Download Nerve activates contraction

The answer to cardiovascular genetics
The Japanese eat very little fat and suffer fewer heart
attacks than the British or Americans.
On the other hand, the French eat a lot of fat and also suffer
fewer heart attacks than the British or Americans.
The Japanese drink very little red wine and suffer fewer
heart attacks than the British or Americans.
The Italians drink excessive amounts of red wine and also
suffer fewer heart attacks than the British or Americans.
Conclusion:
Eat
you.
and drink what you like. It is speaking English that kills
CHAP. 15
THE CHROMOSOMAL BASIS OF INHERITANCE
Homologous
chromosomes separate and alleles recombine
in possible ways during meiosis. – Law of segregation +
Independent Assortment
Genetic
recombination can result from independent
assortment of genes located on nonhomologous
chromosomes or from crossing over of genes located
on homologous chromosomes.
A
a
b
B
Independent Assortment genes on different
chromosomes can be
assorted or ‘mixed up’
to produce all
combinations in
gametes
A
A
a
a
b
b
B
B
A
a
a
B
A
b
b
Normal, bald
A -Normal
a - Albino
B - Normal
b - Bald
B
Albino, Hair
A
a
B
b
A
A
a
a
B
B
b
b
a
b
a
b
A
B
A
B
Normal, Normal
Albino, bald
Drosophila Melanogaster
– fruit fly
- crossed red eye female
with white eye male
Fruitfly P1 Cross:
Female - Red Eye
Male - White Eye
All F1 flies have
Red Eyes
-No difference
between male and
female in F1
- Red is dominant
over white
R
X
R
X
Xr XRXr XRXr
RY
X
Y
XRY
F1 Cross:
Female - Red Eye
Male - Red Eye
F2 flies:
3Red Eyes:1White Eye
R
X
r
X
XR XRXR XRXr
- All white eyed flies are
MALE
-Trait is SEX LINKED
-Independent assortment of
genes; Gene for eye color
linked to a specific
chromosome
RY
X
Y
XrY
Eye color gene on X chromosome
Red
eye = wild type
 Red is dominant allele
White
eye = mutant type.
Sex linked = NonMendelian Genetics

Hemophilia is a sex-linked recessive trait
defined by the absence of one or more clotting
factors.

These proteins (Factor VIII normally slow and then
stop bleeding.
males
are far more likely to inherit sexlinked recessive disorders than are females.
males have only one X chromosome
(hemizygous)
Heterozygous females are carriers


Several serious human disorders are sex-linked.
Duchenne muscular dystrophy affects one in
3,500 males born in the United States.
Dystrophin –
is missing
protein




Genes located on the same
chromosome, linked genes,
tend to be inherited together
because the chromosome is
passed along as a unit.
Non-mendelian inheritance
A 50% frequency of
recombination is observed
for any two genes located on
different (nonhomologous)
chromosomes.
What happens when genes
are linked???
Drosophila Melanogaster
– fruit fly

.

The occasional production of recombinant gametes
during prophase I (crossing over) accounts for the
occurrence of recombinant phenotypes in Morgan’s
testcross (when he was looking at linked genes).
Fig. 15.5a

Morgan reasoned that body color and wing
shape are usually inherited together because
their genes are on the same chromosome
(LINKED GENES).
 Gray, normal
 Few
wing
Black, normal
wing
 Gray, normal
 Black, vestigial wing
 Few
Grey, vestigial
wing
wing
 Black, vestigial wing
Fruitfly Linked Genes Test Cross:
Female - Gray body,
Normal wings (b+bvg+vg )
Male -Black body,
Vestigial wings (bbvgvg;
mutant)
Linked genes show <50% of the
Recombinant type of offspring.
bvg
-the recombinant frequency can be used
as an estimate of the distance between
the 2 genes in the example
b+vg+
bvg
b+bvg+vg
b+vg
bvg+
b+bvgvg
bbvgvg
Parental Type
bbvg+vg
Recombinant Type
Expected
50%
50%
Observed
83%
17%
Fig. 15.5b
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Chromosome map - ordered list of the genetic loci
along a particular chromosome.


The greater the distance between two genes, the more
points between them where crossing over can occur.
Recombination frequencies from fruit fly crosses
used to map the relative position of genes along
chromosomes - a linkage map
One
map unit (sometimes called a centimorgan) is equivalent to
a 1% recombination frequency.
Fig. 15.7

Combined with other methods like chromosomal
banding, geneticists can develop cytological
maps.

