Mendelian Genetics.ppt

(1)

Mendelian

Genetics

(2)

Gregor Mendel

(1822-1884)

Responsible

Responsible

for the Laws

governing

Inheritance of

Traits

(3)

Gregor Johann Mendel



Austrian monkAustrian monk



Studied the Studied the inheritance

inheritance of of

traits in

traits in pea plants_{pea plants}



Developed the Developed the laws of inheritance

laws of inheritance



Mendel's work Mendel's work was not recognized

was not recognized

until the turn of

the

(4)

Gregor Johann Mendel



Between Between 1856 1856 and 1863,

and 1863, Mendel Mendel cultivated and

cultivated and tested some

tested some 28,000 28,000 pea plants

pea plants



He found that He found that

the plants' offspring

retained

retained traits of _{traits of}

the parents



Called theCalled the

“Father of Genetics"

(5)

Site of

Gregor

Mendel’s

experimental

experimental

garden in the

Czech

Republic

(6)



Mendel stated that Mendel stated that physical traits are

physical traits are

inherited as

inherited as “particles”_{“particles”}



Mendel did not know Mendel did not know

that the “particles”

were actually

Chromosomes & DNA

Particulate Inheritance

(7)

Genetic Terminology



Trait

- any characteristic

that can be passed from parent

to offspring



Heredity

- passing of traits

from parent to offspring

(8)

Types of Genetic Crosses



Monohybrid cross

- cross

-

cross

involving a single trait

e.g. flower color



Dihybrid cross

- cross

-

cross

involving two traits

e.g. flower color & plant height

(9)

Punnett Square

Used to help

Used to help

solve genetics

problems

(10)

(11)

Designer

“Genes”



AllelesAlleles - - two forms of a two forms of a gene gene (dominant & recessive)

(dominant & recessive)



DominantDominant - - stronger of two genes stronger of two genes expressed in the hybrid;

expressed in the hybrid;

represented by

represented by a_a capital letter (R)_{capital letter (R)}



RecessiveRecessive - - gene that shows up gene that shows up less often in a cross; represented

less often in a cross; represented

by a

(12)

More Terminology



Genotype

-

gene combination

for a trait

(e.g. RR, Rr, rr)



Phenotype

-

the physical

feature resulting from a

genotype

(13)

Genotype & Phenotype in Flowers

Genotype of alleles:

Genotype of alleles: R

R_{= red flower}= red flower

r

r_{= yellow flower}= yellow flower

All genes occur in pairs, so

All genes occur in pairs, so 2₂

alleles

alleles affect a characteristic affect a characteristic Possible combinations are:

Possible combinations are:

Genotypes

Genotypes RR_RR R_Rr_r rr_rr

(14)

Genotypes



HomozygousHomozygous genotype - gene genotype - gene combination involving 2 dominant

combination involving 2 dominant

or 2 recessive genes

or 2 recessive genes (e.g. RR or _{(e.g. RR or}

rr);

rr); also called_{also called} pure _pure



HeterozygousHeterozygous genotype - gene genotype - gene combination of one dominant &

combination of one dominant &

one recessive allele (

one recessive allele (e.g. Rr);_{e.g. Rr);}

also called

(15)

Genes and Environment

Determine Characteristics

(16)

Mendel’s Pea Plant

Experiments

(17)

Why peas,

Pisum sativum

?



Can be grown in a Can be grown in a small area

small area



Produce Produce lots of lots of offspring

offspring



Produce Produce purepure plants plants when allowed to

when allowed to self-

self-pollinate

pollinate several _several

generations



Can be Can be artificially artificially cross-pollinated

(18)

Reproduction in Flowering Plants

Pollen contains sperm

Produced by the stamen

Ovary contains eggs

Ovary contains eggs

Found inside the flower

Pollen carries sperm to the

eggs for fertilization

Self-fertilization

Self-fertilization can can

occur in the same flower

occur in the same flower

Cross-fertilization

Cross-fertilization can can occur between flowers

(19)

Mendel’s Experimental

Methods

Mendel

Mendel hand-pollinated_{hand-pollinated}

flowers using a

flowers using a paintbrushpaintbrush He could

He could snip the _{snip the}

stamens

stamens to prevent to prevent self-pollination

self-pollination

Covered each flower

with a cloth bag

He traced traits through

He traced traits through

the

(20)

How Mendel Began

(21)

Eight Pea Plant Traits

Seed shape

Seed shape --- Round --- Round (R)(R) or Wrinkled or Wrinkled (r)(r)

Seed Color

Seed Color ---- Yellow ---- Yellow (Y)(Y) or Green or Green ((yy))

Pod Shape

Pod Shape --- Smooth --- Smooth (S)(S) or wrinkled or wrinkled ((ss))

Pod Color

Pod Color --- Green --- Green (G)(G) or Yellow or Yellow (g)(g)

Seed Coat Color

Seed Coat Color ---Gray ---Gray (G)(G) or White or White (g)(g)

Flower position

Flower position---Axial ---Axial (A)(A) or Terminal or Terminal (a)(a)

Plant Height

Plant Height --- Tall --- Tall (T)(T) or Short or Short (t)(t)

Flower color

(22)

(23)

(24)

Mendel’s Experimental Results

(25)

Did the observed ratio match the theoretical ratio?

