SEX

DETERMINATION
GAMETES FORMATION
https://www.youtube.com/watch?v=lH9loPdk_nQ
 Genetic Information

A.An XY combination will

produce a male child.
B.An XX combination will
produce a female child.
C.The father determines
the sex of the child.
 Which parents determines the sex of the offspring?
XY
male

X Y

XX X
Female

It is the male that determines the sex of

the offspring.
 Sex Determination

• When a male have a child there • Crossing a male XY with a female XX

is always a 50% chance the
X Y
child will be female and a 50%
chance the child will be male
• If the egg is fertilized by a
X XX XY

sperm with a Y-chromosomes

it will produce a male. X XX XY

• If the egg is fertilized by a

carrying an X-chromosomes it • 50% male
will produce a female. • 50% female
 The Human Chromosomes
• There are 23 pairs of human chromosomes, or 46 diploid
chromosomes
• autosomes (somatic) are first 22 chromosomes and carry
genes for all the physical traits not associated with sex
• sex chromosomes are the 23rd pair and determine the sex
of the human
• XX – female
• XY – male

Homogametic- two of the same chromosomes like the human female sex chromosome, XX
Heterogametic- two different chromosomes as the human male sex chromosomes, XY.
Sex – related Inheritance
https://www.youtube.com/watch?v=H1HaR47Dqfw
https://www.youtube.com/watch?v=-6RGz1YM11o
https://www.youtube.com/watch?v=h2xufrHWG3E

 Sex – Limited Traits

 Sex – Influence Traits

 Sex – Linked Genes

 A. Sex – Linked Traits

• Traits that are controlled by genes located on the

sex chromosome.
• Alleles for sex linked traits are written as super
scripts on the X or Y chromosomes
• X-linked genes - Genes located on the X
chromosomes .
• Y-linked genes- Genes on the Y chromosomes
 Males
• Men normally have an X and a
Y combination of sex
chromosomes.
• Since only men inherit the Y
chromosome, they are the only
ones that inherit Y-linked traits.
HUMAN MALE KARYOTYPE
 Females

•Women have 2 X chromosomes

•Female can be a carrier or affected
HUMAN FEMALE KARYOTYPE
 Sex – linked disorders

• Genes located on X chromosome

(X-linked)
• Hemophilia - is a rare disorder in which your blood
doesn't clot normally because it lacks sufficient blood-
clotting proteins (clotting factors).

• Protanopia and Deuteranopia - color-blindness

resulting from insensitivity to green light, causing confusion
of greens, reds, and yellows (red-green color blindness).
• Fragile X-syndrome - The fragile X syndrome is an
unusual type of X-linked inherited mental retardation
condition

• G6 PD Deficiency - occurs when a person is missing

or does not have enough of an enzyme called glucose-6-
phosphate dehydrogenase. This enzyme helps red blood
cells work properly. 

• Duchenne Muscular Dystrophy - s a genetic

condition that affects the muscles, leading
to muscle wasting that gets worse over time.
 X Linked Traits
• Men and Women can get the X-linked traits
since both inherit X chromosomes.
• Men only have one X chromosome
• Therefore genes on that chromosome are
expressed in the male phenotype, even if it is a
recessive gene.
• In women, a recessive allele on one x
chromosome is often masked on their phenotype
Genotypes and Phenotypes of color blindness
in human
GENOTYPE PHENOTYPE

1. XCXC Normal female

2. XCXc Normal female, carrier of the

gene
3. XcXc Color –blind female

4. XCY Normal male

5. Xc Y Color- blind male

C – Normal Dominant c – Color blind recessive

Examples of sex-linked recessive traits:

COLOR BLINDNESS
What a red-green colorblind person would see
Normal Red-green colorblind
Examples of sex-linked
recessive traits:

COLOR
BLINDNESS
 Hemophilia

• Is a rare inherited bleeding

disorder in which blood
doesn’t clot normally.
• If you have hemophilia you
may bleed for longer time
than others after injury
Queen Victoria
•Queen Victoria of England was a carrier of
hemophilia and passed The disease to
many of her descendants (including the
Russian emperor’s family and the Spanish
royal family).
Family of Queen Victoria
Pedigree
 Y-linked Traits

• The Y chromosome is small and therefore does not

contain many genes
• Y linked diseases are very rare
• Only passed from father to son.
• Example: Male infertility
• Genes located on Y chromosome
(Y-linked)
• Hypertrichosis pinnae auris - The presence
of the excessive coarse black hair on the auricle of
the human ear 

• Retinitis pigmentosa -  a group of genetic

disorders that affect the retina's ability to respond
to light, causing a slow loss of vision
 LET’S PRACTICE
Identify Phenotype of the following with this given Allele.
Character: wild-type eye color red (R) is dominant over white (r)

XR XR Female Red eye color

XR Y Male Red eye color

Xr Y Male White eye color
XR Xr Female Red eye color

Identify Phenotype of the following with this given Allele.

