1Gregor Mendel

2Mendelian IMendelian Inheritancenheritance

Gregor MendelGregor Mendel

Austrian monkAustrian monkStudied science and mathematics at Studied science and mathematics at University of ViennaUniversity of Vienna

Conducted breeding experiments with the Conducted breeding experiments with the garden pea garden pea Pisum sativumPisum sativum

Carefully gathered and documented Carefully gathered and documented mathematical data from his experimentsmathematical data from his experiments

Formulated fundamental laws of heredity in Formulated fundamental laws of heredity in early 1860searly 1860sHad no knowledge of cells or chromosomesHad no knowledge of cells or chromosomesDid not have a microscopeDid not have a microscope

3Fruit and Flower of the

Garden Pea

4Garden Pea TraitsStudied by

Mendel

5Mendelian IMendelian Inheritancenheritance

Blending InheritanceBlending Inheritance

Theories of inheritance in Mendel’s time:Theories of inheritance in Mendel’s time:

Based on blendingBased on blending

Parents of contrasting appearance produce Parents of contrasting appearance produce offspring of intermediate appearanceoffspring of intermediate appearance

Mendel’s findings were in contrast with thisMendel’s findings were in contrast with this

He formulated the particulate theory of He formulated the particulate theory of inheritanceinheritance

Inheritance involves reshuffling of genes from Inheritance involves reshuffling of genes from generation to generationgeneration to generation

6Mendel’s Monohybrid Crosses:An Example

7Mendelian IMendelian Inheritancenheritance

One-Trait InheritanceOne-Trait Inheritance

Mendel performed cross-breeding Mendel performed cross-breeding experimentsexperiments

Used “true-breeding” (homozygous) plantsUsed “true-breeding” (homozygous) plants

Chose varieties that differed in only one trait Chose varieties that differed in only one trait (monohybrid cross)(monohybrid cross)

Performed reciprocal crossesPerformed reciprocal crosses

­ Parental generation = PParental generation = P

­ First filial generation offspring = FFirst filial generation offspring = F11

­ Second filial generation offspring = FSecond filial generation offspring = F22

Formulated the Law of SegregationFormulated the Law of Segregation

8Mendelian IMendelian Inheritancenheritance

Mendel’s Monohybrid Mendel’s Monohybrid Crosses:Crosses:An ExampleAn Example

9Mendelian IMendelian Inheritancenheritance

Law of SegregationLaw of Segregation

Each individual has a pair of factors (alleles) Each individual has a pair of factors (alleles) for each traitfor each trait

The factors (alleles) segregate (separate) The factors (alleles) segregate (separate) during gamete (sperm & egg) formationduring gamete (sperm & egg) formation

Each gamete contains only one factor (allele) Each gamete contains only one factor (allele) from each pairfrom each pair

Fertilization gives the offspring two factors Fertilization gives the offspring two factors for each traitfor each trait

10Mendelian IMendelian Inheritancenheritance

Modern Genetics ViewModern Genetics View

Each trait in a pea plant is controlled by two Each trait in a pea plant is controlled by two alleles (alternate forms of a gene)alleles (alternate forms of a gene)

Dominant allele (capital letter) masks the Dominant allele (capital letter) masks the expression of the recessive allele (lower-expression of the recessive allele (lower-case)case)

Alleles occur on a homologous pair of Alleles occur on a homologous pair of chromosomes at a particular gene locuschromosomes at a particular gene locus

Homozygous = identical allelesHomozygous = identical alleles

Heterozygous = different allelesHeterozygous = different alleles

11Homologous Chromosomes

12Mendelian IMendelian Inheritancenheritance

Genotype Versus PhenotypeGenotype Versus Phenotype

Genotype Genotype

Refers to the two alleles an individual has for Refers to the two alleles an individual has for a specific traita specific trait

If identical, genotype is homozygousIf identical, genotype is homozygous

If different, genotype is heterozygousIf different, genotype is heterozygous

Phenotype Phenotype

Refers to the physical appearance of the Refers to the physical appearance of the individualindividual

13Mendelian IMendelian Inheritancenheritance

Punnett SquarePunnett Square

Table listing all possible genotypes resulting Table listing all possible genotypes resulting from a crossfrom a cross

