Download DNA Problems - ThinkChemistry

DNA Problems
When you look at chromosomes in a
nucleus you see them as X-shaped
structures like these.
In the nucleus of our cells, there
are 46 chromosomes altogether.
Here is what they look like.
The 46 chromosomes are actually 23
pairs – one of each pair has come
from the mother and the other has
come from the father. When you
pair them up together you get the
karyotype. Here is an example of
the human karyotype.
Each chromosome is made of long
strands of DNA molecule. Sections
of the DNA strand which make up a
chromosome are called genes. Genes
carry the genetic information of
characteristics and can be passed on
to the next generation – e.g. gene
for eye colour, hair colour, etc. In
2003, scientists finished mapping
out all the possible genes of a human
being – the human genome.
Human chromosomes
Can you spot what is different about male and female chromosomes?
_______________________________________________________
_______________________________________________________
This person has Down’s Syndrome.
Can you see what is different about
his/her chromosomes?
Is this person Male or Female?
___________________________
Fertilisation
Fill in the correct number of chromosomes to make a new human being.
Complete the statement below showing the percentage of your genes you inherit
from your parents.
This means that exactly
% come from your mother;
and exactly
% come from your father.
Passing down genes
In this family tree, brown hair is dominant to red hair.
hair
hair
Shade in the correct circles to show how the genes have been passed
down to the children.
Complete the diagram showing the colour of hair the children have.
Punnett Squares
Let’s represent the previous cross in another way.
Fill in the blanks in the Punnett square, to work out what the possible children could look
like.
Try it again but this time cross
Bb
x Bb
What colour of hair will the parents have?
1. In this family tree tongue rolling is dominant to non-tongue rolling.
Represent this cross as a punnett square where T = tongue roller gene
and t = non-tongue roller gene.
2. Use the information in your punnett square to shade in the triangles,
showing all the possible combinations of children.
3. For the girl born in the family what are the chances she could be tt –
i.e. a non-tongue roller?
Look at this family tree.
How many boys did the couple have?
_____________________________________________________
Which gene is dominant?
_________________________________________________________
Complete the punnettt square for the above cross.