Learning
Question
Am I an unique
individual?
Where do my genes come from?
• Genes are found in chromosomes
• parents pass these on to offspring in their
gametes (sperm and egg cells)
Where do my genes come from?
• In most cells chromosomes are matched in
pairs based on their size and shape
• Matching pairs of chromosomes are called
homologous chromosomes
Where do homologous chromosomes come from?
• Each pair of homologous chromosomes
contains one chromosome that has been
inherited from each parent
Where do my genes come from?
Where do my genes come from?
• A pair of chromosomes carry the same genes,
in the same place, on the chromosome.
However, there are different versions of a
gene called alleles
These alleles may be the same on each pair of
chromosomes, or different, for example, blue
eyes or brown eyes
What makes me unique?
Variation due to genetic causes is inherited
variation
For example, children usually look a little like
their father, and a little like their mother, but
they will not be identical to either of their
parents
• Children don’t look exactly like one of their
parents because they get half of their
inherited features from each parent
• They are genetically different to their
parents
What makes me unique?
• Which chromosome we get from each of our
parents pairs of chromosomes is completely
random
• This means different
children in the same
family will each get a
different combination
• therefore are
different to each
other
http://www.neok12.com/video
/Genetics/zX5e724c6f0042
Different Versions of Genes
Pairs of Alleles
Pairs of Alleles
Pairs of Alleles
Pairs of Alleles
Finding Genotype of offspring
Finding Genotype of offspring
Finding Genotype of offspring
How do we represent alleles?
Alleles can be
Dominant
Represented with a
capital letter
Recessive
Represented with a
lower case letter
How do we represent alleles?
Example:
Eye colour
A recessive allele only
shows if the individual has
two copies of it
For example, the allele for
blue eyes is recessive
You need two copies of this
allele to have blue eyes
How do we represent alleles?
Example:
Eye colour
A dominant allele always
shows, even if the individual
only has one copy of it
For example, the allele for
brown eyes is dominant
You only need one copy of it
to have brown eyes
Two copies will still give you
brown eyes
1. Where does offspring inherit genes from?
2. What is the name given to different forms of a
gene?
3. What cells carry the genes that we inherit from our
parents?
4. Explain why offspring are genetically different to
their parents
5. Explain why offspring are genetically different to
each other
6. Explain the difference between dominant and
recessive alleles