The Chromosomal Basis of Inheritance

1
Chapter 15 The Chromosomal Basis of Inheritance
2
Fig. 15-1
0.5 mm
Parent
Bud
(a) Hydra
3
Fig. 15-2a
Yellow-round seeds (YYRR)
Green-wrinkled seeds ( yyrr)
P Generation
y
Y
r
?
R
r
R
Y
y
Meiosis
Fertilization
r
y
Y
R
Gametes
All F1 plants produce yellow-round seeds (YyRr)
4
Fig. 15-2b
All F1 plants produce yellow-round seeds (YyRr)
0.5 mm
F1 Generation
R
R
y
y
r
r
Y
Y
LAW OF SEGREGATION The two alleles for each gene
separate during gamete formation.
LAW OF INDEPENDENT ASSORTMENT Alleles of genes
on nonhomologous chromosomes assort
independently during gamete formation.
Meiosis
r
R
r
R
Metaphase I
Y
y
Y
y
1
1
r
R
R
r
Anaphase I
Y
Y
y
y
Metaphase II
r
R
R
r
2
2
y
Y
y
Y
y
Y
Y
y
Y
Y
y
y
Gametes
r
R
r
R
r
r
R
R
yr
4
4
yR
4
Yr
4
YR
1
1
1
1
3
3
5
Fig. 15-3
Thomas Hunt Morgan and his Fruit Flies
6
Fig. 15-4a
Morgans Experiment
EXPERIMENT
P
?
Generation
F1
All offspring had red eyes
Generation
7
Fig. 15-4b
Morgans Experiment (cont.)
RESULTS
F2
Generation
8
Fig. 15-4c
CONCLUSION

w
w
P
X
X
?
Generation
X
Y

w
w
Sperm
Eggs


F1
w
w

w
Generation
w

w
Sperm
Eggs


w
w

w
F2
Generation
w
w
w

w
9
Fig. 15-6
Sex Determination
10
Fig. 15-7
Sex Linked Genes
XnY
XnY
XNXN
XNXn
?
?
XNY
XNXn
?
Sperm
Sperm
Sperm
Y
Xn
XN
Y
Xn
Y
Eggs
Eggs
XNXN
Eggs
XNXn
XN
XNY
XN
XNY
XNXn
XNY
XN
XNXn
XNY
XnXN
XnY
XnXn
XnY
XN
Xn
Xn
(a)
(b)
(c)
11
Fig. 15-8
X Inactivation
12
Fig. 15-UN1
b vg
b vg
?
Parents in testcross
b vg
b vg
b vg
b vg
Most offspring
or
b vg
b vg
13
Fig. 15-9-1
EXPERIMENT
P Generation (homozygous)
Wild type (gray body, normal wings)
Double mutant (black body, vestigial wings)
?
b b vg vg
b b vg vg
14
Fig. 15-9-2
EXPERIMENT
P Generation (homozygous)
Wild type (gray body, normal wings)
Double mutant (black body, vestigial wings)
?
b b vg vg
b b vg vg
F1 dihybrid (wild type)
Double mutant
TESTCROSS
?
b b vg vg
b b vg vg
15
Fig. 15-9-3
EXPERIMENT
P Generation (homozygous)
Wild type (gray body, normal wings)
Double mutant (black body, vestigial wings)
?
b b vg vg
b b vg vg
F1 dihybrid (wild type)
Double mutant
TESTCROSS
?
b b vg vg
b b vg vg
Testcross offspring
b vg
b vg
b vg
b vg
Eggs
Black- normal
Gray- vestigial
Black- vestigial
Wild type (gray-normal)
b vg
Sperm
b b vg vg
b b vg vg
b b vg vg
b b vg vg
16
Fig. 15-9-4
EXPERIMENT
P Generation (homozygous)
Wild type (gray body, normal wings)
Double mutant (black body, vestigial wings)
?
b b vg vg
b b vg vg
F1 dihybrid (wild type)
Double mutant
TESTCROSS
?
b b vg vg
b b vg vg
Testcross offspring
b vg
b vg
b vg
b vg
Eggs
Black- normal
Gray- vestigial
Black- vestigial
Wild type (gray-normal)
b vg
Sperm
b b vg vg
b b vg vg
b b vg vg
b b vg vg
PREDICTED RATIOS
1
If genes are located on different chromosomes
1
1
1



