Textbook Question
In a population of tomato plants, mean fruit weight is 60 g and h² is 0.3. Predict the mean weight of the progeny if tomato plants whose fruit averaged 80 g were selected from the original population and interbred.
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Ch. 25 - Quantitative Genetics and Multifactorial Traits
Chapter 24, Problem 20
Many traits of economic or medical significance are determined by quantitative trait loci (QTLs) in which many genes, usually scattered throughout the genome, contribute to expression.
What is meant by the term cosegregate in the context of QTL mapping? Why are markers such as RFLPs, SNPs, and microsatellites often used in QTL mapping?
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Understand the term 'cosegregate': In the context of QTL mapping, 'cosegregate' refers to the phenomenon where a genetic marker and a trait of interest are inherited together more often than would be expected by chance. This suggests that the marker is physically close to a gene influencing the trait on the chromosome.
Explore the role of genetic markers: Genetic markers like RFLPs (Restriction Fragment Length Polymorphisms), SNPs (Single Nucleotide Polymorphisms), and microsatellites are used in QTL mapping because they serve as reference points on the genome. They help in identifying regions of the genome that are associated with specific traits.
Consider the advantages of using RFLPs: RFLPs are variations in DNA sequences that can be detected by the presence of fragments of different lengths after digestion with specific restriction enzymes. They are useful in QTL mapping because they are co-dominant markers, allowing for the detection of heterozygotes.
Examine the benefits of SNPs: SNPs are the most common type of genetic variation among people. They are single base-pair changes in the DNA sequence and are abundant throughout the genome, making them highly useful for fine mapping of QTLs.
Discuss the utility of microsatellites: Microsatellites, or short tandem repeats (STRs), are repeating sequences of 2-6 base pairs of DNA. They are highly polymorphic, which makes them excellent markers for QTL mapping as they provide high resolution in detecting genetic linkage.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Cosegregation
Cosegregation refers to the phenomenon where two or more genetic markers are inherited together more often than would be expected by chance. In the context of QTL mapping, it indicates that a specific marker is linked to a trait of interest, allowing researchers to track the inheritance of traits alongside these markers. This is crucial for identifying the genetic basis of quantitative traits.
Quantitative Trait Loci (QTL)
Quantitative Trait Loci (QTL) are regions of the genome that are associated with the variation in a quantitative trait, which is typically influenced by multiple genes. QTL mapping helps identify these regions by correlating phenotypic data with genetic markers, enabling researchers to understand the genetic architecture of complex traits, such as height or disease susceptibility.
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Genetic Markers
Genetic markers, such as RFLPs (Restriction Fragment Length Polymorphisms), SNPs (Single Nucleotide Polymorphisms), and microsatellites, are specific sequences in the genome that can be used to identify individuals or species. In QTL mapping, these markers serve as reference points to track the inheritance of traits and help in locating QTLs by providing a means to analyze genetic variation and linkage to phenotypic traits.
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Related Practice
Textbook Question
In a population of 100 inbred, genotypically identical rice plants, variance for grain yield is 4.67. What is the heritability for yield? Would you advise a rice breeder to improve yield in this strain of rice plants by selection?
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Textbook Question
Many traits of economic or medical significance are determined by quantitative trait loci (QTLs) in which many genes, usually scattered throughout the genome, contribute to expression.
What general procedures are used to identify such loci?
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Textbook Question
A 3-inch plant was crossed with a 15-inch plant, and all F₁ plants were 9 inches. The F₂ plants exhibited a 'normal distribution,' with heights of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 inches.
What ratio will constitute the 'normal distribution' in the F₂?
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Textbook Question
A 3-inch plant was crossed with a 15-inch plant, and all F₁ plants were 9 inches. The F₂ plants exhibited a 'normal distribution,' with heights of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 inches.
What will be the outcome if the F₁ plants are testcrossed with plants that are homozygous for all nonadditive alleles?
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Textbook Question
In a cross between a strain of large guinea pigs and a strain of small guinea pigs, the F₁ are phenotypically uniform, with an average size about intermediate between that of the two parental strains. Among 1014 F₂ individuals, 3 are about the same size as the small parental strain and 5 are about the same size as the large parental strain. How many gene pairs are involved in the inheritance of size in these strains of guinea pigs?
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