In pea plants, yellow is dominant to green. What results would be expected if you crossed a homozygous yellow with a homozygous green?
Homozygous = same
Yellow – Y; green – y
Homozygous yellow = YY
Homozygous green = yy

41. Y Y y y Yy Yy Yy Yy Genotype – 4 Yy Phenotype – 4 yellow; 100% yellow

42. Practice
Black fur is dominant to brown fur in mice. What results should you expect if you crossed a homozygous black with a homozygous brown?
Black is dominant so use B; brown - b
Homozygous black = BB
Homozygous brown = bb

43. b b B B Genotype – 100% Bb Bb Bb Phenotype – 100% black Bb Bb Black

44. Law of Independent Assortment
Are Traits Inherited Together (dependently) or Separately (independently)?

45. Law of Independent Assortment
Round (R) is dominant to wrinkled (r)
Yellow (Y) is dominant to green (y)
Result from crossing two traits?
If you inherit a dominant trait does the other trait also have to be dominant?
Dihybrid cross – result of crossing two traits together

46. Dihybrid Cross
Homozygous (pure-breeding) round (RR), and yellow (YY) with:
Homozygous recessive; wrinkled (rr), green (yy)

47. Dihybrid Cross
Are the two traits inherited together (in a ‘package’) or can they be inherited separately?
Mendel crossed the P’s (yellow, round x green, wrinkled)
F1’s were all dominant (yellow, round)
Allowed the F1’s to self-pollinate

48. Dihybrid Cross 9:3:3:1 ratio 9/16 = yellow, round
3/16 = yellow, wrinkled
3/16 = green, round
1/16 = green, wrinkled

50. Independent Assortment:
Parent: 1 & 2
YyRr yr yR YR Yr

51. Law of Independent Assortment
Yy Rr YR Yr yR yr
Yy Rr

52. YR Yr yR yr
YYRR
YYRr
YyRR
YyRr
YYrr
Yyrr
yyRR
yyRr
yyrr

53. Law of Independent Assortment:
Each pair of alleles segregates independently of other pairs of alleles
Can recombine independently of each other
Genetic variation
Biggest cause of genetic variation in sexually reproducing organisms

54. Independent Assortment
Budgies inherit two colors INDEPENDENTLY
Color (Yellow) or no color on the outer surface of the feather
Melanin or no melanin in the inner core of the feather

55. Variation and Patterns of Variation
Wild type - most common traits in the wild
Budgies = green feathers
Knowing patterns and rules of inheritance allows breeders to produce blues, yellows, and whites

56. Budgie Color Two genes inherited separately Outside color of feather
Inside color of feather
Independent assortment; the two characteristics are inherited independently of each other

57. Green = Y_B_

58. Blue = yyB_

59. Yellow; Y_bb

60. White; yybb

61. How can We Use Genetics to Determine if Our Organism is Pure-breeding?
Test Cross
How can We Use Genetics to Determine if Our Organism is Pure-breeding?

62. Test cross
Mate an individual whose genotype is not known (dominant phenotype) with a homozygous recessive for that trait
Ex. Is your favorite Labrador a ‘pure’ black or does he carry a recessive allele?

63. Test cross Cross the unknown with a homozygous recessive
Eight puppies born, 3 are brown (recessive) ?

64. B B b Bb Bb b Bb Bb
If the unknown is homozygous (pure) then all the offspring are dominant

65. B b b Bb bb b Bb bb
If the unknown is heterozygous (carrier) then some offspring are recessive

66. Variations of Mendel Complete dominance Incomplete dominance
Codominance
Multiple alleles
Pleiotropy
Polygenic inheritance
Linkage

67. Incomplete Dominance Red x white = pink
Dominant allele does not totally mask recessive allele
Some recessive trait is expressed: blended
Red x white = pink

68. Curly hair + straight hair = wavy

69. Incomplete Dominance
Heterozygotes express a trait between the dominant and recessive
Familial hypercholesterolemia
hh = very high cholesterol
Hh = mild cholesterol
HH = low cholesterol; ‘normal’

70. Codominance Both traits are EQUALLY dominant;
Both traits are expressed (not blended)
Roan color
Sickle cell
Blood types

71. Codominance Two different traits and both show equally Roan color
Blood types

72. Blood Types
Antigens = proteins on the surface of red blood cells (RBC’s)
Antibodies = proteins floating in the plasma of blood that bind with ‘foreign’ proteins (antigens)
Antibodies stick to ‘foreign’ antigens forming a clot

73. Blood Types
‘B’ into ‘A’ causes a clot
‘A’ into ‘B’ causes a clot

74. Blood Types Antibodies will be the opposite of the antigens
“A” blood will have “B” antibodies
‘B’ blood will have ‘A’ antibodies
Antibodies are like guard dogs; they attack foreign cells with the wrong antigens

75. Blood Types Codominance
Multiple alleles = 1 gene but three possible allele combinations
A, B, O

76. Blood Types: Phenotypes
Antigens = proteins on the surface of cells (RBC’s)
Cell-to-cell recognition
Antibodies = proteins floating in the plasma of blood that bind with ‘foreign’ proteins (antigens)

77. Blood Types: Phenotypes
Antibodies agglutinate to antigens that are ‘foreign’
Agglutinate = clot, clump
“B” into “A” causes agglutination

78. Blood Types: Phenotypes
Blood type = type of antigens on the surface
Antibodies will be the opposite of the antigens
“A” blood will have “B” antibodies

79. ‘A’ antigens A
‘B’ Antibodies

80. ‘B’ antigens B
‘A’ Antibodies

81. B antibodies attach to B antigens; causes blood to agglutinate
Person with ‘A’ blood:
‘B’ antigens B
B antibodies attach to B antigens; causes blood to agglutinate
‘B’ Antibodies

