Transcript video slide

Chapter 13-15
Meiosis, Sexual Life Cycles
Mendelian Genetics
Exceptions to the Rule
Overview: Living Things Can
Reproduce!!
 Heredity
• Is the transmission of traits from one generation
to the next
 Variation
• Shows that offspring differ somewhat in
appearance from parents and siblings
 Genetics
• Is the scientific study of heredity and
hereditary variation
Asexual Reproduction
 In asexual reproduction
• One parent produces genetically identical
offspring by mitosis
Parent
Bud
Figure 13.2
0.5 mm
Sexual Reproduction
 In sexual reproduction
• Two parents give rise to offspring that
have unique combinations of genes
inherited from the two parents
Life Cycle
 Fertilization & meiosis alternate in sexual life
cycles
 A life cycle
• Is the generation-to-generation sequence of
stages in the reproductive history of an
organism
After Replication: identical
sister chromatids
Key
Maternal set of
chromosomes (n = 3)
2n = 6
Paternal set of
chromosomes (n = 3)
Two sister chromatids
of one replicated
chromosome
Centromere
Figure 13.4
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)
The Human Life Cycle
Key
Haploid gametes (n = 23)
Haploid (n)
Ovum (n)
Diploid (2n)
Sperm
Cell (n)
MEIOSIS
Ovary
FERTILIZATION
Testis
Diploid
zygote
(2n = 46)
Mitosis and
development
Figure 13.5
Multicellular diploid
adults (2n = 46)
Meiosis reduces chromosome
from diploid to haploid
Interphase
Homologous pair
of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated chromosomes
Sister
chromatids
Diploid cell with
replicated
chromosomes
Meiosis I
1 Homologous
chromosomes
separate
Haploid cells with
replicated chromosomes
Meiosis II
2 Sister chromatids
separate
Figure 13.7
Haploid cells with unreplicated chromosomes
INTERPHASE
MEIOSIS I: Separates homologous chromosomes
PROPHASE I
Centrosomes
(with centriole pairs)
Sister
chromatids
Nuclear
envelopeTetrad
METAPHASE I
Chiasmata
ANAPHASE I
Sister chromatids
remain attached
Centromere
(with kinetochore)
Spindle
Metaphase
plate
Homologous
Microtubule
chromosomes
attached to
Chromatin
separate
kinetochore
Pairs of homologous
Chromosomes duplicate
Tertads line up
Homologous chromosomes
chromosomes split up
(red and blue) pair and exchange
segments; 2n = 6 in this example
Figure 13.8
MEIOSIS II: Separates sister chromatids
TELOPHASE I AND
CYTOKINESIS
PROPHASE II
Cleavage
furrow
Figure 13.8
Two haploid cells
form; chromosomes
are still double
METAPHASE II
ANAPHASE II
TELOPHASE II AND
CYTOKINESIS
Sister chromatids
separate
Haploid daughter cells
forming
During another round of cell division, the sister chromatids finally separate;
four haploid daughter cells result, containing single chromosomes
MITOSIS
MEIOSIS
Chiasma (site of
crossing over)
Parent cell
(before chromosome replication)
MEIOSIS I
Prophase I
Prophase
Chromosome
replication
Duplicated chromosome
(two sister chromatids)
Chromosome
replication
Tetrad formed by
synapsis of homologous
chromosomes
2n = 6
Metaphase
Chromosomes
positioned at the
metaphase plate
Anaphase
Telophase
Sister chromatids
separate during
anaphase
2n
Tetrads
positioned at the
metaphase plate
Homologues
separate
during
anaphase I;
sister
chromatids
remain together
Metaphase I
Anaphase I
Telophase I
Haploid
n=3
Daughter
cells of
meiosis I
2n
MEIOSIS II
Daughter cells
of mitosis
n
n
n
n
Daughter cells of meiosis II
Figure 13.9
Sister chromatids separate during anaphase II
Genetic Variations contributes
to Evolution
 Reshuffling of genetic material in
meiosis
• Produces genetic variation due to the
chromosome behaviors
• Homologous pairs orient randomly
• Independent assortment
• Crossing over
• Random fertilization
• mutations
Figure 14.4
Words to know
Allele for purple flowers
Locus for flower-color gene
Pair of
homologous
chromosomes
Allele for white flowers
Mendel and Genetics
 Law of Segregation:
• Two alleles for a trait separate during
gamate formation.
