Chapter 14~Mendel & The Gene Idea

Mendelian genetics

Trait– variant for a character ex:

purple

True-breeding – all offspring same variety

Hybridization – Cross of two pure breeding

P generation = parents F1 generation = first

filial generation

Leading to the Law of Segregation Alleles = Different

versions of genes – one from each parent

If the two alleles are different – the dominant allele is

expressed– the recessive allele is

“hidden” Mendel’s Law of

Segregation– The alleles for each

character segregate during gamete production

Genetic vocabulary……. Punnett square: predicts

the results of a genetic cross between individuals of known genotype

Homozygous: alleles are the same

Heterozygous: two alleles are different

Phenotype: an organism’s traits (what you SEE)

Genotype: an organism’s genetic makeup: TT, Tt, tt

Testcross: cross with a homozygous recessive x dominant phenotype (but unknown genotype)

The Law of Independent Assortment

Monohybrid cross vs. dihybrid cross

The two pairs of alleles segregate independently of each other.

Mendel’s Law of Independent Assortment

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

Genes working together Incomplete dominance:

blending of the phenotypes of the 2 parents. – Ex: snapdragons

Codominance: two alleles affect the phenotype in separate ways – Ex: human blood types A & B

Multiple alleles: more than 2 possible alleles for a gene. – Ex: human blood types

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

Gene Interaction

Pleiotropy: genes with multiple phenotypic effect. – Ex: sickle-cell anemia

Epistasis: a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus. – Ex: mice coat color

Polygenic Inheritance: an additive effect of two or more genes on a single phenotypic character Ex: human skin pigmentation and height

Pleiotropy

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

Epistasis

•Polygenic inheritance

•Quantitative variation usually is additive effect of two or more genes on a phenotype

•Skin color in humans is an example

Human disorders

The family pedigree: – Diagram showing family relationships:

• Circle - female• Square - Male

Recessive disorders:– •Cystic fibrosis– •Tay-Sachs– •Sickle-cell

Dominant disorders:•Huntington’s

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)

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)

TESTING

•Amniocentesis: (between week: 15-18) Prenatal diagnosis of chromosomal abnormalities

•CVS = Chorionic villi (villus) sampling (10-12 weeks)

Bozeman: Mr. Anderson

https://www.youtube.com/watch?v=rIe7mPXkYhs