1. 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

2. SEX DETERMINATION
SEX DETERMINATION
The natural event by which an individual of a
dioecious species become male or female
Enviromental
Sex
In some species sex is determined
after fertilization by environment
factors
Two main
mechanisms
Genetic sex
determination
Sex is determined at fertilization by
the combination of genes that the
zygote recieves

3. 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

4. Environmental Sex Determination

Sex Determination : Enviroment
• Sex Determination : social
• Sex Determination : chance
• Sex Determination : number
of offspring

5. Sex Determination
: Enviroment

Sex is determined by extrinsic factors
after the process of fertilization
-temperature
-population size
-sex of others

6. 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

7. 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

8. 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

9. Modes of sex Determination
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

11. 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 chromosome
Example: Drosophila, mammals and some plants

13. 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

14. 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)

15. 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

17. 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

18. 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.

19. Sex Determination in
Humans XX-XY

Y chromosome contains less genes
than X chromosome.

20. 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.

21. 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.

22. TDF Factor

23. 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

24. 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

25. 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

26. 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

28. 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, Xinactivation prevents them from having twice as many X
chromosome genes products as males, which only possess a
single copy of the X chromosome

29. FemALE MAMMALS ARE
ACTUALY MOSAIC FOR X
CHROMOSOME EXPRESSION
Inactivated chromosome can come
from either mother/father
 Inactivation occurs early in
development
 nactivation-permanent


30. Effects of random xchromosome
inactivation

Can causes twins with identical genotypes to
have different phenotypes

Calico cats

31. 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

32. Sex-linked gene

Colour blindness, an X-linked vision disorder

33. Sex-linked gene

Hemophilia, an X-linked blood-clotting disorder in Russian imperial family

34. 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

35. 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