Chapter 5, Problem 1P

Choose the phrase from the right column that best fits the term in the left column.

a. recombination	1. a statistical method for testing the fit between observed and expected results
b. linkage	2. an ascus containing spores of four different genotypes
c. chi-square test	3. one crossover along a chromosome makes a second nearby crossover less likely
d. chiasma	4. when two loci recombine in less than 50% of gametes
e. tetratype	5. the relative chromosomal location of a gene
f. locus	6. the ratio of observed double crossovers to expected double crossovers
g. coefficient of coincidence	7. individual composed of cells with different genotypes
h. interference	8. formation of new genetic combinations by exchange of parts between homologs
i. parental ditype	9. when the two alleles of a gene are segregated into different cells at the first meiotic division
j. ascospores	10. an ascus containing only two non-recombinant kinds of spores
k. first-division segregation	11. structure formed at the spot where crossing-over occurs between homologs
l. mosaic	12. fungal spores contained in a sac

Summary Introduction

a.

To determine:

The phrase that describes “recombination” among the options given below.

1. A statistical method for testing the fit between observed and expected results.

2. an ascus containing spores of four different genotypes

3. one crossover along a chromosome makes a second nearby crossover less likely

4. when two loci recombine in less than 50% of gametes

5. the relative chromosomal location of a gene

6. the ratio of observed double crossovers to expected double crossovers.

7. individual composed of cells with different genotypes

8. formation of new genetic combinations by exchange of parts between homologs

9. when the two alleles of a gene are segregated into different cells at the first meiotic division

10. an ascus containing only two nonrecombinant kinds of spores

11. structure formed at the spot where crossing-over occurs between homologs

12. fungal spores contained in a sac.

Introduction:

Gene is the basic unit of hereditary information. The way genes transmit physiological, anatomical, and behavioral traits from parents to offspring is termed as heredity.

Answer to Problem 1P

Correct answer:

Recombination: formation of new genetic combinations by exchange of parts between homologs

Explanation of Solution

The process of production of the offspring having a combination of traits, which differ from the parental traits is termed as recombination. It occurs during meiosis in eukaryotes.

Summary Introduction

b.

To determine:

The phrase that describes “linkage” among the options given below.

1. A statistical method for testing the fit between observed and expected results.

2. an ascus containing spores of four different genotypes

3. one crossover along a chromosome makes a second nearby crossover less likely

4. when two loci recombine in less than 50% of gametes

5. the relative chromosomal location of a gene

6. the ratio of observed double crossovers to expected double crossovers.

7. individual composed of cells with different genotypes

8. formation of new genetic combinations by exchange of parts between homologs

9. when the two alleles of a gene are segregated into different cells at the first meiotic division

10. an ascus containing only two nonrecombinant kinds of spores

11. structure formed at the spot where crossing-over occurs between homologs

12. fungal spores contained in a sac.

Introduction:

Gene is termed as a single functional sequence of a DNA or RNA. They are present in the fixed position on a chromosome called locus.

Answer to Problem 1P

Correct answer:

Linkage: when two loci recombine in less than 50% of gametes

Explanation of Solution

The genes that are present too close to each other on the same chromosome tend to inherit together. This phenomenon is termed as linkage. When two loci recombine and form less than 50% of gametes, then the linkage occurs.

Summary Introduction

c.

To determine:

The phrase that describes “chi-square test” among the options given below.

1. A statistical method for testing the fit between observed and expected results.

2. an ascus containing spores of four different genotypes

3. one crossover along a chromosome makes a second nearby crossover less likely

4. when two loci recombine in less than 50% of gametes

5. the relative chromosomal location of a gene

6. the ratio of observed double crossovers to expected double crossovers.

7. individual composed of cells with different genotypes

8. formation of new genetic combinations by exchange of parts between homologs

9. when the two alleles of a gene are segregated into different cells at the first meiotic division

10. an ascus containing only two nonrecombinant kinds of spores

11. structure formed at the spot where crossing-over occurs between homologs

12. fungal spores contained in a sac.

Introduction:

Genetics is the science of heredity in which we study a precise explanation of the biological structures and mechanisms that determine inheritance. Chi-square test is a statistical method in genetics.

Answer to Problem 1P

Correct answer:

Chi-square test: statistical method for testing the fit between observed and expected results.

Explanation of Solution

The chi-square test is a statistical test that compares the observed data with predicted data and measures the deviation of the results from the prediction. In this method, the difference between the observed value and the predicted value is calculated to predict the extent of deviation or match.

Summary Introduction

d.

To determine:

The phrase that describes “chiasma” among the options given below.

1. A statistical method for testing the fit between observed and expected results.

2. an ascus containing spores of four different genotypes

3. one crossover along a chromosome makes a second nearby crossover less likely

4. when two loci recombine in less than 50% of gametes

5. the relative chromosomal location of a gene

6. the ratio of observed double crossovers to expected double crossovers.