All possible sperm genotypes are lined up on All possible sperm genotypes are lined up on one sideone side

All possible egg genotypes are lined up on the All possible egg genotypes are lined up on the other sideother side

Every possible zygote genotypes are placed Every possible zygote genotypes are placed within the squareswithin the squares

14Punnett Square ShowingEarlobe Inheritance

Patterns

15Try this one

MONOHYBRID CROSSMONOHYBRID CROSSCross a heterozygous tall plant with Cross a heterozygous tall plant with a heterozygous tall plant (use T = a heterozygous tall plant (use T = tall and t = short) Determine tall and t = short) Determine expected genotype and phenotype expected genotype and phenotype ratios.ratios.

16

Try these!Show work

1.Cross­a­heterozygous­red­flower­with­a­white­flower.­­What­is­the­genotype­and­phenotype­ratio­for­the­offspring?­­Key:­­R­=­red­­­r­=­white

17Mendelian IMendelian Inheritancenheritance

Two-Trait InheritanceTwo-Trait Inheritance

Dihybrid cross uses true-breeding plants Dihybrid cross uses true-breeding plants differing in two traitsdiffering in two traits

Observed phenotypes among FObserved phenotypes among F22 plants plants

Formulated Law of Independent AssortmentFormulated Law of Independent Assortment

­ The pair of factors for one trait segregate The pair of factors for one trait segregate independently of the factors for other traitsindependently of the factors for other traits

­ All possible combinations of factors can occur All possible combinations of factors can occur in the gametesin the gametes

18Mendelian IMendelian Inheritancenheritance

Try Mendel’s Classic Dihybrid CrossTry Mendel’s Classic Dihybrid Cross

Cross two heterozygous tall, heterozygous Cross two heterozygous tall, heterozygous green pod producing plants. Use a punnett green pod producing plants. Use a punnett square to show expected offspring and square to show expected offspring and complete a phenotype ratio.complete a phenotype ratio.

Key:Key:

T = tallT = tall G = green podsG = green pods

t = shortt = short g = yellow podsg = yellow pods

19Two-Trait (Dihybrid) Cross

20Must Know Your Vocab!

Homozygous?Homozygous?Heterozygous?Heterozygous?Genotype?Genotype?Phenotype?Phenotype?

21Try this one – DIHYBRID CROSS2 traits

Key:­­T­=­tall R­=­red­ ­­­t­=­shortr­=­white­ Cross­two­heterozygous­tall,­

heterozygous­red­flowered­plants.­ What­is­the­phenotypic­ratio­of­the­

offspring?

22Two-Trait (Dihybrid) Cross

23P-square practice

Practice crosses – on a separate Practice crosses – on a separate sheet of paper.sheet of paper.

• Show parental crossShow parental cross• Show p-squareShow p-square• Show phenotype ratioShow phenotype ratio

24

WHAT’s IN YOUR GENES?WHAT’s IN YOUR GENES?

Mom = 22 autosomes plus X sex Mom = 22 autosomes plus X sex chromosomechromosome

Dad = 22 autosomes plus X or Y Dad = 22 autosomes plus X or Y chromosomechromosome

25

26Boy or Girl?

Dad determines this – sperm carries Dad determines this – sperm carries 22 autosomes and either an X or Y 22 autosomes and either an X or Y sex chromosomesex chromosome

BOYS – your mom gave you the X BOYS – your mom gave you the X and dad gave you the Y – so what?and dad gave you the Y – so what?

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29Sex-linked – disorders carried on the

X chromosome

- ColorblindnessColorblindness- HemophiliaHemophilia- Baldness (?)Baldness (?)

30Analyze Sex-linked traits

Due tom!Due tom!

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- Albinism ppt - Albinism ppt - Huntingtons pptHuntingtons ppt- Final conceptsFinal concepts

34Autosomal Recessive Pedigree Chart

35Autosomal Dominant Pedigree Chart

36

INHERITING A GENE - ALBINISM

37This is an albino

skunk. The cells are not

able to produce the protein that

causes color.

38

Cells in the skin produce a black-brown pigment called melanin.

39The chemical melanin is

produced by specialized cells in the epidermis

called melanocytes.

