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Bell Work
• Who is Gregor Mendel and what did he do?
Biology – Lecture 47
Genetics with Punnett Squares
Genetics Vocabulary
• Allele – different versions of the same gene
• Because they are the same gene, they are
given the same letter.
• Example – height can either be tall or short
• Genotype - the set of alleles for a given
organism
• Phenotype - the observable traits of the
organism
• Homozygous - Diploid organisms with two
copies of the same allele of a given gene.
• Both alleles will be capital letters or lower
case letters.
• Heterozygous - Diploid organisms with two
different alleles of a given gene.
• One allele will be capital, one allele will be
lowercase.
• Dominant allele – The allele in a heterozygous
set of alleles that has dominant qualities in
the phenotype. (capital letter)
• Recessive allele – the allele in a heterozygous
set of allele that has receding qualities and are
not observed in the phenotype. (lower-case
letter)
• Incomplete dominance - expressing an
intermediate phenotype
• Co-dominance - expressing both alleles at
once
• Punnett Square - a diagram that is used to
predict an outcome of a particular cross or
breeding experiment.
Punnett Square Example
• In rabbits, black fur is dominant over white fur.
Show the cross of a heterozygous black male with
a homozygous white female.
• Phenotype:
• Genotype:
Punnett Square Example
• In humans, free-ear lobes are dominant to attached.
Two parented that are both heterozygous free are
expecting a child. What are the chances that the child
will have free ear lobes of attached?
• Phenotype:
• Genotype:
Punnett Square Practice
• Wrinkled seed are recessive to smooth seeds.
Show a plant that always produces wrinkled
seeds crossed with a heterozygous smooth seeds
producing plant.
• Phenotype:
• Genotype:
Punnett Square Practice
• Wrinkled seed are recessive to smooth seeds.
Show a heterozygous smooth plant crossed with
another heterozygous smooth seed producing
plant.
• Phenotype:
• Genotype:
Punnett Square Practice
• Blue eyes are dominant to red eyes in rabbits.
Show a heterozygous blue-eyed rabbit crossed
with a red-eyed rabbit.
• Phenotype:
• Genotype:
Punnett Square Practice
• In fruit flies, red eyes are dominant over white
eyes. Show a cross between two white-eye
fruit flies.
• Phenotype:
• Genotype:
Punnett Square Practice
• Curly hair is recessive, and straight hair is
dominant. A woman with curly hair marries a
man who is homozygous dominant for straight
hair. Predict the outcomes for their children.
• Phenotype:
• Genotype:
Punnett Square Practice
• Black hair is homozygous dominant. Brown hair
is heterozygous. Blonde hair is homozygous
recessive. (This is an example of incomplete
dominance.) A woman with brown hair marries a
man with brown hair. What are the possible
outcomes for their kids?
• Phenotype:
• Genotype:
Punnett Square Practice
• Freckles are recessive. No freckles are
dominant. Mom= heterozygous
Dad=homozygous recessive. What are the
possible outcomes for kids?
• Phenotype:
• Genotype:
Pop Quiz
Pop Quiz - Punnett Square
• Tall is dominant over short in pea plants. Show
the cross of a homozygous short plant is crossed
with a homozygous tall plant.
• Phenotype:
• Genotype: