Achondroplasia

Taylor BagenLiam Trampota

January 27, 2010Period 9/10

What is Achondroplasia?

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 femaleCharacteristics

1. Short arms and legs2. Restricted elbow movement3. Macrocephaly, or an “enlarged heard” and prominent forehead4. Fingers are usually short and the ring finger is commonly far apart from the

middle finger.5. Average intelligence6. Bowed legs7. 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).

Punnett Squares1 r r

R Rr Rr

r rr rr

2 W W

w Ww Ww

w Ww Ww

3 C c

C CC Cc

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.

*A Punnett Square determines the probability for one child to have any one

gene.*

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.

When given two recessive alleles you are left with a homozygous recessive pair.

-Homozygous means two of the same alleles. (two dominant or two recessive)

-Heterozygous means two different alleles. (one dominant allele, one recessive allele.

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 : 2

Rr rr

Percentages:

50% : 50%

Rr rr

*Using the Punnett Square, we can learn the likeliness of which allele will be given to the offspring.

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)

*If R represents the dominant allele RED, and r represents the recessive allele brown…

Phenotype vs. Genotype

How to Use Phenotype and GenotypePhenotype

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!

T t

T TT Tt

t Tt tt

F a t h e r ’ s G e n e s

Mother’s

Genes

T=tall, t=short

Genotype: Ratio-1 TT: 2 Tt: 1 tt

Percentages-25% TT: 50% Tt: 25% tt

Ratio-3 tall: 1 short

Percentages-75% tall: 25% short

Phenotype:

Autosomal Dominant Pattern

0 1

01 10 1

1 1 0 1

Male

Female

1 1

0 0

The person has the disease but only has one copy of the gene.

Homozygous recessive gene, person is fine and has healthy genes

*Homozygous dominant gene, person has disorder and two bad genes. (not shown)

1

2

3

Student Practice

2 1

2 1 10 0

01 1

Male

Female

1 1

0 0

One copy of each

Homozygous recessive gene

2 2 Homozygous dominant gene

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?