The theoretical or expected ratio of The theoretical or expected ratio of

plants producing round or wrinkled seeds plants producing round or wrinkled seeds

is

is 3 round :1 wrinkled_{3 round :1 wrinkled}

Mendel’s observed ratio was 2.96:1 Mendel’s observed ratio was 2.96:1

The discrepancy is due to

The discrepancy is due to statistical _statistical

error

The

The larger the samplelarger the sample the more nearly the more nearly the results approximate to the

(26)

Generation “Gap”

Parental P

Parental P₁₁ Generation Generation = the parental generation = the parental generation in a breeding experiment

in a breeding experiment..

F

F₁₁ generation generation = the first-generation offspring in = the first-generation offspring in a breeding experiment.

a breeding experiment. (1st filial generation)(1st filial generation) From breeding individuals from the P

From breeding individuals from the P₁₁

generation

F

F₂₂ generation generation = the second-generation offspring = the second-generation offspring in a breeding experiment.

in a breeding experiment.

(2nd filial generation)

From breeding individuals from the F

From breeding individuals from the F₁₁

generation

(27)

Following the Generations

Cross 2

Cross 2

Pure

Plants

Results

in all

Hybrids

Cross 2 Hybrids

get

3 Tall & 1 Short

(28)

Monohybrid

Crosses

(29)

Trait: Seed Shape

Trait: Seed Shape

Alleles:

Alleles: R_R – Round_{– Round} r_r – Wrinkled_{– Wrinkled}

Cross:

Cross: RoundRound seedsseeds xx Wrinkled Wrinkled seedsseeds RR

RR xx rr rr

P

₁₁

Monohybrid Cross

R R r r Rr Rr Rr Rr Genotype:

Genotype: Rr_Rr

Phenotype

Phenotype: RoundRound Genotypic

Genotypic

Ratio:

Ratio: All alikeAll alike Phenotypic

(30)

P

₁₁

Monohybrid Cross Review



Homozygous dominant x Homozygous dominant x

Homozygous recessive

Homozygous recessive



OffspringOffspring allall HeterozygousHeterozygous (hybrids)

(hybrids)



Offspring calledOffspring called FF₁₁ generation generation



Genotypic & Phenotypic ratio isGenotypic & Phenotypic ratio is ALL ALIKE

(31)

Alleles:

Cross:

Cross: RoundRound seeds seeds xx Round Round seedsseeds Rr

Rr xx Rr Rr

F

₁₁

Monohybrid Cross

R r r R RR rr Rr Rr Genotype:

Genotype: RR, Rr, rr_{RR, Rr, rr}

Phenotype

Phenotype: Round &Round & wrinkled

wrinkled

G.Ratio:

G.Ratio: 1:2:11:2:1 P.Ratio:

(32)

F

₁₁

Monohybrid Cross Review



Heterozygous x heterozygousHeterozygous x heterozygous



Offspring:Offspring:

25% Homozygous dominant

25% Homozygous dominant RR_RR

50% Heterozygous

50% Heterozygous Rr_Rr

25% Homozygous Recessive

25% Homozygous Recessive rr_rr



Offspring calledOffspring called FF₂₂ generation generation



Genotypic ratio isGenotypic ratio is 1:2:11:2:1

(33)

What Do the Peas Look Like?

(34)

…

And Now the Test Cross

Mendel then crossed a

Mendel then crossed a pure_pure & a _{& a}

hybrid

hybrid from his _{from his}F_F₂₂generation_generation

This is known as an

This is known as an F_F₂₂ or test _{or test}

cross

There are

There are two_two possible testcrosses:_{possible testcrosses:}

Homozygous dominant x Hybrid

Homozygous recessive x Hybrid

(35)

Trait: Seed Shape

Alleles:

Cross:

Cross: RoundRound seedsseeds xx Round Round seedsseeds RR

RR xx Rr Rr

F

₂₂

Monohybrid Cross (1

stst

)

R R r R RR Rr RR Rr Genotype:

Genotype: RR, Rr_{RR, Rr}

Phenotype

Phenotype: RoundRound Genotypic

Genotypic

Ratio:

