Coat colour genetics

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I dont want a white rabbit- give me a red
rabbit for the NEW YEAR
By Tan Kok
Hwee, Ong Lay Hua
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• Lesson Objectives
• At the end of the lesson, you should be able to
• explain the concept of monohybrid inheritance
• predict the characteristics of offspring that
  result from simple monohybrid crosses of various
  dominant and recessive traits
• compare the expression of incomplete dominance
  and co-dominance

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Scenario
Ah Bengs father has just passed away, leaving Ah
Beng to take charge of the family business - a
rabbit breeding farm. Ah Beng has no idea how to
feed the rabbits, let alone breed them. Over
the last 40 years, Ah Bengs father had developed
a special breed of rabbit - a RED coloured one!
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The Year of the Rabbit is round the corner. Ah
Beng hopes to make megabucks by selling RED
coloured Ang Pow rabbits. However, he has one
problem his father only left him one male RED
rabbit! He needs to breed more RED rabbits.
Oh no! How am I supposed to get more Red rabbits
when I only have one left?
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Suddenly, Ah Beng remembered his dad saying that
the RED colour of the rabbit was due to a
dominant allele. Ah Beng Aha! My biology
teacher said that if you cross an animal
displaying a dominant trait with an animal
displaying a recessive trait, the babies will
show the dominant trait. Ah Beng went through
his O Level textbook and came up with a chart.
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Ah Bengs chart
Parental phenotypes
RED
White
Parental genotypes
rr
RR
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With the help of his chart, Ah Beng successfully
bred 8 Ang Pow Rabbits. He sold 4 of them for
4000!!! Feeling like an entrepreneur, Ah Beng
thought Will Ah Beng be able to make
24000?
Using my remaining Ang Pow Rabbits, if I mate
the only male with the 3 females and if each
female produces 8 rabbits, ... I will have 24
Ang Pow Bunnies and they will earn me 24000.
Im going to be RICH !!!
YES
NO
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Can you cross Rr with Rr and still get offspring
which are all RED?? Think about it ...
Click to retry question
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Yes, you are correct. Ah Beng is not going to
make 24000 even if he gets 24 bunnies.
Only 18 out of every 24 rabbits will be Ang Pows.
The rest will be albinos. So he will earn at most
18 000.
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Ah Beng soon become very famous in Singapore. One
day, he received a phone call from a Miss Lao,
offering to pay 3000 for each PINK rabbit he
could produce. Ah Beng is keen to try. His
former Biology teacher told him to check out
incomplete dominance and co-dominance. Which one
of these will generate the pink rabbits?
Incomplete dominance
Co-dominance
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Very Good! In incomplete dominance, neither
allele is completely dominant over the other.
Both Red and White alleles will exert their
effects giving rise to an intermediate
phenotype...... PINK!
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In co-dominance, both alleles express themselves
equally. Offspring will show both traits. If that
happens, your rabbit will look like this.
Click here to see for yourself
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Can Ah Beng create such rabbits from his current
stock?
YES
NO
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Incorrect.
His current stock of rabbits are
red even when the animals are heterozygous!
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Correct! The alleles controlling
colour in his present stock of rabbits are either
dominant (red) or recessive (albino).
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Created by Tan Kok Hwee and Ong Lay Hwa
Click to end
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Glossary Gene A hereditary factor carried
on a particular locus in chromosomes which
controls a particular trait. E.g. Gene for fur
colour. Alleles Different forms of the same
gene. E.g. Allele for black fur colour, allele
for white fur colour, etc. Dominant allele The
allele whose effect is always shown when it is
present. E.g. If allele for black fur (B) is
dominant over the allele for white fur (b), then
the animal has black fur. Recessive allele The
allele whose effect is always masked when it is
present with a dominant allele. Eg. Allele for
white fur (b) in the above case. Genotype The
combination of genes in an organism. E.g. BB, Bb
or bb. Phenotype The observable traits of an
organism. E.g. Black fur colour, white fur
colour.
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Homozygous An organism with identical alleles
for the same trait. E.g. BB or bb Heterozygous
An organism with different alleles for the same
trait. E.g. Bb Co-dominance Both alleles exert
their effects equally such that the organism
show s patches of pure colour.
E.g. If allele B and
allele b are co-dominant, a heterozygous animal
will have patches of black and white fur
Incomplete dominance Both alleles exert their
effects equally such that the organism shows an
intermediate trait.
E.g. If allele B and allele b
demonstrate incomplete dominance, a heterozygous
animal will have gray fur.