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My name is Dorota Kolodziejczyk
I am a lecturer at Siedlce University of Natural Sciences
and Humanities in the Institute of Animal Science and Fisheries.
It is my pleasure to present to you
the topic of the genetics of sex.
The essence of the science of heredity is to study the mechanisms
by means of which are developmental plan is imposed on the offspring,
leading to the formation of an organism with general structural features
and functions characteristic of all individuals of this species,
and similar in specific features to its parents.
The concept of the origin of the trait, later called a gene,
was introduced by Mendel,
while Strasbourger
and Meisel made a significant contribution to the discovery and description of chromosomes
and the understanding of the mechanisms of cell division
mitosis and meiosis
At the beginning of the 20th century,
geneticist Thomas Morgan developed the chromosomal theory of inheritance
proving that chromosomes are the carrier of genetic information.
They are nucloproteins
and their essential component is deoxyribonucleic acid DNA,
which is a hereditary substance.
Chromosomes are divided into two basic groups, namely
autosomes and heterosomes, otherwise known as sex chromosomes.
Sex chromosomes are formed from a pair of autosomal chromosomes,
which, through progressive specialization,
have accumulated a large number of genes responsible
for gender determination.
Sex determining genes are not only localized
in both heterosomes and autosomes.
Moreover in different groups of animals
The mutual importance of hetero and autosomes
in genetics sex determination is not the same. In mammals
there is a genetic sex determination mechanism XX/YX, with a few exceptions,
among the order of marsupials.
The heterogametic sex, i.e.
the one that produces two types of gametes, is male x y
in mammals, while females are the homogametic sex XX,
The decisive role in sex determination in
mammals is played by the male Y chromosome,
which exerts an influence
on the initially female determined embryo.
This is due to the SRY
sex determining region y gene located on this chromosome.
It is this gene that initiates and conditions
the transformations that result in the development of primary sex characteristics.
Testicles.
Determining male sex.
The absence of the SRY gene on the
Y chromosome leads to the creation of an individual with a female phenotype.
Despite the presence of this Y chromosome
in the gonads, testes and ovaries.
Meiotic cell division occurs resulting in the formation of gametes.
In this process,
the sex chromosomes are randomly sorted and all eggs carrying an X chromosome are produced in the female,
and the X
or Y chromosome goes to the sperm
in order for female cells
not to make twice as many proteins encoded on the sex chromosomes,
one must be turned off in some way.
This happens in early embryonic development,
where one of the X chromosomes is randomly inactivated in cells and becomes visible as a lump of sex.
Chromatin.
The following illustration presents
the scheme of genetic sex determination in mammals created by Boczkowski
in 1983.
Unlike mammals, birds are characterized
by the genetic mechanism of sex determination, ZZ/ZW
The heterogametic
sex
in birds is the female z W,
and the males are the homogametic sex Z.Z.
It is interested that in birds as in
mammals, sex chromatin was observed in females, which indicates that the sex chromatin clump
is not formed as a result of the fusion of two homologous sex chromosomes.
It has been shown that in birds the ovary is the dominant gonad, and if the ovary is implanted
next to the testis, it transforms into an ovary, according to the other authors.
The role that the Z and W chromosomes is not yet fully resolved. In birds
The SRY gene responsible for the formation of the male phenotype was not found.
Scientists believe that the level of the DMRT1 gene product mapped on
the Z chromosome, is responsible for determining the bed sex.
Research on genetic
sex determination in insects has become the basis
for examining the genetic mechanisms of sex determination.
The turning point was Jan Dzierżoń discovery in 1845
of the phenomenon of parthenogenesis.
A Polish priest and beekeeper stated
and proved that the Queen bee lays two types of eggs
fertilized and unfertilized from the latter.
Males are formed - drones. Fertilized eggs,
on the other hand hatch into workers or queens depending on the diet.
If it is poor in protein, it causes sexual
underdevelopment of workers.
Based on research on Drosophila,
it was found that sex depends on the ratio of the number
of X chromosomes to the number of haploid autosomal suits,
with X chromosomes affecting the development of females
and autosomes affecting male development.
The presence of the Y chromosome does not determine sex,
but it is important for the full development
of testicular function.
Fish show the greatest variety of sexual differentiation.
Unlike other vertebrates, hermaphroditism, bisexuality
is a physiological condition in fish
and there are five
types of hermaphroditism in this group of animals
a synchronous hermaphroditism,
a state in which an individual is capable of functioning as both male and female simultaneously.
Alternating functional hermaphroditism
that is, an individual functions once as female, once as male.
Protandric hermaphroditism a state
in which an individual functions first as male, then as female,
Protogynoid hermaphroditism a state
in which an individual functions first as female and then as male
the residual hermaphroditism
means the existence of hermaphroditic features
in an individual
functioning only
as male or female.
Many traits in humans and animals are
determined by genes located on the sex chromosomes.
Hence, they are called sex linked traits.
Some of them are hemophilia in humans
and dogs, a leg twisting in pigs, a lethal gene
causing the absence of teeth and the death of male fetuses in cattle.
The black and yellow coloration of the coat in cats
hawklike plumage.
In hens, polledness in cattle.
Fruit fly eye color
The illustration below shows how the inheritance of plumage color in chickens works.
Sex-linked traits are those that are determined
by genes located in autosomes
but their phenotypic expression depends on the sex of the individual.
For example, red or mahogany color in cattle is determined by the Mm gene pair.
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
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.
The genes determining these traits can be located on both autosomes and sex chromosomes.
Some of them are:
milk secretion in mammals
egg-laying in birds
cryptorchidism in males,
impotence of Friesian bulls
fertility disorders of white shorthorn heifers (Maciejowski i Zięba, 1982; Świderek, 2015).
Understanding the molecular basis of sex determination plays an important role in breeding.
Early assessment of the sex of the embryos makes it possible to obtain offspring of a specific, desired sex.
Embryos can be obtained by in vitro fertilization,
cloning, or from superovulatory donor females and transferred to recipient females.
A useful method of determining the sex of embryos is
the detection of the gene sequence of DNA isolated from the cells of the male embryo.
This is done on the basis of PCR amplification
of a selected DNA fragment and electrophoresis of the obtained products
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.
thank you for your attention.