Chapter 14

Chapter 14Chapter 14

Mendel and the Gene IdeaMendel and the Gene Idea

LE 14-2

Removed stamensfrom purple flower

Transferred sperm-bearing pollen fromstamens of whiteflower to egg-bearing carpel ofpurple flower

Carpel Stamens

Parentalgeneration(P)

Pollinated carpelmatured into pod

Planted seedsfrom pod

Examinedoffspring:all purpleflowers

Firstgenerationoffspring(F1)

LE 14-3

P Generation

(true-breedingparents)

F1 Generation

(hybrids)

F2 Generation

Purpleflowers

Whiteflowers

All plants hadpurple flowers

Table 14-1

Mendel’s LawsMendel’s Laws

Law of dominanceLaw of dominance– Dominant allelesDominant alleles– Recessive allelesRecessive alleles

Law of segregationLaw of segregation– Distribution of homologous Distribution of homologous

chromosomeschromosomes Law of independent assortmentLaw of independent assortment

LE 14-4

Allele for purple flowers

Homologouspair ofchromosomes

Allele for white flowers

Locus for flower-color gene

LE 14-6Phenotype

Purple

Purple3

Purple

Genotype

PP(homozygous

Pp(heterozygous

Pp(heterozygous

pp(homozygous

1

2

1

Ratio 1:2:1

White

Ratio 3:1

1

LE 14-5_2

Appearance:

P Generation

Genetic makeup:

Gametes

F1 Generation

Appearance:Genetic makeup:

Gametes:

F2 Generation

Purple flowersPp

P p1 21 2

P p

F1 sperm

F1 eggsPP Pp

Pp pp

P

p

3 : 1

Purpleflowers

PP

Whiteflowers

pp

P p

LE 14-7

Dominant phenotype,unknown genotype:

PP or Pp?

If PP,then all offspring

purple:

p p

P

P

Pp Pp

Pp Pp

If Pp,then 1

2 offspring purpleand 1

2 offspring white:

p p

P

Ppp pp

Pp Pp

Recessive phenotype,known genotype:

pp

LE 14-8

P Generation

F1 Generation

YYRR

Gametes YR yr

yyrr

YyRr

Hypothesis ofdependentassortment

Hypothesis of independent assortment

SpermEggs

YR

Yr

yrYR

YR

yr

Eggs

YYRR YyRr

YyRr yyrr yR

yrPhenotypic ratio 3:1

F2 Generation(predictedoffspring)

YYRR YYRr YyRR YyRr

YYRr YYrr YyRr Yyrr

YyRR YyRr yyRR yyRr

YyRr Yyrr yyRr yyrr

Phenotypic ratio 9:3:3:1

YR Yr yR yr

Sperm

12

14

14

14

14

1 43

4

12

12

12

14

916

316

316

316

14

14

14

LE 14-9

Segregation ofalleles into eggs

Rr

Sperm

R r

R

rR

R

R

r

Eggs

r

R

r

r

Segregation ofalleles into sperm

Rr

12

12

14

14

14

14

12

12

Complex Inheritance PatternsComplex Inheritance Patterns

CodominanceCodominance Incomplete dominanceIncomplete dominance Multiple allelesMultiple alleles PleiotropyPleiotropy EpistasisEpistasis Polygenic inheritancePolygenic inheritance Norm of reaction/MultifactorialNorm of reaction/Multifactorial

LE 14-10

RedCRCR

Gametes

P Generation

CR CW

WhiteCWCW

PinkCRCW

CRGametes CW

F1 Generation

F2 Generation Eggs

CR CW

CR

CRCR CRCW

CRCW CWCW

CW

Sperm

12

12

12

12

12

12

Table 14-2

LE 14-11

Sperm

BC bC Bc bc

BbCcBBCcBbCCBBCC

BbCC bbCC BbCc bbCc

BbccBBccBbCcBBCc

BbCc bbCc Bbcc bbcc

BC

bC

Bc

bc

BbCc BbCc

14

14

14

14

14

14

14

14

916

316

416

LE 14-12

aabbcc Aabbcc AaBbcc AaBbCc AABbCc AABBCc AABBCC

AaBbCcAaBbCc

20/64

15/64

6/64

1/64

Fra

ctio

n o

f p

rog

eny

Figure 14-13

LE 14-14a

Ww ww ww Ww

Ww wwWwwwwwWw

WW wwor

Ww

No widow’s peak

Thirdgeneration

(two sisters)

Widow’s peak

Second generation(parents plus aunts

and uncles)

First generation(grandparents)

Dominant trait (widow’s peak)

LE 14-14b

First generation(grandparents) Ff Ff

FF or Ff ff ff Ff Ff

ff

ff

Ff

Second generation(parents plus aunts

and uncles)

Thirdgeneration

(two sisters)

Attached earlobe Free earlobe

ff FForFf

Recessive trait (attached earlobe)

Human Traits and Mendelian Human Traits and Mendelian InheritanceInheritance

Pedigree chartsPedigree charts Recessive DisordersRecessive Disorders

– AlbinismAlbinism– Tay-SachsTay-Sachs– Cystic fibrosisCystic fibrosis– Sickle-Cell DiseaseSickle-Cell Disease

More on human traits…More on human traits…

Dominant disordersDominant disorders– Less common than recessive alleles that Less common than recessive alleles that

cause diseasecause disease– Huntington’s diseaseHuntington’s disease

Multifactorial disordersMultifactorial disorders– Heart diseaseHeart disease– DiabetesDiabetes– CancerCancer– SchizophreniaSchizophrenia

Testing and CounselingTesting and Counseling

Identifying carriersIdentifying carriers Fetal testingFetal testing

– AmniocentesisAmniocentesis– Chorionic villus samplingChorionic villus sampling

LE 14-17a

Amniocentesis

Amnioticfluidwithdrawn

Fetus

A sample ofamniotic fluid canbe taken starting atthe 14th to 16thweek of pregnancy.

Centrifugation

Placenta Uterus Cervix

Fluid

Fetalcells

Biochemical tests can beperformed immediately onthe amniotic fluid or lateron the cultured cells. Biochemical

tests

Severalweeks

Karyotyping

Fetal cells must be culturedfor several weeks to obtainsufficient numbers forkaryotyping.

LE 14-17b

Chorionic villus sampling (CVS)

Placenta Chorionic villi

Fetus

Suction tubeinserted throughcervix

Fetalcells

Biochemicaltests Karyotyping and biochemical

tests can be performed onthe fetal cells immediately,providing results within a dayor so.

Severalhours

A sample of chorionic villustissue can be taken as earlyas the 8th to 10th week ofpregnancy.

Karyotyping

LE 14-UN273

George Arlene

MichaelAnn

Carla

WilmaSam

TinaAlanDaniel

TomSandra

Christopher