Achondroplasia
Kelly Correia and Alyssa Antonucci
January 28, 2010
Hour 3
Achondroplasia is…
• A genetic condition
• Results in abnormally short stature
-> Otherwise known as ‘Dwarfism.’
• has to do with the bones and how they make bone instead
of cartilage.
What are some symptoms?
• a baby will have a relatively long torso and narrow torso and short extremities
(arms & legs).
• typically have unusually large heads with prominence of the forehead.
• baby’s fingers appear short & the ring and middle finger move in different
directions, giving the hand a three-pronged (trident) appearance.
Did you know…
• Achondroplastic dwarfs’ average height is usually four feet 3 inches in males
and four feet for females.
• There is no treatment for Achondroplasia.
• Jyoti Amge from India was diagnosed with Achondroplasia and is the
shortest person in the world measuring in at 23 inches tall and weighs 11
pounds.
Achondroplasia is
located on…
Chromosome 4
Achondroplasia is
inherited…
• as an autosomal dominant trait
• only a single copy of the
abnormal gene is required to cause
Achondroplasia.
• the chance of a baby being born
and diagnosed with this condition
has been shown to increase with
paternal age, or the age of the
father.
What are Alleles?!
• an Allele is one member of a pair or series of genes that
occupy a specific position on a specific chromosome.
• We represent dominant alleles with a capital letter, like “R”
and we represent recessive alleles with a lowercase letter, like
“r”. When these two letters are put together, like Rr, it means
the uppercase “R” is the dominant gene and the lowercase “r” is
the recessive gene.
•You get one Allele from your mother and another allele from
your father. You get two alleles for each gene.
•If the two alleles for one gene are the same, then the individual
is homozygous for that gene. If the two alleles are different then
the individual is heterozygous.
Punnett Squares Are Fun!
Punnett
Square 1:
F
f
Punnett
Square 3:
g
G
F
f
FF
Ff
Ff
ff
G
g
Gg gg
GG Gg
Punnett
Square 2:
a
A
Punnett
Square 4:
R
r
a
A
Aa aa
AA Aa
R
r
RR Rr
Rr rr
Punnett
Square:
F
f
F
f
FF
Ff
Ff
ff
Percentages
Homozygous
Dominant: 25 %
Heterozygous
Dominant: 50 %
Homozygous
Recessive: 25 %
There are four different
possibilities. When getting
percentage the total has to
be 100%. This means that
each box represents 25%
since 100 divided by 4 is 25.
Ratios
Homozygous Dominant :1 GG
Heterozygous Dominant: 2 Ff
Homozygous Recessive: 1 ff
There has to be a total of four
combinations in the Punnet Square.
There has to be four because that’s
the number of possibilities a punnet
square can have.
F
f
F
FF
Ff
f
Ff
ff
Phenotype:
Ratio: 3 dominant genes (1 homozygous dominant, 2 heterozygous dominant) ,
1 recessive gene (homozygous)
Percentage: 75% dominant (25% homozygous dominant, 50% heterozygous
dominant) , 25% recessive (homozygous)
Genotype:
Ratio: 1 FF, 2 Ff, 1 ff
Percentage: 25% FF, 50 % Ff, 25% ff
Punnett Square Practice
Father’s Genes
M
o
t
h
e
r
’
s
G
e
n
e
s
F
F
F
f
Genotype:
Ratio: 2 FF, 2 Ff
Percentages: 50% FF, 50% Ff
Phenotype:
Ratio: 2 homozygous
dominant, 2 heterozygous
dominant
Percentages: 50% homozygous
dominant, 50% heterozygous
dominant
White= (homozygous recessive)
The person doesn’t have any of the
bad genes.
Half-Blue=The person has 1 bad
gene and 1 healthy gene
Full blue- (homozygous dominate)
The person has both bad genes
=Girl
=Boy