Ratio: 1:11:1 Phenotypic

(36)

Alleles:

Cross:

Cross: WrinkledWrinkled seedsseeds xx Round Round seedsseeds rr

rr xx Rr Rr

F

₂₂

Monohybrid Cross (2nd)

r r r R Rr rr Rr rr Genotype:

Genotype: Rr, rr_{Rr, rr}

Phenotype

Phenotype: Round & Round & Wrinkled

Wrinkled

G. Ratio:

G. Ratio: 1:11:1 P.Ratio:

(37)

F

₂₂

Monohybrid Cross Review



Homozygous x heterozygous(hybrid)Homozygous x heterozygous(hybrid)



Offspring:Offspring:

50% Homozygous

50% Homozygous RR or rr_{RR or rr}

50% Heterozygous

50% Heterozygous Rr_Rr



Phenotypic RatioPhenotypic Ratio is 1:1 is 1:1



Called Called Test CrossTest Cross because the because the offspring have

offspring have SAME_SAME genotype as _{genotype as}

parents

(38)

Practice Your Crosses

Work the P

₁₁

, F

₁₁

, and both

F

₂₂

Crosses for each of the

other Seven Pea Plant

Traits

(39)

Mendel’s Laws

(40)

Results of Monohybrid Crosses

Inheritable

Inheritable factors or genesfactors or genes are are responsible for all heritable

responsible for all heritable

characteristics

Phenotype

Phenotype is based on _{is based on}Genotype_Genotype

Each trait

Each trait is based on_{is based on} two genes_{two genes}, _,one _one

from the mother and the other from

from the mother and the other from

the father

True-breeding individuals are

homozygous ( both alleles)

homozygous ( both alleles) are the are the same

(41)

Law of Dominance

In a cross of parents that are

In a cross of parents that are

pure for contrasting traits

pure for contrasting traits, only _{, only}

one form of the trait will appear in

the next generation.

All the offspring will be

All the offspring will be

heterozygous and express only the

dominant trait.

(42)

Law of Dominance

(43)

Law of Segregation

During the

During the formation of gametes_{formation of gametes}

(eggs or sperm), the

(eggs or sperm), the two alleles_{two alleles}

responsible for a trait

responsible for a trait separate_separate

from each other.

Alleles for a trait are then

"recombined" at fertilization

"recombined" at fertilization, _,

producing the genotype for the

traits of the offspring

(44)

Applying the Law of Segregation

(45)

Law of Independent

Assortment

Alleles for

Alleles for different_different traits are traits are distributed to sex cells (&

distributed to sex cells (&

offspring) independently of one

another.

This law can be illustrated using

dihybrid crosses

(46)

Dihybrid Cross

A breeding experiment that tracks

A breeding experiment that tracks

the

the inheritance of two traits_{inheritance of two traits}..

Mendel’s

Mendel’s “Law of Independent _{“Law of Independent}

Assortment”

a. Each pair of alleles segregates

independently

independently during gamete formation_{during gamete formation}

b. Formula: 2

(47)

Question:

Question:

How many gametes will be produced

for the following allele arrangements?

Remember:

Remember: 22nn (n = # of heterozygotes) (n = # of heterozygotes)

1.

1. RrYyRrYy

2.

2. AaBbCCDdAaBbCCDd

3.

(48)

Answer:

1. RrYy: 2

1. RrYy: 2nn = 2 = 222 = 4 gametes = 4 gametes RY Ry rY ry

RY Ry rY ry

2. AaBbCCDd: 2

2. AaBbCCDd: 2nn = 2 = 233 = 8 gametes = 8 gametes ABCD ABCd AbCD AbCd

ABCD ABCd AbCD AbCd

aBCD aBCd abCD abCD

3. MmNnOoPPQQRrssTtQq: 2

3. MmNnOoPPQQRrssTtQq: 2nn = 2 = 266 = 64 = 64 gametes

(49)

Dihybrid Cross

Traits: Seed shape & Seed color Traits: Seed shape & Seed color

Alleles:

Alleles: R round

r wrinkled Y yellow

y green

RrYy x RrYy

RY Ry rY ry

(50)

Dihybrid Cross

RY

RY RyRy rYrY ryry

RY

Ry

rY

ry

(51)

Dihybrid Cross

RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy RrYy Rryy rrYy rryy

Round/Yellow: 9

Round/green: 3

wrinkled/Yellow: 3

wrinkled/green: 1

RY

RY RyRy rYrY ryry

(52)

Dihybrid Cross

Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1

(53)

Test Cross

A mating between an individual of

A mating between an individual of unknown unknown genotype

genotype and a and a homozygous recessivehomozygous recessive individual. individual. Example:

