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Chapter 3 - Lecture 3

Modifications of the Mendelian Ratios

Allelic interaction

Modifications of the 3:1 ratio

Gene Interaction

Modifications of the 9:3:3:1 ratio

The Principles of Genetics

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Incomplete dominanceFlower colour in Snapdragons

RR Rr rrred pink white

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Incomplete DominanceFlower colour in Snapdragon

Red RR rr whiteRr Pink

R r

R RRRed

RrPink

r RrPink

rrwhite

1 Red 2 Pink 1 white

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Co-dominance

Coat colour in shorthorn Cattle

Red r1r1 r2r2 whiter1r2 Roan

r1 r2

r1 r1r1Red

r1r2Roan

r2 r1r2Roan

r2r2white

1 Red 2 Roan 1 white

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HbAHbA HbAHbS HbSHbS

Normal - anemia - Lethal

SYMPTOMS

Sickle shapedRed Blood Cells

in HbA HbS persons

Circulatory problemsLoss of blood cells

(anemia)

Organ damage

DEATH

Co-dominance in humans; Sickle cell anemia

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Sickle cell anemiaCAUSE: autosomal recessive on chromosome 11

A changed to T (glu to val)

Gene on chromosome #11 that codes for

part of hemoglobin protein

More common in Africans

1 in 500 = hh, 1 in 10 = Hh carriers for gene HbAHbS persons have sickle cell TRAIT

make some normal RBCs, some sickled cells

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Sickle cell anemia

Mutation of hemoglobin A to hemoglobin S

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Lethal genes, coat color in mice

Dominant lethal

Yellow Yy Yy Yellow

Y Y

Y YY

Yellow Dies

Yy

Yellow

y Yy

Yellow

Yy

Black

2- Yellow 1- Black

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Albinism in Maize, Recessive lethal

G g

G GG

Green

Gg

Green

g Gg

Green

Gg

White, Dies

3- Green 1- white, Dies

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Lethal genes, short phalanges in man

Short phalanges Bb Bb Short phalanges

B b

B BB

No Phalanges

Bb

Short phalanges

b Bb

Short phalanges

bb

Normal phalanges

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Discovery of Gene InteractionTwo Genes Controlling one Character

Crown shape in domestic fowl

WalnutRRPPRRPp

RrPPRrPp

PearrPP

rrPp

Rose

RRppRrpp

Singlerrpp

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Two Genes Controlling the Same Character

Feather color in sparrow

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Epistatic genes (Inhibiting genes)Feather colour in domestic fowl

Leghorn White CCII ccii Silki WhiteCI ciCcIi White

cicICiCI

CcIiCcIICCIiCCIICI

CciiCcIiCciiCCIiCi

ccIiccIICcIiCcIIcI

cciiccIiCciiCcIici

13 White

3 Colored

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Complementary genesFlower color in Lathyrus odoratus

White CCpp ccPP WhiteCp cP

CcPp Colored

cpcPCpCP

CcPpCcPPCCPpCCPPCP

CcppCcPpCCppCCPpCp

ccPpccPPCcPpCcPPcP

CcppccPpCcppCCPpcp

9 Colored

7 White

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Duplicate genesCapsule shape in Shephers purse (Capsella bursa pastoris)

Trianular T1T1T2T2 t1t1t2t2 Spindle

T1T2 t1t2T1t1t2t2 Trianular

T1T2 T1t2 t1T2 t1t2

T1T2 T1T1T2T2Trianular

T1T2T1t2Trianular

T1T2T1T2Trianular

T1T2t1t2Trianular

T1t2 T1T2T1t2Trianular

T1t2T1t2Trianular

T1t2T1t2Trianular

T1t2T1t2Trianular

t1T2 T1T2t1T2Trianular

T1t2t1T2Trianular

t1T2t1T2Trianular

t1T2t1T2Trianular

t1t2 T1T2t1t2Trianular

T1t2t1t2Trianular

t1t2t1T2Trianular

t1t2t1T2Spindle

15 Trianular 1 Spindle

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Modifying Genes = Supplementary GenesCoat Color in mice

Black aaCC AAcc AlbinoaC Ac

AaCc Agouti

AC Ac aC ac

AC AACC AACc AaCC AaCc

Ac AACc AAcc AaCc Aacc

aC AaCC AaCC aaCC aaCc

ac AaCc Aacc aaCc aacc

9 Agouti : 4 Albino : 1 Black

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Chapter 3 test

Mark the correct answers with () and the

wrong answers with (x)1. Sickle cell anemia is a classical example of co-

dominance and lethal genes.

2. The failure to synthesize chlorophyll in maize is anexample of lethal genes

3. Yellow coat color in mice is an example ofdominant lethal genes

Circle the correct answer of the following

Complementary genes modify the classical dihybridratio 9:3:3:1 to:- a. 15:1 - b. 9:7 - c. 13:4 - d. 9:4:3

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Thank you

End of Lecture THREE