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Chapter 4: Problem 7

The trait of medium-sized leaves in iris is determined by the genetic condition \(P P\) '. Plants with large leaves are \(P P\), whereas plants with small leaves are \(P^{\prime} P^{\prime} . A\) cross is made between two plants each with medium-sized leaves. If they produce 80 seedlings, what would be the expected phenotypes, and in what numbers would they be expected? What is the term for this allelic relationship?

Short Answer

Expert verified
Answer: The expected phenotypes and their numbers in the offspring are 20 seedlings with large leaves, 40 seedlings with medium-sized leaves, and 20 seedlings with small leaves. The term for this allelic relationship is "incomplete dominance."

Step by step solution

01

Set up the Punnett Square

Create a 2x2 Punnett Square grid and label each row and column with the respective alleles from each parent plant. In our case, the parent plants are both heterozygous (\(P P'\)), so we can label our square as follows: \begin{tabular}{c c|c c} & & P & P' \\ \hline P & & & \\ P' & & & \\ \end{tabular}
02

Fill the Punnett Square

Fill in the boxes of the square by combining one allele from each parent plant, considering the genetic condition of the offspring. We should get the following completed Punnett Square: \begin{tabular}{c c|c c} & & P & P' \\ \hline P & PP & PP' \\ P' & PP' & P'P' \\ \end{tabular}
03

Interpret the Punnett Square

Based on the Punnett Square, we can see there are three different genetic combinations in the offspring: 1. \(PP\) - Large leaves (25% of the offspring) 2. \(PP'\) - Medium leaves (50% of the offspring) 3. \(P'P'\) - Small leaves (25% of the offspring) The percentages can be found by dividing the number of each genotype by the total number of offspring (4 in this case).
04

Calculate the Expected Number of Offspring

We are given that they produce 80 seedlings. To find the expected number of offspring with each phenotype, multiply the percentage of each phenotype by the total number of seedlings: 1. Large leaves: \(0.25 * 80 = 20\) seedlings 2. Medium leaves: \(0.50 * 80 = 40\) seedlings 3. Small leaves: \(0.25 * 80 = 20\) seedlings
05

Determine the Term for the Allelic Relationship

The term for this type of allelic relationship is "incomplete dominance." In incomplete dominance, neither of the alleles is completely dominant over the other, resulting in a heterozygous individual showing a blend of the traits associated with each allele. In our example, the medium-sized leaves are the result of the blended traits from the large (\(P P\)) and small (\(P' P'\)) leaf alleles.

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Most popular questions from this chapter

In four o'clock plants, many flower colors are observed. In a cross involving two true-breeding strains, one crimson and the other white, all of the \(F_{1}\) generation were rose color. In the \(F_{2}\) four new phenotypes appeared along with the \(P_{1}\) and \(F_{1}\) parental colors. The following ratio was obtained: Propose an explanation for the inheritance of these flower colors.

In this chapter, we focused on extensions and modifications of Mendelian principles and ratios. In the process, we encountered many opportunities to consider how this information was acquired. On the basis of these discussions, what answers would you propose to the following fundamental questions? (a) How were early geneticists able to ascertain inheritance patterns that did not fit typical Mendelian ratios? (b) How did geneticists determine that inheritance of some phenotypic characteristics involves the interactions of two or more gene pairs? How were they able to determine how many gene pairs were involved? (c) How do we know that specific genes are located on the sex-determining chromosomes rather than on autosomes? (d) For genes whose expression seems to be tied to the sex of individuals, how do we know whether a gene is X-linked in contrast to exhibiting sex-limited or sex-influenced inheritance?

In foxes, two alleles of a single gene, \(P\) and \(p,\) may result in lethality \((P P),\) platinum coat \((P p),\) or silver coat \((p p) .\) What ratio is obtained when platinum foxes are interbred? Is the \(P\) allele behaving dominantly or recessively in causing (a) lethality; (b) platinum coat color?

The \(A\) and \(B\) antigens in humans may be found in water-soluble form in secretions, including saliva, of some individuals \((\text {Se/Se and Se/se})\) but not in others (se/se). The population thus contains "secretors" and "nonsecretors." (a) Determine the proportion of various phenotypes (blood type and ability to secrete) in matings between individuals that are blood type \(A B\) and type \(O,\) both of whom are \(S e / s e\) (b) How will the results of such matings change if both parents are heterozygous for the gene controlling the synthesis of the H substance \((H h) ?\)

In rats, the following genotypes of two independently assorting autosomal genes determine coat color: A third gene pair on a separate autosome determines whether or not any color will be produced. The \(C C\) and \(C c\) genotypes allow color according to the expression of the \(A\) and \(B\) alleles. However, the \(c c\) genotype results in albino rats regardless of the \(A\) and \(B\) alleles present. Determine the \(F_{1}\) phenotypic ratio of the following crosses: (a) \(A A b b C C \quad \times \quad\) aaBBcc (b) \(A a B B C C \quad \times \quad A A B b c c\) (c) \(A a B b C c \quad \times \quad\) AaBbcc (d) \(A a B B C c \quad \times \quad A a B B C c\) (e) \(A A B b C c \quad \times \quad A A B b c c\)
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