4.4 Punnett Squares
What is a Genotype?
Genotype
• genes that are passed on from parents to
offspring.
• Showed using Letters
– LL, Ll, ll
– WW, Ww, ww
– RR, Rr, rr
What is a Phenotype?
Phenotype
• trait that is seen
• Think pheno “photo”
• Examples
–
–
–
–
Blue eyes
Widows peak
Hitch hackers thumb
Curly hair
What is an Allele?
Allele
• Different version of the same gene
• We usually refer to it as either the dominant
allele or the recessive allele
• Example
– Allele for straight hair (recessive)
– Allele for curly hair (dominant)
What is a Dominant Allele?
Dominant Allele
• Genotype – Capital Letter (W)
• Phenotype – Guaranteed to see it
What is a Recessive Allele?
• Genotype – Lower case letter (a)
• Phenotype – Will not be seen unless both
alleles are recessive (aa)
What does Homozygous mean?
Homozygous
• Both Alleles are Alike
• Homo = Same
• Examples:
» aa
» AA
» WW
» ww
What does Heterozygous mean?
• Alleles are opposite
• Hetero = different
• Examples
» Hh
» Aa
» Ee
» Gg
» Yy
How to fill in a Punnett Square
Review
Sample Problem:
Cross a male chicken who is Heterozygous for his
blue color with a female chicken who is
homozygous recessive black.
Cross a male chicken who is Heterozygous for his
blue color with a female chicken who is
homozygous recessive black.
Genotype Results:
50% Bb
50% bb
What does the Phenotype results
look like for this punnett square?
2 out of 4 (50%) Blue Chickens
2 out of 4 (50%) Black Chickens