Dominant and Recessive Traits Cornell Notes:

How are traits different?Are some traits more common

than other traits?1/23/14 & 1/27/14

Pd. 1 = pg. 77Pd. 2 & 3 = pg. 73

Pd. 4 = pg. 61

What are traits?• Traits are characteristics• Physical Traits– Can be seen by others (they are observable)– Eye color, hair color, curly hair vs. straight hair, hairline,

tongue roll, left handed vs. right handed• Acquired Traits– Learned skills– Playing a sport, riding a bike, playing a musical

instrument• Behavioral Traits– Instincts (behaviors that do not need to be learned)– Nest building and migration in birds and some mammals– Behaviors can be learned

Genetics Vocabulary• Genotype– The alleles (forms of genes) an individual has in its DNA

(2 copies per trait – 1 copy from each parent)

– Genes are inherited (passed down) from your biological parents

– Genes control your traits

• Phenotype– An individual’s observable traits (expression of the genotype)

• What people can SEE when they look at you• Photograph = picture (what you see) like the Phenotype is the

observable trait (what you see)

Genetics Vocabulary• An individual with different alleles of a gene is

heterozygous for that gene– Examples: Bb, Tt, Aa, (one dominant gene and one recessive

gene)

*Note: We use letters to represent the alleles or forms of a gene. Capital letter = dominant; Lower case letter = recessive

• An individual with the same alleles of a gene is homozygous for that gene– Examples: BB or bb, TT or tt, (two dominant genes OR two

recessive genes)

Genetics Vocabulary• An allele is dominant if its effect hides the effect

of a recessive allele paired with it• A recessive trait shows up in the phenotype

ONLY if two recessive alleles are in the genotype– Capital letters (A) signify dominant alleles; lower

case letters (a) signify recessive alleles– Homozygous dominant (AA)– Homozygous recessive (aa)– Heterozygous (Aa)