Organism’s level of realization Organism’s level of realization of hereditary information. of hereditary information.

Interaction of Interaction of genes.genes.Chromosomal Chromosomal theory of theory of heredity. Variation in human heredity. Variation in human

beings as a quality of life and a beings as a quality of life and a genetic phenomenon.genetic phenomenon.

Lecturer: ass. Nedoshytko Kh.Yu.Lecturer: ass. Nedoshytko Kh.Yu.

GENETICSGENETICS

It is a branch of It is a branch of biology that deals biology that deals with heredity and with heredity and variation of variation of organisms.organisms.

Chromosomes carry Chromosomes carry the hereditary the hereditary information:information:

DNA DNA RNA RNA Proteins Proteins

Genetics terms you need to know:Genetics terms you need to know: 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 MendelGregor Johann Mendel Austrian Monk, born in Czech Austrian Monk, born in Czech

Republic in 1822.Republic in 1822. He was on of peasant farmer, He was on of peasant farmer,

he studiedhe studiedTheology and was ordainedTheology and was ordainedpriest Order St. Augustine.priest Order St. Augustine.

He went to the university of He went to the university of Vienna, where he studied Vienna, where he studied botany and learned the botany and learned the Scientific Method.Scientific Method.

He worked with pure lines of He worked with pure lines of peas for eight years.peas for eight years.

Prior to Mendel, heredity was Prior to Mendel, heredity was regarded as a "blending" regarded as a "blending" process and the offspring process and the offspring were essentially a "dilution"of were essentially a "dilution"of the different parental the different parental characteristics. characteristics.

1.1. The law of monotony of the The law of monotony of the first filial generationfirst 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 ♂ aaG (Gametes): A aF1 (First Filial Generation): Aa

(yellow)

2. The law of segregation2. The law of segregation 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: ♀ Rr x ♂ RrG: R, r R, r F2 : RR; Rr; Rr; rr

Alleles of one gene pair segregate independently from other gene pairs during gamete formation.

Phenotype Ratio Phenotype Ratio = 9:3:3:1= 9:3:3:1

3. The law of independent 3. The law of independent assortmentassortment

Gene interactionsGene interactions

Complete DominanceComplete Dominance Incomplete DominanceIncomplete Dominance CodominanceCodominance SuperdominanceSuperdominance

PolimeryPolimery EpistasisEpistasis ComplementarityComplementarity

Allelic genes  control the two alternative expressions of the same character and have the same loci (sites) in the homologous chromosomes.       

Non-allelic genes  have  the different loci (sites) in the homologous chromosomes or are situated in the different (non-homologous) chromosomes.

Complete DominanceComplete Dominance It is when one allele is completely

dominant over the other allele.

Incomplete DominanceIncomplete Dominance It is when

one allele is not completely dominant over the other allele. The intermediate trait occurs.

CodominanceCodominance

It is when both alleles are equally dominant.

SuperdominanceSuperdominance

It is when It is when one dominant allele in one dominant allele in heterozygous has more expressive heterozygous has more expressive manifestation than in homozygous manifestation than in homozygous state. state.

Example. Dominant gene B determines brachydactyly (short fingers). Homozygous dominant persons with genotype BB don’t survive, they die in the embryonic stage.

PolimeryPolimery

Different dominant non-allele's genes affect on one trait, making it more expressive.

EpistasisEpistasis 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.

ComplementarityComplementarity

It is an interaction between two dominant genes in which they give new phenotype.

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.

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 theoryChromosome theory of linkage: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 in the chromosome determines the strength of linkage. Linkage strength between two genes turn out to the distance between them.

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-overCrossing-over

Sex determination in humansP: 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 populationRatio 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 AnalysisPedigree Analysis

Pedigree – a diagram of an individual’s ancestors, used by the human genetics for the analysis of inheritance.

Types of inheritance:Types of inheritance:

Autosomal-Dominant inheritanceAutosomal-Dominant inheritance Autosomal-Recessive inheritanceAutosomal-Recessive inheritance X-Linked Dominant inheritanceX-Linked Dominant inheritance X-Linked Recessive inheritanceX-Linked Recessive inheritance Y-Linked inheritanceY-Linked inheritance

Autosomal-Dominant inheritanceAutosomal-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: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: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: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: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 Thank you for attention!for attention!