Transcript 03.Organism`s level of realiization of genetic information. Gene

Theme: Organism’s level
of realization of genetic
information.
Gene interactions
Lecturer: ass. prof. Tatyana Bihunyak
Questions:
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Introduction to Genetics and heredity
Gregor Mendel – a brief bio
Genetic terminology
Monohybrid and dihybrid crosses
Patterns of inheritance
Test cross
Gene interactions
Introduction to Genetics
• GENETICS – branch of biology
that deals with heredity and
variation of organisms
• Chromosomes carry the hereditary
information (genes)
• Arrangement of nucleotides in DNA
• DNA  RNA  Proteins
2. Gen
1. DNA
Cell
4. Genotype
3. Chromosome
7. Population
5. Person
6. Family (generation)
Gregor Johann Mendel
• Austrian Monk, born in what is now
Czech Republic in 1822
• Son of peasant farmer, studied
Theology and was ordained
priest Order St. Augustine.
• Went to the university of Vienna,
where he studied botany and learned
the Scientific Method
• Worked with pure lines of peas for
eight years
• Prior to Mendel, heredity was
regarded as a "blending"
process and the offspring were
essentially a "dilution"of the different
parental characteristics.
•Mendel looked at seven traits or characteristics of
pea plants
• In 1866 he published
Experiments in Plant
Hybridization, (Versuche über
Pflanzen-Hybriden) in which he
established his three Principles of
Inheritance
• He tried to repeat his work
in another plant, but didn’t
work because the plant
reproduced asexually! If…
• Work was largely ignored for
34 years, until 1900, when
3 independent botanists
rediscovered Mendel’s work.
• Mendel was the first biologist
to use Mathematics – to
explain his results
quantitatively.
• Mendel predicted
The concept of genes
That genes occur in pairs
That one gene of each pair is
present in the gametes
Genetics terms you need to know:
• Human genetics is the science that
learns the peculiarities of the
hereditary and variability in human
organism
• Heredity – is the transmission of
characteristics from parent to
offspring through the gametes
Genetics terms you need to know:
• Inheritance – is the way of passing of
hereditary information which depends on
the forms of reproduction
During asexual reproduction the main
traits are inherited through spores or
vegetative cells, that's why the maternal
and daughter cells are very similar.
During sexual reproduction the main
traits are inherited through gametes.
Genetics terms you need to know:
Gene – a unit of heredity; a section of
DNA sequence encoding a single protein
Genotype – is the genetic constitution of
an organism (a diploid set of genes)
Genome – is a collection of genes of an
organism in sex cells (a haploid set of
genes)
Alleles – two genes that occupy the same
position on homologous chromosomes
and that cover the same trait
Locus – a fixed location on a strand of
DNA where a gene or one of its alleles is
located
Genetics terms you need to know:
1
2
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1
2
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XX
17 18
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X
diploid set of genes
Genotype
haploid set of genes
Genome
Genetics terms you need to know:
Homozygous – having identical genes (one
from each parent) for a particular
characteristic.
Heterozygous – having two different genes
for a particular characteristic.
Dominant – the allele of a gene that masks
or suppresses the expression of an
alternate allele; the trait appears in the
heterozygous condition.
Recessive – an allele that is masked by a
dominant allele; does not appear in the
heterozygous condition, only in
homozygous.
Dominant allele is symbolize with a capital
letter
Recessive allele is symbolize with the
corresponding small letter
If both alleles are recessive, the individual is
homozygous recessive aa
An individual with two dominant alleles is
homozygous dominant AA
An individual with Aa alleles is a
heterozygote
• Genotype – describes the organism’s alleles
(the genetic makeup of an organisms)
• Phenotype – the physical appearance
of an organism (Genotype + environment)
• Monohybrid cross: a genetic cross involving a
single pair of genes (one trait); parents differ by
a single trait
P = Parental generation
F1 = First filial generation; offspring from a
genetic cross
F2 = Second filial generation of a genetic cross
1. The law of monotony of the first filial
generation
A - yellow seed; a - green seed
P:
♀ AA x ♂ aa
G (Gametes):
A
a
F1:
Aa (yellow)
During crossing two homozygous which are differ
from each other by one trait all progeny in the
first filial generation is monogyny as well as
phenotypic and genotypic
2. The law of segregation
A cross between plants obtained from F1 plants.
P:
♀ Aa
x
♂ Aa
G:
A, a
A, a
F2 :
AA; Aa; Aa; aa
From a pair of contrasting characters (alleles)
only one is present in a single gamete and
in F2 these characters are segregated in the
ratio of three to one (3:1) by phenotype and
1:2:1 by genotype.
