Organism’s level of realization
of hereditary information.
Interaction of
genes.Chromosomal theory of
heredity. Variation in human
beings as a quality of life and a
genetic phenomenon.
Lecturer: ass. Nedoshytko Kh.Yu.
GENETICS
 It
is a branch of
biology that deals
with heredity and
variation of
organisms.
 Chromosomes carry
the hereditary
information:
DNA  RNA  Proteins
Genetics terms you need to know:
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Heredity – is the transmission of characteristics from parent to
offspring through the gametes.
Inheritance – is the way of passing of hereditary information
which depends on the forms of reproduction.
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. Homozygous – having identical genes (one
from each parent) 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.
Gregor Johann Mendel
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Austrian Monk, born in Czech
Republic in 1822.
He was on of peasant farmer,
he studied
Theology and was ordained
priest Order St. Augustine.
He went to the university of
Vienna, where he studied
botany and learned the
Scientific Method.
He 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.
1. The law of monotony of the
first filial generation
During crossing two homozygous
which differ from each other by
one trait all progeny in the first
filial generation is monogyny
as well as phenotypic and
genotypic
P (Parental): ♀ AA x ♂ aa
G (Gametes): A
a
F1 (First Filial Generation): Aa
(yellow)
2. The law of segregation
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The law of segregation states
that 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.
P:
G:
F2 :
♀ Rr
x
♂ Rr
R, r
R, r
RR; Rr; Rr; rr
3. The law of independent
assortment
Alleles of one
gene pair
segregate
independently
from other gene
pairs during
gamete
formation.
Phenotype Ratio
= 9:3:3:1
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Gene interactions
Allelic genes control the two alternative expressions of the same
character and have the same loci (sites) in the homologous
chromosomes.
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Complete Dominance
Incomplete Dominance
Codominance
Superdominance
Non-allelic genes have the different loci (sites) in the homologous
chromosomes or are situated in the different (non-homologous)
chromosomes.
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Polimery
Epistasis
Complementarity
Complete Dominance
 It
is when one allele is completely
dominant over the other allele.
Incomplete Dominance
 It
is when
one allele is
not
completely
dominant
over the
other allele.
The
intermediate
trait occurs.
Codominance
 It
is when
both alleles
are equally
dominant.
Superdominance
 It
is when 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.
Polimery

Different
dominant
non-allele's
genes affect
on one trait,
making it
more
expressive.
Epistasis
 It
is when one gene
masks the
phenotypic effect of
another entirely
different gene.
The B/b gene determines the
pigment color (B for black and b
for brown).
The epistatic C/c gene controls
whether or not any pigment will
be deposited in the hair.
A homozygous recessive ccmouse
has no hair pigment and is
albino regardless of
its B/bgenotype.
Complementarity
 It
is an
interaction
between two
dominant
genes in
which they
give new
phenotype.
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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.
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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.
Chromosome theory of linkage:
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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 in the
chromosome determines the strength of linkage.
Linkage strength between two genes turn out to the
distance between them.
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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.
Crossing-over
Sex determination in humans
P:
44 A + XX

44A + XY
Gametes: 22A + X
22A + X; 22A + Y
F1: 44 A + XX; 44A + XY.
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.
Ratio of Sexes in Human population
The stages of Human
Development
Male
Female
Zygotes
114-135
100
At birth (newborns)
106
100
10 years
100
100
50 years
85
100
80 years
50
100
Pedigree Analysis
Pedigree – a
diagram of
an
individual’s
ancestors,
used by the
human
genetics for
the analysis
of
inheritance.
Types of inheritance:
 Autosomal-Dominant
inheritance
 Autosomal-Recessive inheritance
 X-Linked Dominant inheritance
 X-Linked Recessive inheritance
 Y-Linked inheritance
Autosomal-Dominant inheritance
occurs when:
 1) a trait can effect both sexes
(female and male can be ill);
 2)
the trait is inherited vertically
in the pedigree (it affects every
generation);
 3)
one or both parents of ill child
are ill.
Autosomal-Recessive inheritance:
occurs when:
 1) a trait can effect both sexes
(female and male can be ill);
 2)
the trait is inherited horizontally in
the pedigree (it does not affect every
generation);
 3)
parents of ill child can be healthy in
the phenotype, but they are heterozygous
and carriers of mutant gene (individuals
who have affected children must both be
carriers);
 4) probability of the sick children birth is
higher in family marriages (members are
closely related).
X-Linked Dominant inheritance:
occurs when:
 1) a trait affects mostly females;
 2)
if the affected female is
heterozygous, she will pass the trait
to a half of her offspring (male and
female);
 3)
an affected male passes the
trait to his daughters.
Enamel hypoplasia (hereditary defect that cause
holes and cracks to appear around the crowns of
the teeth) is sex-linked dominant trait.
X-Linked Recessive inheritance:
occurs when:
 1) a trait affects mostly males;
 2)
the trait does not
pass from father to son.
Hemophilia (absence of clotting factors VIII or IX, blood
fails to coagulate; coagulates very slowly after an
external or internal injury) is a sex-linked recessive
disorder.
Y-Linked inheritance:
occurs when:
 1) a trait affects only males;
 2) father passes a trait to all sons.
Hairy pinnae (hairy ears) – Y-linked trait
Thank
you
for
attention!