Complete Dominance Mendelian Genetics Worksheet Answer Key - Fill ... - Free Printable

Explanation:
Let’s solve each part step by step.

Part 1: Rabbit fur color (black dominant over white)
- Black is dominant → use B for black allele, b for white (recessive).
- Homozygous black male = BB
- Homozygous white female = bb

Cross: BB × bb

Punnett square:
```
b b
B Bb Bb
B Bb Bb
```

All offspring = Bb → all black (since B is dominant).

So:
- Phenotype genotype ratio: All offspring have genotype Bb, so 100% Bb → 1:0 (or just “all Bb”)
But the worksheet asks for:
- *Phenotype genotype ratio:* ___ : ___
Usually this means ratio of phenotypes (black:white) — but wording says “phenotype genotype ratio”, which is confusing. Looking at context, in genetics worksheets, they often ask:
- Genotype ratio: e.g., 0 BB : 4 Bb : 0 bb → 0:4:0 or simplified 0:1:0
- Phenotype ratio: black:white = 4:0 = 1:0

Since the blank says “Phenotype genotype ratio: _____ : _____”, and there are only two blanks, it likely means phenotype ratio (black:white), as genotype would need three categories. Many worksheets simplify and ask for phenotype ratio with two numbers.

So:
- Genotype: all Bb → 100% heterozyous
- Phenotype: all black → 4 black : 0 white → simplified to 1 : 0

But let’s check standard format used in such worksheets: For a monohybrid cross like this, they usually expect:
- Genotype ratio: 0 : 4 : 0 (BB : Bb : bb) → written as 0:4:0 or simplified 0:1:0
- Phenotype ratio: 4:0 → 1:0

However, the worksheet has only two blanks for “Phenotype genotype ratio” — that suggests they want phenotype ratio (two categories: dominant : recessive). So answer: 1 : 0

Also, they ask:
- Genotype ratio: ______
Here, since only one genotype appears (Bb), it's all Bb → often written as 100% Bb, but in ratio form with three categories: 0 BB : 1 Bb : 0 bb, so ratio = 0:1:0

But the blank is a single line — maybe they expect “Bb only” or “100% Bb”. However, looking at typical high school worksheets, for this cross, they write:
- Genotype ratio: 0 : 1 : 0
- Phenotype ratio: 1 : 0

We’ll go with that.

Part 2: Tall vs short pea plants (tall dominant)
- Tall dominant → use T for tall, t for short.
- Heterozygous short plant? Wait — short is recessive, so a *short* plant must be tt (homozygous recessive).
But the problem says:
> “Show the cross between a heterozygous short plant and a homozygous tall plant.”

That’s impossible — a *short* plant cannot be heterozygous, because short is recessive. Heterozygous (Tt) would be tall.

This is likely a typo. In standard problems, it’s:
> “cross between a heterozygous *tall* plant and a homozygous *short* plant”
OR
> “heterozygous tall × homozygous short”

But the text says:
“a heterozygous short plant and a homozygous tall plant”

Since short = recessive, heterozygous short is genetically impossible. So we must assume it’s a mistake, and they meant heterozygous tall (Tt) and homozygous short (tt) — that’s the classic test cross.

Alternatively, maybe they meant “heterozygous” (for tall trait) and “short” is describing the phenotype of the other parent — but it says “heterozygous short plant**, which is contradictory.

Let’s re-read:
> “2. Tall is dominant over short in pea plants. Show the cross between a heterozygous short plant and a homozygous tall plant.”

This is an error. In real biology, a short plant must be tt, so it can’t be heterozyous. The only logical fix is that “heterozygous short” is a misprint, and should be heterozygous tall.

But wait — maybe the worksheet expects students to catch that? Unlikely for homework.

Looking at common textbook problems: The standard cross here is Tt × TT (heterozygous tall × homozygous tall) — that gives all tall, but with genotype mix.

Or Tt × tt (test cross) — gives 1:1.

Given that part 1 was BB × bb (dominant homozygote × recessive homozygote), part 2 may be Tt × TT (heterozygous × homozygous dominant) — that also makes sense.

Let’s consider both possibilities:

Option A: “heterozygous short” is a mistake → intended: heterozygous tall (Tt) × homozygous tall (TT)
Cross: Tt × TT
Punnett:
```
T T
T TT TT
t Tt Tt
```
Offspring: 2 TT, 2 Tt → genotypes: 1 TT : 1 Tt
Phenotype: all tall → 4 tall : 0 short → 1:0

Option B: intended: heterozygous tall (Tt) × homozygous short (tt)
Cross: Tt × tt
Punnett:
```
t t
T Tt Tt
t tt tt
```
Offspring: 2 Tt, 2 tt → genotype ratio: 1 Tt : 1 tt → 1:1
Phenotype: 2 tall, 2 short → 1:1

Which one fits better? In part 1, they did homozygous dominant × homozygous recessive. In part 2, if they say “heterozygous short” (impossible), but if we assume they meant “heterozygous” (without specifying phenotype incorrectly), and “homozygous tall”, then Tt × TT is plausible.

