Achondroplasia Cutie dwarf! By Stephanie Correa, Emma Rodriguez, Kylie Wiegel
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)
Location of Disorder: • On the short arm of Chromosome four • Proteins are coded for here. These proteins are for growth (fibroblast growth factor receptor 3) Right there!!(:
Mode of Inheritance • 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%. There is a 25% chance of the child being normal and a 25% chance of the child having homozygous Achondroplasia (the most severe case. It is when both bad genes come from the parents. Usually causes death).
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 d Daddy d d Mommy D d Mommy D d Homozygous recessive Homozygous dominant Heterozygous dominant Daddy d d Daddy D D Mommy d d Mommy D D
Probability • 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? • 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)
Probability in Phenotypes and Genotypes • 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
Student Practice Daddy’s Genes D d DD Dd D Mommy’s Genes Dd dd d (Genes) Genotype: -Ratio: -Percentage: (Physical) Phenotype: -Ratio: -Percentage: 1:2:1 25% DD: 50% Dd: 25% dd 3:1 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= • Square= • Shaded in= • Not shaded in= • Half shaded in= Female Male I Bad Gene Steph Brad Pitt Good Gene II Half bad half good gene Emma Jeff Ventura Dasia Jenn Matt III What do you think will be in the next generation? What would happen if both of the starting parents had the “bad” gene? What type of pedigree is this? Gabby Josue Jess Vivek Yvenson Janice Gabi Lorena Matthew Steffy Luke Kylie Autosomal Dominant