Transcript Lecture 10 and lecture 11(70 slides) - Dr-Manar-KSU

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Around 1857, Mendel began breeding
garden peas to study inheritance.
Because they are available in many
varieties with distinct heritable
characters with different traits (genes).

• Each pea plant has male (stamens)
and female (carpal) sexual organs.
• In nature, pea plants typically
self-fertilize, fertilizing ova with their
own pollens.
• However, Mendel could also move
pollens from one plant to another to
cross-pollinate plants.
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Pea plant
PP X
P
Dominant
allele
Pp
pp
Pp
X
P
p
PP
Pp
P
p
p
Pp
Recessive
allele
100% Purple
3 Purple
Pp
:
pp
1 White
Homozygous
Heterozygous
F1 generation
F2 generation
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Phenotype
(Colour)
Phenotype:
Is the organism’s appearance ‫المظهر‬.
Genotype:
Is the organism’s genetic makeup
‫الطرز الـﭽينى‬.
PP
PP Homozygous pp
An organism having a pair of
identical alleles
Genotype
(Genetic make up)
Pp Heterozygous
An organism having a pair of two
different alleles
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The two pairs of alleles segregate independently of each other.

on ‫تأثير‬The presence of one specific allele for one trait has no impact 
the presence of a specific allele for the second trait.
• When sperm and ova each with
four classes of alleles
combine, there would be 16
equally probable ways in which
the alleles can combine
in the F2 generation.
• These combinations produce
four distinct phenotypes in a
9:3:3:1 ratio.
• This was consistent with
Mendel’s results.
• Each character appeared to be
inherited independently.
Fig. 14.7b, Page 253
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It is a mating between two parent plants differing in two characters.
YY RR
Y
R
X
yy rr
YR
y r
y
r
Y y Rr
F1 Yellow Round
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Yy Rr
YR
YR
X
Yr
Yy Rr
yR
yr
YYRR
Yellow Round
Yr
YYrr
Yellow Wrinkled
yR
yyRR
Green Round
yr
yyrr
Green Wrinkled
F2:
% of Phenotype ?
Page 253, Fig. 14.7
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It is not possible to predict the genotype of an organism
with a dominant phenotype.
The organism must have one dominant allele, but it could be
homozygous dominant or heterozygous.


Test cross, 
is breeding a
homozygous recessive
with dominant phenotype,
but unknown genotype,
can determine the identity
of the unknown allele.
Q: What is the result of
Cross hybridization of
purple X white colored
flowers ?
Fig. 14.6
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‫الصفة السائدة‬Dominant character (allele)

Is fully expressed in the organism’s appearance.
‫الصفة ال ُمتنحية‬Recessive character (allele)
on the organism’s appearance.‫تأثير غير ملحوظ‬

Has no noticeable effect
‫ ُمتماثل الجينات‬Homozygous

An organism with two identical alleles for a character.
‫ ُمختلف الجينات‬Heterozygous

An organism with two different alleles for a character.
‫الطرز الكروموسومى‬Karyotype

The display of an organism’s chromosomal pattern
‫الطرز المظهرى‬Phenotype
).‫مظهر‬

A description of an organism’s traits (feature
‫الطرز الجينى‬Genotype

A description of an organism’s genetic makeup.
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Thousands of genetic disorders, including disabling or deadly hereditary
diseases, are inherited as simple recessive traits.
) to life-threatening ‫ البُهاق‬،‫األلبينو‬These range from the relatively mild (albinism
(cystic fibrosis).
Heterozygotes have a normal phenotype because one “normal” allele
produces enough of the required factors (for normal trait).
A recessively inherited disorder shows up only in the individuals
who inherit homozygous recessive allele from parents.
Thus, individuals who lack the disorder are either homozgyous dominant
or heterozygous.
Heterozygous member may have no clear phenotypic effects, but is a carrier
who may transmit a recessive allele to their offspring.
Most people with recessive disorders are born from carrier parents with
normal phenotypes.
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Two carriers have a 1/4 chance of having a child with the disorder, 1/2 chance of a 
carrier, and 1/4 free.
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A- Recessively inherited disorders
Cystic fibrosis: a lethal recessive disorder
One in 25 person is a carrier.
The normal allele codes for a membrane protein that transports Clbetween cells and the environment.
If these channels are absent, there are abnormally high extracellular
levels of chloride that causes the mucus coats of certain cells to
become thicker and stickier than normal.
This mucus build-up in the pancreas, lungs, digestive tract, and
elsewhere favors bacterial infections.
Without treatment, affected children die before five, but with
treatment can live past their late 20’s.
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Tay-Sachs disease a lethal recessive disorder.
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It is caused by a dysfunctional enzyme that fails to break down
specific brain lipids.
The symptoms begin with seizures, blindness, and degeneration of
motor and mental performance a few months after birth.
Inevitably, the child dies after a few years.
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Sickle-cell disease.
It is caused by the substitution of a single amino acid in
hemoglobin.
When oxygen levels in
the blood of an affected
individual are low,
sickle-cell hemoglobin
crystallizes into long
rods.
This deforms red blood
cells into a sickle shape.
Doctors can use regular
blood transfusions to
prevent brain damage
and new drugs to
prevent or treat other
problems.
• The two alleles are codominant as both normal and abnormal
hemoglobins are synthesized.
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Many other disorders have a multifactorial basis.
These have a genetic component plus a significant environmental 
influence.
:Multifactorial disorders include 
heart disease, diabetes, cancer, alcoholism, and certain mental illnesses, 
such a schizophrenia and manic-depressive disorder.
The genetic component is typically polygenic. 
At present, little is understood about the genetic contribution to most
multifactorial diseases
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CHAPTER 15
THE CHROMOSOMAL BASIS
OF INHERITANCE
Section B: Sex Chromosomes
1. The chromosomal basis of sex varies with the organism
2. Sex-linked genes have unique patterns of inheritance
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In human and other mammals, there are
two varieties of sex chromosomes, X & Y.