These indicate the positions of genes with respect to
chromosomal features.
 Linked
genes, genes located on the same chromosome,
tend to move together through meiosis and fertilization.
 If completely linked, we should expect to see a 1:1:0:0
ratio with only parental phenotypes among offspring.
The chromosomal
basis of sex varies
with the organism


This X-Y system
of mammals
X-0 system, the ZW system, and the
haplo-diploid
system.
Karyotype
Drosophila
Human
2A XX
female
female
2A XY
male
male
2A XO
male
female
2A XXX
female
female
2A XXY
female
male


In humans, the anatomical signs of sex first
appear when the embryo is about two months
old.
In individuals with the SRY gene (sex
determining region of the Y chromosome), the
generic embryonic gonads are modified into
testes.
Only one X chromosome is active in females


During female embryonic development, one X
chromosome per cell condenses into a compact object, a
Barr body.
This inactivates most of its genes.
The condensed Barr body chromosome is reactivated
in ovarian cells that produce ova.
Fig. 15.10
Chromosomal Aberrations:


Alterations in chromosome structure or number
Deviations from chromosome theories of inheritance
NONDISJUNCTION
first meiotic division: prophase: leptotene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: prophase: leptotene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: prophase: leptotene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: prophase: leptotene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: prophase: leptotene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: prophase: leptotene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: prophase: leptotene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: prophase: leptotene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: prophase: zygotene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: prophase: pachytene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: prophase: pachytene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: prophase: diplotene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: prophase: diplotene
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: metaphase I
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: metaphase I
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: anaphase I
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: telophase I
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: telophase I
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: telophase I: first polar body
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: telophase I: first polar body
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
first meiotic division: telophase I: first polar body
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: metaphase II
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: metaphase II
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: anaphase II
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: telophase II
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: telophase II
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: second polar bodies
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: second polar bodies
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: second polar bodies
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: second polar bodies
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: second polar bodies
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: second polar bodies
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: second polar bodies
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: second polar bodies
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: second polar bodies
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
second meiotic division: second polar bodies
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
fertilization
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.
cleavage (mitosis): prophase
chromosome 21
other chromosomes
normal
trisomy 21
© 2003 H. NUMABE M.D.

Offspring results from fertilization of a normal gamete with one after
nondisjunction will have an abnormal chromosome number or
aneuploidy.
 Trisomic cells = 2n + 1 chromosomes.
 Monosomic cells =2n - 1 chromosomes.
 Aneuploidy can also occur during failures of the mitotic spindle
Sex chromosome aneuploidy
Turner’s
syndrome
Female (Monosomy)
XO
Klienfelter’s syndrome
Male

XXY
“The pediatrician said, `Oh, it’s just Turner Syndrome. She’ll be short.
She’ll be sterile, but her intelligence will be fine.’ Then he walked out.”
XYY syndrome
Male
XYY



Organisms with more than two complete sets of
chromosomes, have undergone polypoidy.
One gamete has Nondisjunction of all its chromosomes.
 The resulting zygote would be triploid (3n).
2n gametes + self –fertilization = a tetraploid (4n) embryo
PLANT
domestic oat
peanut
sugar cane
banana
white potato
tobacco
cotton
apple
Chromosome
42
40
80
22, 33
48
48
52
34, 51
#
Ploidy
6n
4n
8n
2n, 3n
4n
4n
4n
2n, 3n



Breakage of a chromosome can lead to four
types of changes in chromosome structure.
A deletion - chromosome fragment lacking a
centromere is lost during cell division.
A duplication -a fragment becomes attached as
an extra segment to a sister chromatid.


Inversion = chromosomal fragment reattaches
to the original chromosome but in the reverse
orientation.
Translocation = a chromosomal fragment joins
a nonhomologous chromosome.

Some translocations are reciprocal, others are not.

Cri du chat, results from a specific deletion in
chromosome 5.


These individuals are mentally retarded, have a
small head with unusual facial features, and a cry
like the mewing of a distressed cat.
This syndrome is fatal in infancy or early
childhood.

Chromosomal translocations have been
implicated in certain cancers, including chronic
myelogenous leukemia (CML).


CML occurs when a fragment of chromosome 22
switches places with a small fragment from the tip of
chromosome 9.
Some individuals with Down syndrome have the
normal number of chromosomes but have all or
part of a third chromosome 21 attached to
another chromosome by translocation.
The phenotypic effects of some mammalian
genes depend on whether they were inherited
from the mother or the father (imprinting)


The difference between the disorders is due to
genomic imprinting.
In this process, a gene on one homologous
chromosome is silenced, while its allele on the
homologous chromosome is expressed.
Fig. 15.15
Extranuclear genes exhibit a non-Mendelian
pattern of inheritance




Not all of a eukaryote cell’s genes are located in
the nucleus.
Extranuclear genes are found on small circles of
DNA in mitochondria and chloroplasts.
These organelles reproduce themselves.
Their cytoplasmic genes do not display
Mendelian inheritance.

They are not distributed to offspring during meiosis.



Karl Correns in 1909 first observed cytoplasmic
genes in plants.
He determined that the coloration of the
offspring was determined only by the maternal
parent.
These coloration patterns are due to genes in
the plastids which are inherited only via the
ovum, not the pollen.
Fig. 15.16


Because a zygote inherits all its mitochondria
only from the ovum, all mitochondrial genes in
mammals demonstrate maternal inheritance.
Several rare human disorders are produced by
mutations to mitochondrial DNA.



These primarily impact ATP supply by producing
defects in the electron transport chain or ATP
synthase.
Tissues that require high energy supplies (for
example, the nervous system and muscles) may
suffer energy deprivation from these defects.
Other mitochondrial mutations may contribute to
diabetes, heart disease, and other diseases of aging.