When gametes are formed in heterozygous diploid
individuals, the two alternative alleles segregate
from one another.
• Getting all yellow seeds was an interesting
result in itself
• Having viewed these results, Mendel then let
the F1 generation, was 6022 yellow seeds and
2001 green seeds.
Two things stand out
• green seeds disappeared in F1, but come
back in F2.
• green seeds came back in F2 as a specific
proportion of the seeds as a whole.
• Today, we know that inheritance occurs
by way of gametes, and that it is due to
meiosis that each gamete carries only
one factor for each trait.
• Today, we know that the genes within the
gametes are unaffected by the somatic
cells.
• Mendel's law of segregation is in keeping
with a particulate theory of inheritance
because individual and separate factors
are passed on from generation to
generation.
• It is the reshuffling of these factors that
explains how variations come about and
why offspring differ from their parents.
Human case: CF
• Mendel’s Principles of Heredity
apply universally to all
organisms.
• Cystic Fibrosis: a lethal genetic
disease affecting Caucasians.
• Caused by mutant recessive gene
carried by 1 in 20 people of
European descent
• CF disease affects transport
in tissues – mucus is
accumulated
in lungs, causing infections.
Inheritance pattern of CF
If two parents carry the recessive gene of
Cystic Fibrosis (c), that is, they are
heterozygous (Cc), one in four of their
children is expected to be homozygous for
CF and have the disease:
CC = normal
Cc = carrier, no symptoms
cc = has cystic fibrosis
P:
♀ Cc
x
G:
C, c
F2 : CC; Cc; Cc; cc
C
c
C
CC
Cc
c
Cc
cc
♂ Cc
C, c
Dihybrid crosses
• Matings that involve parents
that differ in two genes (two
independent traits)
For example, flower color:
P = purple (dominant)
p = white (recessive)
and stem length:
T = tall
t = short
Dihybrid cross: flower color and
stem length
TT PP  tt pp
(tall, purple)
Possible Gametes for parents
T P and t p
(short, white)
tp
TP TtPp
TP TtPp
tp
TtPp
TtPp
F1 Generation: All tall, purple flowers (Tt Pp)
Dihybrid cross F2
If F1 generation is allowed to self pollinate,
Mendel observed 4 phenotypes
Tt Pp  Tt Pp
(tall, purple)
Possible gametes:
TP Tp tP tp
TP
(tall, purple)
Tp
tP
TP TTPP TTPp TtPP
Tp TTPp TTpp TtPp
tp
TtPp
Ttpp
TtPP
TtPp
ttPP
ttPp
tp TtPp
Ttpp
ttPp
ttpp
tP
Four phenotypes observed
Tall, purple (9); Tall, white (3); Short, purple (3); Short white (1)
Dihybrid cross: 9 genotypes
Genotype ratios (9):
Four Phenotypes:
1
TTPP
2
TTPp
Tall, purple (9)
2
TtPP
4
TtPp
1
TTpp
Tall, white (3)
2
Ttpp
1
ttPP
Short, purple (3)
2
ttPp
Short, white (1)
1
ttpp
Principle of Independent Assortment
• Based on these results, Mendel
postulated the
3. Principle of Independent
Assortment:
“Members of one gene pair
segregate independently from other
gene pairs during gamete formation”
Genes get shuffled – these many
combinations are one of the advantages
of sexual reproduction
Relation of gene segregation to
meiosis…
• There’s a correlation between the
movement of chromosomes in meiosis
and the segregation of alleles that
occurs in meiosis
True or False?
1.____Homozygous has identical genes for a
particular characteristic
2. ____Heterozygous forms one type of gametes
3. ____ Recessive allele masks the expression of
an alternate allele
4._____ Cystic Fibrosis is dominant trait
5. _____ Members of one gene pair segregate
independently from other gene pairs during
gamete formation
Beyond Mendelian Genetics:
Incomplete Dominance
Mendel was lucky!
Traits he chose in the
pea plant showed up
very clearly…
One allele was dominant over another, so
phenotypes were easy to recognize.
But sometimes phenotypes are not very
obvious…
Incomplete Dominance
Snapdragon flowers come in many colors.
If you cross a red snapdragon (RR) with a white
snapdragon (rr)
RR
You get PINK flowers (Rr)!
 rr
Genes show incomplete dominance
when the heterozygous phenotype
is intermediate.
Rr
Incomplete dominance
When F1 generation (all pink flowers) is self
pollinated, the F2 generation is 1:2:1
red, pink, white
Incomplete Dominance
R
r
R
r
R R
Rr
Rr
rr
Examples of incomplete dominance
• A child with wavy hair as a result of one parent's curly hair and
the other's straight hair.
