Genes
• The basic unit of genetic information
• They determine the nature and the
function of the cell.
• The human genes (about 120,000) are
referred to as the human genome.
• A genome is the full set of genes in each
cell of an organism. 2
The Genetic Code (cont.)
•Human genome: the code for making a
human being
•Every person has a slightly different
code, but the human genome is 99.5%
the same for any 2 people.
Berger: The Developing Person Through Childhood and
Adolescence, 7th Edition, Chapter 3
The Beginnings of Life
• Development begins at conception, when the
sperm penetrates the ovum.
• The organism is first called a zygote, and is the
fused nuclei of sperm and egg.
• The genotype of the zygote is the genetic
information on the 23 chromosome pairs.
Berger: The Developing Person Through Childhood and
Adolescence, 7th Edition, Chapter 3
Gene Pairs
• Gene pairs are closely matched on 22
of the 23 chromosomes.
• In some cases, an allele occurs: an
alternate version of variable genes.
• On the 23rd pair, XX = female, XY = male.
Berger: The Developing Person Through Childhood and
Adolescence, 7th Edition, Chapter 3
Controversial Issues
Will it be ethical for parents to have their
children screened prior to birth and decide not
to have a child with a genome that is merely
undesirable ?
What about employers not hiring people with
bad genomes and insurance companies
refusing to insure them? 6
Cell Division and Reproduction
When the cell is ready to divide and reproduce:
•the DNA staircase unwinds and the two long
chains separate
•each chain attracts new biochemical material
from the cell to synthesize a new and
complementary chain
•Ultimately a new cell is formed 7
Terms
• Gametes:
Sex cells (ovum or sperm)
• Diploid cells:
Cells having 2 copies of each chromosome
• Haploid gametes:
Gametes having 1 copy of each chromosome 8
Meiosis
• Meiosis takes place in the testicles and ovaries.
• A diploid cell (having 2 copies of each
chromosome) undergoes a special form of cell
division to create haploid gametes (having 1 copy
of each chromosome).
• An egg and a sperm fuse together to form a new
diploid cell called zygote (a process called
fertilization) 9
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What is mitosis?
Mitosis specifically refers to
the process of nuclear
division that occurs before a
cell physically divides in
two.
During mitosis, the cell’s DNA
is copied into each of the two
daughter cells. In multicellular
organisms, mitosis provides
new cells for growth and
tissue repair.
Mitosis
• In the first step of mitosis, all chromosomes are
copied, so that instead of 2 copies, the cell briefly
has 4 copies of each chromosome.
• Shortly afterwards, the cell divides in half, resulting
in two cells each has a complete copy of the genetic
information.
• These cells grow larger and eventually undergo
mitosis.
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•Mitosis: each cell divides and
duplicates itself exactly
•Meiosis: How reproductive cells (ova
and sperm) are produced
•Results in gametes, cells that contain
only 23 chromosomes
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1. What is spermatogenesis?
- Spermatogenesis is the process in
which an animal produces
spermatozoa from spermatogonial
stem cells by way of mitosis and
meiosis.
2. What is oogenesis?
- Oogenesis is the process by
which the female gametes, or
ova, are created.
3. What are the similarities between
spermatogenesis and oogenesis?
- Both occur in the reproductive
organs.
- Both produce haploid (n) gametes
that are involved in fertilization.
- Both involve meiosis.
4. What are the differences between
spermatogenesis and oogenesis in terms of
the number of the end products?
- A male will produce literally millions of
sperm every single day for the rest of his life.
- A female will produce four egg cells, 3
smaller cells which will disintegrate and 1 big
ovum which will develop into a mature egg
cell.
1. What is the basic function of
spermatogenesis?
- The basic function of spermatogenesis
is to turn each one of the diploid
spermatogonium into four haploid sperm
cells.
2. When does the exchange of genetic
material happened?
- Before the first meiotic division,
3. Where can we find the primary oocytes?
- Ovaries
4. How will you describe the four daughter
cells that the primary oocyte produces after
meiosis?
- A female will produce four egg cells, 3
smaller cells which will disintegrate and 1 big
ovum which will develop into a mature egg
cell.
