4.3 THEORETICALGENETICS To be able to define the key terms of

theoretical genetics To describe inheritance patterns using

inheritance diagrams To be able to explain sex linkage

DEFINITIONS

Genotype: the alleles of an organismPhenotype: The characteristics of an organismDominant allele: the allele that gets expressed in heterozygous conditionRecessive allele; the allele that has an effect on the phenotype when present in the homozygous state.Codominant alleles: pairs of alleles that are both expressed when presentLocus: specific position of a gene in a chromosomeHomozygous; having two copies of the same allele.Heterozygous: having two different alleles of a geneCarrier: a person with one recessive faulty allele for a genetic disorderTest cross: testing a suspected heterozygote by crossing with the homozygous recessive

MONOHYBRID CROSSES

Complete Dominance

Incomplete Dominance

Codominance

#1 - COMPLETE DOMINANCEP: RR rrF1: Genotype Phenotype Type of Genotype

Rr red heterozygousF1 Cross: Rr RrPunnett Square:

F2: Genotype Phenotype Type of GenotypeRR red homozygousRr red heterozygousRr red heterozygousrr white homozygous

RR Rr

Rr rr

R

r

R r

F2 Genotypic Ratio:1 RR : 2 Rr : 1 rrF2 Phenotypic Ratio:3 red: 1 white

#4 - INCOMPLETE DOMINANCEP: RR rrF1: Genotype Phenotype Type of Genotype

Rr pink heterozygousF1 Cross: Rr RrPunnett Square:

F2: Genotype Phenotype Type of GenotypeRR red homozygousRr pink heterozygousRr pink heterozygousrr white homozygous

RR Rr

Rr rr

R

r

R r

F2 Genotypic Ratio:1 RR : 2 Rr : 1 rrF2 Phenotypic Ratio:1 red: 2 pink : 1 white

#7 - CODOMINANCEP: RR WWF1: Genotype Phenotype Type of Genotype

RW red & white heterozygousF1 Cross: RW RWPunnett Square:

F2: Genotype Phenotype Type of GenotypeRR red homozygousRW red & white heterozygousRW red & white heterozygousWW white homozygous

RR RW

RW WW

R

W

R W

F2 Genotypic Ratio:1 RR : 2 RW : 1 WWF2 Phenotypic Ratio:1 red : 2 red & white : 1 white

ABO BLOOD TYPING

ABO BLOOD TYPING% of Blood Types in U.S. Caucasions

O+38%

O-7%AB+

3%AB-1%

A+34%

A-6%

B+9%

B-2%

ABO BLOOD TYPING

ABO BLOOD TYPING

A B AB O

A Y Y

B Y Y

AB Y

O Y Y Y Y

DONOR

RECIPIENT

#15 - BLOOD TYPINGP: IAi IBiPunnett Square:

F1: Genotype PhenotypeIAIB ABIAi AIBi Bii O

IAIB IAi

IBi ii

IA

i

IB i

ADDITIONAL CROSSES

Sex Determination

Sex Linkage

ABO Blood Typing

#12 - SEX LINKAGE- HAEMOPHILIAP: XHY XHXh

Punnett Square:

F1: Genotype Phenotype Sex Type of GenotypeXHXH normal F homozygousXHXh carrier F heterozygousXHY normal M hemizygousXhY hemophilia M hemizygous

XHXH XHXh

XHY XhY

XH

Y

XH Xh

#11 - SEX DETERMINATIONP: XY XX

XX XX

XY XY

X

Y

X X

Ratio:1 XX : 1 XY

DIHYBRID CROSSES

Complete Dominance

#8 - COMPLETE DOMINANCEP: yyrr YYRRF1: Genotype Phenotype Type of Genotype

YyRr yellow/round heterozygousF1 Cross: YyRr YyRrPunnett Square:

F2: Genotype Phenotype9 Y_R_ yellow/round3 Y_rr yellow/wrinkled3 yyR_ green/round1 yyrr green/wrinkled

yR

yr

YR

Yr

YYRR YYRr YyRR YyRr

YYRr YYrr YyRr Yyrr

YyRR YyRr yyRR yyRr

YyRr Yyrr yyRr yyrr

YR Yr yR yr

PEDIGREES

PEDIGREES

Normal

Affected

Carrier

PEDIGREESExample:You are a normal female (homozygous). Both of your parents are normal. Your younger brother is normal and your older brother has hemophilia.

You!

XHXh XHY

XHYXhY XHXH

#18 - PEDIGREES

XCXC XcYXCXc XCY

XCY XCXc XCY

XcYXCXC

You!