Transcript File - Science with Ms. Tantri

•
Mendel’s experiments illustrate
complete dominance - offspring
always resembled one of the
two parents
•
The dominant allele had the
same phenotypic effect whether
present in one or two copies
•
All Mendel’s plants displayed
dominant or recessive alleles.
In other words, only one trait
showed up.
•
There are some crosses where
both alleles of a pair are
expressed in a heterozygote
Incomplete dominance heterozygous individuals
have an intermediate or
blended phenotype
Neither of the alleles is
dominant because they
do not mask the other
colour
Example:
Snap dragon colour
• Red flower (CRCR) and
white flower (CWCW) form
a pink flower (CRCW)
Crossing red and white snap dragons
produces pink snap dragons
1.
What are the phenotypic
and genotypic ratios for
the F2 generation of the
snap dragon example?
1.
Indicate the ratios that
would be expected if the
following crosses are
made:
a) red x pink
b) white x white
c) pink x pink
Codominance – both
alleles are expressed
fully to produce offspring
with a third mixed
phenotype
Example: Rooster Colour
• Black rooster (FBFB) and
white rooster (FWFW)
form a black and white
rooster (FBFW)
Crossing black and white roosters
produces roosters with both black &
white feathers

Multiple alleles – more than
2 alleles for the trait

a combination of codominant
and dominant genetic traits
Example: Blood Types




Blood phenotypes are
controlled by a combination of
two of three different alleles
Three blood type alleles: IA, IB ,
I
The alleles for blood types A
and B are Codominant
Blood type O is homozygous
recessive
BLOOD GROUPS
PHENOTYPE
GENOTYPE
•
Erythrocytes (red blood cell) have cell-surface proteins called
antigens
•
Blood types are based upon the types of antigens one has
•
Defensive chemicals called antibodies are produced by your body
to protect itself from foreign cells or organisms
•
Antibodies circulate through the body in the fluid blood plasma
Type A
Type B
Type AB
Type O
Blood clumping results when certain antibodies bind to specific antigens
1.
a.
b.
A woman with A type
blood marries a man with
B type blood. They have
a child with type O blood.
The man says the child
cannot be his. Is he
correct? Show your work
to prove you are right.
If this child belongs to
this father, what were the
chances of having this
child with type O blood.