Suppose you observe a bird with a very broad and thick beak. You want to know why the bird’s beak is shaped that way. How could
2 answers:
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Explanation:
- Dull fruit (D) is dominant over glossy (d) fruit.
- Orange friut (R) is dominant over cream fruit (r).
- Bitter cotyledon (B) is dominant over non-bitter cotyledons (b).
The three genes are independent.
<h3>a)</h3>- A plant homozygous for dull, orange fruit and bitter cotyledons has the genotype <em>DDRRBB</em><em>.</em>
- A plant homozygous for glossy, cream fruit and non-bitter cotyledons has the genotype <em>ddrrbb</em>.
100% of the F1 will have dull, orange fruit and bitter cotyledons and will be heterozygous for all genes: <em>DdRrBb</em>.
<u>The F2 will have 8 possible phenotypes:</u>
- 27 D_R_B dull, orange fruit and bitter cotyledons
- 9 D_R_bb dull, orange fruit and non-bitter cotyledons
- 9 D_rrB_ dull, cream fruit and bitter cotyledons
- 3 D_rrbb dull, cream fruit and non-bitter cotyledons
- 9 ddR_B_ glossy, orange fruit and bitter cotyledons
- 3 ddR_bb glossy, orange fruit and non-bitter cotyledons
- 3 ddrrB_ glossy, cream fruit and bitter cotyledons
- 1 ddrrbb glossy, cream fruit and non-bitter cotyledons
<h3>b)</h3>
An F1 plant is crossed with a plant that has glossy, cream fruit and non-bitter cotyledons.
<h3>DdRrBb x ddrrbb </h3>
The F1 individual can produce 8 types of gametes: DRB, DRb, DrB, Drb, dRB, dRb, drB and drb. The cream fruit and non-bitter cotyledons individual can only produce drb gametes. This cross also produces a progeny with the following genotypes and phenotypic proportions:
- 8 DdRrBb dull, orange fruit and bitter cotyledons
- 8 DdRrbb dull, orange fruit and non-bitter cotyledons
- 8 DdrrBb dull, cream fruit and bitter cotyledons
- 8 Ddrrbb dull, cream fruit and non-bitter cotyledons
- 8 ddRrBb glossy, orange fruit and bitter cotyledons
- 8 ddRrbb glossy, orange fruit and non-bitter cotyledons
- 8 ddrrBb glossy, cream fruit and bitter cotyledons
- 8 ddrrbb glossy, cream fruit and non-bitter cotyledons
