). In the type of corn we will be using in our class, the pericarp is always col
ID: 204704 • Letter: #
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). In the type of corn we will be using in our class, the pericarp is always colorless, but the aleurone may be colorless, purple, or red, and the endosperm yellow or white. Keep in mind that because the endosperm is underneath the aleurone, a purple or red aleurone will mean that the endosperm will not be visible (regardless of whether it is yellow or white). The color of the aleurone comes from the production of anthocyanin pigments (also responsible for the color of red onions and blueberries). Two separate genes, C and R, play a role in the production of anthocyanin. Genes C and R are located on separate chromosomes and segregate.
For the aleurone to be colored, alleles C and R must be present. The genotypes C/C R/_ and C/c R/_ both result in a purple (Fig. 2) or red kernel. The homozygous recessive of either allele (c/c or r/r) disrupts anthocyanin production and results in a colorless aleurone. As a result, a _/_ r/r or a c/c _/_ kernel will show the color of the endosperm.
A red aleurone color is determined by another gene, Pr, which we will not be working with in this laboratory. Thus, for these experiments, the presence of the C/C R/_ or C/c R/_ genotypes will result in a purple kernel only.
In addition to C and c, the C gene has a third possible allele, C1. The CI allele is dominant over both C and c. CIinhibits anthocyanin production, giving a colorless aleurone, regardless of the genotype at the R locus.
If the aleurone is colorless, the kernel color will be that of the endosperm, either yellow or white (see Fig. 2). Normal corn endosperm color (yellow) occurs when the Y gene carries the allele Y. causes the production of carotenoid pigments in the endosperm (carotenoids are also responsible for the color of carrots and hot or sweet peppers). In the recessive condition (y/y) carotenoids are not produced and the endosperm is white. The Y alleles are masked by the presence of a colored aleurone. The Y gene is independent of the C and R genes
Although purple color is known to be determined by more than one gene, you may assume that a single gene is responsible in this case, with purple (R) being dominant over yellow (r) .
Kernel texture
Normal corn endosperm is high in amylose starch, a large complex carbohydrate. The gene Su in the homozygous recessive condition (su/su) produces endosperm that is high in sugars that are much simpler in their structure than starch. As corn dries, the sugary endosperm of sweet kernels lose water, and they wrinkle (see Fig. 3). Starchy kernels remain smooth.
Fig. 3. A corn ear showing starchy (smooth surface) and sweet (wrinkled) kernels. Note that the kernels are all yellow, meaning that the aleurone is colorless and the Y genotype for each kernel must be Y/_.
You may assume that: 1) both of the ears represent the F2 generation from an F1 generation, produced in turn from true-breeding parents (P), and 2) the true-breeding parents (P) of the F1 are different phenotypes for the trait you observe.
Ear #6500 is the F2 generation. The F1 generation was selfed to yield F2 ears. Two parental (P) corn breeds, one true-breeding purple and the other true-breeding yellow, were crossed to yield F1 progeny. Although purple color is known to be determined by more than one gene, you may assume that a single gene is responsible in this case.
Ear #6540 is the F2 generation. The F1 generation was selfed to yield F2 ears. Two parental (P) corn breeds, one true-breeding starchy and the other true-breeding sweet, were crossed to yield F1 progeny.
You may assume that: 1) the ears represent the F2 generation from an F1 generation, produced in turn from true-breeding parents (P); 2) the true-breeding parents (P) of the F1 are different phenotypes for the traits you observe; and 3) the F1 are double heterozygotes. Although purple color is known to be determined by more than one gene, you may assume that a single gene is responsible in this case.
Ear #6600 is the F2 generation. The F1 generation was selfed to yield F2 ears. Two parental (P) corn breeds, one true-breeding purple and starchy, and the other true-breeding yellow and sweet, were crossed to yield F1 progeny. Although purple color is known to be determined by more than one gene, you may assume that a single gene, R, is responsible for color.
QUESTIONS
1. For ear #6500, provide the genotype/s and expected ratios with phenotype/s for: (3 pts)
The P generation
The F1 generation
The F2 generation
2. For ear #6540, provide the genotype/s and expected ratios with phenotypes for: (3 pts)
The P generation
The F1 generation
The F2 generation
3. For ear #6600, provide the genotype/s and expected ratios with phenotypes for: (3 pts)
The P generation
The F1 generation
The F2 generation
Explanation / Answer
1) For ear 6500:
Parent : RR + rr
F1 : Rr
F2 : RR,Rr,Rr,rr
F2 Phenotype : 3/4= purple, 1/4= yellow
For ear 6540 :
Parent : susu + SUSU
F1 : SUsu
F2 : SUSU,SUsu,SUsu, susu
F2 Phenotype : 3/4= sweet, 1/4= starchy
For ear 6600:
Parent : Rsu + rSU
F1 : RSU,Rsu,rSU,rsu
F2 : RRSUSU, RRSUsu,RrSUSU,RrSUsu,RRSUsu,RRsusu, RrSUsu,Rrsusu,RrSUSU, RrSUsu,rrSUSU,rrSUsu,RrSUsu, RrSUsu, rrSUsu,rrsusu
F2Phenotype : 9/16=purple sweet, 3/16 =purple starchy, 3/16= yellow starchy, 1/16=yellow sweet
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