Solving Genetics Problems : Monohybrid Crosses
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Transcript of Solving Genetics Problems : Monohybrid Crosses
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Solving Genetics Problems : Monohybrid Crosses
Two organismsOne characteristic
Complete dominance
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Solving Genetics Problems : Monohybrid Crosses
• Complete dominance
• the dominant allele completely masks the effect of the recessive allele in heterozygous condition.
• Bb
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Solving Genetics Problems : Monohybrid Crosses
• Incomplete dominance
• dominance occurring in heterozygotes in which the dominant allele is only partially expressed
– Pp – Sweet peas
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Solving Genetics Problems : Monohybrid Crosses
• The problem involved two gerbils named Honey and Ritz.
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Solving Genetics Problems : Monohybrid Crosses
• The gene in question is a fur color gene which has two alleles
• dominant brown (B) and recessive black (b)
An allele is one of two or more forms of a gene
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Solving Genetics Problems : Monohybrid Crosses
• Step One: Figure out the genotypes of the parents. – address the question of all of
the possible kinds of babies they could produce
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Solving Genetics Problems : Monohybrid Crosses
• Step Two: Figure out what kinds of gametes the parents can produce.– Now you need to determine all the possible ways
that his sperm can combine with her eggs.– Punnett Square
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Solving Genetics Problems : Monohybrid Crosses
• Step Three: Set up a Punnett Square .– You need to create a chart
with one column for each of the female's egg types, and one row for each of the male's sperm types
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Solving Genetics Problems : Monohybrid Crosses
• Step Four: Fill in the babies inside the table by matching the egg allele at the top of the column with the sperm allele at the head of the row.
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Solving Genetics Problems : Monohybrid Crosses
Figure out the genotypic ratio for your predicted babies.
• So we have now figured out that, if Honey and Ritz have a lot of babies, we can predict that:
• 25% should be BB homozygous
• 50% should be Bb homozygous recessive
• 25% should be bb heterozygous
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Solving Genetics Problems : Monohybrid Crosses
Step Five: Figure out the Phenotype ratio for your predicted babies.
• This is where dominance really enters the picture
• If B is completely dominant to b, all gerbils with at least one B will look pretty much alike, no matter what their second allele is
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Solving Genetics Problems : Monohybrid Crosses
Phenotype will be:• 75% brown fur• 25% black fur
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Solving Genetics Problems : Monohybrid Crosses
• Where do we come from, as a species, and how are we all related
• See how our species shares its genetic history with all other species on the planet
• Genetic engineering
• DNA fingerprinting in areas such as drug discovery and forensics