Chromosomes and genes lesson for IGCSE
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Transcript of Chromosomes and genes lesson for IGCSE
Learning out comes
• Define inheritance.
• State the meaning of the term
Chromosome , Gene and DNA.
why do children look like their parents?
How are traits passed from parents to
the children?
What is a chromosome?
What is a gene?
How are genes and chromosomes
related?
Here are the answers...............
Inheritance
• The transfer or transmission of the
features from one generation to the next
is called inheritance.
The characters are
controlled by genes
which are like coded
instructions.
Genes play an
important role in
determining physical
traits — how we look
and lots of other stuff
about us.
Inheritance
They carry
information that
makes you who
you are and what
you look like:
curly or straight
hair, long or short
legs, even how
you might smile
or laugh.
Inheritance
What is genetics?
The study of inheritance is
called as genetics.
In genetics
you will study
the ways in
which
hereditary
information is
passed on
from parents
to offspring.
What is genetics
From where the genetic information
comes
• Genes from one generation are
transmitted to the next in the gametes.
• At fertilization the gametes fuse to form a
zygote which contains the genetic
information from both the parents.
• A new individual grows from the zygote
• Half of its genetic information comes
from male parent and half from the
female parent.
The information comes from both the
parents in equal proportions.
Chromosomes
• We cant see genes through a light microscope, but we
can see chromosomes.
• Most cells have nuclei containing chromosomes.
• The first step in visualizing the genetic information that
we inherit is looking at the chromosomes.
•
•
The photograph shows the
chromosomes of a human
white blood cell
• Chromosomes are visible
through a microscope
during cell division.
• There are 46
chromosomes in the
nucleus of a human cell.
This is called the diploid
number.
Chromosomes
What is diploid and haploid condition ?
• A diploid cell is a cell that contains two sets
of chromosomes. One set of chromosome is
donated from each parent. E.g. Somatic
cells.
• Haploid cells have half the number of
chromosomes (n) as diploid.
• Haploid cells are a result of the process of meiosis.
E.g. Gametes.
What is diploid and haploid condition ?
• The
chromosomes
are in different
shapes and
sizes.
• They can be
sorted into pairs
based on their
size and shape.
Chromosomes
• You can see that the
chromosomes in the
photo on the right is
double stranded.
• They have two strands
joined together usually at
the centre.
Chromosomes
• If we could unravel
a chromosome, it
would form an
extremely long
thread.
• That thread is
made up of a long
chain of molecule
called DNA which
stands for
deoxyribonucleic
acid.
Chromosomes
• The DNA is wound around
molecules of protein.
During cell division the
DNA and protein are
packed very tightly
together and the
chromosomes are coiled
up.
• At other times they are
un coiled so the cell can
use the information in the
DNA.
Chromosomes
• Genes are length of
DNA and is a piece of
genetic information.
• Thousands of genes
make up each
chromosome .
What is a gene?
• The number of
genes in a
chromosome
depends on the
length of the
chromosome.
• The longest
chromosomes
posses more
number of genes.
What is a gene?
• Each gene is a unit of inheritance in that
it codes for a specific protein.
• It is a chemical code that the cell
interprets as an instruction to make a
protein molecule.
• You know about several proteins —
hemoglobin, amylase and lipase for
example.
• There is a gene for each of these proteins
and many more.
• Humans have between 20000 to 25000
different genes.
How a gene controls traits?
• The proteins produced by cells influence how the body
works and what it looks like.
• Some features that genes control are influenced by the
environment.
• Your height is determined by both genes you inherit and
your environment — for example by your diet and how
much exercise you take.
• Our blood group is determined by a gene and the
environment has no affect on this at all.
How a gene controls traits?
Key points
• Inheritance is the transfer of genetic
information from generation to
generation.
• A chromosome is a thread of DNA
made up of genes.
• A gene is a length of DNA that
codes for a protein.