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Theme: Organism’s level of
organization of hereditary
information.
Interaction of genes. Genetic
linkage. Genetic of sex.
Variation in human being as
a quality of life and genetic
phenomenon
Lecturer: ass. prof. Tetyana Bihunyak
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
• 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 (like
‘flavors’ of a 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
3
4
5
6
7
8
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
9
10
11
12
13
14
15
16
17
18
19
20
21
22
XX
17 18
19
20
21
22
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 F2 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.
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
C
c
C
CC
Cc
c
Cc
cc
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
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
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
Continuous variation
• 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
•
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
• Marfan syndrome symptoms
include lens dislocation, long
limbs, spindly fingers, and a
caved-in 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
•Gene is a small segment of DNA that
codes the synthesis of a specific protein.
•Genes are located on the chromosomes.
•In human karyotype there are 46
chromosomes. In human diploid number
there are thousands of different genes.
•Many genes may be present on the same
chromosome. Such genes are said to be
linked, or to constitute a linkage group.
•Linked genes were discovered by great
American geneticist Thomas Hunt
Morgan of Columbia University in 1910.
Unlinked Genes
Linked Genes
Thomas Hunt
Morgan (1866-1945)
Nobel prize in 1933 for
his research on the fly
Drosophila in linkage and
crossing-over, which he
used to map the linear
arrangement of genes
along the chromosome.
T. H. Morgan studied chromosomes
of Drosophila melanogaster (fruit-fly)
The fruit-fly was selected because 1) it breeds rapidly, attaining
maturity in twelve days; 2) 30 generations can be bred in one
year; 3) it has only eight chromosomes.
L = long wings
l = short wings
G = gray body
g = black body
Autosomal Linkage. Dihybrid Testcross
F2 :
41.5%
8.5%
8.5%
41.5%
Distance between the linked genes
is measured in centimorgans (cM)
or map units.
1 cM = 1 map unit = 1% of
crossing over = 1% crossover
gametes = 1% recombinants
Linkage between genes on the same
chromosome
1) complete linkage - when genes stay
together at a very short distance on the
chromosome; person with complete linked
genes can form only noncrossover gametes.
2) incomplete linkage - when genes stay
together at a far apart (under 50 cM); person
with incomplete linked genes can produce
crossover and noncrossover gametes,
because during meiosis crossing-over takes
place.
Chromosome theory of linkage:
1) Genes lie in a linear order on the chromosomes. The
position of a gene on a chromosome is locus.
2) Genes located on the same chromosome are linked
or constitute a linkage group. The number of linkage
groups is exactly the number of chromosome pairs in the
organism.
3) Linkage between two genes can be interrupted by
crossing-over (alleles exchanges between homologous
chromosomes during meiosis).
4) The distance between the linked genes on the
chromosome determines the strength of linkage. Linkage
strength between two genes turn out to the distance
between them.
Sex determination in humans
P:
44 A + XX

Gametes: 22A + X
F1: 44 A + XX; 44A + XY.
44A + XY
22A + X; 22A + Y
In human being sex inherits as Mendelian Trait.
•The sex of the offspring is determined by the kind of
sperm that will fertilize an egg.
•If fertilization is by an X-bearing sperm, the resulting
zygote will be XX and will develop into a female.
•If fertilization is by a Y-bearing sperm, the resulting
zygote will be XY and will develop into male.
Sex determination in humans
•Sex differentiation in humans takes place
during embryonic development.
•Gene Sry (for sex determining region of the
Y chromosome) that directs development of
gonad to testis and secreting of androgens is
presence on the short arm of the Ychromosome.
•If it is absence, the gonad becomes an ovary
and female structures (uterus, Fallopian
tubes) develop.
Variation is deviation in
characters in an individual
from those typical of the
species to which it belongs.
Variation of organisms is
subdivided into:
1) non-hereditary (phenotypic
or modification) and
2) hereditary (genetic variation).
Phenotypic (modification)
variation are changes of phenotype
without changes of the genotype,
these changes are adaptive
reactions to external stimuli and
they do not inherit.
Hereditary (genetic variation) is
subdivided into: 1) combinatorial
variation and 2) mutation.
Combinatorial variation is formation of new
combinations of genotypes by shuffling of
parental genes.
New genotypes arise in 3 ways:
1) recombination of linked genes in
chromosomes by crossing over in the
prophase of meiosis;
2) independent assortment of chromosomes
during meiosis;
3) random combination of chromosomes
during fertilization.
As a result of combinatorial variation is
deviation in characters of the offspring from
those of its parents.
Crossing-over
Mutation is a permanent transmissible
change in the genetic material
(modification in chromosomes and
genes).
There are 3 main types of mutations:
1) chromosome mutations (genomic
mutation) are changes in number of
chromosomes in karyotype;
2) chromosome aberrations are changes
in structure of chromosomes;
3) gene (point) mutations are changes in
structure of the nucleotides.
Сhromosome
mutations
are
subdivided into:
1) polyploidy is the state of having
more than diploid set of
chromosomes: 3n (triploid), 4n
(tetraploid), 5n (pentaploid), 6n
(hexaploid);
2) aneuploidy is any deviation of the
diploid number of chromosomes,
an individual or cell having a
missing (2n-1) or extra (2n+1)
chromosomes.
Human Trisomy 21 XY male
(47,XY,21+)
Duplication - a segment of a chromosome
joins a part of homologous chromosome
Inversion - a segment of a chromosome
breaks off and rotates through 180º and
rejoining the chromosome
Translocation - a segment of a
chromosome breaks off and joins a nonhomologous chromosome
A good example is
the translocation
between
chromosomes 9 and
22, creating the
“Philadelphia
chromosome”
This causes about
90% of the cases of
chronic
myelogenous
leukemia
A gene mutation or
point mutation (since it
applies to a particular gene
locus) is the result of a change
in the nucleotide sequence of
the DNA molecule in a
particular region of the
chromosome
Such a change in the base
sequence of the gene is
transmitted to mRNA during
transcription and may result in a
change in the amino acid
sequence of the polypeptide
chain produced from it during
translation at the ribosomes
Gene mutations
Gene mutations occurring
during gamete formation are
transmitted to all the cells of the
offspring and may be significant
for the future of the species.
Somatic gene mutations
which arise in the organism are
inherited only by those cells
derived from the mutant cells by
mitosis.
Sickle cell anaemia in
humans is an example of base
substitution mutation affecting
a base in one of the genes
involved in the production of
haemoglobin
Hemoglobin and Sickle Cell Anemia
• Single base mutation in DNA
– A to T transversion
• Single amino acid change in the protein
– Glutamine to Valine
H 2N
H 2C
O
H 3C H CH 3
C
CH 2
C
H 2N H
O
C
H 2N H
O
OH
OH
Glutamine
Valine
Sickling Cells
Polymers of Normal
hemoglobin
deform red Sickle
blood cells
Sickle Cell Anemia
• Recessive trait
• Symptoms:
–
–
–
–
Chronic hemolytic anemia
Severe pain
Rapid septicemia (infection)
Asplenia (no spleen left)
How Was the Mutation Selected?
• Malaria
– Mosquito born plasmodium
parasite
– Some sickling is good
• Heterozygotes have the
advantage!
“He who likes to eat fruit
must climb the tree”
(English proverb)