INHERITED TRAITS
Did you know that although we all look quite different from each other
we are surprisingly alike at the DNA level… in fact the DNA of most
people is 99.9% the same!
… so only about 0.1% of our DNA is what makes us unique
We inherit traits from our parents through sexual reproduction → we
get genes for all our traits from each parent (via 23 chromosomes
from each parent). So for hair colour (for example) we will have a
gene from our mother that determines hair colour and we will have a
gene from our father that determine hair colour. These different
forms of the same gene are called ALLELES.
… How then do we end up with one trait (1 colour of hair)?
Some traits are dominant and some are recessive. A trait is essentially
a characteristic… like hair colour, eye colour, dimples, freckles, type of
ear lobes, etc.
If you get 2 alleles that are the same for a particular trait then you
will have that trait… you are a purebred! EG) 2 alleles for blond hair
and you will have blond hair.
If you get 2 alleles that are different for a particular trait then one
will dominate over the other… you are a hybrid! EG) if you get 1 allele
for black hair and 1 allele for blond hair you will have black hair
because dark hair is a dominant trait and light hair is a recessive trait.
So a DOMINANT TRAIT is one that will always be visible if it is
present, and a RECESSIVE TRAIT will always be hidden unless no
dominant trait is present.
SHOW CAT DIAGRAM
1
INHERITED TRAITS
Different populations of people, or different animals, or different
plants can have different predominating characteristics or traits. For
example, traits such as black hair and brown eyes are most common in
Asian populations while traits such as blue eyes and blond hair are most
common in populations in Northern Europe. Can you predict the traits
for a child if the mother has black hair and brown eyes and the father
has blond hair and green eyes?
But sometimes the dominant-recessive patter of inheritance does not
happen like you would expect. For example, if we were to cross a
purebred snapdragon with red flowers with a purebred snapdragon with
white flowers the offspring are neither red nor white. Instead the
flowers are PINK – an intermediate colour between the 2 parents. In
this case neither the red nor the white traits are truly dominant or
recessive… leading to INCOMPLETE DOMINANCE.
And sometimes the offspring is not like either parent. This is because
genetics is not as simple as we are learning it here. For example, both
parents have black hair and brown eyes as their DOMINANT TRAITS,
but their baby has red hair and green eyes. This is possibly because
each parent has red hair and green eyes as their RECESSIVE TRAIT.
We can use something called a Punnett Square to predict how this
happens… draw example on board.
But it can be even more complex than this! How would you explain a
child that has one green eye and one brown eye? Some thing, like the
inheritance of eye colour, is too complex to be explained solely by
patterns of dominant-recessive traits or even by incomplete dominance.
2