Problem Analysis
We are tasked with solving a genetic cross involving two traits in rabbits:
1.
Hair color: Black hair (dominant, \( B \)) vs. Brown hair (recessive, \( b \)).
2.
Ear type: Long ears (dominant, \( E \)) vs. Floppy ears (recessive, \( e \)).
The genotypes of the parents are:
- Male rabbit: \( BBee \) (black hair, floppy ears).
- Female rabbit: \( bbEe \) (brown hair, long ears).
We need to:
1. Fill out a Punnett square for this cross.
2. Determine the phenotypes and proportions of the offspring.
3. Answer specific questions about the number of offspring with certain combinations of traits.
---
Step 1: Identify Gametes Produced by Each Parent
#### Male Rabbit (\( BBee \)):
- Since \( B \) is homozygous dominant and \( ee \) is homozygous recessive, the male will produce only one type of gamete:
- \( Be \)
#### Female Rabbit (\( bbEe \)):
- The female is heterozygous for both traits. She will produce four types of gametes:
- \( bE \)
- \( be \)
---
Step 2: Construct the Punnett Square
We now set up the Punnett square using the gametes from the male and female rabbits.
| | Be | Be | Be | Be |
|-----|------|------|------|------|
|
bE | bBEE | bBEe | bBEE | bBEe |
|
be | bBee | bBee | bBee | bBee |
|
bE | bBEE | bBEe | bBEE | bBEe |
|
be | bBee | bBee | bBee | bBee |
---
Step 3: Determine Phenotypes of Offspring
Using the Punnett square, we can determine the phenotypes of the offspring based on the following rules:
-
Hair color:
- \( BB \) or \( Bb \): Black hair.
- \( bb \): Brown hair.
-
Ear type:
- \( EE \) or \( Ee \): Long ears.
- \( ee \): Floppy ears.
Now, let's analyze each box in the Punnett square:
1.
bBEE: Black hair, long ears.
2.
bBEe: Black hair, long ears.
3.
bBEE: Black hair, long ears.
4.
bBEe: Black hair, long ears.
5.
bBee: Black hair, floppy ears.
6.
bBee: Black hair, floppy ears.
7.
bBee: Black hair, floppy ears.
8.
bBee: Black hair, floppy ears.
9.
bBEE: Black hair, long ears.
10.
bBEe: Black hair, long ears.
11.
bBEE: Black hair, long ears.
12.
bBEe: Black hair, long ears.
13.
bBee: Black hair, floppy ears.
14.
bBee: Black hair, floppy ears.
15.
bBee: Black hair, floppy ears.
16.
bBee: Black hair, floppy ears.
---
Step 4: Count the Phenotypes
From the Punnett square, we can see the following phenotypes and their counts:
-
Black hair, long ears: 8 offspring.
-
Black hair, floppy ears: 8 offspring.
-
Brown hair, long ears: 0 offspring.
-
Brown hair, floppy ears: 0 offspring.
---
Step 5: Answer the Specific Questions
1.
How many out of 16 have black hair and long ears?
-
Answer: 8
2.
How many out of 16 have black hair and floppy ears?
-
Answer: 8
3.
How many out of 16 have brown hair and long ears?
-
Answer: 0
4.
How many out of 16 have brown hair and floppy ears?
-
Answer: 0
---
Final Answer
\[
\boxed{8, 8, 0, 0}
\]
Parent Tip: Review the logic above to help your child master the concept of genetic crosses worksheet answer key.