However, many worksheets use the test cross (Tt × tt) as second example.

But the phrase is: “a heterozygous short plant” — this is almost certainly a typo, and should be “a heterozygous tall plant” — because you can’t be heterozygous and show the recessive trait.

So we’ll assume:
- Parent 1: heterozygous tall = Tt
- Parent 2: homozygous tall = TT

Then:
- P: Tt × TT
- Genotype ratio: 2 TT : 2 Tt → 1 : 1 (TT : Tt)
- Phenotype ratio: all tall → 1 : 0

But wait — the worksheet says “homozygous tall plant” — yes, that’s TT.

Alternatively, if the teacher meant “homozygous short” (tt), then it would be Tt × tt → 1:1 genotype and phenotype.

Given that part 1 gave a 1:0 phenotype ratio, part 2 might be designed to give 1:1 to contrast.

Also, the instruction says: “Show the cross between a heterozygous short plant and a homozygous tall plant.” Since “short” is recessive, the only way a plant is short is tt, so “heterozygous short” is invalid. Therefore, the intended cross is almost certainly:
heterozygous tall (Tt) × homozygous short (tt)
— and “short
” was mistakenly placed with “heterozygous”.

This is a very common typo. In fact, searching memory: many worksheets say “heterozygous plant” (implying for the dominant trait) and “short” refers to the other parent.

But the sentence structure: “a heterozyous short plant” — two adjectives for one noun — is wrong.

Given educational context, the expected cross is Tt × tt, giving 1:1.

Let me verify with standard curriculum:
- Problem 1: BB × bb → all Bb, all black
- Problem 2: Tt × tt → 1/2 Tt (tall), 1/2 tt (short) → phenotype 1:1

Yes, that’s the classic pair.

So we’ll use:
- P: Tt × tt
- Genotype ratio: 1 Tt : 1 tt → 1 : 1
- Phenotype ratio: 1 tall : 1 short → 1 : 1

Now fill in:

Part 1:
- Phenotype genotype ratio: (they likely mean phenotype ratio) → 1 : 0
- Genotype ratio: 0 : 1 : 0 (BB : Bb : bb) — but only two blanks? Wait, the worksheet shows:
- Phenotype genotype ratio: _____ : _____
- Genotype ratio: __________
So first is two blanks → phenotype ratio (dominant : recessive) = 4:0 → 1:0
Second is one line → write “all Bb” or “100% Bb” or “0 BB : 4 Bb : 0 bb”. In many worksheets, they write “4 Bb” or “all heterozygous”.

But to match expectations, I’ll use:
- Phenotype genotype ratio: 1 : 0
- Genotype ratio: all Bb

However, the instruction says “Fill out the table below using your notes or the text” — the table above has terms like Homozygous, Heterozygous, etc., but the questions below are separate.

Given the blanks:
1. Phenotype genotype ratio: ____ : ____
→ answer: 1 : 0
Genotype ratio: ______
→ 100% Bb or Bb only — but standard is to write ratio: since 4 offspring, 0 BB, 4 Bb, 0 bb → 0:4:0 — but only one blank. So likely they accept “all Bb”.

In practice, teachers accept:
- Genotype ratio: 0:1:0
But with one blank, maybe write “0 BB : 1 Bb : 0 bb”

However, looking at the format of the worksheet (from experience), for part 1, they expect:
- Phenotype ratio: 1 : 0
- Genotype ratio: all Bb

For part 2, assuming Tt × tt:
- Genotype ratio: 1 Tt : 1 tt → write “1:1”
- Phenotype ratio: 1 tall : 1 short → “1:1”

The worksheet asks for:
- Genotype ratio: _____
- Phenotypic ratio: _____

So two separate lines.

Thus:

Final decisions:
1. Rabbits:
- Phenotype genotype ratio (i.e., phenotype ratio): 1 : 0
- Genotype ratio: all Bb (or if ratio format, 0:1:0 — but since one blank, we’ll write “100% Bb” — however, to be safe and standard, many answer keys use “0:4:0", but that’s 3 numbers. Given the blank is one line, I think they expect “Bb only” or simply the ratio of genotypes present: since only one genotype, it's not a ratio — so best: all Bb

But let’s check: the student is to fill in blanks. In countless similar worksheets, for BB × bb, they write:
- Phenotypic ratio: 1:0
- Genotypic ratio: 0:1:0

Even if there’s one blank, they write “0:1:0”.

I will go with that.

2. Pea plants: assuming typo, cross is Tt × tt
- Genotype ratio: 1:1 (Tt : tt)
- Phenotypic ratio: 1:1 (tall : short)

Now write final answers as required.

Final Answer:
1. Phenotype genotype ratio: 1 : 0
Genotype ratio: 0 : 1 : 0
2. Genotype ratio: 1 : 1
Phenotypic ratio: 1 : 1