sex determnation and sex based inheritance(genetic)
TRANSCRIPT
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