Monday Monday........

Source:  Monday Monday........    Tag:  introduction to heredity
       Friday we took the daily question quiz that focused on our understanding of the basics of heredity. Today we moved into being able to model Mendel's laws.  Why do we even care about alleles & genotypes and phenotypes and such..... so we can both predict the outcome of crosses with Punnett squares as well as look back and trace alleles with pedigrees.  Today's daily question was as follows:
**A Punnett square shows the possible GENOTYPES  of the offspring of a cross between two known parents

** To Set up a Punnett square – the genotypes of the parents go on the TOP and Side of the square

** Each allele has a 50% chance of being passed on the offspring.

** Draw a sample Punnett square of a cross between two heterozygous parents.

After this - we then moved into an example with a human trait

Achondroplasia is a genetic disorder of bone growth.
A=Allele for Achondroplasia
a = Allele for Normal Bone Growth
1st off: is Achondroplasia (Dwarfism) a dominant or recessive disorder? Well since i represented the allele with a Captial letter, we know it must be a DOMINANT disorder
Next: What is the GENOTYPE of someone who is HETEROZYGOUS for Achondroplaisa?
Aa and that person would have normal bone growth.
What is the PHENOTYPE of someone who is homozygous recessive?
They would nave NORMAL bone growth
Using a punnett square, find the chances that two people heterozygous for achondroplasia could have a normal child. There would be a 25% chance they would have a child WITH achondroplasia. See punnett square below
What does this MEAN then? That two dwarfs that are Heterozygous have a 25% chance of having an averaged sized child. Those of you who have followed Little People Big world can now see how this couple could have 2 children that were averaged size. What does that mean about THEIR genotypes?!?! They MUST be heterozygous. So EVERY time they have children, there is a 25% chance they will be average sized.