Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

4. Genetic Mapping and Linkage

Mapping Genes

Genetics

4. Genetic Mapping and Linkage

Mapping Genes

Previous problemNext problem

0:55 minutes

Problem 26

Textbook Question

In a certain plant, fruit is either red or yellow, and fruit shape is either oval or long. Red and oval are the dominant traits. Two plants, both heterozygous for these traits, were testcrossed, with the following results.

Determine the location of the genes relative to one another and the genotypes of the two parental plants.

Verified step by step guidance

Step 1: Define the alleles for the traits. Let 'R' represent the dominant allele for red fruit, 'r' for yellow fruit, 'O' for the dominant allele for oval shape, and 'o' for long shape. Since both plants are heterozygous for these traits, their genotypes are RrOo.

Step 2: Perform a testcross. A testcross involves crossing the heterozygous plants (RrOo) with a homozygous recessive plant (rroo). This allows us to observe the offspring phenotypes and determine the linkage or independent assortment of the genes.

Step 3: Analyze the offspring phenotypes. If the genes are on different chromosomes (independent assortment), the offspring phenotypes will follow a 1:1:1:1 ratio. If the genes are linked (on the same chromosome), the offspring phenotypes will show a deviation from this ratio, with more parental-type offspring and fewer recombinant-type offspring.

Step 4: Calculate the recombination frequency. Use the formula:

\frac{Number of recombinant offspring}{Total number of offspring}

. A recombination frequency of less than 50% indicates linkage, while a frequency of 50% or more suggests independent assortment.

Step 5: Determine the parental genotypes and gene location. Based on the recombination frequency and the observed offspring phenotypes, deduce whether the genes are linked or assort independently. If linked, identify the parental genotypes and the arrangement of alleles on the chromosomes (cis or trans configuration).

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

55s

Play a video:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Dominance and Recessiveness

In genetics, dominance refers to the relationship between alleles, where the dominant allele masks the effect of the recessive allele in a heterozygous individual. In this scenario, red fruit color and oval shape are dominant traits, meaning that a plant with at least one dominant allele for either trait will express that trait. Understanding this concept is crucial for predicting the phenotypes of offspring based on parental genotypes.

Heterozygosity and Testcross

Heterozygosity occurs when an individual has two different alleles for a given gene, such as one dominant and one recessive allele. A testcross involves crossing an individual with a homozygous recessive individual to determine the genotype of the heterozygous parent based on the phenotypic ratios of the offspring. This method is essential for revealing the genetic makeup of the plants in the question.

Gene Linkage and Mapping

Gene linkage refers to the tendency of genes located close to each other on a chromosome to be inherited together during meiosis. The results of the testcross can provide insights into whether the genes for fruit color and shape are linked or assort independently. Understanding gene linkage is vital for determining the relative positions of genes on chromosomes and predicting inheritance patterns.

Watch next

Master Mapping Genes with a bite sized video explanation from Kylia

Start learning

Related Videos

Related Practice

Textbook Question

Gene R and gene T are genetically linked. Answer the following questions concerning a dihybrid organism with the genotype Rt/rT:

If r = 0.20, give the expected frequencies of gametes produced by the dihybrid.

415

views

Textbook Question

In a cross in Drosophila, a female heterozygous for the autosomally linked genes a, b, c, d, and e (abcde/ +++++) was testcrossed with a male homozygous for all recessive alleles. Even though the distance between each of the loci was at least 3 map units, only four phenotypes were recovered, yielding the following data:

Why are many expected crossover phenotypes missing? Can any of these loci be mapped from the data given here? If so, determine map distances.

771

views

Textbook Question

Based on our discussion of the potential inaccuracy of mapping (see Figure 5.12), would you revise your answer to Problem 22? If so, how?

544

views

Textbook Question

Traditional gene mapping has been applied successfully to a variety of organisms including yeast, fungi, maize, and Drosophila. However, human gene mapping has only recently shared a similar spotlight. What factors have delayed the application of traditional gene-mapping techniques in humans?

464

views

Textbook Question

Two plants in a cross were each heterozygous for two gene pairs (Ab/aB) whose loci are linked and 25 mu apart. Assuming that crossing over occurs during the formation of both male and female gametes and that the A and B alleles are dominant, determine the phenotypic ratio of their offspring.

1076

views

Textbook Question

Neurofibromatosis 1 (NF1) is an autosomal dominant disorder inherited on human chromosome 17. Part of the analysis mapping the NF1 gene to chromosome 17 came from genetic linkage studies testing segregation of NF1 and DNA genetic markers on various chromosomes. A DNA marker with two alleles, designated 1 and 2, is linked to NF1. The pedigree below shows segregation of NF1 (darkened symbols) and gives genotypes for the DNA marker for each family member.

What is the estimated recombination frequency between the NF1 gene and the DNA marker?

638

views

Textbook Question

Based on the phase of alleles on chromosomes in generation II, is there any evidence of recombination among the eight offspring in generation III? Explain.

447

views

Textbook Question

Determine the alleles for the NF1 gene and the DNA marker gene on each chromosome carried by the four family members in generation I and generation II. Use N for the dominant NF1 allele and n for the recessive allele and assume I-1 is heterozygous for the disease allele (Nn).

790

views

Show more practices

Download the Mobile app

Privacy

Do not sell my personal information

Accessibility

Patent notice

Sitemap