If genes are located on the same chromosome
and parental alleles are always inherited
together
1
1
0
0



965
185


944
206

RESULTS
17
Fig. 15-UN2
Gametes from yellow-round heterozygous parent
(YyRr)
Yr
YR
yr
yR
Gametes from green- wrinkled homozygous recessive
parent ( yyrr)
yr
yyRr
YyRr
yyrr
Yyrr
Parental- type offspring
Recombinant offspring
18
Fig. 15-10
Testcross parents
Gray body, normal wings (F1 dihybrid)
Black body, vestigial wings (double mutant)
b vg
b vg
b vg
b vg
Replication of chromo- somes
Replication of chromo- somes
b vg
b vg
b vg
b vg
b vg
b vg
b vg
b vg
Meiosis I
b vg
Meiosis I and II
b vg
b vg
b vg
Meiosis II
Recombinant chromosomes
b vg
b vg
b vg
b vg
Eggs
Testcross offspring
965 Wild type (gray-normal)
944 Black- vestigial
206 Gray- vestigial
185 Black- normal
b vg
b vg
b vg
b vg
b vg
b vg
b vg
b vg
b vg
Sperm
Parental-type offspring
Recombinant offspring
391 recombinants
Recombination frequency

? 100 17
2,300 total offspring
19
Fig. 15-10a
Testcross parents
Black body, vestigial wings (double mutant)
Gray body, normal wings (F1 dihybrid)
b vg
b vg
b vg
b vg
Replication of chromo- somes
Replication of chromo- somes
b vg
b vg
b vg
b vg
b vg
b vg
b vg
b vg
Meiosis I
b vg
Meiosis I and II
b vg
b vg
b vg
Meiosis II
Recombinant chromosomes
b vg
b vg
b vg
b vg
b vg
Sperm
Eggs
20
Fig. 15-10b
Recombinant chromosomes
b vg
b vg
b vg
b vg
Eggs
965 Wild type (gray-normal)
944 Black- vestigial
185 Black- normal
206 Gray- vestigial
Testcross offspring
b vg
b vg
b vg
b vg
b vg
b vg
b vg
b vg
b vg
Sperm
Recombinant offspring
Parental-type offspring
Recombination frequency
391 recombinants
? 100 17

2,300 total offspring
21
Chromosomal Mutations

• Alteration of chromosome number
• Aneuploidy
• Monosomic (2n 1)
• Trisomic (2n 1)
• Polyploidy
• Alteration in chromosome structure

22
Chromosomal Mutations

• Alteration of chromosome number
• Aneuploidy
• Monosomic (2n 1)
• Trisomic (2n 1)
• Polyploidy
• Alteration in chromosome structure

23
Fig. 15-13-2
Meiosis I
Nondisjunction
Meiosis II
Nondisjunction
(b) Nondisjunction of sister chromatids in
meiosis II
(a) Nondisjunction of homologous chromosomes
in meiosis I
24
Fig. 15-13-3
Meiosis I
Nondisjunction
Meiosis II
Nondisjunction
Gametes
n 1
n 1
n 1
n
n
n 1
n 1
n 1
Number of chromosomes
(b) Nondisjunction of sister chromatids in
meiosis II
(a) Nondisjunction of homologous chromosomes
in meiosis I
25
Fig. 15-16
Autosomal Aneuploidy
26
Aneuploidy in Sex Chromosomes
27
Chromosomal Mutations

• Alteration of chromosome number
• Aneuploidy
• Monosomic (2n 1)
• Trisomic (2n 1)
• Polyploidy
• Alteration in chromosome structure

28
Chromosomal Mutations

• Alteration of chromosome number
• Aneuploidy
• Monosomic (2n 1)
• Trisomic (2n 1)
• Polyploidy
• Alteration in chromosome structure

29
Fig. 15-15
A B C D E F G H
A B C E F G H
Deletion
(a)
A B C D E F G H
A B C B C D E F G H
Duplication
(b)
A B C D E F G H
A D C B E F G H
Inversion
(c)
A B C D E F G H
M N O C D E F G H
(d)
Reciprocal translocation
M N O P Q R
A B P Q R
30
Fig. 15-17
Reciprocal translocation
Normal chromosome 9
Translocated chromosome 9
Translocated chromosome 22 (Philadelphia
chromosome)
Normal chromosome 22
31
Exceptions to Chromosome Theory

• Genomic imprinting
• Organelle genes