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This presentation has been supported by the Erasmus Plus

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K2 Cooperation Partnerships.

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Innovation of the structure and content of study programs
in the field of animal

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genetic and food resources management

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with the use of digitalization innovation.

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digitalization innovation.

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The European Commission.

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Support for the production of this presentation
does not constitute

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an endorsement of the contents,
which reflects the views only of the authors.

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And the Commission cannot be held responsible for any use
which may be made

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of the information contained therein.

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My name is Dorota Kolodziejczyk

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I am a lecturer at Siedlce University of Natural Sciences

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and Humanities
in the Institute of Animal Science and Fisheries.

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It is my pleasure to present to you

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the topic of the genetics of sex.

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The essence of the science of heredity is to study
the mechanisms

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by means of which are developmental
plan is imposed on the offspring,

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leading to the formation of an organism
with general structural features

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and functions
characteristic of all individuals of this species,

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and similar in specific features to its parents.

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The concept of the origin of the trait, later called a gene,

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was introduced by Mendel,

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while Strasbourger

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and Meisel made a significant contribution to the discovery
and description of chromosomes

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and the understanding of the mechanisms of cell division

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mitosis and meiosis

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At the beginning of the 20th century,

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geneticist Thomas Morgan
developed the chromosomal theory of inheritance

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proving that chromosomes
are the carrier of genetic information.

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They are nucloproteins

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and their essential component is deoxyribonucleic acid DNA,

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which is a hereditary substance.

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Chromosomes are divided into two basic groups, namely

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autosomes and heterosomes, otherwise known as sex chromosomes.

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Sex chromosomes are formed
from a pair of autosomal chromosomes,

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which, through progressive specialization,

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have accumulated a large number of genes responsible

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for gender determination.

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Sex determining genes are not only localized

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in both heterosomes and autosomes.

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Moreover in different groups of animals

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The mutual importance of hetero and autosomes

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in genetics sex determination is not the same. In mammals

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there is a genetic sex determination mechanism
XX/YX, with a few exceptions,

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among the order of marsupials.

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The heterogametic sex, i.e.

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the one that produces two types of gametes, is male x y

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in mammals, while females are the homogametic sex XX,

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The decisive role in sex determination in

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mammals is played by the male Y chromosome,

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which exerts an influence

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on the initially female determined embryo.

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This is due to the SRY

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sex determining region y gene located on this chromosome.

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It is this gene that initiates and conditions

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the transformations that result in the development
of primary sex characteristics.

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Testicles.

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Determining male sex.

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The absence of the SRY gene on the

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Y chromosome leads to the creation of an individual
with a female phenotype.

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Despite the presence of this Y chromosome

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in the gonads, testes and ovaries.

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Meiotic cell division occurs
resulting in the formation of gametes.

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In this process,

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the sex chromosomes are randomly sorted and all eggs
carrying an X chromosome are produced in the female,

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and the X

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or Y chromosome goes to the sperm

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in order for female cells

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not to make twice
as many proteins encoded on the sex chromosomes,

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one must be turned off in some way.

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This happens in early embryonic development,

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where one of the X chromosomes is randomly inactivated in cells
and becomes visible as a lump of sex.

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Chromatin.

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The following illustration presents

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the scheme of genetic sex determination in mammals
created by Boczkowski

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in 1983.

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Unlike mammals, birds are characterized

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by the genetic mechanism of sex determination, ZZ/ZW

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The heterogametic

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sex

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in birds is the female z W,

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and the males are the homogametic sex Z.Z.

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It is interested that in birds as in

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mammals, sex chromatin was observed in females,
which indicates that the sex chromatin clump

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is not formed as a result of the fusion of two homologous
sex chromosomes.

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It has been shown that in birds
the ovary is the dominant gonad, and if the ovary is implanted

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next to the testis, it transforms into an ovary,
according to the other authors.

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The role that the Z and W chromosomes is not yet
fully resolved. In birds

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The SRY gene responsible for the formation of the male
phenotype was not found.

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Scientists
believe that the level of the DMRT1 gene product mapped on

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the Z chromosome, is responsible
for determining the bed sex.

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Research on genetic

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sex determination in insects has become the basis

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for examining the genetic mechanisms of sex determination.

