Download Ch15ChromoBasisInheritance

Ch. 15 Chromosomal Basis
of Inheritance
AP Biology
2006-2007
Classes of chromosomes
autosomal
chromosomes
sex
chromosomes
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Sex linked traits
 Located on sex chromosomes




1910 | 1933
as opposed to autosomal chromosomes
first discovered by T.H. Morgan at Columbia U.
Was the first to trace a gene to a specific chromsome
Drosophila breeding
 good genetic subject
 prolific
 2 week generations
 4 pairs of chromosomes
 XX=female, XY=male
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Discovery of sex linkage
P
F1
true-breeding
red-eye female
X
true-breeding
white-eye male
100%
red eye offspring
Huh!
Sex matters?!
generation
(hybrids)
F2
generation
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100%
red-eye female
50% red-eye male
50% white eye male
What’s up with Morgan’s flies?
x
RR
r
R
Rr
x
rr
Rr
r
Rr
Rr
R
R
r
RR
Rr
Rr
rr
Doesn’t work
that way!
R
Rr
Rr
100% red eyes
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r
3 red : 1 white
Genetics of Sex
Elaborate!
 In humans & other mammals, there are 2
sex chromosomes: X & Y

2 X chromosomes
 develop as a female: XX
 gene redundancy,
like autosomal chromosomes

an X & Y chromosome
X
Y
X
XX
XY
X
XX
XY
 develop as a male: XY
 no redundancy
50% female : 50% male
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Let’s reconsider Morgan’s flies…
x
XR XR
Elaborate!
XR
XR
Xr
XR Xr
XR Xr
x
XrY
Y
XRY
XRY
100% red eyes
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
XR
BINGO!
Xr
XR Xr
XRY
XR
Y
XR XR
XRY
XRXr
XrY
100% red females
50% red males; 50% white males
Genes on sex chromosomes
 Y chromosome

few genes other than SRY
 sex-determining region
 master regulator for maleness
 turns on genes for production of male hormones
 many effects = pleiotropy!
 X chromosome

other genes/traits beyond sex determination
 mutations:
 hemophilia
 Duchenne muscular dystrophy
 color-blindness
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Where are the deer?
There are three of them in
this image.
Red-Green
colorblindness is an
adaptation for finding
camouflaged objects- a
very important skill for
males during the Stone
Age. It helps in finding
game animals and
avoiding predators.
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Map of Human Y chromosome?
< 30 genes on
Y chromosome
Sex-determining Region Y (SRY)
Channel Flipping (FLP)
Catching & Throwing (BLZ-1)
Self confidence (BLZ-2)
Devotion to sports (BUD-E)
Addiction to death &
destruction movies (SAW-2)
note: not linked to ability gene
Air guitar (RIF)
Scratching (ITCH-E)
Spitting (P2E)
Inability to express
affection over phone (ME-2)
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linked
Selective hearing loss (HUH)
Total lack of recall for dates (OOPS)
Map of Human X chromosome?
Sex-determining Region X (SRY)
HunDuList
Pop-Up Screen (IE)
Grudge-note: linked to EFO
WatRUThnkg (HUH)
Eye-Rolling(IROL)
linked
and Tore-U-Up2
Drama (DisCh)
Aversion to death &
destruction movies (SAW-2-3-4)
Razor (YMine)
linked
Talking (YAK-E)
Ear/phone attachment (EPA-2)
Error Finding
Obsessiveness (EFO)
Total Offense Recall (Tore-U-Up2)
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Human X chromosome
 Sex-linked
usually
means
“X-linked”
 more than
60 diseases
traced to
genes on X
chromosome

