Genetics Worksheets and Printables - Free Printable

Here are the answers to the worksheet problems, broken down step-by-step.

Question 1

a. What is the genotype(s) of the parents?
* Parent 1 (Light purple, short stem): The problem states light purple is `Pp` and short stem is `ss`. So, the genotype is Ppss.
* Parent 2 (Violet, heterozygous long stem): The problem states violet is `pp` and heterozygous long stem is `Ss`. So, the genotype is ppSs.

b. Is the egg plant skin color trait an example of co-, incomplete-, or complete dominance?
* Answer: Incomplete dominance.
* *Reasoning:* When you have two different alleles (`Pp`), the result is a "blend" (light purple) rather than one trait hiding the other completely.

c. Is egg plant stem length an example of co-incomplete-, or complete dominance?
* Answer: Complete dominance.
* *Reasoning:* There are only two options: Long (`SS` or `Ss`) or Short (`ss`). The "Long" trait completely covers up the "Short" trait if present.

d. What are the four possible allele combinations for each parental gamete?
To find these, we take one letter from the first pair and one from the second pair (FOIL method).
* Parent 1 (Ppss): Can pass on `Ps` or `ps`. Since it has two `s`'s, the combinations repeat.
* Gametes: Ps, Ps, ps, ps
* Parent 2 (ppSs): Can pass on `pS` or `ps`. Since it has two `p`'s, the combinations repeat.
* Gametes: pS, pS, ps, ps

e. Fill out the dihybrid cross (Punnett Square):

| | Ps | Ps | ps | ps |
| :--- | :---: | :---: | :---: | :---: |
| pS | PpSs | PpSs | ppSs | ppSs |
| pS | PpSs | PpSs | ppSs | ppSs |
| ps | Ppss | Ppss | ppss | ppss |
| ps | Ppss | Ppss | ppss | ppss |

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Question 2

*Using the Punnett square above (16 total squares):*

a. Violet with short stems:
* Genotype: `ppss`
* Count: 4 squares
* Proportion: 4/16 (or 1/4, or 25%)

b. Light purple with long stems:
* Genotype: `PpS_` (PpSS or PpSs)
* Count: 4 squares (all are PpSs)
* Proportion: 4/16 (or 1/4, or 25%)

c. Dark purple:
* Genotype: `PP...`
* Count: 0 squares (Neither parent had a dominant `P` to give)
* Proportion: 0/16 (or 0%)

d. Long stems:
* Genotype: `__S_` (Any with at least one big S)
* Count: 8 squares (The top two rows)
* Proportion: 8/16 (or 1/2, or 50%)

e. Dark purple with short stems:
* Genotype: `PPss`
* Count: 0 squares
* Proportion: 0/16 (or 0%)

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Question 3

*Determine the genotypes of this specific cross based on phenotypes.*

a. Light purple with short stems:
* Phenotype: Light Purple = `Pp`; Short Stem = `ss`
* Genotype: Ppss

b. Violet with long stems:
* Phenotype: Violet = `pp`; Long Stem = `S_`
* Looking at the offspring list provided in the "Advanced" section, the genotype listed for this group is `ppSs`.
* Genotype: ppSs

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Advanced Question 3

a. What are the likely genotypes of the parents?
Let's look at the traits separately:
1. Color: We see Dark Purple (`PP`) and Light Purple (`Pp`) offspring, but zero Violet (`pp`). This means at least one parent must be `PP` (so no baby can get two small `p`s). Since we have Light Purple babies (`Pp`), the other parent must contribute a `p`. To get both `PP` and `Pp` babies in equal numbers (50 vs 50), the cross is likely PP x Pp.
2. Stem: We see Long (`Ss`) and Short (`ss`) offspring in equal numbers (100 vs 100). This is a classic test cross ratio, which happens when you cross a heterozygote with a homozygous recessive: Ss x ss.

Combining these, the parents are:
Answer: PPSs and Ppss

*(Self-Check: If you cross PPSs x Ppss, you get 50% PPSs, 50% PPss, 50% PpSs, 50% Ppss. This matches the data perfectly: 50 Dark/Long, 50 Dark/Short, 50 Light/Long, 50 Light/Short).*

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Final Answer:

1a. Parent 1: Ppss; Parent 2: ppSs
1b. Incomplete dominance
1c. Complete dominance
1d. Parent 1 Gametes: Ps, ps; Parent 2 Gametes: pS, ps
1e. See the table in the explanation above.
2a. 4/16 (25%)
2b. 4/16 (25%)
2c. 0/16 (0%)
2d. 8/16 (50%)
2e. 0/16 (0%)
3a. Ppss
3b. ppSs
Advanced 3a. PPSs and Ppss