1

Mendelian Inheritance

... the outward physical manifestation of internally coded, inheritable, information.

2

Genetics vs Heredity?

Genetics: the branch of biology that studies heredity

Heredity: the passing of characteristics (or traits) from parents to offspring

3

Gregor Mendel

Father of Genetics

1823-1884Monk in

Austria/Czech Republic

Experimented with garden peas

4

Mendel…Why do you think?

His experiments were successful?He used peas?He controlled his experiments?

How did he do it?Why would his profession be

beneficial?

5

Short

Tall

Tall

6

Mendel’s Hypotheses

Each parent has two factors (alleles)

Each parent gives one of those factors to the offspring

Tall has TTShort has ttTall is dominantShort is recessive

7

TT tt

T t

Tt

8

TT TT

T T

TT

9

tt tt

t ttt

10

A Monohybrid cross..What’s the answer?The original parents differ by what?The original parents are called the?Their offspring are called what (the

kids)?And their offspring are called what

(the grandkids)?

11

Discovery of Chromosomes in 1900 Confirms Law of SegregationChromosomes

are in pairsEach

chromosome has one of the allele pairs for each trait

12

Homologous Chromosomes

Chromosomes of the same pairEach homologue will have one

allele for a paired geneHomologous chromosomes pair

up during meiosisOnly one of each homologue will

be in each gamete

13

Chromosomes line up in a double row.

Meiosis Metaphase

Assume a T allele on each red chromatid and a t allele on each blue chromatid

T T t t

14

Chromosomes separate

Each each daughter cell gets doubled chromosomes

T T t t

15

Doubled Chromosomes Separate in Second Meiotic Division

T T t t

16

Each gamete will have a T allele or a t allele

T T t t

17

Allele

Member of a paired gene– One allele comes from each parent

Represented by a single letter

18

Mendel’s Law of Dominance

Dominant alleles are expressedRecessive alleles are not

expressed in the presence of a dominant allele– Recessive alleles are only expressed

if both alleles are present

19

Gene

A unit of heredity that controls the development of one trait

Made of DNAMost genes are

composed of two alleles

My genes are Tommy genes!

20

Keeping Up Quick Check:

What is the relationship between DNA & genes & homologs ^ homolgous chromosomes?

Can you draw a picture?

21

Homozygous

Both alleles alikeAA or aa

A A a a

22

Heterozygous

Alleles are differentAa

A a

23

Law of Segregation

Mendel’sGametes have 1 allele for each trait2 alleles for each trait separate

during meiosis During fertilization, the alleles for that trait reunite.

This happens at random to create individuals of the next generation.

24

Genotype

Genetic make upRepresented by allelesTT & Tt are genotypes for tall pea

plants

This is the "internally coded, inheritable information" carried by all living organisms.

25

PhenotypeThe

characteristicGenotype

determines the phenotype

Tall is a phenotype

“Think adjective!”

Descriptive

This is the "outward, physical manifestation" of the organism.

26

A flower….Phenotype: red

flowersCells contain red

granules & enzymes help convert colorless pigment into red pigment

Most enzymes are proteins

Most traits are produced by the action of proteins.

27

Sickle Cell AnemiaRBCs sickle

shapedAnemiaPainStrokeLeg ulcersJaundiceGall stonesSpleen, kidney &

lungs

28

Sickle Cell Anemia

Recessive allele, s codes for hemoglobin S – Long rod-like molecules– Stretches RBC into sickle shape

Homozygous recessive, ss have sickle cell anemia

Heterozygous, Ss are carriers

29

Albinism

Lack of pigment– Skin– Hair– Eyes

30

Amino Acids Melanin PigmentEnzyme

A a

AA = Normal pigmentation

Aa = Normal pigmentation

aa = Albino

31

PKU Disease

Phenylalanine excess

Mental retardation if untreated

Molly’s Story

32

Phenylalanine TyrosineEnzyme

P p

PP = Normal

Pp = Normal

pp = PKU

33

A man & woman are both carriers (heterozygous) for albinism. What is the chance their children will inherit albinism?