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The turning point was Jan Dzierżoń discovery in 1845

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of the phenomenon of parthenogenesis.

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A Polish priest and beekeeper stated

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and proved that the Queen bee lays two types of eggs

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fertilized and unfertilized from the latter.

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Males are formed - drones. Fertilized eggs,

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on the other hand
hatch into workers or queens depending on the diet.

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If it is poor in protein, it causes sexual

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underdevelopment of workers.

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Based on research on Drosophila,

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it was found that sex depends on the ratio of the number

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of X chromosomes to the number of haploid autosomal suits,

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with X chromosomes affecting the development of females

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and autosomes affecting male development.

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The presence of the Y chromosome does not determine sex,

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but it is important for the full development

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of testicular function.

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Fish show the greatest variety of sexual differentiation.

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Unlike other vertebrates, hermaphroditism, bisexuality

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is a physiological condition in fish

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and there are five

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types of hermaphroditism in this group of animals

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a synchronous hermaphroditism,

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a state in which an individual is capable of functioning
as both male and female simultaneously.

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Alternating functional hermaphroditism

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that is, an individual functions
once as female, once as male.

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Protandric hermaphroditism a state

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in which an individual functions first as male, then as female,

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Protogynoid hermaphroditism a state

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in which an individual functions first as female
and then as male

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the residual hermaphroditism

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means the existence of hermaphroditic features

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in an individual 

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functioning only 

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as male or female.

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Many traits in humans and animals are

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determined by genes located on the sex chromosomes.

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Hence, they are called sex linked traits.

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Some of them are hemophilia in humans

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and dogs, a leg twisting in pigs, a lethal gene

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causing the absence of teeth
and the death of male fetuses in cattle.

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The black and yellow coloration of the coat in cats

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hawklike plumage.

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In hens, polledness in cattle.

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Fruit fly eye color 

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The illustration below shows how the inheritance of plumage color in chickens works.

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Sex-linked traits are those that are determined 

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by genes located in autosomes

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but their phenotypic expression depends on the sex of the individual.

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For example, red or mahogany color in cattle is determined by the Mm gene pair. 

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Dominant homozygotes - MM, regardless of sex, are mahogany, homozygous recessive - mm, are red, both males and females, while the color of heterozygotes - Mm depends on sex - males are mahogany and females are red

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Sex-restricted traits are traits that occur in only one sex, even though the genes for that trait are passed onto offspring by both parents.

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The genes determining these traits can be located on both autosomes and sex chromosomes.

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Some of them are:

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milk secretion in mammals

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egg-laying in birds

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cryptorchidism in males,

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impotence of Friesian bulls

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fertility disorders of white shorthorn heifers (Maciejowski i Zięba, 1982; Świderek, 2015).

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Understanding the molecular basis of sex determination plays an important role in breeding.

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Early assessment of the sex of the embryos makes it possible to obtain offspring of a specific, desired sex.

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Embryos can be obtained by in vitro fertilization, 

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cloning, or from superovulatory donor females and transferred to recipient females.

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A useful method of determining the sex of embryos is 

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the detection of the gene sequence of DNA isolated from the cells of the male embryo.

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This is done on the basis of PCR amplification
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of a selected DNA fragment and electrophoresis of the obtained products  

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BIBLIOGRAPHY
Boczkowski K., 1983. Determinacja i różnicowanie płci. PWN Warszawa. 
Charon K.M., Świtoński M., 2000. Genetyka zwierząt. PWN Warszawa. 
https://pl.wikipedia.org/wiki/System_determinacji_p%C5%82ci_XY#/media/Plik:Types_of_sex_determination.png
https://zpe.gov.pl/a/film-samouczek/DuQIqjlMV
Jobling M.A., Tyler-Smith C., 1995. Fathers and sons: the Y chromosome and human evolution, Trends in Genetics., 11(11), s. 449-56. 
Maciejowski J., Zięba J., 1982. Genetyka zwierząt i metody hodowlane. PWN Warszawa. 
Świderek W., 2015. Dziedziczenie i determinacja płci. W Genetyka zwierząt w teorii i praktyce. Nowak Z. (red.), SGGW Warszawa.
Walker R., 2012. Kim jestem? Wydawnictwo Olesiejuk.


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thank you for your attention.