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Chapter 3: Problem 14

Mendel crossed peas with round, green seeds with peas having wrinkled, yellow seeds. All \(\mathrm{F}_{1}\) plants had seeds that were round and yellow. Predict the results of testcrossing these \(F_{1}\) plants.

Short Answer

Expert verified
Answer: The phenotypic ratios of the offspring are 50% round, green seeds and 50% wrinkled, yellow seeds.

Step by step solution

01

Identify the traits and their alleles

In this problem, we have two traits: seed shape (round vs. wrinkled) and seed color (green vs. yellow). Let's assign a letter to represent each trait's dominant and recessive alleles: - Round (dominant): R - Wrinkled (recessive): r - Yellow (dominant): Y - Green (recessive): y The parent plants are: - Round, green seeds: RRyy - Wrinkled, yellow seeds: rrYY
02

Determine the genotypes of \(\mathrm{F}_{1}\) plants

To find the genotype of the \(\mathrm{F}_{1}\) plants, we perform a cross between the parent plants, using a Punnett square: ``` RY Ry rY ry RY RRYY RRYy rrYY rrYy Ry RRYY RRYy rrYY rrYy rY RRyy RRyy rryy rryy ry RRyy RRyy rryy rryy ``` All \(\mathrm{F}_{1}\) plants have the genotype RrYy: round and yellow seeds.
03

Perform a testcross with the \(\mathrm{F}_{1}\) plants

A testcross involves crossing the \(\mathrm{F}_{1}\) plants with an individual that is homozygous recessive for both traits (rryy). This allows us to determine the possible genotypes of the offspring: - \(\mathrm{F}_{1}\) genotype: RrYy - Testcross genotype: rryy
04

Construct a Punnett square for the testcross

Perform a cross between the \(\mathrm{F}_{1}\) plants (RrYy) and the testcross plants (rryy): ``` Ry rY Ry ry ry Rryy rryy Rryy rryy ry Rryy rryy Rryy rryy ry RRyy rrYY RRyy rrYy ry RRyy rrYY RRyy rrYy ```
05

Determine the phenotypes of the offspring

Based on the Punnett square obtained in Step 4, the resulting genotypes and phenotypes of the offspring are: 1. RRyy: round, green seeds (25%) 2. Rryy: round, green seeds (25%) 3. rrYY: wrinkled, yellow seeds (25%) 4. rrYy: wrinkled, yellow seeds (25%) Hence, the predicted phenotypic ratio for the offspring resulting from testcrossing these \(\mathrm{F}_{1}\) plants is 50% round, green seeds, and 50% wrinkled, yellow seeds.

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Most popular questions from this chapter

In Drosophila, gray body color is dominant over ebony body color, while long wings are dominant over vestigial wings. Work the following crosses through the \(F_{2}\) generation, and determine the genotypic and phenotypic ratios for each generation. Assume that the \(P_{1}\) individuals are homozygous: (a) gray, long \(\times\) ebony, vestigial, and (b) gray, vestigial \(\times\) ebony, long, and (c) gray, long \(\times\) gray, vestigial.

How many different types of gametes can be formed by individuals of the following genotypes? What are they in each case? (a) \(A a B b\) (b) \(A a B B\) (c) \(A a B b C c\) (d) \(A a B B c c\) (e) \(A a B b c c,\) and (f) \(A a B b C c D d E e ?\)

Distinguish between homozygosity and heterozygosity.

To assess Mendel's law of segregation using tomatoes, a true- breeding tall variety (SS) is crossed with a true-breeding short variety \((s s) .\) The heterozygous tall plants \((S s)\) were crossed to produce the two sets of \(\mathrm{F}_{2}\) data as follows: $$\begin{array}{cc} \text { Set I } & \text { Set II } \\ 30 \text { tall } & 300 \text { tall } \\ 5 \text { short } & 50 \text { short } \end{array}$$ (a) Using chi-square analysis, analyze the results for both datasets. Calculate \(\chi^{2}\) values, and estimate the \(p\) values in both cases. (b) From the analysis in part (a), what can you conclude about the importance of generating large datasets in experimental settings?

Correlate Mendel's four postulates with what is now known about homologous chromosomes, genes, alleles, and the process of meiosis.
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