Transcript Document 7204293

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 organism
Phenotype: The characteristics of an organism
Dominant allele: the allele that gets expressed in
heterozygous condition
Recessive 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 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
genetic disorder
Test cross: testing a suspected heterozygote by crossing
with the homozygous recessive
MONOHYBRID CROSSES
Complete Dominance
Incomplete Dominance
Codominance
#1 - COMPLETE DOMINANCE
P:
F1:
RR  rr
Genotype
Phenotype
Rr
red
F1 Cross:
Rr  Rr
Punnett Square: R
r
F2:
R
RR
Rr
r
Rr
rr
Genotype
RR
Rr
Rr
rr
Type of Genotype
heterozygous
F2 Genotypic Ratio:
1 RR : 2 Rr : 1 rr
F2 Phenotypic Ratio:
3 red: 1 white
Phenotype
red
red
red
white
Type of Genotype
homozygous
heterozygous
heterozygous
homozygous
#4 - INCOMPLETE DOMINANCE
P:
F1:
RR  rr
Genotype
Phenotype
Rr
pink
F1 Cross:
Rr  Rr
Punnett Square: R
r
F2:
R
RR
Rr
r
Rr
rr
Genotype
RR
Rr
Rr
rr
Type of Genotype
heterozygous
F2 Genotypic Ratio:
1 RR : 2 Rr : 1 rr
F2 Phenotypic Ratio:
1 red: 2 pink : 1 white
Phenotype
red
pink
pink
white
Type of Genotype
homozygous
heterozygous
heterozygous
homozygous
#7 - CODOMINANCE
P:
F1:
RR  WW
Genotype
Phenotype Type of Genotype
RW
red & white heterozygous
F1 Cross:
RW  RW
Punnett Square: R
W
R
W
F2:
RR
RW F2 Genotypic Ratio:
RW WW
Genotype
RR
RW
RW
WW
1 RR : 2 RW : 1 WW
F2 Phenotypic Ratio:
1 red : 2 red & white : 1 white
Phenotype
red
red & white
red & white
white
Type of Genotype
homozygous
heterozygous
heterozygous
homozygous
ABO BLOOD TYPING
ABO BLOOD TYPING
% of Blood Types in U.S. Caucasions
B+
9%
B2%
A6%
O+
38%
A+
34%
AB- AB+
1% 3%
O7%
ABO BLOOD TYPING
ABO BLOOD TYPING
RECIPIENT
A
D
O
N
O
R
A
B
Y
B
O
Y
Y
AB
O
AB
Y
Y
Y
Y
Y
Y
#15 - BLOOD TYPING
P:
I Ai  I Bi
Punnett Square:
IB
F1:
i
IA
I AI B
I Ai
i
I Bi
ii
Genotype
IAIB
I Ai
I Bi
ii
Phenotype
AB
A
B
O
ADDITIONAL CROSSES
Sex Determination
Sex Linkage
ABO Blood Typing
#12 - SEX LINKAGE- HAEMOPHILIA
P:
XHY  XHXh
Punnett Square:
XH
Xh
XH XHXH XHXh
Y
F1:
Genotype
XHXH
XHXh
XHY
XhY
XHY
XhY
Phenotype
normal
carrier
normal
hemophilia
Sex
F
F
M
M
Type of Genotype
homozygous
heterozygous
hemizygous
hemizygous
#11 - SEX DETERMINATION
P:
XY  XX
X
X
X
XX
XX
Y
XY
XY
Ratio:
1 XX : 1 XY
DIHYBRID CROSSES
Complete Dominance
#8 - COMPLETE DOMINANCE
P:
F1:
yyrr  YYRR
Genotype
Phenotype Type of Genotype
YyRr
yellow/round heterozygous
YR
Yr
yR
yr
F1 Cross:
YyRr  YyRr
Punnett Square:
YR YYRR YYRr YyRR YyRr
YyRr
Yyrr
yR YyRR YyRr yyRR
yyRr
Yr
F2:
Genotype
9 Y_R_
3 Y_rr
3 yyR_
1 yyrr
YYRr
yr YyRr
Phenotype
yellow/round
yellow/wrinkled
green/round
green/wrinkled
YYrr
Yyrr
yyRr
yyrr
PEDIGREES
PEDIGREES
Normal
Affected
Carrier
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.
XHXh
XhY
XHY
XHY XHXH
You!
#18 - PEDIGREES
XCXC
XcY
XCY
XCXc
XCY
XCXC
XCXc
XcY
You!
XCY