Mendel Ext

Modifications to Mendelian Ratio Key Points • • • • • • • •

Incomplete dominance and codominance Lethal genes Gene interaction Epistasis Polygenic inheritance Linkage Pleiotropy Incomplete expressivity & incomplete penetrance

Modifications to Mendelian Ratio F2 Genotipic Ratio Monohybrid Aa x Aa

Gamet: A

a

Genotype

Frequency

AA

1/4

Aa

1/2

aa

1/4

F2 (Punnett Square) A

a

F2 Phenotipic Ratio

A

AA

Aa

Genotype

Frequency

a

Aa

aa

A_

3/4

aa

1/4

F2 Genotype Frequency AABB

1

AABb

2

AAbb

1

AaBB

2

AaBb

4

Aabb

2

aaBB

1

aaBb

2

aabb

1

Mendelian dihybrid cross AaBb x AaBb Phenotype Frequency A_B_

9

A_b_

3

aaB_

3

aabb

1

Modifications in Monohybrid Cross • Incomplete Dominance • Codominance • Lethal genes

Incomplete Dominance / Codominance Snapdragon flower colour (1:2:1 ratio)

Rr

x

RR 1

Rr

Rr :

2

rr :

1

Lethal Genes (1:2 ratio)

Y, the yellow-lethal mutation in mice: a dominant visible that is also a recessive lethal.

Modifications in Dihybrid Cross • Incomplete Dominance/Codominance – in both pairs of alleles (1 example) – on one pair of alleles (1 example)

• Gene Interaction (2 examples) • Epistasis (5 examples) • Polygenic Inheritance (1 example)

F2 Genotype Frequency AABB

1

AABb

2

AAbb

1

AaBB

2

AaBb

4

Aabb

2

aaBB

1

aaBb

2

aabb

1

Mendelian dihybrid cross AaBb x AaBb Phenotype Frequency A_B_

9

A_bb

3

aaB_

3

aabb

1

Codominance in both pairs

Genotype Phenotype I I

A

A A

II

B

B B

I I

AB

A B

L L M

M

M

L L N N

N

L L M

N

MN

IAIBLMLN x IAIBLMLM

Genotype

Phenotype

Ratio

IAIALMLM

AAMM

1

IAIALMLN

AAMN

2

IAIALNLN

AANN

1

IAIBLMLM

ABMM

2

IAIBLMLN

ABMN

4

IAIBLNLN

ABNN

2

IBIBLMLM

BBMM

1

IBIBLMLN

BBMN2

IBIBLNLN

BBNN

1

Incomplete Dominance in one pair

Ddh1h2 x Ddh1h2

Genotype Phenotype

Genotype

Phenotype

Ratio

DD/DdTinggi

D_ h1h1

Tall, Smooth

3

dd

Dwarf

D_ h1h2

Tall, Sparse

6

h1h1

Smooth

D_ h2h2

Tall, Hairy

3

h1h2

Sparse

dd h1h1

Dwarf, Smooth

1

h2h2

Hairy

dd h1h2

Dwarf, Sparse

2

dd h2h2

Dwarf, Hairy

1

Gene Interaction Chicken Comb Shapes (9:3:3:1 ratio) a. rose, Wyandottes b. pea, Brahmas c. walnut, hybrid d. single, Leghorns

Comb shapes in chickens of different breeds.

RRpp (rose)

rrPP (pea)

X

RrPp (walnut)

9 R_P_ walnut 3 R_pp rose 3 rrP_

pea

1 rrpp

single

Gene Interaction AABB

Pig Coat Colour (9:6:1 ratio) x

red F1

aabb white

AaBb red

F2 9

A_B_ red (interaction between A & B)

3

A_bb sand yellow (because of A)

3

aaB_

sand yellow (because of B)

1

aabb

white (no A or B)

Modifications to Mendelian Ratio Key Points • • • • • • • •

Incomplete dominance and codominance Lethal genes Gene interaction Epistasis Polygenic inheritance Linkage Pleiotropy Incomplete expressivity & incomplete penetrance

Epistasis (recessive) Mice Coat Colour (9:3:4 ratio) CCaa

x

black F1

ccAA albino

CcAa agouti

F2 9

C_A_ agouti (A determines agouti)