Example: bbC__ bbC__ x x bbccbbcc

BB = brown eyes

Bb = brown eyes

bb = blue eyes

CC = curly hair

Cc = curly hair

Cc = curly hair

cc = straight hair

bC

bC b___b___

bc

(54)

Test Cross

Possible results:

Possible results:

bC

bC b___b___

bc

bc bbCc bbCc

C bCbC b___b___ bc

bc bbCc bbcc or

(55)

Summary of Mendel’s laws

LAW

LAW PARENT PARENT _CROSS_CROSS OFFSPRINGOFFSPRING

DOMINANCE

DOMINANCE TT x ttTT x tt

tall x short

tall x short 100% Tt 100% Tt talltall

SEGREGATION

SEGREGATION tall x talltall x tallTt x TtTt x Tt 25% short25% short75% tall 75% tall

INDEPENDENT

INDEPENDENT

ASSORTMENT

RrGg x RrGg RrGg x RrGg

round & green

x

9/16 round seeds & green pods

3/16 round seeds & yellow

pods

3/16 wrinkled seeds & green

(56)

Incomplete Dominance

and

Codominance

(57)

F1 hybrids

F1 hybrids have an appearance somewhat

in between

in between the phenotypes _phenotypesof the two parental varieties.

Example:

Example: snapdragons (flower)_{snapdragons (flower)} red (RR) x white (rr)

RR = red flower

rr = white flower

R

(58)

Incomplete Dominance

Rr Rr Rr Rr Rr Rr Rr Rr R R R R r r

All Rr =

All Rr = pink_pink

(heterozygous pink)

produces the

produces the F

(59)

Incomplete Dominance

(60)

Codominance

Two alleles

Two alleles are expressed ( are expressed (multiple multiple alleles

alleles) in _{) in}heterozygous individuals_{heterozygous individuals}._. Example:

Example: blood type_{blood type}

1.

1. type Atype A = I= IAAIIAA or I or IAAii

2.

2. type Btype B = I= IBBIIBB or I or IBBii

3.

3. type AB_{type AB} = I_{= I}AAIIBB

4.

(61)

Codominance Problem

Example: homozygous male Type B (IBIB)

x heterozygous female Type A (IAi)

IAIB IBi

1/2 = IAIB 1/2 = IBi

IB

(62)

Another Codominance Problem

• Example:_Example: male Type O (ii) x

female type AB (IAIB)

IAi IBi

1/2 = IAi 1/2 = IBi

i

IA IB

(63)

Codominance

Question

:

If a boy has a blood type O and

If a boy has a blood type O and

his sister has blood type AB,

what are the genotypes and

phenotypes of their parents?

boy -

boy - type O (ii) type O (ii) X girl - X girl - type type

AB (I

(64)

Codominance

Answer:

Answer:

IAIB

ii

Parents:

genotypes

genotypes = IAi_andIBi

phenotypes

phenotypes = A and B IB

IA i

(65)

Sex-linked Traits

Traits (genes) located on the

Traits (genes) located on the sex _sex

chromosomes

Sex chromosomes are

Sex chromosomes are X and Y_{X and Y}

XX

XX genotype for females_{genotype for females}

XY

XY genotype for males_{genotype for males}

Many

Many sex-linked traitssex-linked traits carried on carried on X

(66)

Sex-linked Traits

Sex Chromosomes

Sex Chromosomes

XX chromosome - female Xy chromosome - male

fruit fly eye color

Example:

(67)

Sex-linked Trait Problem

Example: Eye color in fruit flies

(red-eyed male) x (white-eyed female)

XRY x XrXr

Remember: the Y chromosome in males does not carry traits.

RR = red eyed Rr = red eyed rr = white eyed XY = male

XX = female

XR

Xr Xr

(68)

Sex-linked Trait Solution:

XR Xr

Xr Y

XR Xr

Xr Y

50% red eyed

female

50% white eyed

male

XR

Xr Xr

(69)

Female Carriers

(70)

Genetic Practice

Problems

(71)

Breed the P

₁₁

generation

tall (TT) x dwarf (tt) pea plants tall (TT) x dwarf (tt) pea plants

T T

(72)

Solution:

T

t t

Tt

Tt All Tt = tall

(heterozygous tall) produces the

F

F₁₁ generation generation

tall (TT) vs. dwarf (tt) pea plants

(73)

Breed the F

₁₁

generation

tall (Tt) vs. tall (Tt) pea plants tall (Tt) vs. tall (Tt) pea plants

T t

(74)

Solution:

TT Tt Tt tt T t T t produces the F

F22 generation generation

1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt

1:2:1 genotype

3:1 phenotype

tall (Tt) x tall (Tt) pea plants

(75)