Transcript Dihybrid Crosses

Dihybrid Crosses
Predicting TWO traits at once!
Mendel’s Law of
Independent Assortment
What is the Law of Independent Assortment?
Genes for different traits can segregate
independently during the formation of gametes.
What does that really mean?
The inheritance of one gene does not influence the
inheritance of another gene.
Just because you got your dad’s “tall” gene doesn’t mean you
will also necessarily get his “blue eye” gene –
the two aren’t connected!
We said…
Just because you got your dad’s “tall” gene doesn’t mean you
will also necessarily get his “brown eye” gene –
the two aren’t connected!
But what if we want to know the chances that you DO
get both genes?
Or what if we want to know the chances of not one
particular gene, but TWO particular genes?
Would a regular Punnett Square work?
In order to predict TWO traits at once,
you will need to do a...
Four possible combinations
of genes on the top and side
(parental gametes)
Sixteen total possible gene
combinations (offspring)
Now lets try our own
example….
People like to eat green, round peas – not
wrinkled and not yellow! So a farmer would
want to know, if he was breeding plants,
what the chances are that he would get the
ideal crop (and make the most money!).
R = round
r = wrinkled
Y = yellow
y = green
Both plants he is
starting with are RrYy
So we need to make a GIANT
Punnett Square to cross RrYy x
RrYy…and then figure out the
“chances” that the farmer will
get round, green offspring!
When you are predicting only one trait, each parent has
two possible genes to give. When you are predicting two
traits, each parent has FOUR possible genes to give!
Parent 1:
Parent 2:
So Parent 1 could give the following four
combinations of genes to their offspring…
And Parent 2 could give the following four
combinations of genes to their offspring…
Parent 2:
Parent 1:
Parent 1:
Round, Yellow
Round, Yellow
Round, Yellow
Round, Yellow
Round, green
Round, Yellow
Round, green
Round, Yellow
Round, Yellow wrinkled, Yellow wrinkled, Yellow
Round, Yellow
Round, green
Parent 2:
Round, Yellow
wrinkled, Yellow wrinkled, green
Parent 1:
NOW LET’S MAKE
SOME
PREDICTIONS!
Round, Yellow
Round, Yellow
Round, Yellow
Round, Yellow
Round, green
Round, Yellow
Round, green
Round, Yellow
Round, Yellow wrinkled, Yellow wrinkled, Yellow
Round, Yellow
Round, green
Parent 2:
Round, Yellow
wrinkled, Yellow wrinkled, green
How many of the farmer’s plants will
produce the desired Round, green peas?
How many will
produce the yellow
peas, which no one
will want to buy?
So would it be wise
for the farmer to
cross these two
RrYy plants?
Round,
Yellow
Round,
Yellow
Round,
Yellow
Round,
Yellow
Round,
Yellow
Round,
green
Round,
Yellow
Round,
green
Round,
Yellow
Round,
Yellow
wrinkled,
Yellow
wrinkled,
Yellow
Round,
Yellow
Round,
green
wrinkled,
Yellow
wrinkled,
green
Ready for another
example?!?
Dog-faced Man
This husband and wife want
the ultimate circus freak kid
– one with elephant skin
and a hairy face!
If they have a baby, what
are the chances that they’ll
have the ideal circus freak?
And what are the chances
that they will just have a
normal kid?!?!
Dog-faced Man
Normal Face = F
Hairy Face = f
Normal Skin = Q
Elephant Skin = q
Dad must be ff for face.
Genetic tests show he is Qq for skin.
Mom must be qq for skin.
Her dad was also “dog-faced”, so we
know that she must be Ff for face.
So Mom is Ffqq
And Dad is ffQq
Which means that Mom and Dad each can give FOUR possible
combination of the two genes….
Mom could give
Fq or Fq or fq or. fq
Dad could give
fQ or fQ or fq or. fq
If they each can give FOUR possible combination of genes,
how many boxes is our Punnett
Square going to have?
Mom = Ffqq
Dad = ffQq
Fq
Fq
fq
fq
fQ FfQq
FfQq
ffQq
ffQq
Ffqq
Ffqq
ffqq
ffqq
FfQq
fQ
FfQq
ffQq
ffQq
Ffqq
Ffqq
ffqq
ffqq
fq
fq
Mom = Ffqq
Fq
Fq
fq
fq
FfQq
ffQq
ffQq
normal skin
Normal face,
normal skin
Hairy face,
normal skin
Hairy face,
normal skin
Normal face,
elephant skin
Normal face,
elephant skin
Hairy face,
elephant skin
Hairy face,
elephant skin
Normal face,
normal skin
Normal face,
normal skin
Hairy face,
normal skin
Hairy face,
normal skin
Ffqq
Ffqq
ffqq
ffqq
Normal face,
elephant skin
Normal face,
elephant skin
Hairy face,
elephant skin
Hairy face,
elephant skin
FfQq
fQ Normal
face,
Dad = ffQq
NOW LET’S MAKE
Ffqq
Ffqq
ffqq
ffqq
fq
SOME
FfQq
FfQq
ffQq
ffQq
PREDICTIONS!
fQ
fq
How many of the circus freaks children will
be “ideal” circus freaks themselves, with
elephant skin and a hairy face?
How many of their
kids will be
perfectly normal?
How many will have
just one circus freak
trait?
How many will
carry a recessive
gene that they may
pass on to their
children?
fQ
fq
fQ
fq
Fq
Fq
fq
fq
FfQq
FfQq
ffQq
ffQq
Normal face,
normal skin
Normal face,
normal skin
Hairy face,
normal skin
Hairy face,
normal skin
Ffqq
Ffqq
ffqq
ffqq
Normal face,
elephant skin
Normal face,
elephant skin
Hairy face,
elephant skin
Hairy face,
elephant skin
FfQq
FfQq
ffQq
ffQq
Normal face,
normal skin
Normal face,
normal skin
Hairy face,
normal skin
Hairy face,
normal skin
Ffqq
Ffqq
ffqq
ffqq
Normal face,
elephant skin
Normal face,
elephant skin
Hairy face,
elephant skin
Hairy face,
elephant skin