7. individual composed of cells with different genotypes

8. formation of new genetic combinations by exchange of parts between homologs

9. when the two alleles of a gene are segregated into different cells at the first meiotic division

10. an ascus containing only two nonrecombinant kinds of spores

11. structure formed at the spot where crossing-over occurs between homologs

12. fungal spores contained in a sac.

Introduction:

Chiasma is a site where the crossing-over or DNA exchange happens in between two homologous chromatids.

Answer to Problem 1P

Correct answer:

Chiasma: the structure formed at the spot where crossing-over occurs between homologs

Explanation of Solution

Chiasma occurs during the prophase I stage of meiosis. It represents linkage and shows the assorting of genes is dependent.

Summary Introduction

e.

To determine:

The phrase that describes “tetratype” among the options given below.

1. A statistical method for testing the fit between observed and expected results.

2. an ascus containing spores of four different genotypes

3. one crossover along a chromosome makes a second nearby crossover less likely

4. when two loci recombine in less than 50% of gametes

5. the relative chromosomal location of a gene

6. the ratio of observed double crossovers to expected double crossovers.

7. individual composed of cells with different genotypes

8. formation of new genetic combinations by exchange of parts between homologs

9. when the two alleles of a gene are segregated into different cells at the first meiotic division

10. an ascus containing only two nonrecombinant kinds of spores

11. structure formed at the spot where crossing-over occurs between homologs

12. fungal spores contained in a sac.

Introduction:

tetratype (T) is a fungal ascus that has four kinds of spores, or haploid cells: two different parental types and two different recombinant types.

Answer to Problem 1P

Correct answer:

Tetratype: an ascus containing spores of four different genotypes

Explanation of Solution

A two-strand single crossover or a three-strand double crossover between the two genes that result in the formation of both parental and non-parental type recombination is termed as tetratype. All four genotypes are present (50% parental type and 50% non-parental type).

Summary Introduction

f.

To determine:

The phrase that describes “locus” among the options given below.

1. A statistical method for testing the fit between observed and expected results.

2. an ascus containing spores of four different genotypes

3. one crossover along a chromosome makes a second nearby crossover less likely

4. when two loci recombine in less than 50% of gametes

5. the relative chromosomal location of a gene

6. the ratio of observed double crossovers to expected double crossovers.

7. individual composed of cells with different genotypes

8. formation of new genetic combinations by exchange of parts between homologs

9. when the two alleles of a gene are segregated into different cells at the first meiotic division

10. an ascus containing only two nonrecombinant kinds of spores

11. structure formed at the spot where crossing-over occurs between homologs

12. fungal spores contained in a sac.

Introduction:

Locus is a designated location on a chromosome and it refers to a gene.

Answer to Problem 1P

Correct answer:

Locus: the relative chromosomal location of a gene

Explanation of Solution

Gene is located on a chromosome at a specific location, called locus. In a homologous pair of chromosomes, alternate forms of a gene are present at the same loci for a particular trait.

Summary Introduction

g.

To determine:

The phrase that describes “coefficient of coincidence” among the options given below.

1. A statistical method for testing the fit between observed and expected results.

2. an ascus containing spores of four different genotypes

3. one crossover along a chromosome makes a second nearby crossover less likely

4. when two loci recombine in less than 50% of gametes

5. the relative chromosomal location of a gene

6. the ratio of observed double crossovers to expected double crossovers.

7. individual composed of cells with different genotypes

8. formation of new genetic combinations by exchange of parts between homologs

9. when the two alleles of a gene are segregated into different cells at the first meiotic division

10. an ascus containing only two nonrecombinant kinds of spores

11. structure formed at the spot where crossing-over occurs between homologs

12. fungal spores contained in a sac.

Introduction:

The ratio of observed double crossovers to expected double crossovers is termed as Coefficient of coincidence.

Answer to Problem 1P

Correct answer:

Coefficient of coincidence: the ratio of observed double crossovers to expected double crossovers

Explanation of Solution

Coefficient of coincidence is the ratio between the actual frequency of double crossovers observed in an experiment and the number of double crossovers expected on the basis of independent probabilities.

Summary Introduction

h.

To determine:

The phrase that describes “interference” among the options given below.

1. A statistical method for testing the fit between observed and expected results.

2. an ascus containing spores of four different genotypes

3. one crossover along a chromosome makes a second nearby crossover less likely

4. when two loci recombine in less than 50% of gametes

5. the relative chromosomal location of a gene

6. the ratio of observed double crossovers to expected double crossovers.

7. individual composed of cells with different genotypes

8. formation of new genetic combinations by exchange of parts between homologs

9. when the two alleles of a gene are segregated into different cells at the first meiotic division

10. an ascus containing only two nonrecombinant kinds of spores

11. structure formed at the spot where crossing-over occurs between homologs

12. fungal spores contained in a sac.

Introduction:

Chromosomal interference is the phenomenon of crossovers not occurring independently.