Duchenne muscular dystrophy
Becker muscular dystrophy
Chronic granulomatous disease
Retinitis pigmentosa-3
Norrie disease
Retinitis pigmentosa-2
Hypophosphatemia
Aicardi syndrome
Hypomagnesemia, X-linked
Ocular albinism
Retinoschisis
Adrenal hypoplasia
Glycerol kinase deficiency
Ornithine transcarbamylase
deficiency
Incontinentia pigmenti
Wiskott-Aldrich syndrome
Menkes syndrome
Androgen insensitivity
Sideroblastic anemia
Aarskog-Scott syndrome
PGK deficiency hemolytic anemia
Anhidrotic ectodermal dysplasia
Agammaglobulinemia
Kennedy disease
Pelizaeus-Merzbacher disease
Alport syndrome
Fabry disease
Immunodeficiency, X-linked,
with hyper IgM
Lymphoproliferative syndrome
Albinism-deafness syndrome
Fragile-X syndrome
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Ichthyosis, X-linked
Placental steroid sulfatase deficiency
Kallmann syndrome
Chondrodysplasia punctata,
X-linked recessive
Charcot-Marie-Tooth neuropathy
Choroideremia
Cleft palate, X-linked
Spastic paraplegia, X-linked,
uncomplicated
Deafness with stapes fixation
PRPS-related gout
Lowe syndrome
Lesch-Nyhan syndrome
HPRT-related gout
Hunter syndrome
Hemophilia B
Hemophilia A
G6PD deficiency: favism
Drug-sensitive anemia
Chronic hemolytic anemia
Manic-depressive illness, X-linked
Colorblindness, (several forms)
Dyskeratosis congenita
TKCR syndrome
Adrenoleukodystrophy
Adrenomyeloneuropathy
Emery-Dreifuss muscular dystrophy
Diabetes insipidus, renal
Myotubular myopathy, X-linked
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sex-linked recessive
Hemophilia
H Xh x X
HY
HH
XHh
XH
female / eggs
male / sperm
XH
XH
Y
XH XH
XH Y
XH Xh
Xh
XH
Xh
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XH Xh
XhY
carrier
disease
XHY
Y
X-inactivation
Elaborate!
 Female mammals inherit 2 X chromosomes

one X becomes inactivated during
embryonic development
 condenses into compact object = Barr body
 which X becomes Barr body is random in each
cell
 patchwork trait = “mosaic”
patches of black
XH 
XH Xh
tricolor cats
can only be
female
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Xh
patches of orange
Male pattern baldness
Elaborate!
 Sex influenced trait

autosomal trait influenced by sex hormones
 age effect as well = onset after 30 years old

dominant in males & recessive in females
 B_ = bald in males; bb = bald in females
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Environmental effects
 Phenotype is controlled by
both environment & genes
Human skin color is influenced
by both genetics &
environmental conditions
Coat color in arctic
fox influenced by
heat sensitive alleles
Color of Hydrangea flowers
APinfluenced
Biology
is
by soil pH
Crossing Over and Recombination
data to map a chromosome’s
genetic loci
 One of Morgan’s students, Alfred
Sturtevant, used crossing over of linked
genes to develop a method for
constructing a chromosome map - an
ordered list of the genetic loci along a
particular chromosome.
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Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
 Crossing Over – segments exchanged
between homologous chromosomes during
prophase I.
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 The occasional production of recombinant gametes
during prophase I accounts for the occurrence of
recombinant phenotypes in Morgan’s testcross.
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 Frequency of recombinant offspring reflected
the distances between genes on a chromosome.
 The farther apart two genes are, the higher
the probability that a crossover will occur
between them and therefore a higher
recombination frequency.

The greater the distance between two genes,
the more points between them where crossing
over can occur.
 Sturtevant used recombination frequencies
from fruit fly crosses to map the relative
position of genes along chromosomes, a
linkage map.
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Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Elaborate!
 Sturtevant used the test cross design to map the relative
position of three fruit fly genes, body color (b), wing size (vg),
and eye color (cn).
 The recombination frequency between cn and b is 9%.
 The recombination frequency between cn and vg is 9.5%.
 The recombination
frequency between
b and vg is 17%.
 The only possible
arrangement of these
three genes places
the eye color gene
between the other two.
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Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 15.6
0
B
Cn 9 0
Vg 17 9.5 0
B Cn Vg
B
Cn
Rb
Vg
0
9
19%
3.5% 6.5%
B
Rb Cn
0
3.5 6.5
0
19 9.0 16
0
B Cn Rb Vg
B
9%
Vg
9%
16%
Rb Cn
Vg
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Vg
Copyright © 2002B
Pearson Rb
Education,Cn
Inc., publishing as
Benjamin Cummings
Fig. 15.6
 Sturtevant expressed the distance between genes, the


recombination frequency, as map units.
 One map unit (sometimes called a centimorgan) is
equivalent to a 1% recombination frequency.
You may notice that the three recombination
frequencies in our mapping example are not quite
additive: 9% (b-cn) + 9.5% (cn-vg) > 17% (b-vg).
This results from multiple crossing over events.
 A second crossing over “cancels out” the first and
reduced the observed number of recombinant
offspring.
 Genes father apart (for example, b-vg) are more
likely to experience multiple crossing over events.
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Errors of Meiosis
Chromosomal Abnormalities
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2006-2007
Chromosomal abnormalities
 Incorrect number of chromosomes

nondisjunction
 chromosomes don’t separate properly
during meiosis

breakage of chromosomes
 deletion
 duplication
 inversion
 translocation
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Nondisjunction
 Problems with meiotic spindle cause errors in
daughter cells



