Learning outcomes:
1 I can investigate the transmission of characteristics from parents to offspring, and
identity.
2 I can identify examples of dominant and recessive characteristics.
3.3 Patterns of Inherittance
Long before the science of genetics started, people trying reproducing
organisms with only the preferred traits. This was most common with
domestic animals such as cats and dogs.

To produce a purebred organism, a breeder would choose pure bred
parents.

If a breeder chooses two different ‘true-breeds’ then a hybrid would be
produced.
Is a trait that dominates over another trait when both traits are located
on individual’s genes.
Ex: Your mother gives you the blue eyed allele (b) but your dad gives you
the brown eye allele (B).
So your genetic code is Bb (Brown – blue). Because you have brown
eyes, we know that the Brown eyed allele dominates over the blue eyed
allele.
In this picture which child has Sickle
Cell Disease?
Which allele is the dominant trait?
How do you know?
What percentage of the parent’s
children would not have the disease?
Is a trait that is dominated by another trait when both traits are located
on individual’s genes.
Ex: Your mother gives you the blue eyed allele (b) but your dad gives you
the brown eye allele (B).
So your genetic code is Bb (Brown – blue). Because you have brown
eyes, we know that the Blue eyed trait is recessive.
Which allele (color) is the
recessive trait?
White
How do you know?
Because when it’s a hybrid,
the R(purple color) is
obvious/seen
What percentage of the
parent’s offspring will be
pure-bred of the recessive
trait?
¼ or 25%
: occurs because the dominant-recessive pattern does not alwys prevail.
When the alleles are neither dominant, nor recessive, an intermediate
trait will occur (combining the two traits).
Looking at the picture,
what proof is there that
these alleles are neither
dominant nor recessif?
Activity – Eye color
Let’s see what color the eyes of your children could be if you married
someone with: Blue eyes (bb), Brown eyes (BB), or Brown eyes (Bb)
Green/Brown – B (dominant)
Blue – b (Recessif)



If you have Blue eyes, lets say you are pure bred of that trait: bb
If you have Brown or green eyes and none of your parents have
blue eyes, lets say you are pure bred of that trait if none of your
parents have blue eyes: BB
If you have Brown or green eyes and one of your parents have
blue eyes, lets say you are a hybrid of that trait if none of your
parents have blue eyes: Bb
Example: I have brown eyes and my dad has blue eyes (So I am Bb)
If I marry someone with blue eyes (bb) these would be my possibilities.
Me \ Partner
B
b
b
Bb
bb
b
Bb
bb
50 % of my children would have blues eyes.
50 % of my children would have green/brown eyes.
Blue eyes
Me \ Partner
b
________ of my children would have blues eyes.
________ of my children would have green/brown eyes.
b
Brown eyes (hybrid Bb)
Me \ Partner
B
b
________ of my children would have blues eyes.
________ of my children would have green/brown eyes.
Brown eyes (pure bred, BB)
Me \ Partner
B
________ of my children would have blues eyes.
________ of my children would have green/brown eyes.
B