Cutie dwarf!
Dwarfism
•A genetic disorder that affects bone growth.
• Some characteristics include:
- a long narrow torso
- short limbs
- unusually flexible limbs
- limited rotation of the elbows and hips
- a small hump on the mid to lower back (it goes
away later in life)
- big head (because of the enlarged brain)

On the short arm of Chromosome four
› Proteins are coded for here. These proteins are
for growth (fibroblast growth factor receptor 3)
Right
there!!(:


80% of documented cases are not inherited.
They are simply a new mutation to
Chromosome 4.
The other 20% is inherited from the parents.


If one parent has Achondroplasia, the chances of the
offspring getting it is 50%
If both parents have, Achondroplasia, the chances of
the offspring having it is a 50% of the child having
Achondroplasia a 25% of the child being normal, and
a 25% chance of the child having homozygous
Achondroplasia.
 This is when the gene comes from both the parents.
Alleles

You get one allele from your mommy
and one allele from your daddy.
 they come from the sex cells. (ova and
sperm)
 Our alleles are D (dominant) and d
(recessive).
 Dominant: always overpowers the recessive gene
 Recessive: you get the this gene only when there is
no dominant allele present.
The Punnett Squares
Daddy
D
Mommy
D
d
Homozygous
dominant
d
DD
Dd
Dd
dd
Daddy
d
Mommy
D
d
Dd
dd
dd
dd
Homozygous
recessive
Heterozygous
dominant
Daddy
d
Mommy
d
d
d
Daddy
d
dd
dd
dd
dd
D
Mommy
D
D
D
DD
DD
DD
DD
DD
Dd
Dd
dd
 Ratio and Percentage 1:2:1 or 25%:50%:25%
 (Homozygous dominant: Heterozygous dominant: Homozygous
recessive)
 1:3 or 25%:75%
 (Heterozygous dominant: Homozygous recessive)
 4 or 100%
 (All Homozygous recessive)
 4 or 100%
 (All Homozygous dominant)
What Does All
This Mean?
DD
Dd
Dd
dd
• A capital D means that the gene is dominant and a
lower case d means it is recessive.
• Phenotype:
– DD- a person with this gene will be a dwarf. So, you will see
a person 4’10” and under.
– Dd(x2)- a person with this gene will also be a dwarf.
– dd- a person with this gene will not be a dwarf. They will
live normal lives.
• Genotype:
– DD- Homozygous dominant(a dwarf)
– Dd(x2)- Heterozygous dominant(a dwarf)
– dd- Homozygous recessive(not a dwarf)

Phenotype:
› Ratio- 3 dwarf: 1 not dwarf
› Percentage- 75% dwarf: 25% not
dwarf

Genotype:
› Ratio- 1DD: 2 Dd: 1dd
› Percentage- 25% DD: 50% Dd: 25%
dd
DD
Dd
Dd
dd
Student Practice
Daddy’s Genes
D
d
D
DD
Dd
d
Dd
dd
Mommy’s
Genes
(Genes) Genotype:
-Ratio: 1:2:1
25% DD: 50% Dd: 25% dd
-Percentage:
(Physical) Phenotype:
-Ratio: 3:1
-Percentage:
75% dwarf: 25% not dwarf
Pedigree- Autosomal Dominant





Circle: female
Square: male
All White: homozygous recessive
gene: a person has 2 “healthy” genes
All Green: homozygous dominant:
this person has achondroplasia(2
“bad” genes.
Half Green/Half White: person has
achondroplasia. The dominant gene
takes over. Half “good” gene and half
“bad” gene.
Student Practice
•
•
•
•
•
Circle= Female
Square= Male
Shaded in= Bad Gene
Not shaded in= Good Gene
Half shaded
in= Half bad half good gene
1. What do you think will be in the next
generation?
2. What would happen if both of the
starting parents had the “bad” gene?
3. What type of pedigree is this?
Autosomal Dominant
I
Steph
Brad Pitt
II
III Dasia
Jeff Ventura Emma Jenn
Gabby Josue
Gabi
Jess
Matt
Vivek Yvenson Janice
Lorena Matthew Steffy Luke
Kylie
THE END! 