• In Females
• In Males
Meiosis takes place in the Meiosis begins in the
testes and involves 2 ovaries before birth and
rounds of division partly completes all of the
Results in 4 fertile sperm roughly 400,000 ova a
cells woman will ever have.
By puberty, males begin It occurs in a two-stage
producing many process..
thousands of sperm cells Results in one relatively big
on an ongoing basis, and ovum and 2 small polar
they continue to do so
through out their life
bodies that aren’t capable
span of being fertilized
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Chromosomal Aberrations
• Brainstorm with your team mates on what to do. You can do
any of the following:
• Conduct a survey around your neighborhood if there are
children who have chromosomal abnormalities and how they
are coping with it. And be sensitive when you do the interview.
• Conduct a research over the internet about the different
chromosomal abnormalities most Filipinos have for the past
year.
• Cut out pictures of people who are suffering chromosomal
abnormalities; include their possible cause, the affected
chromosome and the signs & symptoms.
Gregor Mendel (1800s)
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Genotype Phenotype
The genetic makeup of a The traits that are
given individual expressed in the
individual
Recessive Gene Dominant Gene
The gene pair that One gene of a gene pair
determines a trait in an that will cause a
individual only if the particular trait to be
other member of that expressed
pair is also recessive
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Alleles
A pair of genes, found on corresponding chromosomes, that affect
the same trait
The child might inherit an allele for brown eyes (B) from the father and
an allele for blue eyes (b) from the mother
The child’s genotype for eye color would be Bb.
What actual eye color will the child display?
The allele for brown eyes is dominant (B).
The allele for blue eyes is recessive (b).
The dominant trait will be expressed as the phenotype
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Homozygous Heterozygous
Referring to the arrangement Referring to the arrangement
in which the two alleles for in which the two alleles for
a simple dominant- a simple dominant-
recessive trait are the recessive trait differ.
same.
Homozygous Individual Heterozygous Individual
(Eye Color) (Eye Color)
Could be BB or bb Could be Bb, or bB
The chance for having blue
eyes is 25%
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Incomplete Dominance
Where people with a single recessive gene for a trait show some of the
trait along with other normal manifestations.
Example:
Sickle-cell anemia
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Sickle-Cell Anemia
• Occurs at its highest rate in individuals of black African ancestry.
• People with a single recessive gene for the trait have a marked
percentage of abnormal “sickle-shaped” red blood cells that interfere
with oxygen transport throughout the body.
• They also have normal (dominant) red blood cells as well.
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Sickle-Cell Anemia
• The sickle cells are resistant to malarial infection, so those individuals
with the trail would have survived long enough to have children in
areas of the world where mosquito-borne malaria is highly prevalent.
• Sickle-cell carriers experience pain in the joints, blood clotting,
swelling and infections under conditions of oxygen shortage.
• It occurs when a person inherits both recessive alleles
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Codominance
Where neither the dominant nor recessive allele is dominant and the
resulting phenotype is a blend of the two.
Example:
If an individual gets an allele for each blood types A and B, the result is
type AB blood type
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Polygenic Inheritance
The overall system of interactions among genes and gene pairs
More complex traits do not result from the alleles of a single gene pair,
but rather from a combination of many gene pairs
In determining height, several gene pairs combine to create people
with taller or shorter phenotype.
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Inherited Disorders
• Sex-Linked Disorders
• Genetic Disorders
• Chromosomal Disorders
• Autosomal Disorders
• Genetic Disorders
• Chromosomal Disorders
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Sex-Linked Disorders
• Involve the sex chromosome # 23
• Occur via dominant-recessive patterns
• A recessive gene on the X chromosome is more likely to be expressed
as the phenotype males because the Y chromosome has no allele
that might contract the gene.
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Genetic Sex-Linked Disorders
1- Color Blindness
Genetic X-linked recessive disorder. Occurs in 1 of 10 males
2- Hemophilia A and B
Recessive disorders that affect 1 of 5,000 males. These interfere with
normal blood clotting and occur at different loci (the position on a
chromosome occupied by a particular gene) on the X chromosome.
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