Character: normal /non-bleeder (H) is dominant over hemophiliac/bleeder (h)

XHXH Female normal X hY Male hemophiliac

XHXh Female carrier Xh X h Female hemophiliac
 Color blindness is an X-linked recessive trait (Xc) whereas normal color
vision is dominant (XC).
What is the resulting offspring between the carrier mother (X CXc ) and the
unaffected father (XY)

Genotype Male:
Genotype Female

Phenotype Male:
Phenotypic Female:
 Hemophilia is an X-linked recessive disorder characterized by the
absence of one or more of the proteins required for blood clotting.
Show the result of the cross when a hemophiliac father (Xh Y )
marries a normal mother (XHXH)

Genotype Male:
Genotype Female

Phenotype Male:
Phenotypic Female:
 Y-Linked Traits
Pedro who has a disorder hypertrichosis pinnae
Auris (XYh) marries Laura (normal female).

Genotype Male:
Genotype Female

Phenotype Male:
Phenotypic Female:
B. Sex-Influenced Traits

Male and Female Pattern Baldness

• In the previous section, we learned about sex-
linked traits that were controlled by alleles
found on the sex-chromosomes.

• In this section, we will discuss sex-influenced

traits, traits that are controlled by alleles on
autosomal chromosomes.
 CHROMOSOMES

AUTOSOMES SEX CHROMOSOMES

first 22 23rd chromosomes

chromosomes that that determine the sex
responsible for
physical traits SEX-LINKED TRAITS

SEX-INLUENCED X-LINKED TRAITS Y-LINKED TRAITS

TRAITS
Color Blindness
SEX-LIMITED TRAITS Hypertrichosis
pinnae
Hemophilia
 Sex-influenced trait

• a trait controlled by a pair of alleles found on the

autosomal chromosomes (pairs 1 through 22) but
it’s phenotypic expression is influenced by the
presence of certain hormones.
Estrogen, Progesterone, Testosterone, etc.

• It can be seen in BOTH sexes, but will vary in

frequency between the sexes, or in the degree of
the phenotypic expression.
 Example of Sex-Influenced Traits

• Pattern Baldness
• Pattern Baldness can occur in both males and females,
however it is much more common in males.
• Why is this?

Because the pattern baldness trait is

influenced by the hormone testosterone.
 Pattern Baldness
• The combination of alleles for pattern
baldness will lead to different phenotypic
expressions depending on the sex of the
individual.

• For example: Let B represent the bald allele

- BB genotype: bald in both sexes
- bb genotype: non-bald in both sexes
- Bb genotype: bald in men; non-bald in females
 Pattern Baldness

• The “B” allele acts as a recessive allele in the heterozygous

genotype in females, but acts as a dominant allele in the
heterozygous genotype of the male.
Expression of Pattern in Baldness in Human
Male Genotype Male Phenotype
XYBB Male Bald
XYBb Male Bald
XYbb Male nonbald
Female Genotype Female Phenotype
XXBB Female bald
XXBb Female nonbald
XXbb Female nonbald
 Pattern Baldness

• What would this bald guy’s genotype be?

• Bb or bb

• What about his balding mother?

• BB
 Try this out!

• What is the probability that YOU will be bald if

your father is homozygous and balding, and your
mother is homozygous and not balding?

Father’s genotype: BB X Mother’s genotype: bb

All offspring are Bb
If you are a male, you will be bald! If you are a female,
you will not demonstrate pattern baldness.
 Baldness in humans behaves like a dominant allele in males
while recessive in females. Predict the offspring if the mother
is non-bald ( XXbb) and the father is bald (XYBB).

Genotype Male:
Genotype Female

Phenotype Male:
Phenotypic Female:
 C. Sex – Limited Trait

A trait, produced by an autosomal gene, in which the

expression of a specific genotype is limited to only one
gender
Example: Hen-feather vs. rooster-feather patterns in
chickens
In cattle lactation is expressed in females but never in
males.
Genotype Male Female
Phenotype Phenotype
HH Hen – Hen -
Feathers Feathers
Hh Hen - Hen -
Feathers Feathers
hh Cock- Hen -
feathers Feathers
 Expression of Lactation in Cattle
Female Genotype

XXLL Female Lactating

XXLI Female Lactating

XXII Female not Lactating

Male Genotype

XYLL Male not Lactating

XYLI Male not Lactating

XYII Male not Lactating

Both male and female cattle possess a gene pair of lactation. The
gene for lactation (L) is dominant over the non-lactating gene(l).
These genes are carried by both males and females, but it is only
expressed in females.
 Key Concepts
Sex – related Inheritance

• Sex-limited traits are those that are expressed

exclusively in one sex.
• Sex-influenced traits are expressed in both sexes
but more frequently in one than in the other sex
• Sex-linked traits are traits that are controlled by
the genes found in sex chromosomes