Thursday 24th September 2020
Genetics
Learning Objectives
● What is the difference between
dominant and recessive alleles?
● How can I use a Punnet square to
show a genetic cross?
Key Question
Use a punnet square to calculate and
explain the probability of a person
inheriting green eyes if both mother
and father have the alleles Gg. (G=blue,
g=green)
Starter
Using the following key words, explain what is meant by fertilisation
mother
offspring
egg
father
sperm
Explain how this links to genetics
Key words
Inheritance
• We all inherit
chromosomes
from our
parents:
+
Mum
Dad
• 50% maternal
• 50% paternal
Child
Key words
Genes
A characteristic e.g. eye colour, is controlled by
the two forms of a gene present in an individual.
(but the particular combinations are limited by the
genetic makeup of your parents).
The different forms of a gene are called alleles.
One characteristic may have a number of alleles…
Key words
Alleles
allele which
controls the
characteristic
whenever it is
present.
BB or Bb
Key words
allele whose
characteristics only
show up when it is
present on both
chromosomes
bb
Key words
Genetics Key Words
physical
appearance of
an organism.
when the two
alleles are
different
Key words
the set of genes
(alleles) that an
organism possesses
when two alleles
(gene types) are
identical
Punnett Squares
• A punnett square shows the possible
combinations of genes from 2 parents that
they can pass on to their offspring.
Possible combinations of
genes for their offspring.
Upper
case
letters
show
dominant
genes
Key words
This also shows how likely
they are to have certain
genes, i.e. chances of being
born with bb is 50%
Lower case letters show
recessive genes
Key words