Genotypes and Phenotypes

What is an allele?• A version of a geneExample:

There is a gene that controls eye color.One allele is for blue eyes.Another allele is for brown eyes.

Processing Piece:

1) There is a gene that controls hair color. What do you think two different alleles for this gene might be?

How many alleles for each gene are in every cell?

• Haploid cells (like gametes) only have one allele for every gene, because they only have one set of chromosomes.

• Diploid cells have 2 alleles for every gene, because they have 2 sets of chromosomes.

What is a dominant trait?• A trait that always shows up if an allele

for it is there. • Represented with capital letters.• Example: B = brown eyes

What is a recessive trait?• A trait that only shows up if there are no

dominant alleles present• Represented with lower case letters.• Example: b = blue eyes

Processing Piece:

• Draw a picture to represent allele, dominant, and recessive.

What is phenotype?• Physical traits • Example: height, hair color

What is genotype?• The alleles in your DNA

Processing Piece:• Draw a picture to illustrate the difference

between phenotype and genotype.

What are 3 types of genotypes?• Homozygous recessive = 2 recessive alleles–Example: bb

• Heterozygous = 1 recessive, 1 dominant–Example: Bb

• Homozygous dominant = 2 dominant alleles–Example: BB

(“Homo” = same, “Hetero” = different)

Sample Question 1• B = brown eyes b = blue eyes• A baby is born with a genotype of BB.• What is its genotype? (Circle one.)

Heterozygous Homozygous Homozygousrecessive

dominant• What is its phenotype? (Circle one.)

Blue eyes Brown eyes

Sample Question 2• D = dimples d = no dimples• A baby is born with a genotype of Dd.• What is its genotype? (Circle one.)

Heterozygous Homozygous Homozygousrecessive

dominant• What is its phenotype? (Circle one.)

Dimples No dimples

Baby Dimples

Exit TicketT = tall and t = short. A pea plant has the genotype Tt.1) Which trait is dominant: tall or short?2) Is this pea plant homozygous dominant, homozygous recessive, or heterozygous?3) What will its phenotype be?