Answer to Problem 1P

Correct answer:

Interference: one crossover along a chromosome makes a second nearby crossover less likely

Explanation of Solution

Crossing over does not uniformly take place along a chromosome. In addition, the formation of one chiasma decreases the probability of another chiasma formation in an immediately adjacent region of the chromosome. This lack of independence is termed as interference.

Summary Introduction

i.

To determine:

The phrase that describes “parental ditype” among the options given below.

1. A statistical method for testing the fit between observed and expected results.

2. an ascus containing spores of four different genotypes

3. one crossover along a chromosome makes a second nearby crossover less likely

4. when two loci recombine in less than 50% of gametes

5. the relative chromosomal location of a gene

6. the ratio of observed double crossovers to expected double crossovers.

7. individual composed of cells with different genotypes

8. formation of new genetic combinations by exchange of parts between homologs

9. when the two alleles of a gene are segregated into different cells at the first meiotic division

10. an ascus containing only two nonrecombinant kinds of spores

11. structure formed at the spot where crossing-over occurs between homologs

12. fungal spores contained in a sac.

Introduction:

Parental ditype (PD) is a tetrad that has four parental class haploid cells.

Answer to Problem 1P

Correct answer:

Parental ditype: an ascus containing only two nonrecombinant kinds of spores

Explanation of Solution

Parental ditype condition only considers parental type. It means no crossing over occurs, and therefore, overall parental combinations are obtained.

Summary Introduction

j.

To determine:

The phrase that describes “ascospores” among the options given below.

1. A statistical method for testing the fit between observed and expected results.

2. an ascus containing spores of four different genotypes

3. one crossover along a chromosome makes a second nearby crossover less likely

4. when two loci recombine in less than 50% of gametes

5. the relative chromosomal location of a gene

6. the ratio of observed double crossovers to expected double crossovers.

7. individual composed of cells with different genotypes

8. formation of new genetic combinations by exchange of parts between homologs

9. when the two alleles of a gene are segregated into different cells at the first meiotic division

10. an ascus containing only two nonrecombinant kinds of spores

11. structure formed at the spot where crossing-over occurs between homologs

12. fungal spores contained in a sac.

Introduction:

Ascospores of fungi are the haploid cells that result from meiosis. They are also known as haplospores.

Answer to Problem 1P

Correct answer:

Ascospores: fungal spores contained in a sac

Explanation of Solution

Various species of fungi provide a unique opportunity for genetic analysis because they house all four haploid products of each meiosis in a sac called an ascus. A spore that is contained in an ascus or was produced inside an ascus is termed as an ascospore.

Summary Introduction

k.

To determine:

The phrase that describes “first-division segregation” among the options given below.

1. A statistical method for testing the fit between observed and expected results.

2. an ascus containing spores of four different genotypes

3. one crossover along a chromosome makes a second nearby crossover less likely

4. when two loci recombine in less than 50% of gametes

5. the relative chromosomal location of a gene

6. the ratio of observed double crossovers to expected double crossovers.

7. individual composed of cells with different genotypes

8. formation of new genetic combinations by exchange of parts between homologs

9. when the two alleles of a gene are segregated into different cells at the first meiotic division

10. an ascus containing only two nonrecombinant kinds of spores

11. structure formed at the spot where crossing-over occurs between homologs

12. fungal spores contained in a sac.

Introduction:

Segregation is the separation of alleles during gamete formation, in which one allele of each gene goes to each gamete.

Answer to Problem 1P

Correct answer:

First-division segregation: when the two alleles of a gene are segregated into different cells at the first meiotic division

Explanation of Solution

The alleles of the gene must separate in the first meiotic division in the absence of crossing over between a gene and its centromere. This separation is termed as first division segregation.

Summary Introduction

l.

To determine:

The phrase that describes “mosaic” among the options given below.

1. A statistical method for testing the fit between observed and expected results.

2. an ascus containing spores of four different genotypes

3. one crossover along a chromosome makes a second nearby crossover less likely

4. when two loci recombine in less than 50% of gametes

5. the relative chromosomal location of a gene

6. the ratio of observed double crossovers to expected double crossovers.

7. individual composed of cells with different genotypes

8. formation of new genetic combinations by exchange of parts between homologs

9. when the two alleles of a gene are segregated into different cells at the first meiotic division

10. an ascus containing only two nonrecombinant kinds of spores

11. structure formed at the spot where crossing-over occurs between homologs

12. fungal spores contained in a sac.

Introduction:

Genetic mosaic is an organism containing tissues of different genotypes.

Answer to Problem 1P

Correct answer:

Mosaic: individual composed of cells with different genotypes

Explanation of Solution

An individual composed of cells with different genotypes is termed as a mosaic. For example, the females have two alleles for every gene on the X-chromosome. The males have only one allele on the X-chromosome. The female is a mosaic for the expression of the genes on the X chromosome.