2. Lesson Objective
By the end of this lesson, you should be able to
distinguish among DNA,chromosomes, genes
3. What is Genetics
● Genetics is the study of how genes
and how traits are passed down
from one generation to the next.
● Our genes carry information that
affects our health, our appearance,
and even our personality!
4. The Cell: Nucleus
● All humans are made up of cells.
● Nearly all cells that make up the
human body have a nucleus, with a
few exceptions, such as red blood
cells.
● The nucleus controls the activities
of the cell.
5. Inside the Nucleus
● Inside the nucleus of cells, there are
a number of long thread-like
structures called chromosomes.
● The genetic information to build
your body is inside the nucleus of
each cell.
6. Chromosomes
Under the
Microscope
● Most of the time, the chromosomes
are too thin to be seen with a regular
light microscope.
● However, when cell is dividing, the
chromosomes get shorter and fatter
and so can be seen with a light
microscope.
8. Structure of the Chromosome
● Each chromosome is made up of one long molecule called a DNA
and a protein called a histone.
● A single chromosome is made up of the entire length of the DNA that
was used to make it. This means that one chromosome contains one
DNA molecule.
9. Structure of the Chromosome
● DNA is extremely long and must be wound together tightly to fit in
the nucleus.
● The role of the histone is to organise and condense the DNA tightly
so that it fits into the nucleus
10. Structure of the Chromosome
● The DNA is folded and
coiled so that it can be
packed into a small space.
● The DNA (shown as green
strands) is coiled around
proteins called histones
(shown as blue balls)
11. Structure of the Chromosome
● Every organism has a certain number
of chromosomes in each nucleus.
● Humans have 23 pairs of
chromosomes, giving a total of 46
chromosomes in the nucleus of
somatic (body) cell
● NB: Somatic cells are any cell in the
body that are not gametes (sperm or
egg)
13. What is DNA?
● DNA is short for deoxyribonucleic
acid
● DNA is an essential molecule for
life.
● It is found in ALL living things
● It acts like a recipe holding the
instructions telling our bodies how
to develop and function.
14. Structure of DNA
● The DNA molecule consists
of two strands that wind
around one another to form a
shape known as a double
helix.
17. What are
Genes?
● The length of DNA in a
chromosome is divided into
segments known as genes
● A gene is a short length of
DNA found on a chromosome
18. What are
Genes?
● In other words, a gene is a
section of DNA.
● Each gene is an instruction for
assembling amino acids to make
a specific protein.
● Proteins are made of large
numbers of amino acids joined
19. What are Genes?
● This means that a gene tells a cell
how to make a specific protein.
● Proteins are used by the cell to
perform certain functions, to grow,
and to survive.
● For example, one gene will define
your hair colour, another will define
the colour of your eyes.
20. What are Genes?
● Each gene codes for a particular sequence of amino acids
● These sequences of amino acids form different types of proteins
● There are many different types of proteins but some example of
these could be:
○ structural proteins such as collagen found in skin cells
○ Enzymes
○ hormones
23. How Genes Help to Make
Proteins?
● All proteins are made up of only 20 amino acids.
● The DNA acts a code to place each amino acid in the correct
position to make the protein.
● The actual protein is made on the ribosomes in the cytoplasm of
the cell.
● Because the DNA is in the nucleus, the plan has to be carried to
the ribosomes.
24. What are Genes?
● Many of these traits are passed
from one generation to the next
in a family by genes.
25. What are Genes?
● All of the genes and genetic material an organism
possesses is called its genome.
● At this time, it is estimated that the human genome
contains 20,000-25,000 genes.
