Garden Peas
• Studied the traits in garden peas– Tall/short– Round/wrinkled– Green/yellow pods– Purple/white flowers
Alleles
• Each trait or characteristic has 2 copies of DNA that code for that trait
• Each copy of the trait is called an allele
• Different form of a gene
The Rule of Dominance
• Alleles can be either dominant or recessive (strong or weak)– Dominant (A) alleles are observable– Recessive (a) alleles are not usually
observable, when the dominant allele is present
Dominant
• The allele that is expressed – you can see it
• Represented by capital letters
• C curly hair
• B brown hair
Recessive
• The allele that is not expressed when covered up by the dominant allele– It is there you just cannot see it
• Use the lower case for the recessive allele
• c for straight hair• b blonde hair
Homozygous (homo = same)
• Pure
• When an organism has 2 copies of the same allele
• BB – homozygous dominant
• bb – homozygous recessive
Heterozygous (hetero = different)
• Hybrid
• When an organism has 2 different alleles for a gene
• Bb, Gg, etc.
Law of Independent Assortment
• Alleles for different genes are distributed to sperm and egg independently
• Could be – tall and fat– short and thin– tall and thin– short and fat
• This is why all siblings do not look exactly alike