Congrats! You’re Having
A Baby!
Objective #1
Explore the various types of gene
interactions which contribute to
genetic diversity
The way an organism looks is result of the way in which the
alleles interact. The genotype determines the phenotype.
Simple Dominance is defined as when one allele
completely expresses a trait and does not allow the other
allele to express itself.
Albinism is a disorder in which a person cannot make the pigment,
melanin. A person who is “aa” has albinism. The “AA” and the
“Aa” genotype produce normal skin pigment.
Incomplete Dominance is when both the dominant and the
recessive cannot fully express the trait
Snapdragons are flowers. Note that the dominant R allele
will produce a red petal flower. When it combines with a recessive r
allele, notice the petals are pink. The combination of R and r do not
Allow for complete red.
What is the phenotypic ratio for the F1 Generation?
What is the phenotypic ratio for F2 Generation
Between the F1 pink and white flower?
Codominance is defined as when two different alleles fully
express the trait
Roan Cattle have a lighter color almost pinkish appearance. It is not because they
Have red hair. It is by the arrangement of red and white hairs. This cow inherited
The dominant R allele for red and the recessive r for white hairs.
Sickle Cell Anemia is a genetic
Disorder caused by a point mutation.
A person with this disorder would have
red blood cells that are sickle shaped.
Note the genotype is aa. Look at the
Genotype AA, describe the normal cells.
Polygenic Inheritance is when many genes control a trait.
As in the diagram below, skin color is controlled by (3) genes. Noticed the letters A,
B, and C. These letters represent the (3) genes.
The more dominant alleles inherited, the
darker the skin.
Geneticists try to predict the possible genotypes and phenotypes of the next generation. Sometimes
they use a simple Punnett square or the mathematics of probability. Below is a Punnett square for a
monohybrid cross for flower color.
About the Lab
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Parents will be heterozygous for a given trait
Simple Dominance – coin: head=D; tail=R
Codominance – coin: head=D; tail=R
Polygenic Inheritance – coin: head=D; tail=R
Sex Determination – coin: head=X; tail=Y
Read the directions carefully
Complete Data for your two babies
Example of a Monohybrid Cross in Humans
(both parents heterzygotes)
Objective #2
Compare expected phenotypic ratio to the
observed phenotypic ratio
Trait
# Dominant
Individuals
#Recessive
individuals
Observed
Phenotypic
Ratio
Expected
Phenotypic
Ratio
Expected ratio comes from the punnett square.
Observed ratio comes from sampling a population
Objective #3
Calculate the expected genotypic and observed
genotypic ratios for a monohybrid cross for
several types of gene interactions.
In this part of the lab, you should realize that it is only the
phenotypic ratio that change when the allele interaction no
longer exhibits a simple dominance interaction.