Genetics of Dimples The use of Dimples is just an example how genetics can explain what you observe.

Cause A shorter than normal muscle pulling on the skin causing an indentation. Muscle is made of protein.

Review Proteins are made up of amino acids. Amino acids are coded for by sections of DNA on chromosomes called genes.

Therefore… The gene caused the dimple! Knowing that is something to smile about

How does one get the dimple gene? Scenario #1- Both Parents have dimples Scenario #2- Neither Parent has dimples (dimpleless) Scenario #3- Parent 1 has dimples, but Parent 2 is dimpleless

Scenario #1 Both Parents have dimples Outcome with “4 kids” – Expect to see all of the kids (100%) with dimples – Sometimes this is correct. However, other times the outcome is 3 with dimples and 1 without!!!

Scenario #2 Neither Parent has dimples Outcome with “4 kids” – Expect to see all of the kids (100%) without dimples.

Scenario #3 Parent 1 has dimples, but Parent 2 is dimpleless Outcome with “4 kids” – Expect to see 2 with dimples and 2 without – However ALL 4 of them have dimples.

A deeper look into Scenario#1 Both Parents have dimples Sometimes the outcome was 3 with dimples and 1 without. WHY???? There must have been a hidden gene passed by the parents that allowed the 1 offspring to be dimpleless! This means both parents must have 2 genes for the same trait.

Alleles An allele is a variation of a gene for the same trait. It gives a different physical form. – Example: thumb shape – allele 1= hitch hikers thumb – allele 2= straight thumb The appearance of an organism is called its phenotype (ph- for physical). The alleles an organism has is called its genotype (geno- for genetic).

Genotypes Homozygous – 2 of the same allele for a trait Heterozygous- 1 of each allele for a trait

Predicting Mating Outcomes Scenario #1 using a Punnet Square This shows the 25% (1 out of 4) that was dimpleless and the 75% (3 out of 4) that had dimples

Dominant versus Recessive Dominant trait is the phenotype expressed when both alleles are present (Heterozygous Dd) Recessive trait is only expressed when there is not a dominant allele present (Homozygous Recessive dd) Homozygous Dominant is when an organism has 2 dominant alleles (DD)