An individual who inherits two X 
chromosomes usually develops as a female.
An individual who inherits an X and a Y 
chromosome usually develops as a male.
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•
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This X-Y system of mammals is not the
only chromosomal mechanism of
determining sex.
Other options include the X-0 (in locust)
system, the Z-W system (in birds), and the
haplo-diploid system (in bees).
In Human, the SRY gene (Sex-determining
Region of the Y chromosome) modifies
embryonic gonads into testes.
Females lack the SRY gene, thus, the
embryonic gonads develop into ovaries.
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Fig. 15.8, Page
In the X-Y system, Y and X chromosomes behave as
homologous chromosomes during meiosis.
In reality, they are only partially homologous and rarely
undergo crossing over
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In both testes (XY) and ovaries (XX), the two sex
chromosomes segregate during meiosis and each
gamete receives one.
Each egg receives an X chromosome.
Half the sperm receive an X chromosome and half receive a Y
chromosome.
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Because of this, each conception has about a fifty-fifty
chance of producing a particular sex.
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The sex chromosomes, especially the
X chromosome, have genes for many
characters unrelated to sex.
These sex-linked genes follow the
same pattern of inheritance
as the
white-eye locus in Drosophila.
If a sex-linked trait is due to a recessive
allele, a female have this phenotype
only if homozygous.
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Heterozygous females will be carriers. 
Fig. 15.9, Page 277
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• Because males have only one X chromosome
(hemizygous), any male receiving the recessive allele
from his mother will express the trait.
• Therefore, males are far more likely to inherit sexlinked recessive disorders than are females.
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Sex-linked disorders in human.
1.
Duchenne muscular dystrophy: affects one in 3,500 males
born in the United States.
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Affected individuals rarely live past their early 20s.
This disorder is due to the absence of an X-linked gene for a key
muscle protein, called dystrophin.
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The disease is characterized by a weakening ‫ ضعف‬of the muscles and
loss of coordination ‫فـقـْد التوازن‬.
Hemophilia: is a sex-linked recessive trait defined by the
absence of one or more clotting factors ‫عوامل تجلط‬.
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These proteins normally slow and then stop bleeding.
Individuals with hemophilia have prolonged bleeding because a firm
clot ‫ تجلط‬forms slowly.
Individuals can be treated with intravenous injections of the missing
protein.
This gene is transmitted to offspring via the mothers.
Thus, Sons borne from hemophilic woman should be exempted from
circumcision.
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is a ‫عمى األلوان‬Color blindness:
disorder inherited as a recessive sexlinked character and affect both
males and females.
A color blind female (XaXa) may be
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born to a color blind father (XaY) and a
carrier mother (XAXa)
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Chromosomal aberration.
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It is common ‫ شائع‬in meiosis and includes:
a) Chromosomal deletions/translocations
 Homologous chromatids may break ‫ تـَنكسر‬and rejoin at incorrect
places, thus, one chromatid will loose more genes than it receives.
b) Chromosomal duplications (Polyploidy).
 result from nondisjunction during gamete production in one
parent.
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A diploid embryo that is homozygous for a large deletion
or male with a large deletion to its single X chromosome
is usually missing many essential genes and this leads
to a lethal outcome.
–
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Duplications and translocations are very harmful.
Translocation or inversion can alter phenotype because
a gene’s expression is influenced by its location.
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A)- Aneuploidy (Chromosomal
duplication)
1- Down syndrome [Polyploidy (2n + 1), trisomy in autosomes]:
Is due to three copies of chromosome 21 (Trisomies).
Although chromosome 21 is the smallest human chromosome, it severely
an individual’s phenotype in specific ways. ‫يُغير‬alters
Fig. 15.14
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Most cases of Down syndrome result from nondisjunction
during gamete production in one parent.
