Genetics problem please help the whole homework assignment is due tomorrow at 4:10 pm
A researcher is interested in two important phenotypes in sorghum: stem color and seed sweetness. Use G for red stems and g for green stems. Use S for sweet seeds and s for bitter seeds. After crossing two plants red-stemmed sweet seed plants (GgSs) he observes 3/4 of the progeny being red and having sweet seeds, 3/16 being green and sweet, and 1/16 being green and bitter. What is a possible explanation for this?
The fractions are weird because it goes from having a 4 space Punnett square to 16 because of the inclusion of a second trait in the genotype. The majority has both dominant alleles, 3/16 has only one dominant allele. 1/16 is both recessive alleles no dominant alleles
To solve this genetics problem, we need to consider the principles of Mendelian inheritance and Punnett squares. Let's break it down step by step.
First, let's write out the parental genotypes:
Plant 1: GgSs (red-stemmed sweet seed)
Plant 2: unknown genotype (denoted as XY)
We know that 3/4 of the progeny have red stems and sweet seeds (G_S_), 3/16 have green stems and sweet seeds (ggS_), and 1/16 have green stems and bitter seeds (ggs_).
Step 1: Determine the possibilities for Plant 2 (XY):
Since 3/4 of the progeny have red stems and sweet seeds (G_S_), it means that one of the parents (Plant 2) has to carry the G allele for stem color and the S allele for seed sweetness.
Therefore, the genotype of Plant 2 (XY) must be G_S_.
Step 2: Determine the genotypes and phenotypes of the progeny:
Now that we know the genotype of Plant 2 (XY), we can use a Punnett square to determine the genotypes and phenotypes of the offspring.
| G | g
---|-------|-------
S | G_S_ | G_s_
s | G_ss | g_ss
From the Punnett square, we can see that there are four possible genotypes:
1/4 (25%) G_S_ (red-stemmed, sweet seed)
1/4 (25%) G_s_ (red-stemmed, bitter seed)
1/4 (25%) g_ss (green-stemmed, bitter seed)
1/4 (25%) G_ss (green-stemmed, sweet seed)
Comparing these results to the given proportions, we can explain the observed ratios as follows:
- 3/4 of the progeny being red and having sweet seeds (G_S_): This matches the expected 25% G_S_ plus 50% G_s_, resulting in a total of 75% (3/4).
- 3/16 being green and sweet (G_ss): This corresponds to the expected 25% G_ss, resulting in 18.75% (3/16) when rounded.
- 1/16 being green and bitter (g_ss): This corresponds to the expected 25% g_ss, resulting in 6.25% (1/16) when rounded.
Therefore, the possible explanation for the observed ratios is that the researcher crossed a red-stemmed, sweet seed plant (GgSs) with a green-stemmed, sweet seed plant (G_S_), resulting in the observed phenotypic ratios among the progeny.