Chromosomes, Genes, DNA
Unit 7 – Genes and inheritance
Learning Objective
To understand that chromosomes contain thousands of genes, and that
chromosomes and genes are made of DNA
DNA
Where on the diagram should these labels go?
chromosome
nucleus
DNA
Can you put them in size order, smallest to largest?
gene
DNA
chromosome
gene
nucleus
DNA
DNA is short for deoxyribonucleic acid. DNA can
be found inside a cell that contains a nucleus.
Gene
Cell
Nucleus
Pair of
Chromosomes
DNA
Within the nucleus, there are 23 pairs of different sized
chromosomes. DNA, which is tightly coiled around
bead-like structures of a protein called histone, forms
the chromosomes. A gene is a section of DNA that
contributes to a function.
Chromosomes
Chromosomes
The genome of an organism is the entire
genetic material of that organism.
Humans have 23 pairs of chromosomes.
One of each set from their mum and
one from their dad.
Different species of organism have
different numbers of chromosomes in
the nuclei of their cells
Human cells have 46 chromosomes.
Fruit fly cells have eight chromosomes.
Mango trees have 40 chromosomes
This means that almost every cell in
the human body contains 46
chromosomes.
Chromosomes
Scientists number the chromosomes in
a cell according to how long the
chromosomes are. In a human cell, the
longest chromosome is chromosome 1,
the next longest is chromosome 2, and
so on
We have two of each kind of
chromosome
Each chromosome looks like a cross
shape, because – just before a cell
divides – each chromosome makes a
copy of itself
The two copies stay joined together
part way along their length
Chromosomes
 Chromosomes are the form DNA becomes
in the nucleus when the cell is preparing
to divide.
 Humans have 46 chromosomes.
 One set of 23 chromosomes from mom.
 One set of 23 chromosomes from dad.
 Chromosomes are only visible when a
cell is dividing so we usually see them in
their double-stranded form
Chromosomes
 Chromosomes
containing the same type
of genetic information
 One comes from male
parent
 One comes from female
parent
Chromatid
Difference between chromosome
and Chromatid