Monohybrid Cross Homework PDF | PDF | Dominance (Genetics) | Zygosity - Free Printable

Here are the answers to your Monohybrid Cross Worksheet.

Part A: Vocabulary

1–5. Match the definitions:
1. D (Homozygous) — Genotypes made of the same alleles (like AA or aa).
2. A (Alleles) — Different forms of genes for a single trait.
3. B (Dominant) — Gene that is always expressed if present.
4. E (Recessive) — Gene that is expressed only in the homozygous state (needs two copies, like aa).
5. C (Heterozygous) — Genotypes made of two different alleles (like Aa).

6–11. Circle the correct examples:
*(Note: In genetics, capital letters usually represent dominant alleles and lowercase letters represent recessive alleles.)*

6. Dominant allele (Look for Capital letters):
- D, L, N, R, S

7. Recessive allele (Look for lowercase letters):
- n, d, r, k
*(Note: M, F, G, P are capitalized, so they are dominant.)*

8. Homozygous dominant (Two Capital letters):
- AA, KK, TT
*(Note: Gg, Rr are heterozygous. mm, uu are homozygous recessive.)*

9. Homozygous recessive (Two lowercase letters):
- ee, qq, ww
*(Note: Ff, Oo, Uu are heterozygous. HH is homozygous dominant.)*

10. Genotypes in which dominant gene MUST show (Any genotype with at least one Capital letter):
- AA, Dd, EE, Jj, RR, Ss
*(Note: ff is the only one here that does not have a dominant gene.)*

11. Genotypes in which recessive gene MUST show (Only genotypes with two lowercase letters):
- aa, rr
*(Note: For the recessive trait to physically show up, there cannot be any dominant capital letters hiding it. Gg, Ff, KK, Oo, Tt all have dominant traits showing.)*

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Part B: Punnett Squares

12. Examine the following Punnett squares and circle those that are correct.

Let's check them one by one:
* Square 1 (Left): Parents are `d` and `d` on top; `d` and `d` on the side. All offspring should be `dd`. The square shows `Dd` and `dd`. This is Incorrect.
* Square 2 (Middle-Left): Parents are `D` and `D` on top; `d` and `d` on the side. All offspring should be `Dd`. The square shows `DD` and `Dd`. This is Incorrect.
* Square 3 (Middle-Right): Parents are `A` and `a` on top; `A` and `a` on the side.
* Top-Left: A + A = AA
* Top-Right: a + A = Aa (The square says `aa`, which is wrong).
* This is Incorrect.
* Square 4 (Right): Parents are `A` and `a` on top; `a` and `a` on the side.
* Top-Left: A + a = Aa
* Top-Right: a + a = aa
* Bottom-Left: A + a = Aa
* Bottom-Right: a + a = aa
* This matches the square perfectly. This is Correct.

Answer: Circle the fourth square (the one on the far right).

13. What do the letters on the outside of the Punnett square stand for?
They stand for the alleles (or genes) contributed by each parent. Specifically, they represent the gametes (sex cells) that each parent passes down to the offspring.

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Final Answer:

Part A
1. D
2. A
3. B
4. E
5. C
6. D, L, N, R, S
7. n, d, r, k
8. AA, KK, TT
9. ee, qq, ww
10. AA, Dd, EE, Jj, RR, Ss
11. aa, rr

Part B
12. Circle the 4th square (far right).
13. The alleles (genes) from the parents.