- both of the parent corn plants that produced the kernel offspring you’re assesing were heterozygous for each caracter (kernel color and sugar content). The parent plants were the result of a cross between a “grandparent” plant that was true-breeding for the dominant traits for both characters (purple color and low sugar content), and a “grandparent” plant that was true-breeding for the recessive traits for both characters (yellow color and high sugar content). Based on this information, what were the genotypes and phenotypes of the “grandparent” plants?
Grandparent Plant 1: DDLL
Grandparent Plant 2: ddll
- Looking at your kernel offspring, you should see both purple and yellow kernels. Instead of crossing two parents that were both heterozygous for the kernel color gene, could these offspring have been obtained by a cross between a parent that was heterozygous for the kernel color gene and a parent that was homozygous dominant for the kernel color gene? In a few words explain you answer
No, they could not have been obtained by crossing Dd and DD.
A cross between heterozygous (Dd) and homozygous
dominant (DD) would only produce DD and Dd offspring (both showing
purple color). You would never get yellow (dd) kernels, but you
observed yellow kernels in the offspring.
- Still focusing on color, could these offspring have been obtained by a cross between a parent that was heterozygous for the kernel color gene and a parent that was homozygous recessive for the kernel color gene? In a few words explain your answer.
Yes, they could have been obtained by crossing Dd and dd.
A cross between heterozygous (Dd) and homozygous
recessive (dd) would produce 50% Dd (purple) and 50% dd (yellow)
offspring, which matches the observation of both purple and yellow
kernels.
Monohybrid Analysis: Sugar Content
Table 1. Monohybrid Kernel Color and Sugar-Content Predictions
| Kernel Color | Kernel Sugar Content | |
|---|---|---|
| Possible Offspring Genotypes and Probabilities | 25% DD 50% Dd 25% dd | 25% LL 50% Ll 25% ll |
| Possible Offspring Phenotypes and Probabilities | 75% Purple 25% Yellow | 75% Low sugar 25% High sugar |
Table 2. Monohybrid Analysis Kernel Color Data
| # Kernels Counted | Expected # of Kernels | |
|---|---|---|
| purple | 143 | 137.25 |
| yellow | 40 | 45.75 |
| TOTAL | 183 | --- |
| Chi-squared p-value | --- |
Table 3. Monohybrid Analysis Kernel Sugar Content Data
| # Kernels Counted | Expected # of Kernels | |
|---|---|---|
| smooth(low sugar) | 139 | 136.5 |
| wrinkled(high-sugar) | 43 | 45.5 |
| TOTAL | 182 | --- |
| Chi-squared p-value | --- |
- Does your population of kernel offspring match your predidtions for kernel color? If so, how do you know? If not, give one reason why actual offspring phenotype ratios can differ from predicted ratios.
Yes, as the chi-squared p-value is greater than 0.05, we fail to reject the null hypothesis, indicating that the observed ratios do not significantly differ from the expected ratios.
~.3 is consistent with the 3:1 ratio predicted for a monohybrid cross.
- DOes your population of kernel offspring match your predictions for kernel sugar content? If so, how do you know? If not, give one reason why actual offspring phenotype ratios can differ from predicted ratios.
Yes, as the chi-squared p-value is greater than 0.05, we fail to reject the null hypothesis, indicating that the observed ratios do not significantly differ from the expected ratios.
~.66 is consistent with the 3:1 ratio predicted for a monohybrid cross.
Dihybrid Analysis
- The parents that produced the kernel offspring you’re analyzing inherited one allele for each gene - kernel color and kernel sugar content - from each “grandparent” plant. Looking back at your answer for the first question, what are the possible gamete genotype(s) produced by each “grandparent” plant?
Grandparent that was true breeding for purple kernels and low sugar content: The only possible gamete genotype is DL.
Grandparent that was true breeding for yellow kernels and high sugar content: The only possible gamete genotype is dl.
- Alleles for two genes (eg kernel color / sugar content) can be inherited independently - no matter whichc allele is inherited for one of the genes, theres an equal change of inheriting either allele for the other gene. Or alleles for two genes can be inherited together - only certain allele pairs are observed in the offspring.
a. based on waht you know about meiosis ans sexual reproduction, what causes the alleles for two genes to be inherited independently? hint, think about the buttferly diagram we used to illustrate meiosis
The alleles for two genes are inherited independently due to the random assortment of homologous chromosomes during meiosis I. This means that the way one pair of alleles segregates does not influence how another pair segregates, leading to independent combinations of alleles in the gametes.
b. Based on what you know about meiosis and sexual reproduction, what can cause alleles for two genes to be inherited together?
The alleles for two genes can be inherited together if the genes are located close to each other on the same chromosome. This physical proximity reduces the likelihood of recombination occurring between them during meiosis, leading to the alleles being passed on as a linked group.
a. How many different phenotypes shoudl there be in the corn kernel population ifalleles for the kernel color and sugar content genes are inherited independently?
There should be 4 different phenotypes in the corn kernel population if alleles for the kernel color and sugar content genes are inherited independently. The possible phenotypes would be:
b. Howm any different phenotypes should there be in the corn kernel population if alleles for the kernel color and sugar content genes are inherited together?
There should be 2 different phenotypes in the corn kernel population if alleles for the kernel color and sugar content genes are inherited together. The possible phenotypes would be:
Table 4. Dihybrid Predictions
| Offspring (Kernel) Phenotype | Phenotype Probabilities(inherited independently) | Phenotype Probabilities(inhereted together) |
|---|---|---|
| purple, smooth | 56.25% | 75% |
| purple, wrinkled | 18.75% | 0% |
| yellow, smooth | 18.75% | 0% |
| yellow, wrinkled | 6.25% | 25% |
Table 5. Dihybrid Data
| # Kernels Counted | Expected # of Kernels (inherited independently) | Expected # of Kernels (inherited together) | |
|---|---|---|---|
| purple, smooth | 30 | 25.3 | 33.75 |
| purple, wrinkled | 5 | 8.44 | 0.0001 |
| yellow, smooth | 9 | 8.44 | 0.0001 |
| yellow, wrinkled | 1 | 2.81 | 11.25 |
| TOTAL | 45 | none | none |
| Chi-squared p-value | none | 0.3241 | 0.0000 |