BIO 1150 Genetics Exam 5 Study Guide – Step-by-Step Guidance

Q1a. What would be the genotype of a person with type B blood who has a parent with type O blood?

Background

Topic: Mendelian Genetics – Multiple Alleles & Codominance

This question tests your understanding of how the ABO blood group system is inherited, specifically how codominance and multiple alleles interact to determine blood type.

Key Terms and Concepts:

• Alleles: $I^A$ (Type A antigen), $I^B$ (Type B antigen), $i$ (no antigen)

• Codominance: $I^A$ and $I^B$ are both expressed if present together

• Recessive: $i$ is recessive to both $I^A$ and $I^B$

• Genotype: The combination of alleles an individual has

• Phenotype: The observable trait (here, blood type)

Step-by-Step Guidance

1. Recall that type B blood can result from two possible genotypes: $I^B I^B$ or $I^B i$.

2. Type O blood is only possible with the genotype $ii$ (since $i$ is recessive).

3. Since one parent is type O ($ii$), they can only pass on the $i$ allele to their child.

4. For the child to have type B blood, they must have at least one $I^B$ allele (from the other parent) and one $i$ allele (from the type O parent).

Try solving on your own before revealing the answer!

Final Answer: $I^B i$

The only way for a child to have type B blood with a type O parent is to inherit $I^B$ from one parent and $i$ from the other, resulting in the genotype $I^B i$.

Q1b. Describe the phenotype of someone whose genotype is $I^A I^B$. Don’t just list what their blood type would be—describe what the surface of their red blood cells would look like.

Background

Topic: Codominance in Blood Types

This question is testing your understanding of how codominant alleles are both expressed in the phenotype, specifically in the context of the ABO blood group system.

Key Terms and Concepts:

• Codominance: Both $I^A$ and $I^B$ alleles are expressed equally in the phenotype.

• Antigen: A protein on the surface of red blood cells that determines blood type.

Step-by-Step Guidance

1. Recognize that the genotype $I^A I^B$ means the individual has one allele for the A antigen and one for the B antigen.

2. Because of codominance, both antigens will be produced and displayed on the surface of the red blood cells.

3. Think about what this means for the cell surface: both types of antigens (A and B) will be present simultaneously.

Try describing the phenotype in your own words before revealing the answer!

Final Answer:

The red blood cells would have both type A and type B antigens on their surface. This means that both proteins are present and detectable, which is characteristic of the AB blood type.

Q2a. Draw a Punnett square depicting a cross between a GgSs plant and a ggSs plant.

Background

Topic: Dihybrid Crosses

This question tests your ability to set up and analyze a dihybrid cross, which involves two genes (here, leaf color and leaf pattern) each with two alleles.

Key Terms and Concepts:

• Dihybrid Cross: A cross between individuals heterozygous for two traits.

• Punnett Square: A tool to predict the genotypes and phenotypes of offspring.

• Alleles: G/g for leaf color, S/s for leaf pattern.

Step-by-Step Guidance

1. Determine the possible gametes each parent can produce:

   • GgSs parent: can produce GS, Gs, gS, gs gametes.

   • ggSs parent: can produce gS, gs gametes.

2. Set up a Punnett square with the GgSs parent's gametes on one axis and the ggSs parent's gametes on the other axis.

3. Fill in each box by combining the alleles from the corresponding gametes to show the possible genotypes of the offspring.

4. List out the genotypes in each box, but do not calculate the phenotype ratios yet.

Try drawing and filling in the Punnett square before revealing the answer!

Final Answer:

The completed Punnett square will show all possible combinations of the two traits for the offspring. For example, you should see genotypes like GgSS, GgSs, ggSS, ggSs, Ggss, ggss, etc.

Q2b. What is the phenotype ratio of the offspring from this cross?

Background

Topic: Dihybrid Crosses – Phenotype Ratios

This question tests your ability to interpret the results of a dihybrid cross and determine the expected phenotypic ratios among the offspring.

Key Terms and Concepts:

• Phenotype: Observable traits (here, leaf color and pattern)

• Dominant/Recessive: Green is dominant to yellow; striped is dominant to solid

Step-by-Step Guidance

1. From your Punnett square, identify the genotype of each offspring and determine the phenotype for each (e.g., green striped, green solid, yellow striped, yellow solid).

2. Count the number of each phenotype among the offspring.

3. Express the ratio of each phenotype in the simplest whole numbers.

Try calculating the phenotype ratio before revealing the answer!

Final Answer: 3 Green Striped : 1 Green Solid : 3 Yellow Striped : 1 Yellow Solid

This ratio reflects the expected distribution of phenotypes based on the genotypes produced in the Punnett square.