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

3. Extensions to Mendelian Inheritance

Variations of Dominance

Genetics

3. Extensions to Mendelian Inheritance

Variations of Dominance

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2:26 minutes

Problem 3

Textbook Question

In shorthorn cattle, coat color may be red, white, or roan. Roan is an intermediate phenotype expressed as a mixture of red and white hairs. The following data were obtained from various crosses:

How is coat color inherited? What are the genotypes of parents and offspring for each cross?

Verified step by step guidance

Understand the problem: The coat color in shorthorn cattle exhibits three phenotypes—red, white, and roan. Roan is an intermediate phenotype, suggesting incomplete dominance or codominance. We need to determine the inheritance pattern and assign genotypes to the parents and offspring.

Step 1: Assign symbols to represent the alleles. Let 'R' represent the allele for red coat color and 'W' represent the allele for white coat color. Since roan is an intermediate phenotype, it is likely that roan individuals are heterozygous (RW).

Step 2: Analyze the crosses provided in the problem. For each cross, determine the phenotypes of the parents and offspring. Use a Punnett square to predict the genotypic and phenotypic ratios for each cross. For example, if a red (RR) is crossed with a white (WW), all offspring will be roan (RW).

Step 3: For each cross, assign genotypes to the parents based on their phenotypes. Then, use the Punnett square to determine the expected genotypes and phenotypes of the offspring. For example, if two roan (RW) individuals are crossed, the Punnett square will show a 1:2:1 genotypic ratio (1 RR: 2 RW: 1 WW) and a 1:2:1 phenotypic ratio (1 red: 2 roan: 1 white).

Step 4: Summarize the inheritance pattern. Based on the results of the crosses, coat color in shorthorn cattle is inherited through codominance, where both alleles (R and W) are expressed in the heterozygous state (RW) as the roan phenotype. The genotypes of the parents and offspring for each cross can be determined using the Punnett square analysis.

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Key Concepts

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

Inheritance Patterns

Coat color in shorthorn cattle demonstrates a classic example of incomplete dominance, where neither allele is completely dominant over the other. In this case, the red and white alleles produce a roan phenotype when combined, resulting in offspring that exhibit a blend of both parental traits. Understanding this pattern is crucial for predicting the phenotypes and genotypes of the offspring based on the parental combinations.

Genotype and Phenotype

The genotype refers to the genetic makeup of an organism, while the phenotype is the observable expression of that genotype. In shorthorn cattle, the genotypes can be represented as RR (red), WW (white), and RW (roan). Analyzing the genotypes of the parents allows us to determine the possible phenotypes of the offspring in various crosses, which is essential for answering the question.

Punnett Squares

Punnett squares are a tool used in genetics to predict the genotypes of offspring from parental crosses. By laying out the possible gametes from each parent, a Punnett square helps visualize the potential combinations and their corresponding phenotypes. This method is particularly useful in this scenario to systematically analyze the inheritance of coat color in shorthorn cattle and derive the genotypes of both parents and offspring.

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