• Tay-Sachs disease is an example of the result of incomplete
dominance because the gene that makes the antibodies only
creates half of the necessary antibodies which creates a
vulnerability in the individual to get Tay-Sachs.
• One parent has a large lip protrusion, the other parent has a
small lip protrusion and the child has an average lip protrusion.
• One parent has a high voice, the other parent has a low-pitched
voice, so the child has a voice of medium pitch.
• Sickle cell disease is the result of incomplete dominance as
those who have the disease carry 50% normal and 50%
abnomal hemoglobin.
• If a red tulip and a white tulip are cross pollinated they result is
a pink tulip.
• A person with big hands and a person with small hands have
offspring with hands of average size.
Sickle cell disease is the
result of incomplete
dominance as those who
have the disease carry 50%
normal and 50% abnormal
hemoglobin.
P: ♀ HbAHbA
G:
HbA
F1 :
HbAHbS
x
♂ HbSHbS
HbS
Sickling Cells
Polymers of Normal
hemoglobin
deform red Sickle
blood cells
Incomplete dominance
RR - Curly Hair, rr- Straight Hair, RrWavy Hair (Curly + Straight = Wavy)
Incomplete Dominance
R
r
R
r
RR
Rr
Rr
rr
Codominance
Genotype
Phenotype
LMLM
M
LMLN
MN
LNLN
N
• Both alleles are equally
dominant
• Heterozygotes express both
alleles = distinct
expression of the gene
products of both alleles
can be detected
• MN blood group
• F2 genotype and
phenotype ratios are 1:2:1
Multiple Alleles
• Genes can be characterized by more than 2
alleles
• Multiple alleles (>2) can be studied only in
populations, because any individual carries
only 2 alleles at a particular locus at one time
• ABO blood groups
– Each individual is A, B, AB, or O
phenotype
– Phenotype controlled by isoagglutinogen
marker on RBC
– IA and IB alleles are dominant to the IO
allele
– IA and IB alleles are codominant to each
other
Phenotype
Possible
Genotype
Antigen
on RBC
surface
Antibody
Made in
Plasma
A
IAIO, IAIA
A
Anti-B
B
IBIO,IBIB
B
Anti-A
AB
IAIB
AB
Neither
O
IOIO
O
Both
Task 1.
Mother has I (o) group
of blood, father has IV
(AB). Can children
inherit group of blood
of one of their parents?
Task 2.
The boy has I (o)
group of blood, his
sister has III (B).
Which
are
their
parents’ groups of
blood?
So, you must know ABO blood
type for
• *determining of the blood group;
• *blood transfusion;
• *in paternity suits
Blood type tests can never prove that
a certain person is the parent of a
particular child; they can determine
only whether he or she could be
Importance of A, B, O blood group antigens in
medicine
Transfusion compatibility
Blood type:
AB
A
B
O
Donate to:
AB
A or AB
B or AB
O, A, B, AB
Disease resistance
Resistance to cholera and other types of infant
diarrhea:
AB > A > B > O
Possible resistance to other diseases: malaria,
syphillis, cancer
Another sets of cell surface markers on human
red cells are the RH blood group antigens,
named for the rhesus monkey in which they first
described.
• This trait (antigen) is controlled by a single
allele pair in 1 chromosome.
• The rhesus-positive allele Rh is dominant over
the rhesus-negative allele rh.
• About 85 % of adult humans have the Rh cell
surface marker on their red blood cells, and are
called Rh-positive (RhRh, Rhrh).
• Rh-negative persons lack this cell surface
marker because they are homozygous
recessive for the gene encoding it (rhrh).
Hemolytic disease of the newborn
If an Rh-negative person is exposed to Rhpositive blood, the Rh surface antigens of
that blood are treated like foreign invaders
by the Rh-negative person’s immune
system, which proceeds to make antibodies
directed against the Rh antigens. This most
commonly happens when an Rh-negative
woman may have children who are Rh
positive if the father is Rh positive.
RhRh, Rhrh = rhesus-positive
rhrh = rhesus-negative
P:
♀ rhrh
G:
rh
F1 : Rh
x
♂ RhRh
Rh
Hemolytic disease of the
newborn
In the first pregnancy, this factor
causes no complication, but during
birth, blood cells of the child enter
the mother’s bloodstream, where
they induce the production of “antiRh” antibodies. Then, in subsequent
pregnancies, antibodies from the
mother pass to the fetus and cause
its red blood cells to clump, leading
to condition called erythroblastosis
fetalis.