3

C_aa

black (a determines black)

3

ccA_

albino (cc epistasis towards A_)

1

ccaa

albino (cc epistasis towards aa)

Epistasis (Dominant) Cucurbita pepo fruit colour (12:3:1 ratio) AABB

x

white F1

aabb green

AaBb white

F2 9

A_B_

3

A_bb

3

aaB_

yellow (B determines yellow)

1

aabb

green (b determines green)

12 white (A epistasis towards B_ and bb)

Epistasis Fowl plumage colour (13:3 ratio) IICC

Leghorn

x

white F1

iicc white

IiCc white

F2 9

I_C_

white (because of inhibitor I)

3

I_cc

white (because of I and cc)

3

iiC_

coloured (C determines colour)

1

iicc

white (cc has no colour)

Wyandotte

Epistasis Corn kernel colour (9:7 ratio) AAcc

x

yellow F1

aaCC yellow

AaCc purple

F2 9

A_C_

purple (A and C present)

3

A_cc

yellow (C absent)

3

aaC_

yellow (A absent)

1

aacc

yellow (A and C absent)

SUBSTRATE X

SUBSTRATE Y

A

A

Enzyme

Gene

ANTOCYANINE

B

B

Epistasis Seed capsules of the shepherd’s purse (15:1 ratio) AABB

x

triangular F1

aabb ovoid

AaBb triangular

F2 9

A_B_

triangular (A and B present)

3

A_bb

triangular (A present)

3

aaB_

triangular (B present)

1

aabb

ovoid (A and B absent)

© 2003 John Wiley and Sons Publishers

Only when both pathways are blocked by homozygous recessive alleles is the triangular phenotype suppressed and an ovoid capsule produced.

A & B completely dominant

9

3

aa epistasis towards B and b

9

3

A epistasis towards B and b

12

3 1 Squash fruit

A epistasis towards B & b; bb epistasis towards A & a

13*

3

aa epistasis towards B and b; bb epistasis towards A & a

9

7

A epistasis towards B & b; B epistasis towards A and a

15

3 1 Mendel’s cross 4

Mice coat colour colour

Fowl plumage colour Corn kernel colour

1 Fowl leg plumage

Polygenic Inheritance

Colour of wheat kernels

(1:4:6:4:1 ratio) Parents:

AABB dark red

F1

x aabb white

AaBb medium red

F2 Genotype

Phenotype

2

AABB

DARK RED

3

AABb, AaBB

MEDIUM DARK RED

4

AAbb, aaBB, AaBb

MEDIUM RED

5

aaBb, Aabb

LIGHT RED

1

aabb

WHITE

Pleiotropy: A condition where changes in one gene can affect more than one phenotype. Example: Phenylketonuria – a disease caused by the deficiency of phenylalanine hydroxylase leading to accumulation of phenylalanine in the plasma. Clinical manifestation includes fair skin, blonde hair,mental retardation, musty odour.

Incomplete Expressivity is seen in cases where the same genotype may, for unknown reasons, have variability in their phenotypes. Example: Genetic diseases such as diabetes. Incomplete Penetrance is seen when an individual with a particular genotype, for unknown reasons, does not express the phenotype.

Modifications to Mendelian Ratio Key Points • • • • • • • •

Incomplete dominance and codominance Lethal genes Gene interaction Epistasis Polygenic inheritance Linkage Pleiotropy Incomplete expressivity & incomplete penetrance

Berikan hukum-hukum Mendel. Terangkan keadaan-keadaan yang akan memberikan keputusan lain daripada keputusan Mendel. State Mendel’s laws. Explain the conditions whereby Mendel’s laws were modified. Times New Roman, font size 12, single spacing Maximum 3 pages (3 x 49 lines) excluding pictures Last date of submission – 2nd August 2006

Population Genetics 1. Hardy-Weinberg’s law. 2. Allele frequency can be obtained in 2 ways: from the population and from Hardy-Weinberg’s formula. 3. At equilibrium, genotype frequencies can be determined by Hardy-Weinberg’s formula. 4. Factors influencing allele and genotype frequency.