2n
homologous chromosomes do not separate
properly during Meiosis 1
sister chromatids fail to separate during Meiosis 2
too many or too few chromosomes
n-1
n
n+1
n
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Alteration of chromosome number
error in Meiosis 1
error in Meiosis 2
all with incorrect number
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1/2 with incorrect number
Nondisjunction
 Baby has wrong chromosome number

trisomy
 cells have 3 copies of a chromosome

monosomy
 cells have only 1 copy of a chromosome
n+1
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n-1
n
n
trisomy
monosomy
2n+1
2n-1
Human chromosome disorders
 High frequency in humans



most embryos are spontaneously aborted
alterations are too disastrous
developmental problems result from biochemical
imbalance
 imbalance in regulatory molecules?
 hormones?
 transcription factors?
 Certain conditions are tolerated


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upset the balance less = survivable
but characteristic set of symptoms = syndrome
Down syndrome
 Trisomy 21
3 copies of chromosome 21
 1 in 700 children born in U.S.

 Chromosome 21 is the
smallest human chromosome

but still severe effects
 Frequency of Down
syndrome correlates
with the age of the mother
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Down syndrome & age of mother
Mother’s age
Incidence of
Down Syndrome
Under 30
<1 in 1000
30
1 in 900
35
1 in 400
36
1 in 300
37
1 in 230
38
1 in 180
39
1 in 135
40
1 in 105
42
1 in 60
44
1 in 35
46
1 in 20
48
1 in 16
49
1 in 12
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Rate of miscarriage due to
amniocentesis:
 1970s data
0.5%, or 1 in 200 pregnancies
 2006 data
<0.1%, or 1 in 1600 pregnancies
Genetic testing
 Amniocentesis in 2nd trimester
sample of embryo cells
 stain & photograph chromosomes

 Analysis of karyotype
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Sex chromosomes abnormalities
 Human development more tolerant of

wrong numbers in sex chromosome
But produces a variety of distinct
syndromes in humans




XXY = Klinefelter’s syndrome male
XXX = Trisomy X female
XYY = Jacob’s syndrome male
XO = Turner syndrome female
Know inheritance
and characteristics
of each!
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Klinefelter’s syndrome
 XXY male
one in every 2000 live births
 have male sex organs, but
are sterile
 feminine characteristics

 some breast development
 lack of facial hair
tall
 normal intelligence

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Klinefelter’s syndrome
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Jacob’s syndrome male
 XYY Males
1 in 1000 live male
births
 extra Y chromosome
 slightly taller than
average
 more active
 normal intelligence, slight learning disabilities
 delayed emotional maturity
 normal sexual development

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Trisomy X
 XXX
1 in every 2000 live births
 produces healthy females

 Why?
 Barr bodies
 all but one X chromosome is inactivated
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Turner syndrome
 M onosomy X or X0
1 in every 5000 births
 varied degree of effects
 webbed neck
 short stature
 sterile

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replication
error of
Know each and
their cause!
Changes in chromosome structure
 deletion

 duplication
crossing over

error of
loss of a chromosomal segment
repeat a segment
 inversion

reverses a segment
 translocation

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move segment from one chromosome
to another
Genomic Imprinting
The phenotypic effects of some mammalian
genes depend on whether they were inherited
from the mother or the father (imprinting)
 Does depend on which parent passed along the
alleles for those traits.
 The genes involved are not sex linked and may
or may not lie on the X chromosome.
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Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
 Prader-Willi syndrome and Angelman syndrome,
-due to the same cause, a deletion of a specific segment
of chromosome 15.

Prader-Willi syndrome- characterized by mental
retardation, obesity, short stature, and unusually
small hands and feet. These individuals inherit
the abnormal chromosome from their father.

Angelman syndrome exhibit spontaneous
laughter, jerky movements, and other motor and
mental symptoms. This is inherited from the
mother.
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The difference between the disorders is due to
genomic imprinting.
 The imprinting status of a given gene depends on
whether the gene resides in a female or a male.
 Methyl groups are added to cytosine nucleotides on
one of the alleles.
 Heavily methylated genes are turned off.
 The animal uses the allele that is not imprinted.
 Several hundred mammalian genes, many critical
for development, may be subject to imprinting.
Imprinting is critical for normal development.
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Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
 In the new generation,
both maternal and
paternal imprints are
apparently “erased” in
gamete-producing cells.
 Then, all chromosomes
are re-imprinted
according to the sex of
the individual in which
they reside.
Fig. 15.15
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Any Questions?
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2006-2007