This document discusses sex chromosomes and sex determination in humans. It notes that humans normally have 23 pairs of chromosomes, including one pair of sex chromosomes that are XX in females and XY in males. The Y chromosome determines male sex development, while the absence of a Y chromosome allows for female development. Rare conditions like Down syndrome and hermaphroditism are also discussed briefly in terms of their effects on sex chromosomes or development.

1. SEX CHROMOSOMES
and SEX
DETERMINATIONPrepared by:
Luby G.
Canobas

2. CHROMOSOMES
• are the basic building blocks of life where
the entire genome of an organism is
essentially organized and stored in the
form of DNA (deoxyribonucleic acid) which
is present inside every cell making up that
organism.
A genome is an organism’s complete
set of DNA, including all of its genes.
In humans, a copy of the entire
genome—more than 3 billion DNA base
pairs—is contained in all cells that have a
nucleus.

3. CHROMOSOMES
• a normal human has 46
chromosomes or 23 pairs of
chromosomes.
• Twenty-two (22) of these pairs are
called autosomes.
• The 23rd pair, the sex chromosomes,
differ between males and females.
Females have two copies of the X
chromosome, while males have one
X and one Y chromosome.

4. KARYOTYPE
• A karyotype is a picture of all the
chromosomes from an individual’s
cells. A karyotype is a test used to
check for chromosome
abnormalities.

5. KARYOTYPE

6. Down Syndrome
Down syndrome is a congenital
condition caused by an extra
chromosome. The presence of an
extra number 21 chromosome
causes the distinctive facial
features, physical characteristics
and the cognitive impairments
seen in people with Down
syndrome.

7. normal

8. Sex-determination
system
• A sex-determination system is a biological
system that determines the development
of sexual characteristics in an organism.
Most sexual organisms have two sexes.
• The XX/XY sex-determination
system is the most familiar sex-
determination systems, as it is found in
human beings, most other mammals, as
well as some insects.

11. Hermaphroditism
In humans, hermaphroditism is an
extremely rare sex anomaly. A true
hermaphrodite is an individual who has
both ovarian and testicular tissue. The
ovarian and testicular tissue may be
separate, or the two may be combined in
what is called an ovotestis.

12. Karyotype of a
Hermaphrodite

13. ACTIVITY 4
Procedure:
1. Draw a Punnett square which shows
the inheritance of the sex chromosomes.
Represent the female sex chromosomes
with XX and the male sex chromosomes
with XY.

14. Guide Questions:
Q13. What will be the sex of a child
produced when an egg is fertilized by a
sperm that has a Y chromosomes.
Q14. What type of sperm must fertilize an
egg to result in a female child?
Q15. Based on this Punnett square, what
percent of children would you expect to be
male?

15. Q16. Which sex chromosome is present in
both male and female?
Q17. Infer which chromosomes determines
a person's sex.
Q18. What are the other factors that may
influence the expression of human
sexuality?

16. ASSIGNMENT
• Search on Sex-Limited Traits and
Sex-influenced Traits.
• Give examples traits for each.

17. Thank You
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