Traits

Big Idea DNA is the instructions for making proteins, proteins produce traits, traits make you YOU.

What is a trait? A characteristic or feature of an organism

What types of traits are there? Physical traits—height, eye color, hair texture Behavioral traits—intelligence, nurturing behavior, facial expressions Predisposition to medical conditions—high blood pressure, heart disease, cancer

How do we get these traits? Traits can be produced by environmental factors: how you were raised, the food you eat, etc. But many traits you are born with—and they are produced by proteins at work in your cells. Your proteins make you you!

How we get traits Some traits are the work of a single protein—but most are the work of many proteins. These proteins are created based on instructions in our genes.

Genotype and phenotype The observable aspect of the trait is called the phenotype. Example: Trait is eye color Phenotype is brown (or blue, hazel, green, etc.)—the actual color that you see. Genotype is the actual genes you have that produce your phenotype.

Dominant and recessive alleles Different forms of the same genes are called alleles. Every person has two alleles for each gene (although there could be many more alleles in the population as a whole). If it only takes one allele to produce a certain trait, that allele is called dominant: it masks the effect of the other allele. If a trait is produced only when two of the same allele are present, that is called recessive.

Genotype possibilities for single gene traits Trait: ability to roll tongue Tongue rolling is dominant—it takes only one allele (call it R) to be a tongue roller. So the other allele could be another R—or it could be the recessive allele (call it r). So our two possibilities are RR or Rr. For a person who cannot roll their tongue, there is only one possibility because this is a recessive trait: rr

Example: Earlobes—attached (left) or unattached EE or Ee ee

Widow’s peak (left) or straight hairline WW or Ww ww

Big toe longest or second toe SS or Ss ss

Hitchhiker’s thumb or straight thumb TT or Tt tt