Hemolytic disease of the newborn
(erythroblastosis fetalis)
Hemolysis leads to elevated bilirubin levels.
After delivery bilirubin is no longer cleared (via
the placenta) from the neonate's blood and the
symptoms of jaundice (yellowish skin and
yellow discoloration of the whites of the eyes)
increase within 24 hours after birth.
Like any other severe neonatal jaundice, there
is the possibility of acute or chronic kernicterus.
Profound anemia can cause high-output heart
failure, with pallor, enlarged liver and/or spleen,
generalized swelling, and respiratory distress.
The prenatal manifestations are known as
hydrops fetalis; in severe forms this can include
petechiae and purpura. The infant may be
stillborn or die shortly after birth.
Hemolytic disease of the newborn
(erythroblastosis fetalis)
Treatment
After birth, treatment depends on the
severity of the condition, but could include
temperature stabilization and monitoring,
phototherapy, transfusion with compatible
packed red blood, exchange transfusion
with a blood type compatible with both the
infant and the mother, sodium
bicarbonate for correction of acidosis
and/or assisted ventilation.
Hemolytic disease of the newborn
(erythroblastosis fetalis)
Treatment
Rhesus-negative mothers who have had a
pregnancy who are pregnant with a rhesuspositive infant are offered Rh immune
globulin (RhIG) at 28 weeks during
pregnancy, at 34 weeks, and within 72
hours after delivery to prevent sensitization
to the D antigen. It works by binding any
fetal red cells with the D antigen before the
mother is able to produce an immune
response and form anti-D IgG.
Superdominance
one dominant allele in heterozygous
has more expressive manifestation
than in homozygous state
• Example: Dominant gene B determines brachydactyly (short
fingers). Homozygous dominant persons with genotype BB
don’t survive; they die in the embryonic stage.
Person with genotype Bb
Epistasis
one gene masks the phenotypic effect
of another entirely different gene
• A pair of genes at one locus may prevent the
expression of a pair of genes at another locus.
• Such genes are called epistatic genes.
• Color of some fowls is result of
interaction between two non-allelic
genes: C—gene of colored fowls, c—
gene of white fowls, I—gene, that masks
the phenotypic effect of gene C (epistatic
gene), i—gene, that does not masks the
P: ♀ CCII (white) x ♂ ccii (white)
phenotypic effect of gene C. When the
G: CI
ci
CcIi fowls are inbred, F2 includes white
F1 : CcIi (white)
and colored fowls in the ratio of 13:3.
Continuous variation (polimery)
• Different dominant non-allele's genes
affect on one trait, making it more
expressive
• Traits determined by more than one
gene are polygenic - meaning "many
genes" - or quantitative traits.
Continuous variation
• Usually, several genes each contribute to
the overall phenotype in equal, small
degrees
• The combined actions of many genes
produce a continuum, or continuously
varying expression, of the trait.
• Example: Skin color is familiar example of
polygenic trait in humans.
Skin color is quantitative trait, that are controlled by two
pairs of genes A1a1, A2a2.
Let’s sign skin color as
• A1A1A2A2 – very dark
• A1A1A2a2 or A1a1A2A2 — dark
• A1a1A2a2 — medium brown
• A1a1a2a2 or a1a1A2a2 — light
• a1a1a2a2 — white (pale skin).
TASK
A woman with white skin married a
medium-brown man. What is the skin
color possible for their children?
P: ♀a1a1a2a2  ♂ A1a1A2a2
G: a1a2
A1A2, A1a2, a1A2, a1a2
F1: A1a1A2a2; A1a1a2a2; a1a1A2a2; a1a1a2a2
Pleiotropy
• Often an individual allele will have more than
one effect on the phenotype.
• Such allele is said to be pleiotropic.
• Pleiotropic relationships occur because in
examine the characteristics of organisms; we
are studying the consequences of the action of
products made by genes.
• Pleiotropy occurs in genetic diseases that affect
a single protein found in different parts of the
body. This is the case for Marfan syndrome.
Marfan syndrome (MS)
•
Autosomal dominant defect
in elastic connective tissue
protein called fibrillian
• Fibrillian is abundant in the
lens of the eye, in the aorta,
and in the bones of the limbs,
fingers, and ribs
• MS symptoms include lens
dislocation, long limbs,
spindly fingers, and a cavedin chest
True or False?
1.____ Incomplete dominance if heterozygous
phenotype intermediate between the two
homozygous
2. ____A human with 0 blood has both A and B
antigenes
3. ____ Skin color is example of polygenic trait in
humans
4. _____IA and IB alleles are codominant to each
other
5. _____A single pleiotropic gene can affect several
traits
Thank you for attention !