Post on 21-Jan-2017
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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?