chromosomes and genes lesson for igcse
TRANSCRIPT
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Learning out comes
• Define inheritance.
• State the meaning of the term
Chromosome , Gene and DNA.
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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?
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Here are the answers...............
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Inheritance
• The transfer or transmission of the
features from one generation to the next
is called inheritance.
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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
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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
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What is genetics?
The study of inheritance is
called as genetics.
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In genetics
you will study
the ways in
which
hereditary
information is
passed on
from parents
to offspring.
What is genetics
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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.
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The information comes from both the
parents in equal proportions.
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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
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• 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
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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.
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• 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 ?
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• The
chromosomes
are in different
shapes and
sizes.
• They can be
sorted into pairs
based on their
size and shape.
Chromosomes
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• 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
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• 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
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• 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
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• Genes are length of
DNA and is a piece of
genetic information.
• Thousands of genes
make up each
chromosome .
What is a gene?
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• 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?
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• 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?
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• 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?
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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.