Resulting Offspring

Question

Question: A male dragon that is tall, red eyed, and wide winged is mated with a female dragon that is short, white eyed, and narrow winged. The resulting offspring consisted of:

tall, white, wide- 478 tall, red, wide- 21 short, white, wide- 19 short, red, wide- 482

(it was given that the traits are not sex-linked)

Me and my partner have determined that tall and white are located on the same chromosome, as are short and red. We have also figured out that because all offspring had wide wings, that wide is the dominant trait, and the male has 2 dominant alleles while the female only has one.

However, the question is asking if the male dragon could reproduce with itself, what would the resulting offspring be? We are stumped on figuring out the genotype of both the male and female dragon, as well as which alleles are dominant. Help!!

Answer 1

Hi Sydney,

Step 1 – Identify the traits

1. Tall (T) vs Short (t)
2. White eyes (W) vs Red eyes (w)
3. Wide wings (D) vs Narrow wings (d)

The problem says traits are not sex-linked.

Step 2 – Observations from the offspring

1. Offspring ratios:
2. Tall, white, wide = 478
3. Tall, red, wide = 21
4. Short, white, wide = 19
5. Short, red, wide = 482

This looks like a test cross pattern, where tall/white are linked and short/red are linked. That’s why most offspring are either (Tall + White) or (Short + Red), and only a few are recombinants (Tall + Red, Short + White).

Also:

1. All offspring had wide wings, meaning Wide (D) is dominant and the male must be DD (homozygous dominant).

Step 3 – Genotypes of the parents

1. Male dragon: Tall, red, wide = T W / t w ; DD
2. Female dragon: Short, white, narrow = t w / t w ; dd

That explains why the offspring mostly matched the linked combinations.

Step 4 – If the male dragon self-crossed (with itself)

Now we ask: if the male dragon reproduced with itself, what would happen?

1. Male’s genotype = T W / t w ; DD
2. So a self-cross would look like: T W / t w × T W / t w

This is basically a dihybrid cross with linkage.

Expected offspring:

1. Parental combinations (Tall White and Short Red) would be most common.
2. Recombinants (Tall Red and Short White) would appear less often, depending on recombination frequency.
3. For wings: all offspring will be Wide (because parent is DD).

Hope this helps!