40

The melanin leaves the melanocytes and enters other cells closer to the surface of the skin.

41Different shades of skin

colors is determined by the amount of

melanin deposited in

these epidermal cells

42Sunlight causes

melanocytes to increase production of melanin.

43

A tan fades because the cells break down the melanin.

44

Some organisms, such as the

octopus, can

rapidly change

from light to dark.

45

They control the color by scattering the melanin in the cell for a dark color, and concentrating the melanin in the

center for light color.

46

Melanin is made by the melanocytes by chemically changing the amino

acid, phenylalanin, into tyrosine and then into melanin.

47

An enzyme is required to change tyrosine into melanin.

48

If the enzyme is not present, then melanin

cannot be produced by the melanocytes.

49The result of no melanin is an albino.

50

The eyes of an albino appear pink because there is no dark melanin

in the eye to absorb light.

51

The blood in the retina and iris reflects red light, resulting in pink

eyes.

52

The gene that

produces this

enzyme is on

chromo-some 9

53

If both the genes produce

the enzyme tyrosinase,

there is plenty to convert tyrosine to melanin.

54

If neither gene

produces tryosinase,

no melanin is produced

and…

55The crow is

an albino rather

than the normal black

56

What if one gene is

normal and one gene does not produce the enzyme?

57The one normal gene produces enough enzyme to make normal crow

color

58

This albino squirrel received one albino gene from the father and one albino gene from the mother.

59

But what if a squirrel gets a normal gene

from one parent and an albino gene from

the other parent?

60The one functioning

gene produces enough enzyme

to make melanin for

normal coloration.

61Is it possible for two normal colored

cockatiels to have an

albino offspring?

62Yes!

Remember the albino

has two genes for albinism. One gene from the

father and one gene from the mother.

63

To be albino, both genes must be albino

genes

64

A normal colored bird could have one albino

gene and one normal gene.

65

If the sperm of a normal colored male pigeon has an albino gene and the ova it fertilizes has

an albino gene than the offspring will be albino.

66The same happens in humans. A

normal pigment

father and mother can

have an albino

offspring.

67

We can see this in a genetic “family tree” called a pedigree. The circles are

females, the squares are males. The open symbols are normal coloration, the black

symbols are albino.

68

The parents in the circle have normal pigment.

69

Most of the offspring received at least one normal gene from

a parent.

70

But one female offspring received an albino gene from

both the mother and the father.

71A Punnett square is a matrix to show the genetics of a mating.

72

What is the probability of an albino doe giving

birth to a “normal” fawn if she has mated

with a “normal” male?

73The female must

have two albino genes

(use small “a” for

the albino gene

- aa

74Since the albino gene is

relatively rare, the male probably has two normal genes of color. (Capital

“A” stands for the normal gene)

- AA

75AA X aa

76Next, add the possible sperm and ova genes.

A A

a

a

Aa Aa

Aa Aa

77As long as there is one normal gene, none of the offsprings will be albino A A

a

a

Aa Aa

Aa Aa

78Therefore, all offsprings will have a normal and an albino gene.

A A

a

a

Aa Aa

Aa Aa

79An albino must get one

albino gene from the father and one albino gene from the mother.

80Then how could an albino female

penguin have an

albino chick.

81

The “normal” colored father must have one

“normal coloration gene and one albino gene.

82

There is only one way for two normal colored parents to produce an albino

offspring.

83

Both parents must have one normal

gene and one albino gene.

84

Aa X AaBoth parents have one gene for normal and one gene for albinism.

85

Aa X Aa

A

a

The father’s sperm is 50% with normal gene and 50% with albino gene.

86

Aa X Aa

A

a

50% of the mother’s ova have a normal gene and 50% of the ova have the albino gene

A a

87

Aa X Aa

A

a

A a

AA

aaAa

Aa

The ova and sperm may combine to form an offspring with two normal genes, a normal gene and an albino gene, or two albino genes.

88

Aa X Aa

A

a

A a

AA

aaAa

Aa

Only the offspring with two albino genes will lack pigment.

89Sometimes an albino is born and there is no history of albinism in the colony.

90

The color gene in the

cell that produced this white flower

changed to an albino gene.

91

A change in a gene is called a mutation.

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