two-trait inheritance
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Transcript two-trait inheritance
BIOLOGY 12
Two-Trait Inheritance
Dihybrid Cross
Remember Mendel’s Peas…
Character
Seed shape
Seed colour
Trait
Allele
Round
R
Wrinkled
r
Yellow
Y
Green
y
Mendel’s hypothesis was that each trait was
independent of the other
this means that one allele does not have an
effect on another allele
independent assortment – the chromosomes will
randomly align and divide
there is no connection between the two different
chromosomes
Law of Independent Assortment
it appears that the inheritance of seed shape
has no influence over the inheritance of seed
colour
the two characters are inherited
INDEPENDENTLY
the pairs of alleles that control these two
characters assort themselves independently
Determining Gametes
when dealing with two homozygous genotypes,
the gametes will be the same
example: RRYY
x
rryy
gametes: RY, RY, ry, ry
note: the gametes do not need the capital first
Determining Gametes
when dealing with heterozygous genotypes, you
use FOIL (think math!)
example: RrYy
R r Y y
First and Outside
RY and Ry
Inside and Last
rY and ry
Possible Gametes:
RY, Ry, rY and ry
Practice
complete the following Punnett square using the
following cross: AaBb x AaBb
AB
AB
Ab
aB
ab
Ab
aB
ab
How Good Were Mendel’s Results
We could
expect
What Mendel
observed
556 x 9/16 round yellow
313
315
556 x 3/16 round green
104
108
556 x 3/16 wrinkled yellow
104
101
556 x 1/16 wrinkled green
35
32
Practice
In watermelons the genes for green color and
for short shape are dominant over their alleles
for striped color and for long shape. Suppose a
plant with long striped fruit is crossed with a
plant heterozygous for both these characters.
What phenotypes would this cross produce and
in what ratios?
Practice
A heterozygous tall, homozygous green pea
plant is crossed with a heterozygous tall,
heterozygous yellow plant.
What is the probability that the offspring will
be short and green?
Single Trait Practice
In dogs, wire hair is due to a dominant gene
(W), and smooth hair is due to its recessive
allele.
If a homozygous wire-haired dog is mated
with a smooth-haired dog, what would be
possible phenotypes of the offspring?
Single Trait Practice
Two wire-haired dogs (W?) are mated, and
among the offspring of their first litter is a
smooth-haired pup.
If these two wire-haired dogs mate again, what
is the chance that they will produce another
smooth-hair pup? What are the chances that
the pup will be wire-haired?
Two Trait Practice
A female dog is heterozygous for both fur length
and colour. She shows long, brown fur. Her mate
shows short, white fur.
Determine the gametes of each dog.
What is the probability that the pup will be just
like its mother?
Two Trait Practice
In humans, the presence of freckles is due to the
dominant gene (F), and the non-freckled condition is due
to its recessive allele (f). Dimpled cheeks (D) is
dominant to non-dimpled cheeks (d).
Two persons with freckles and dimpled cheeks have two
children. One has freckles but no dimples (F?dd), one
has dimples but no freckles (ffD?).
What are the genotypes and phenotypes of the parents?