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Interesting Facts About
Prof. Liwayway Memije-Cruz
Johann Gregor Mendel (1822-1884)
Father of Genetics
Austrian monk who discovered the
fundamental laws of inheritance
based on his experimental work with
He deduced that genes come in pairs
and are inherited as distinct units,
one from each parent. Mendel
tracked the segregation of parental
genes and their appearance in the
offspring as dominant or recessive
traits. He recognized the
mathematical patterns of inheritance
from one generation to the next.
Mendel's Law of Segregation
Each inherited trait is
defined by a gene pair.
Parental genes are
randomly separated to
the sex cells so that sex
cells contain only one
gene of the pair.
inherit one genetic allele
from each parent when
sex cells unite in
Law of Independent Assortment:
Genes for different
traits are sorted
one another so that
the inheritance of
one trait is not
dependent on the
Law of Dominance
An organism with alternate forms of a gene
will express the form that is dominant.
the science of studying how living things pass on
characteristics or traits and its variations in their
cell make-up from one generation to the other.
the study of how living things inherit features like
eye-colour, nose shape, height and even behavior
from their parents.
What are Genes?
Instruction manuals in our body. They are molecules in our
body that explain the information hidden in our DNA, and
supervises our bodies to grow in line with that information.
It is believed that each cell in our body contains over 25,000
genes, all working together. These genes carry specific
biological codes or information that determine what we
inherit from our parents.
Supervise protein production through the Deoxyribonucleic
Acid (DNA), a chemical that has a genetic code for making
proteins for living cells. Proteins are the building blocks for
living things and almost everything in our body, bones,
blood and muscles are all made up of proteins,
Allele - one alternative
form of a given allelic
pair; tall and dwarf are the
alleles for the height of a
pea plant; more than two
alleles can exist for any
specific gene, but only
two of them will be found
within any individual
Allelic pair - the
combination of two alleles
which comprise the gene
Genotype and Phenotype
Genotype is the genetic
make-up of an individual
organism. Your genotype
functions as a set of
instructions for the
growth and development
of your body. The word
‘genotype’ is usually
used when talking about
the genetics of a
particular trait(like eye
Phenotype is the
observable physical or
characteristics of an
determined by both
genetic make-up and
influences, for example,
height, weight and skin
Genotype and Phenotype
Genotype - the genes that an organism contains for
a particular trait.
Phenotype - the observable traits of an individual.
Homozygous and Heterozygous
Homozygous - an individual
which contains two genes that the
Heterozygote - an individual
which contains two genes that are
What is DNA?
Means Deoxyribonucleic Acid.
It is a hereditary molecule that is found in almost all living
It carries a code (information) that genes use to make
living things grow. It is found in all cells in structures
DNA is located in the nucleus of cells. This is called
‘nuclear DNA. Some DNA is also located in the
mitochondria of the cell and that is also called
mitochondrial DNA. All the cells in that living thing carry
the same DNA.
Four chemical bases that make up the
code in DNA
Adenine (A), Guanine (G), Cytosine (C), Thymine (T)
These chemical bases are contained in the shape of a
twisted ladder called the double helix.
In humans, all the bases are the same — BUT, the
combination or order, or sequence is unique to every
DNA can duplicate or copy itself. This is why all cells
in an individual have the same DNA.
The strand in the DNA is made up of Letters G A T C.
These letters combine in a set way to make words. The
words combine to make sentences. The sentences can
be called “Gene’ It is the gene that instructs all the
cells in the body to perform their functions, as
specified in our DNA, including making protein.
What are chromosomes?
a compact store of
DNA strands folded
together by The
all contained in the
nucleus of the cell.
Number of Chromosomes
Humans have 46 chromosomes in each of the cells of our
organs. These are organized into two sets of 23 chromosomes.
Each human gets 23 chromosomes from their mom, and 23
chromosomes from their dad. This is why almost everyone
has some traits they got from their parents.
the 23rd chromosome is our sex chromosomes.
Boys carry XY chromosomes and girls carry XX
Each parent contributes a cell each. The female
always contributes an X cell (because that all she
has, XX chromosome)
The male contributes either an X or a Y cell. The
male has no control over this, as it is purely random.
If the male releases and X chromosome, it adds to the
X chromosome of the female, it forms an XX— and
the gender of the baby will be a girl. If the male
releases a Y chromosome and adds to the females X
chromosome, it forms an XY and the gender of the
baby is a boy.
Chromosomal Theory of Inheritance
1. Homologous chromosome pairs are independent
of other chromosome pairs.
2. Chromosomes from each homologous pair are
sorted randomly into pre-gametes.
3. Parents synthesize gametes that contain only half
of their chromosomes; eggs and sperm have the
same number of chromosomes.
4. Gametic chromosomes combine during
fertilizationto produce offspring with the same
chromosome number as their parents.
Noted scientists known for the Chromosomal Theory
of Inheritance: chromosomes carry the unit of heredity
known as genes.
a. Walter Sulton b. Theodore Boveri
a technique used in DNA testing which
allows the testee to determine which
segments of DNA came from which
one should test both parents, one of their
children, and a number of first to third
cousins on both the maternal and paternal
sides of the family.
cutting out part of the DNA in a
gene and adding new DNA in its
Genetic Mapping: Linkage Mapping
can offer firm evidence that a disease transmitted from
parent to child is linked to one or more genes.
also provides clues about which chromosome contains the
gene and precisely where the gene lies on that
used successfully to find the gene responsible for relatively
rare, single-gene inherited disorders such as cystic fibrosis
and Duchenne muscular dystrophy.
also useful in guiding scientists to the many genes that are
believed to play a role in the development of more common
disorders such as asthma, heart disease, diabetes, cancer,
and psychiatric conditions.
Gene Therapy: Biotechnology
an experimental technique that uses genes to treat or prevent
disease. In the future, this technique may allow doctors to
treat a disorder by inserting a gene into a patient’s cells
instead of using drugs or surgery.
Researchers are testing several approaches to gene therapy,
1. Replacing a mutated gene that causes disease with a healthy
copy of the gene.
2. Inactivating, or “knocking out,” a mutated gene that is
3. Introducing a new gene into the body to help fight a disease.