Achondroplasia
Taylor Bagen
Liam Trampota
January 27, 2010
Period 9/10
What is Achondroplasia?




1.
2.
3.
4.
5.
6.
7.
Bone growth disorder
Has problems converting cartilage to bone
Commonly effects arms and legs
Average height of someone with Achondroplasia is 4’4 for a male, and 4’1
for a female
Characteristics
Short arms and legs
Restricted elbow movement
Macrocephaly, or an “enlarged heard” and prominent forehead
Fingers are usually short and the ring finger is commonly far apart from the
middle finger.
Average intelligence
Bowed legs
Spinal curve
*80% of all achondroplasia cases are due to sporadic mutation, rather than
inheritance.
Chromosomal Location
Fibroblast Growth Factor Receptor 3 gene
or FGFR3.
FGFR3 gene is located on the short arm of
chromosome 4.
Mode of Inheritance
 Achondroplasia is an autosomal dominant pattern.
 Autosomal dominant means that only one copy of
the disease is still enough to cause the disorder.
 This means that both parents could be normal
sized, yet if they carry the disease their offspring
will also carry the disease.
 In fact, 80% of people with achondroplasia have
normal sized parents.
 While achondroplasia can be inherited in your
genes, the more common way of getting the
disease is simply random. Even if both parents do
not have the disease, their offspring could get it.
However, this is very rare.
Alleles
 One member of a pair of genes that is located on a
specific spot of a chromosome that controls the same
trait. (biology online)
 Each person has one allele from each parent per
gene.
 Recessive and dominant alleles are represented with
either capitalized or lowercased letters.
 RR=dominant, dominant. rr=recessive, recessive.
Rr=dominant, recessive.
 A dominant allele produces it’s trait even if the other
allele is recessive.
 A recessive allele only produces it’s trait if both of the
alleles are recessive.
 Sex linkage determines what gender your child will
be. A female is a homozygous link(XX) and a male
is a heterozygous link (XY).
-Homozygous
means two of the
same alleles.
(two dominant or
two recessive)
Punnett Squares
-Heterozygous
means two different
alleles. (one
dominant allele, one
recessive allele.
1
r
r
2
W
W
3
C
c
R
Rr
Rr
w
Ww
Ww
C
CC
Cc
r
rr
rr
w
Ww
Ww
c
Cc
cc
Punnett Squares:
-The female is the column
going down on the left,
and the father is the
column going across to
the right.
-In Punnett Square 1, the
female has the genes Rr
and the male has the
genes rr.
-There are three different
kind of outcomes.
•Homozygous dominant.
•Homozygous recessive.
•Heterozygous dominant.
When given
two recessive
alleles you
are left with a
homozygous
recessive
pair.
When given a
dominant allele
and a recessive
allele you are
left with a
heterozygous
dominant pair.
When given
two dominant
alleles you
are left with a
homozygous
dominant
pair.
*A Punnett Square determines the
probability for one child to have any one
gene.*
Probability
1
r
r
R
Rr
Rr
r
rr
rr
Using Punnett Square 1 let’s figure out the probability for the offspring showing this
gene.
Ratios:
2
Rr
Percentages:
:
2
50%
rr
Rr
:
50%
rr
*Using the Punnett Square, we can learn the likeliness of which allele will be given to the
offspring.
Phenotype vs. Genotype
*If R represents the dominant allele RED, and r represents the
recessive allele brown…
Phenotype is what you SEE. (think of physical=phenotype, they both start
with ph)
 RR = RED
 Rr = RED (however, this means that the gene for brown hair is carried)
 rr = brown
Genotype is what’s in the GENES. (think of genes=genotype, they both start
with gen)
 RR = Homozygous dominant (RED)
 Rr = Heterozygous dominant (RED)
 rr = Homozygous recessive (brown)
How to Use Phenotype and
Genotype
 Phenotype
Ratio-2 red: 2 brown
Percentage-50% red: 50% brown
 Genotype
Ratio-2 Rr: 2 rr
Percentage-50% Rr: 50% rr
1
r
r
R
Rr
Rr
r
rr
rr
Your turn!
Father’s Genes
M
o
t
h
e
r
’
s
G
e
n
e
s
T
t
T
TT
Tt
t
Tt
tt
T=tall, t=short
Genotype:
Phenotype:
Ratio-1 TT: 2 Tt: 1 tt
Ratio-3 tall: 1 short
Percentages-25% TT: 50% Tt:
25% tt
Percentages-75% tall: 25% short
Autosomal Dominant Pattern
1
1
0
Male
Female
2
1
0
0
1
1
1
1
The person has the
disease but only has
one copy of the
gene.
0
0
Homozygous
recessive
gene, person is
fine and has
healthy genes
3
1
0
1
1
*Homozygous dominant gene, person has
disorder and two bad genes. (not shown)
Male
Student Practice
Female
1
2
2
1
1
0
1
0
1
1
One copy of each
0
0
Homozygous
recessive gene
2
2
Homozygous
dominant
gene
1
0
Review:
1) Can any homozygous recessive
children be formed by a “1” and “2”
spouse? Explain why or why not.
2) How many copies of the bad gene
does “1” have?
3) What’s the only result possible when
“2” and “0” have children?