SEX DETERMINATION AND SEX BASED INHERITANCE

REPRESENT BY:

MUHAMMAD RIFDI SYUKRAN B. ROZLI

MUHAMMAD ASYRAFITRI B. CHE YUSOF

NAGESVARI A/P RAMESH

NOR SYAHIRAH BINTI ROSDI

NUR AZIDA AFFINI BINTI ZAIDI

SEX DETERMINATION

SEX DETERMINATION The natural event by which an individual of a dioecious species become male or female

Two main mechanisms

Enviromental Sex

Genetic sex determination

In some species sex is determined after fertilization by environment factors

Sex is determined at fertilization by the combination of genes that the zygote recieves

SEX DETERMINATION MECHANISMS

Monoecious

-Both male and female reproductive structures in the same organism

Hermaphoditism

-both sex in the same organism

Dioecious

-either male or female reproductive structures in one organism

Environmental Sex Determination

Sex Determination : Enviroment

• Sex Determination : social

• Sex Determination : chance

• Sex Determination : number of offspring

Sex Determination :

Enviroment

Sex is determined by extrinsic factors after the process of fertilization

-temperature

-population size

-sex of others

Sex Determination : Social

For example: Clown fish

Coral reef fish may start out as one sex but later change to the other

The trigger may be a social change , such as the dissapearance of a dominant male or female

Sex Determination : Chance

For example: Bonellia verdis

A marine worm , females are large and attach to rocks in the sea, males are small.

The larvae float in the ocean

When they settle down and land on land a female worm, they become male

If they land elsewhere (on the sea floor),they become female

Sex Determination : Number of offspring

For example : Meloidogyne incognita is a nematode plant parasite.

If nutrient are sparse, they bcome male

If plentifil, the worms become females, which enchances the reproductive potential of the population

Protenor mode(XX-XO system)

FEMALE ( XX)

-Presence of two X chromosomes in the zygote

MALE ( XO)

-Presence of only one X chromosome

Example:some insects:grasshoppers

Modes of sex Determination

The modes of sex determination:

Lygaeus Mode(XX-XY System)FEMALE-XX(Homogametic sex)-Female gametes all have an X chromosome-Zygotes with two X chromosomes

MALE-XY(Heterogametic sex)-Male gametes have either X and Y chromosome-Zygote with one X and Y chromosomeExample: Drosophila, mammals and some plants

The modes of sex determination

ZZ-ZW System

FEMALE

-Heterogametic sex(ZW)

MALE

-Homogametic sex(ZZ)

-The Z chromosome is larger and has more genes

-Example:birds,buttrflies,some fishes

The modes of sex determination

X-Y-XY

-Female gametophytes-Y

-Male gametophytes-X

-Sporophytes-XY

-Example:Occurs in alternation of generation (liverworts,vascular plants)

THE MODES OF SEX DETERMINATION

• Haplodiploidy System(Arrhenotoky)

• Arrhen=male Tokos=childbirth

• -Diplod set-Female-Females arise from fertilized eggs

• -Haploid set-Male-Male develop from unfertilized eggs-Example:Bees,ants,wasps

SEX DETERMINATION IN HUMANS XX-XY

• Females have two X chromosomes

• Males have one Y chromosome

• The male-determining gene is located on the Y chromosome

• A single Y, even in the presence of several X, still produces a male phenotype.

• The absence of Y results in a female phenotype

GENOTYPIC SEX DETERMINATION

Sex ratio always remains close to 0.5, and its not depend on the environment.

Individuals are heterogametic or homogametic.

Fertilization by X sperm yields female, Y sperm produces males.

Sex Determination in Humans XX-XY

Y chromosome contains less genes than X chromosome.

Y Chromosome Contains:

The male-specific region of the Y (MSY)

A sex-determining of the Y (SRY)

SRY gene

Located near the end of the short arm of the Y chromosome .

Important in causing the undifferentiated gonad to develop into a testis.

Determine maleness.

Y Chromosome

Testis-determining factor (TDF)

A protein encoded by a gene in the SRY that triggers testes formation.

The MSY consist of three regions:

X-transposed region.

X-degenerative region.

Ampliconic region.

TDF Factor

Pseudoautosomal Regions (PARs)

Region Y chromosome-share homology with regions on the X chromosome

Synapses and recombine with it during meiosis

Presence of such pairing region is critical to segregation of the X and Y chromosomes during male gametogenesis

Equalizing the expression of X chromosomes in Males and Females

Human females have one X chromosome inactivated in their somatic cells to balance the expression of X-linked genes in male and female

Females have two X-chromosomes,male have one

X chromosomes contain many genes that are unrelated to sex determination,but not present in Y chromosomes

Dosage compensation occurs by X chromosome inactivation

Dosage compensation

-A mechanism that regulates the expression of sex-linked gene products

-Proposed by Marry Lyon(1961)

-Random inactivation of one X chromosome in females equalizes the activity of X-linked genes in males and females

Prevents excessive expression of X-linked genes in humans and other mammals

Balance the dose of X chromosome gene expression in female and males

Barr Body

Barr body The condensed, single X-chromosome, appearing as a densely staining mass, that is found in the nuclei of somatic cells of female mammals.

This occurs in almost all cells of females at blastocyst stage

An inactivated X chromosomes,tightly coiled

X-inactivation

X-inactivation is a process by which one of the two copies of the X chromosome present in female mammals is inactivated.

The inactive X chromosome is silenced by it being packaged in such a way that it has a transcriptionally inactive structure called heterochromatin

As female mammals have two X chromosomes, X-inactivation prevents them from having twice as many X chromosome genes products as males, which only possess a single copy of the X chromosome

FemALE MAMMALS ARE ACTUALY MOSAIC FOR X

CHROMOSOME EXPRESSION

Inactivated chromosome can come from either mother/father

Inactivation occurs early in development

nactivation-permanent

Effects of random x-chromosome inactivation

Can causes twins with identical genotypes to have different phenotypes

Calico cats

Sex-Related Phenotypic Effects

In sex-influenced and sex-limited inheritance, the sex of the individual affects:

Whether the trait is expressed

The degree to which the trait is expressed

Autosomal and sex-linked genes Sex hormone levels modify the expression of genes

Altered phenotypic ratios

Sex-linked gene

Colour blindness, an X-linked vision disorder

Sex-linked gene

Hemophilia, an X-linked blood-clotting disorder in Russian imperial family

Sex-Limited Traits

Genes that produce a phenotype in only one sex

E.g: genes influence how much milk produce by lactating mother

Traits expressed only in females because males die before birth

Examples: Male-lethal X-linked dominant traits

Traits expressed only in males

Example: Duchenne muscular dystrophy (X-linked recessive); males do not have offspring and don’t pass their X onto daughters

Very rare in females

Sex-Influenced Trait

Sex-influenced traits Traits controlled by autosomal genes that are

usually dominant in one sex but recessive in the other sex.

E.g: Pattern Baldness Acts like an autosomal dominant trait in males and

an autosomal recessive trait in females