Mendel’s Punnett Squares
Genes and Alleles
Gene: Place on chromosome
and determines certain trait
Allele: variation of that trait
Ex:
Gene: Eye color
Located on 5th gene from the
top
Alleles: Brown, Blue, Green,
Gray
Mendelian Traits
• Each trait 1 gene with 2 variations or 2 alleles
• For each allele, 1 is Dominant 1 is Recessive
• Dominant has a capital letter while recessive
has lower case letter
• A genotype= is the actual allele combination
(Aa, AA, aa)
• A phenotype= is what trait that expresses (Tall
or Short)
Types of genotypes and phenotypes
•
•
•
•
•
If an individual is purebred=homozygous
If an individual is homozygous dominant= AA
If an individual is homozygous recessive= aa
If an individual is heterozygous= Aa
Phenotypes
– Homo Dom. and Heterozygous expresses dom
allele
– Homo Rec. expresses recessive allele
Genotypes and Phenotypes Example
• Eye color
– The allele for blue eye
color is ‘b’
– The allele for brown eye
color is ‘B’
1. What is the phenotype
of picture A? What is
it’s genotype?
2. What is the phenetype
of picture B? What is its
genotype?
• A
• B
Getting a phenotype from a Genotype
• Eye color
– The allele for blue eye
color is ‘b’
– The allele for brown eye
color is ‘B’
1. What is phenotype of
Bb?
2. What is the phenotype
of bb?
3. What is the phenotype
of BB?
Predicting ratios
• This is where you are
given two individuals an
pretending they are
making a child, but
before they make the
child they want to the
probability of getting a What are the ratios of the
particular trait
genotypes:
• Scenario Blue eyed and BBBrown eyes person with Bbgenotypes of ‘bb’ and
bb‘BB’
What are the ratios of phenotypes:
Blue eyesBrown eyes-
3 Possible Monohybrid Crosses
Type 1
• AA x aa
• Phenotype ratios:
• Genotype ratios
3 Possible Monohybrid Crosses
Type 2
• AA x Aa
• Phenotype ratios:
• Genotype ratios
3 Possible Monohybrid Crosses
Type 3
• Aa x Aa
• Phenotype ratios:
• Genotype ratios
3 Possible Monohybrid Crosses
Type 4
• Aa x aa
• Phenotype ratios:
• Genotype ratios