 Law of Independent Assortment
• Each pair of alleles separates
independently from other pairs.
Inheritance Patterns






Dominance /recessive
Codominance
Incomplete dominance
Levels: ex: Tay-Sachs Disease
Frequencies of dominant allele
Multiple alleles
Pleiotropy
 Most genes have multiple phenotypic
effects, a property called pleiotropy
 For example, pleiotropic alleles are
responsible for the multiple symptoms of
certain hereditary diseases, such as cystic
fibrosis and sickle-cell disease
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EPISTASIS:
BbEe
Eggs
1/
4 BE
1/
4 bE
1/
4 Be
1/
4
be
Sperm
1/ BE
4
1/
BbEe
4 bE
1/
4 Be
1/
4 be
BBEE
BbEE
BBEe
BbEe
BbEE
bbEE
BbEe
bbEe
BBEe
BbEe
BBee
Bbee
BbEe
bbEe
Bbee
bbee
9
: 3
: 4
POLYGENETIC:
AaBbCc
AaBbCc
Sperm
1/
1/
8
8
1/
1/
Eggs
8
1/
1/
8
8
1/
8
1/
1/
8
8
8
8
1/
8
1/
8
1/
1/
8
1/
8
1/
8
1/
8
Phenotypes:
Number of
dark-skin alleles:
1/
64
0
6/
64
1
15/
64
2
20/
64
3
15/
64
4
6/
64
5
1/
64
6
Pedigrees
Nature and Nurture: The Environmental Impact on
Phenotype
 Another departure from Mendelian
genetics arises when the phenotype for a
character depends on environment as well
as genotype
 The norm of reaction is the phenotypic
range of a genotype influenced by the
environment
© 2011 Pearson Education, Inc.
Correlating Behavior of a Gene’s
Alleles with Behavior of a Chromosome
Pair
© 2011 Pearson Education, Inc.
The Chromosomal Basis of Sex
• In humans and other
mammals:
X vs. Y
• Y is tiny!!
• The SRY gene on the Y
chromosome
• Some disorders caused by
recessive alleles on the X:
• Color blindness (mostly X-linked)
• Duchenne muscular dystrophy
• Hemophilia
© 2011 Pearson Education, Inc.
X Inactivation in Female Mammals
 Barr
body
 Females
are
mosaic
© 2011 Pearson Education, Inc.
Figure 15.8
X chromosomes
Allele for
orange fur
Early embryo:
Two cell
populations
in adult cat:
Allele for
black fur
Cell division and
X chromosome
inactivation
Active X
Inactive X
Active X
Black fur
Orange fur
Figure 15.11
Linked genes tend to be inherited together because they
are located near each other on the same chromosome
Recombination
frequencies
9%
Chromosome
9.5%
17%
b
cn
vg
Figure 15.12
Mutant phenotypes
Short
aristae
0
Long aristae
(appendages
on head)
Black
body
Cinnabar Vestigial
eyes
wings
48.5 57.5
Gray
body
Red
eyes
Brown
eyes
67.0
104.5
Normal
wings
Red
eyes
Wild-type phenotypes
(a) Deletion
A B C
D E
F G
Mutations
H
A deletion removes a chromosomal segment.
A B C
 Nondisjunct
ion 
Aneuploidy
 Breakage of
a
chromosome
:
• Deletion
• Duplication
• Inversion
© 2011 Pearson Education, Inc.
E
F G H
(b) Duplication
A B C
D E
F G
H
A duplication repeats a segment.
A B C
B C
D E
F G H
(c) Inversion
A B C
D E
F G H
An inversion reverses a segment within a
chromosome.
A D C
B E
F G H
(d) Translocation
A B C
D E
F G H
M N O
P Q
R
A translocation moves a segment from one
chromosome to a nonhomologous chromosome.
M N O
C D E
F G H
A
B P Q
R
Figure 15.15
Down Syndrome (Trisomy 21)
Aneuploidy of Sex Chromosomes
 Nondisjunctio
n of sex
chromosome
s:
• XXX
• Klinefelter
syndrome
(XXY)
• Monosomy X,
called Turner
syndrome,
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Genomic Imprinting
Mutant Igf2 allele
inherited from mother
Mutant Igf2 allele
inherited from father
Normal-sized mouse (wild type)
Dwarf mouse (mutant)
Normal Igf2 allele
is expressed.
