8/13/2019 4.3 Theoretical Genetics 2

1/20

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

8/13/2019 4.3 Theoretical Genetics 2

2/20

DEFINITIONS

Genotype: the alleles of an organism

Phenotype: The characteristics of an organism

Dominant allele: the allele that gets expressed inheterozygous condition

Recessive allele; the allele that has an effect on thephenotype when present in the homozygous state.

Codominant alleles: pairs of alleles that are both expressedwhen present

Locus: specific position of a gene in a chromosome

Homozygous; having two copies of the same allele.

Heterozygous: having two different alleles of a gene

Carrier: a person with one recessive faulty allele for a geneticdisorder

Test cross: testing a suspected heterozygote by crossingwith the homozygous recessive

8/13/2019 4.3 Theoretical Genetics 2

3/20

MONOHYBRIDCROSSES

Complete Dominance

Incomplete Dominance

Codominance

8/13/2019 4.3 Theoretical Genetics 2

4/20

#1 - COMPLETEDOMINANCEP: RR rr

F1: Genotype Phenotype Type of Genotype

Rr red heterozygous

F1Cross: Rr Rr

Punnett Square:

F2: Genotype Phenotype Type of Genotype

RR red homozygous

Rr red heterozygous

Rr red heterozygous

rr white homozygous

RR Rr

Rr rr

R

r

R r

F2Genotypic Ratio:1 RR : 2 Rr : 1 rr

F2Phenotypic Ratio:

3 red: 1 white

8/13/2019 4.3 Theoretical Genetics 2

5/20

#4 - INCOMPLETEDOMINANCEP: RR rr

F1: Genotype Phenotype Type of Genotype

Rr pink heterozygous

F1Cross: Rr Rr

Punnett Square:

F2: Genotype Phenotype Type of Genotype

RR red homozygous

Rr pink heterozygous

Rr pink heterozygous

rr white homozygous

RR Rr

Rr rr

R

r

R r

F2Genotypic Ratio:1 RR : 2 Rr : 1 rr

F2Phenotypic Ratio:

1 red: 2 pink: 1 white

8/13/2019 4.3 Theoretical Genetics 2

6/20

#7 - CODOMINANCEP: RR WW

F1: Genotype Phenotype Type of Genotype

RW red& white heterozygous

F1Cross: RW RW

Punnett Square:

F2: Genotype Phenotype Type of Genotype

RR red homozygous

RW red& white heterozygous

RW red& white heterozygous

WW white homozygous

RR RW

RW WW

R

W

R W

F2Genotypic Ratio:1 RR : 2 RW : 1 WW

F2Phenotypic Ratio:1 red : 2 red& white: 1 white

8/13/2019 4.3 Theoretical Genetics 2

7/20

ABO BLOODTYPING

8/13/2019 4.3 Theoretical Genetics 2

8/20

ABO BLOODTYPING

% of Blood Types in U.S. Caucasions

O+

38%

O-

7%AB+

3%AB-

1%

A+

34%

A-

6%

B+

9%

B-

2%

8/13/2019 4.3 Theoretical Genetics 2

9/20

ABO BLOODTYPING

8/13/2019 4.3 Theoretical Genetics 2

10/20

ABO BLOODTYPING

A B AB O

A Y Y

B Y Y

AB Y

O Y Y Y Y

D

O

NO

R

RECIPIENT

8/13/2019 4.3 Theoretical Genetics 2

11/20

#15 - BLOODTYPINGP: IAi IBi

Punnett Square:

F1: Genotype Phenotype

IAIB AB

IAi A

IBi B

ii O

IAIB IAi

IBi ii

IA

i

IB i

8/13/2019 4.3 Theoretical Genetics 2

12/20

ADDITIONALCROSSES

Sex Determination

Sex Linkage

ABO Blood Typing

8/13/2019 4.3 Theoretical Genetics 2

13/20

#12 - SEXLINKAGE- HAEMOPHILIAP: XHY XHXh

Punnett Square:

F1: Genotype Phenotype Sex Type of Genotype

XHXH normal F homozygous

XHXh carrier F heterozygous

XHY normal M hemizygous

XhY hemophilia M hemizygous

XHXH XHXh

XHY XhY

XH

Y

XH Xh

8/13/2019 4.3 Theoretical Genetics 2

14/20

#11 - SEXDETERMINATIONP: XY XX

XX XX

XY XY

X

Y

X X

Ratio:

1 XX : 1 XY

8/13/2019 4.3 Theoretical Genetics 2

15/20

DIHYBRIDCROSSES

Complete Dominance

8/13/2019 4.3 Theoretical Genetics 2

16/20

#8 - COMPLETEDOMINANCEP: yyrr YYRR

F1: Genotype Phenotype Type of Genotype

YyRr yellow/roundheterozygousF1Cross: YyRr YyRr

Punnett Square:

F2: Genotype Phenotype

9 Y_R_ yellow/round

3 Y_rr yellow/wrinkled

3 yyR_ green/round

1 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

8/13/2019 4.3 Theoretical Genetics 2

17/20

PEDIGREES

8/13/2019 4.3 Theoretical Genetics 2

18/20

PEDIGREES

Normal

Affected

Carrier

8/13/2019 4.3 Theoretical Genetics 2

19/20

PEDIGREES

Example: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

8/13/2019 4.3 Theoretical Genetics 2

20/20

#18 - PEDIGREES

XCXC XcYXCXc XCY

XCY XCXc XCY

XcYXCXC

You!