The frequency of Down syndrome correlates with the age of the
mother.
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This may be linked to some age-dependent abnormality in the spindle 
checkpoint during meiosis I, leading to nondisjunction.
2- Klinefelter’s syndrome [Polyploidy (2n + 1), trisomy in sex chromosomes ],
(a)- An XXY male, occurs once in every 2000 live births.
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These individuals have male sex organs, but are sterile.
There may be feminine characteristics ‫له صفات أنثوية‬, but their intelligence is
normal.
(b)- An XYY male, tend to somewhat taller than average.
(c)- A trisomy female (XXX), which occurs once in every 2000 live
births, produces healthy females.
3- Turner’s syndrome, a monosomy female (X0), or, which occurs
once in every 5000 births, produces phenotypic, but immature
females ‫غير ناضجة جنسيا‬.
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B)- Chromosomal structure-alterations:
It can also cause human disorders.
Deletions, even in a heterozygous state, cause severe physical and 
mental problems.
,
results ‫عارض مواء القط‬Cri-du-chat .1
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.
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2. Myelogenous, [leukemia (CML)].
Caused by chromosomal translocations since a fragment of
chromosome 22 switches places with a small fragment from the
tip of chromosome 9.
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Plz open the video
www.youtube2_yAbrp=v?hctaw/moc.gKR
Biology - Laws of Heredity - Genetics
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Plz open the video
www.youtube-=v?hctaw/moc.
McEVIwhpRm
Gregor Mendel ttennuP htiw gnikrow
.serauqS
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Plz open the video
www.youtube-=v?hctaw/moc.
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Mendelian Genetics
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Plz
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w/moc.www.youtube :
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Genetics dna Mendel 4
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Plz open the video
www.youtubeQ_bnqLxonZ=v?hctaw/moc.
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Mendel yduts genes stiart detirehni dna
saep gnisu
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Plz open the video
www.youtube85whMoi=v?hctaw/moc.wI18
Mendel's fo waL Heredity
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Q1: Write whether each of the following statements is
True (T) or False (F):
1-( ) Sickle-cell disease is a dominantly inherited
disorder.
2-( ) The 3 : 1 phenotypic ratio is characteristic of the
F1 generation of a monohybrid cross.
3-( )A mating between parents differing in two
characters is called;Monohybrid
4-( )The separation of alleles into separate
gametes is known as Mendel’s law of independent
assortment .
5-( ) An organism’s expressed traits is known as
genotype .
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Q 2: Choose the correct answer (one answer only):
1-Which of the following is a genetic disorder that caused by genes
and
environmental factors (multi-factorial disorder):
a)- colour blindness
b)- Tay-Sachs disease
c)- cancer
d)- cystic fibrosis
2-Which of the following is a dominant genetic disease?
a)- sickle-cell anaemia.
b)- cystic fibrosis
c)- Tay Sachs disease
d)- none of the above
3-Huntington's disease is an example of a genetic disorder caused by:
a)- lethal dominant allele
b)- non-lethal dominant
allele
c)- recessive allele
d)- multiple alleles
4- An organism with two identical alleles for a character (trait) is:
a)- homozygous
b)- heterozygous
c)- semizygous
d)- multizygous
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5-The self-cross of dihybrid (RrYy) will result in which of the following
phenotypic ratio:
a)- 1: 1: 1: 1
b)- 9: 3: 3: 1
c)- 1: 2: 2: 1
d)- 3: 3: 3: 1
6-Mendel's law of segregation means that the two members of an allelic pair are:
a)- distributed to separate gametes.
b)- distributed to the same gamete.
c)- assorted dependently.
d)- segregated pairwise.
7-Which of the following is represented by the appearance (such as colour)
a)- phenotype
b)- genotype
c)- kariotype
d)- none of them
8-Different alleles are ---------------------Alternative version of genes (different molecular forms of a gene).a
b-Different phenotypes.
c-Self-fertilizing,true breeding homozygotes.
d-Organism’s genotype.
9-Crosses between F1 individuals resulting from the cross
AABB X aabb lead to F2 phenotypic ratios close to------------a-1:2:1
b-1:1:1:1
c-3:1
d-9:3:3:1
10-A heterozygote has a---------------for the trait being studied.
a-Pair of identical alleles.
b-Pair of nonidentical alleles.
c-Haploid condition,in genetic terms.
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