Genetics and Inheritance 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: Inheritance of ABO Blood Groups (Multiple Alleles & Codominance)

This question tests your understanding of how blood types are inherited, specifically focusing on the ABO blood group system, which involves codominant and recessive alleles.

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 codominant (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: $I^B I^B$ (homozygous) or $I^B i$ (heterozygous).

2. Remember that type O blood has the genotype $ii$ (since $i$ is recessive, both alleles must be $i$).

3. Consider what alleles the parent with type O blood can pass on to their child. Since their genotype is $ii$, they can only contribute an $i$ allele.

4. Think about which genotype for type B blood allows for one $i$ allele to be inherited from the type O parent, and still results in a type B phenotype.

Try solving on your own before revealing the answer!

Final Answer: $I^B i$

The person must have inherited the $i$ allele from their type O parent and the $I^B$ allele from their other parent, resulting in the genotype $I^B i$ (type B phenotype).

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 ABO Blood Groups

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

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. Recall that the $I^A$ allele codes for the A antigen, and the $I^B$ allele codes for the B antigen on red blood cells.

2. Since both alleles are present and codominant, both types of antigens will be produced and displayed on the surface of the red blood cells.

3. Think about how this differs from someone with only $I^A I^A$ or $I^B I^B$ (who would have only A or only B antigens, respectively).

4. Describe what you would observe if you looked at the surface of the red blood cells under a microscope with antigen-specific stains.

Try solving on your own before revealing the answer!

Final Answer:

The red blood cells would have both type A and type B antigens on their surface, because both alleles are expressed equally due to codominance.

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 diagram used to predict the genotypes of offspring from a genetic cross.

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

Step-by-Step Guidance

1. Determine the possible gametes each parent can produce. For GgSs, use the FOIL method (First, Outside, Inside, Last) to find all combinations: GS, Gs, gS, gs. For ggSs, since both alleles for G are g, the gametes are gS and gs.

2. Set up a Punnett square with the GgSs parent's gametes along the top (GS, Gs, gS, gs) and the ggSs parent's gametes along the side (gS, gs).

3. Fill in each box by combining the alleles from the corresponding row and column to get the genotype of each possible offspring.

4. Check that you have all possible combinations and that the Punnett square is complete before moving on to phenotype ratios.

Try solving on your own before revealing the answer!

Final Answer:

The completed Punnett square will show all possible genotypes for the offspring, such as GgSS, GgSs, ggSS, ggSs, Ggss, ggss, etc.

Be sure to double-check your combinations for accuracy!

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

Background

Topic: Phenotypic Ratios in Dihybrid Crosses

This question tests your ability to interpret a Punnett square and determine the ratio of observable traits (phenotypes) among the offspring.

Key Terms and Concepts:

• Phenotype: The observable traits (e.g., green striped, green solid, yellow striped, yellow solid)

• Genotype: The genetic makeup that determines phenotype

• Dominant/Recessive: Green (G) is dominant to yellow (g); Striped (S) is dominant to solid (s)

Step-by-Step Guidance

1. From your completed Punnett square, list all possible genotypes for the offspring.

2. For each genotype, determine the corresponding phenotype based on dominance relationships (e.g., any genotype with at least one G is green; at least one S is striped).

3. Count the number of offspring for each phenotype (green striped, green solid, yellow striped, yellow solid).

4. Express the counts as a ratio (e.g., 3:1:3:1) to summarize the phenotypic outcomes.

Try solving on your own before revealing the answer!

Final Answer:

The phenotype ratio is 3 Green Striped : 1 Green Solid : 3 Yellow Striped : 1 Yellow Solid.

This reflects the expected outcomes based on the dominance of the alleles and the combinations possible from the cross.