Page 25 - CB1.3 Genetic Varation sciPAD

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CB 1.3 GENETIC VARATION
PRINCIPLES OF GENETIC VARIATION
Passing on Genes
Male
Each cell in the male body
contains 46 chromosomes.
Offspring
Each cell in the baby contains 46
chromosomes, with an absolutely unique
arrangement of alleles.
Sperm
During the production of sperm
cells, the male’s 46 chromosomes
cross over, independently assort
and separate, so each sperm
cell receives 23 genetically
unique chromosomes.
Fertilisation
When the sperm reaches the ova, the 23
chromosomes from the male combine with
the 23 chromosomes from the female. The
fertilised ova is now called a ‘zygote’ and
has 46 genetically unique chromosomes.
Birth
The zygote then grows and divides,
making new cells. This process happens
many thousands of times during the
nine months until birth. Because the
baby has a unique mix of alleles, it is
genetically different to its parents, and
every other human being.
Ova
During the production of an ova,
the female’s 46 chromosomes
cross over, independently assort
and separate, so each ova
receives 23 genetically unique
chromosomes.
Female
Each cell in the female body
contains 46 chromosomes.
46
23 23
46
46
1. Complete the diagram by writing in the white boxes the type of cell division occurring at
that stage.
2. Define the term ‘zygote’
. 


3. Discuss why it is important that gametes contain half the number of chromosomes found
in the parent. 

4. State the two processes that occur during the production of gametes that leads to genetic
variation in the offspring: (a) 
(b) 
5. Identify which of the following statements is incorrect.
Fertilisation leads to genetic variation because:
(a) two genetically unique gametes randomly combine forming unique offspring.
(b) the resulting offspring has a mix of the genetic material of the parents.
(c) male gametes are genetically more diverse than female gametes.
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