Mutant Igf2 allele
is expressed.
Mutant Igf2 allele
is not expressed.
Normal Igf2 allele
is not expressed.
(b) Heterozygotes
Inheritance of Organelle Genes
 Mitochondria, chloroplasts, and
 inherited maternally
© 2011 Pearson Education, Inc.
Ch 15: Chromosomes!
Figure 15.2
P Generation
Yellow-round
seeds (YYRR)
Y
Y
Green-wrinkled
seeds (yyrr)
ry

R R
r
y
Meiosis
Fertilization
y
R Y
Gametes
r
All F1 plants produce
yellow-round seeds (YyRr).
F1 Generation
R
y
r
Y
R
r
Y
y
Meiosis
LAW OF SEGREGATION
The two alleles for each
gene separate during
gamete formation.
r
R
r
R
Y
y
LAW OF INDEPENDENT
ASSORTMENT Alleles of genes
on nonhomologous chromosomes
assort independently during
gamete formation.
Metaphase I
Y
y
1
1
R
r
r
R
Y
y
Anaphase I
Y
y
R
r
Y
y
r
R
Y
y
2
2
Gametes
R
R
1/
4
YR
F2 Generation
3
y
Y
Y
Fertilization recombines
the R and r alleles at
random.
Metaphase II
r
1/
4
Y
Y
y
r
r
r
1/
yr
4
y
y
R
R
1/
Yr
4
yR
An F1  F1 cross-fertilization
3
9
:3
:3
:1
Fertilization results in the
9:3:3:1 phenotypic ratio
in the F2 generation.
Figure 15.4b
CONCLUSION
P
Generation
X
X
w
X
Y
w
w
Eggs
F1
Generation
Sperm
w
w
w
w
w
Eggs
F2
Generation
w
w
w
Sperm
w
w
w
w
w
w
Figure 15.5
X
Y
Figure 15.6
44 
XY
44 
XX
Parents
22 
22 
X or Y
22 
X
Sperm
Egg
44 
XX
or
44 
XY
(a) The X-Y system Zygotes (offspring)
22 
XX
22 
X
76 
ZW
76 
ZZ
32
(Diploid)
16
(Haploid)
(b) The X-0 system
(c) The Z-W system
(d) The haplo-diploid system
Figure 15.8
X chromosomes
Allele for
orange fur
Early embryo:
Two cell
populations
in adult cat:
Allele for
black fur
Cell division and
X chromosome
inactivation
Active X
Inactive X
Active X
Black fur
Orange fur
Figure 15.UN01
Linked Genes
F1 dihybrid female
and homozygous
recessive male
in testcross
b+ vg+
b vg
b vg
b vg
b+ vg+
b vg
Most offspring
or
b vg
b vg
Genetic Recombination and
Linkage
 Offspring with a phenotype matching
one of the parental phenotypes are
called parental types
 Offspring with nonparental phenotypes
(new combinations of traits) are called
recombinant types, or recombinants
 A 50% frequency of recombination is
observed for any two genes on
different chromosomes
Figure 15.UN02
Gametes from yellow-round
dihybrid parent (YyRr)
Gametes from greenwrinkled homozygous
recessive parent (yyrr)
YR
yr
Yr
yR
YyRr
yyrr
Yyrr
yyRr
yr
Parentaltype
offspring
Recombinant
offspring
Figure 15.12
Mutant phenotypes
Short
aristae
0
Long aristae
(appendages
on head)
Black
body
Cinnabar Vestigial
eyes
wings
48.5 57.5
Gray
body
Red
eyes
Brown
eyes
67.0
104.5
Normal
wings
Red
eyes
Wild-type phenotypes
Figure 15.14
(a) Deletion
A B C
D E
F G
H
A deletion removes a chromosomal segment.
A B C
E
F G H
(b) Duplication
A B C
D E
F G
H
A duplication repeats a segment.
A B C
B C
D E
F G H
(c) Inversion
A B C
D E
F G H
An inversion reverses a segment within a
chromosome.
A D C
B E
F G H
(d) Translocation
A B C
D E
F G H
M N O
P Q
R
A translocation moves a segment from one
chromosome to a nonhomologous chromosome.
M N O
C D E
F G H
A
B P Q
R
Figure 15.15
Others
 Imprinting
• Silencing of a gene during gamate
formation (depends on which parent)
 Organelle genes
• Mitochondria, choloroplast
• Maternally inherited