Chapter 3, Mendelian Genetics Video Solutions, Essentials of Genetics

Problem 1

When working out genetics problems in this and succeeding chapters, always assume that members of the $P_{1}$ generation are homozygous, unless the information or data you are given require you to do
otherwise
In this chapter, we focused on the Mendelian postulates, probability, and pedigree analysis. We also considered some of the methods and reasoning by which these ideas, concepts, and techniques were developed. On the basis of these discussions, what answers would you propose to the following questions:
(a) How was Mendel able to derive postulates concerning the behavior of "unit factors" during gamete formation, when he could not directly observe them?
(b) How do we know whether an organism expressing a dominant trait is homozygous or heterozygous?
(c) In analyzing genetic data, how do we know whether deviation from the expected ratio is due to chance rather than to another, independent factor?
(d) since experimental crosses are not performed in humans, how do we know how traits are inherited?

Celine Ibrahim

Numerade Educator

00:45

Problem 2

Review the Chapter Concepts list on p. $31 .$ The first five concepts provide a modern interpretation of Mendelian postulates. Based on these concepts, write a short essay that correlates Mendel's four postulates with what is now known about genes, alleles, and homologous chromosomes.

Jennifer Stoner

Numerade Educator

02:04

Problem 3

In a cross between a black and a white guinea pig, all members of the $F_{1}$ generation are black. The $F_{2}$ generation is made up of approximately $3 / 4$ black and $1 / 4$ white guinea pigs. Diagram this cross, and show the genotypes and phenotypes.

Jackson Miner

Numerade Educator

02:20

Problem 4

Albinism in humans is inherited as a simple recessive trait. Determine the genotypes of the parents and offspring for the following families. When two alternative genotypes are possible, list both.
(a) Two parents without albinism have five children, four without albinism and one with albinism.
(b) A male without albinism and a female with albinism have six children, all without albinism.

Jackson Miner

Numerade Educator

01:16

Problem 5

In a problem involving albinism (see Problem 4 ), which of Mendel's postulates are demonstrated?

Parvati Devi

Numerade Educator

02:12

Problem 6

Why was the garden pea a good choice as an experimental organism in Mendel's work?

Elaine Dorr

Numerade Educator

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Problem 7

Mendel crossed peas having round seeds and yellow cotyledons with peas having wrinkled seeds and green cotyledons. All the $\mathrm{F}_{1}$ plants had round seeds with yellow cotyledons. Diagram this cross through the $\mathrm{F}_{2}$ generation, using both the Punnett square and forked-line methods.

Kaela Piechowicz

Numerade Educator

00:15

Problem 8

Refer to the Now Solve This problem 3.2 on $\mathrm{p} .39 .$ Are any of the crosses in this problem testcrosses? If so, which one(s)?

Amy Jiang

Numerade Educator

05:42

Problem 9

Which of Mendel's postulates can be demonstrated in the Now Solve This problem 3.2 on $\mathrm{p} .39$ but not in Problem 3 above? Define this postulate.

Prabhakar Kumar

Numerade Educator

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Problem 10

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

Marisa A

Numerade Educator

01:09

Problem 11

Distinguish between homozygosity and heterozygosity.

Jackson Miner

Numerade Educator

02:43

Problem 12

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.

Hailey Tomashek

Numerade Educator

03:23

Problem 13

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) $A a B b C c D d E e ?$

Jackson Miner

Numerade Educator

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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.

Kaela Piechowicz

Numerade Educator

02:21

Problem 15

Shown are $\mathrm{F}_{2}$ results of two of Mendel's monohybrid crosses. State a null hypothesis that you will test using chi-square analysis. Calculate the $\chi^{2}$ value and determine the $p$ value for both crosses; then interpret the $p$ values. Which cross shows a greater amount of deviation?
(a) Full pods 882 Constricted pods 299
(b) Violet flowers 705 White flowers

Eric Goldman

Numerade Educator

01:49

Problem 16

A geneticist, in assessing data that fell into two phenotypic classes, observed values of $250: 150 .$ He decided to perform chi- square analysis using two different null hypotheses: (a) the data fit a 3: 1 ratio; and (b) the data fit a 1: 1 ratio. Calculate the $\chi^{2}$ values for each hypothesis. What can you conclude about each hypothesis?

Jackson Miner

Numerade Educator

01:01

Problem 17

The basis for rejecting any null hypothesis is arbitrary. The researcher can set more or less stringent standards by deciding to raise or lower the critical $p$ value. Would the use of a standard of $p=0.10$ be more or less stringent in failing to reject the null hypothesis? Explain.

Harsh Gadhiya

Numerade Educator

01:58

Problem 18

Consider three independently assorting gene pairs, $A / a, B / b,$ and $C / c,$ where each demonstrates typical dominance $(A-, B-, C-)$ and recessiveness $(a a, b b, c c) .$ What is the probability of obtain ing an offspring that is $A A B b C c$ from parents that are $A a B b C C$ and $A A B b C c ?$

Jackson Miner

Numerade Educator

01:05

Problem 19

What is the probability of obtaining a triply recessive individual from the parents shown in Problem $18 ?$

Jackson Miner

Numerade Educator

01:45

Problem 20

Of all offspring of the parents in Problem $18,$ what proportion will express all three dominant traits?

Jackson Miner

Numerade Educator

01:22

Problem 21

The following pedigree follows the inheritance of myopia (nearsightedness) in humans. Predict whether the disorder is inherited as a dominant or a recessive trait. Based on your prediction, indicate the most probable genotype for each individual.

Michelle Bandeira

Numerade Educator

03:52

Problem 22

Draw all possible conclusions concerning the mode of inheritance of the trait expressed in each of the following limited pedigrees. (Each case is based on a different trait.)

Jorge Villanueva

Numerade Educator

01:31

Problem 23

Two true-breeding pea plants are crossed. One parent is round, terminal, violet, constricted, while the other expresses the contrasting phenotypes of wrinkled, axial, white, full. The four pairs of contrasting traits are controlled by four genes, each located on a separate chromosome. In the $F_{1}$ generation, only round, axial, violet, and full are expressed. In the $\mathrm{F}_{2}$ generation, all possible combinations of these traits are expressed in ratios consistent with Mendelian inheritance.
(a) What conclusion can you draw about the inheritance of these traits based on the $\mathrm{F}_{1}$ results?
(b) Which phenotype appears most frequently in the $\mathrm{F}_{2}$ results? Write a mathematical expression that predicts the frequency of occurrence of this phenotype.
(c) Which $\mathrm{F}_{2}$ phenotype is expected to occur least frequently? Write a mathematical expression that predicts this frequency.
(d) How often is either $P_{1}$, phenotype likely to occur in the $F_{2}$ generation?
(e) If the $F_{1}$ plant is testcrossed, how many different phenotypes will be produced?

Anand Jangid

Numerade Educator

02:02

Problem 24

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?

Anna Miller

Numerade Educator