34

AA = Normal pigmentation

Aa = Normal pigmentation (carrier)

aa = Albino

Man = Aa Woman = Aa

A

a a

A

35

A

a

a

A AA

Aa

Aa

aa

36

AA

Aa

Aa

aa

Genotypes1 AA, 2Aa, 1aa

Phenotypes

3 Normal

1 Abino

Probability

25% for albinism

37

A man & woman are both carriers (heterozygous) for PKU disease. What is the chance their children will inherit PKU disease?

38

p

p

PPP

Pp

Pp

pp

P

PP = Normal

Pp = Normal (carrier)

pp = PKU disease

39

PP

Pp

Pp

pp

Genotypes1 PP, 2Pp, 1pp

Phenotypes

3 Normal

1 PKU disease

Probability

25% for PKU disease

40

A man with sickle cell anemia marries a woman who is a carrier. What is the chance their children will inherit sickle cell anemia?

41

s

s

s Ss

Ss

ss

ss

S

SS = Normal

Ss = Normal (carrier)

ss = Sickle Cell

42

Ss

Ss

ss

ss

Genotypes2 Ss, 2ss

Phenotypes

2 Normal (carriers)

2 Sickle cell

Probability

50% for Sickle cell

43

Dwarfism = D

Normal height = d

DD = Dwarfism

Dd = Dwarfism

dd = Normal height

Dwarfism

Oddly a dominant trait

Dwarf Band

44

A man with heterozygous dwarfism marries a woman who has normal height. What is the chance their children will inherit dwarfism? Dwarfism is dominant.

45

d

d

D Dd

dd

Dd

dd

d

DD = Dwarf

Dd = Dwarf

dd = Normal

46

Dd

dd

Dd

dd

Genotypes2 Dd, 2dd

Phenotypes

2 Normal

2 Dwarfs

Probability

50% for Dwarfism

47

Law of Independent Assortment

The inheritance of one gene does not influence the inheritance of another gene if they are on separate chromosomes.

The gene for albinism does not affect the gene for dwarfism

The random distribution of alleles occurs gamete formation & genes on chromosomes sort independently during meiosis

48

A Dihybrid Cross

A heterozygous tall plant that is also heterozygous for yellow seeds self pollinates.

Tall and yellow seeds are dominant to short and green seeds.

What are the genotypes & phenotypes of the offspring in fractions?

49

Tall Yellow

TtYy

TY

What gametes can each parent produce?

TytYty

TtYy

TYTytYty

Tall Yellow

50

9 Tall-Yellow

Match gametes on a Punnent Square

TY

Ty

tY

ty

TY Ty tY ty

TtYy

TtYy

TTYY TTYy TtYY

TTYy TTyy Ttyy

TtYY TtYy ttYY ttYy

TtYy Ttyy ttYy ttyy

3 Tall-Green

3 Short-Yellow

1 Short-Green

51

A man with blue eyes and normal height marries a woman with heterozygous brown eyes and homozygous dwarfism. What are the possible phenotypes of their children? Dwarfism & brown eyes are dominant. (Calculate in % & ratios)

52

Normal height-Blue

ddbb

db

What gametes can each parent produce?

DDBb

DBDbDB

Dwarf-Brown

53

The Answers:

Dwarf-Brown eyes

Dwarf-blue eyes

Normal height-Brown eyes

Normal height-Blue eyes

54

The End of Mendlian Genetics

55

Pedigree

Shows relationships

Used to determine inheritance patterns

56

Pedigree SymbolsFemale

Male

Person has a trait

Parents

Children

Parents

Parents closely related

57

Dominant Pedigree

Affected individual must have a parent with the trait

58

Genotypes

AA

Aa

aaaa

aaaaaa

aa

Aa

Aa

Could have either genotype

59

Recessive Pedigree

May appear when neither parent has the trait

If both parents have the trait, all the children will inherit it

60

Genotypes

aa aa aaaa

aaaa

aa

aa

Aa

Aa

Aa

Aa

AAAa AaAA

61

Is this a dominant or recessive pedigree?

Click for answer

62

Recessive pedigree

Recessive because it appears in individuals when their parents do not have the trait.

63

Give genotypes for marked individuals

Click for answer

64

Genotypes

aa

Aa

AA or Aa

65

Is pedigree dominant or recessive?

Click for answer

66

Dominant pedigree

Dominant because all affected individuals inherited trait from a parent

67

Give genotypes for marked individuals

Click for answer

68

Give genotypes for marked individuals

Aa

aa

69

The End