82. ‘A’ antigens are attacked by ‘A’ antibodies
Person with ‘B’ blood:
‘A’ antigens A
‘A’ antigens are attacked by ‘A’ antibodies
‘A’ Antibodies

83. Person with AB blood:
A, B antigens AB
No antibodies

84. Person with O blood:
No antigens O
A and B antibodies

85. Blood Types: Genotypes
Dominant allele = I
Recessive allele = i (inability)
II, Ii, ii
Dominant allele can carry A or B
Ia or IB

86. Blood Types 2 alleles for each gene: ‘A’ = IAIA or IA i
‘B’ = IBIB or IB i
‘AB’ = IAIB
‘O’ (zero) = ii

87. A IAIA IAi Anti-B A or O B IBIB IBi Anti-A B or O AB IAIB A,B None
phenotype
genotype
antigens
antibodies
Receive
From: A
IAIA
IAi
Anti-B
A or O B
IBIB
IBi
Anti-A
B or O AB
IAIB
A,B
None
A, B, O O ii

89. How to do Punnett Squares With Blood Types:

90. Heterozygous IA i
Homozygous
IAIA
IA i IA
IAIA
IA i IA

91. Can 2 people With A and B Blood Have a Child With O Blood?

92. Heterozygous A IA i
Heterozygous B
IAIB
IB i IB B AB
i i
IA i i O A

93. Pleiotropy One gene has multiple effects Sickle-cell anemia; p. 160
Abnormal blood cells
Difficulty breathing
Brain, heart, kidney damage

95. Pleiotropy: Heterozygote Advantage
High incidence of sickle-cell in areas where there is a lot of malaria
Malaria does not effect sickle-cell
People w/ sickle-cell don’t suffer malaria

96. Polygenic Inheritance
Multiple genes produces a continuous effect; very dark-very light
Skin, hair, eye color
6 – 10 alleles
AABBCC - aabbcc

97. Linkage Early 1900’s; TH Morgan Fruit flies
Inheritance patterns did not follow Mendelian Laws of Probability (?)
Genes are linked

99. Linkage Genes on the same chromosome are inherited together
Sex – linked genes
Gene located on the sex chromosome (usually X)

101. Sex linkage and Punnett Squares

102. Linkage The sex-linked trait is usually on the X chromosome
X X = female
X Y = male
XH = ‘normal’
Xh = hemophilia

104. Hemophilia Sex-linked, recessive disorder
‘Bleeders disease’; lack protein for blood clotting
Czar Nicholas’ son “Nicki”; p. 168

105. Normal phenotypes: XH XH XH
XH XH
XH XH Y
XH Y
XH Y

106. Hemophilia phenotype:XH Xh XH
XH XH
XH Xh Y
XH Y
Xh Y

107. Sex-linked Traits: Hemophilia Duchenne’s Muscular dystrophy
Color-blindness
Mostly males
Smartness

108. Sex-linked Traits: Y Chromosome
“Maleness”

109. Censored
Censored
Censored

112. Pedigrees Tracing traits back over generations
Dominance does NOT mean that a phenotype is ‘normal’ or more common
Wild type

113. Pedigrees Dominance = heterozygote displays the trait
Recessive expression occurs only if the genotype is homozygous
bb, tt, ff

114. Pedigrees Used to predict probability of genetic disorders
Carriers = individuals who do not express the trait but have the recessive allele in their genotype

116. Human Disorders Single gene: 2 types; Dominant expression
Recessive expression

117. Human Disorders: Dominant
Only requires one allele for trait to be expressed
Polydactyly; multiple fingers
Achondroplasia; dwarfism, heterozygotes

118. Human Disorders: Dominant
Most dominant disorders are not lethal
Huntington’s disease; midlife expression, degeneration of the nervous system
Hypercholesterolemia – high cholesterol; heart disease

119. Human Disorders: Recessive
Homozygous for the disorder to be expressed
Cystic fibrosis;
Sickle cell anemia
Tay-Sachs disease
PKU

120. Fetal Testing
Amniocentesis = removal of amniotic fluid (surrounds the developing baby); 20 ml
Biochemical tests (spina bifida, infections)
Cells karyotyping (Down’s, Tay-Sachs)

121. Fetal Testing
Chorionic villus sampling (CVS) fetal cells removed from placenta
Karyotyped quickly

122. Fetal Testing Ultrasound = view of baby
Fetoscopy = direct view of baby

123. Recessive Disorders
Cystic fibrosis – whites; build up of mucus in lungs, pancreas

125. Recessive Disorders
Sickle cell anemia – Black and SE Asia; 1/500 (lethal), 1/10 carrier;
Codominant – one allele is normal, other forms hemoglobin that crystallizes in low oxygen

126. Recessive Disorders
Tay-Sachs – Jewish; lack gene that produces enzyme that breaks down lipids in the brain; causes brain degeneration, lethal by age 3-4
PKU – phenylketonuria; lack the gene needed to make the enzyme that breaks down phenylalanine. Phenylalanine accumulates causing nervous disorders. Treated with diet

127. Pedigrees Tracing traits back over generations
Dominance does NOT mean that a phenotype is ‘normal’ or more common
Wild type

128. Pedigrees Used to predict probability of genetic disorders
Carriers = individuals who do not express the trait but have the recessive allele in their genotype

129. Pedigree
Family tree
Shows how a trait is passed down from one generation to the next
= male
= female

130. Pedigree number 1

131. Pedigree number 2

132. Pedigree number 3