Solving Genetics Problems : Monohybrid Crosses

Two organismsOne characteristic

Complete dominance

Solving Genetics Problems : Monohybrid Crosses

• Complete dominance

• the dominant allele completely masks the effect of the recessive allele in heterozygous condition.

• Bb

Solving Genetics Problems : Monohybrid Crosses

• Incomplete dominance

• dominance occurring in heterozygotes in which the dominant allele is only partially expressed

– Pp – Sweet peas

Solving Genetics Problems : Monohybrid Crosses

• The problem involved two gerbils named Honey and Ritz.

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

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

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

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

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.

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

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

Solving Genetics Problems : Monohybrid Crosses

Phenotype will be:• 75% brown fur• 25% black fur

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