Quantitative Genetics Overview

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is heritability and explain the difference between broad-sense heritability (H²) and narrow-sense heritability (h²)?

Heritability is the proportion of phenotypic variation that is due to genetic variation. Broad-sense heritability (H²) is the proportion of phenotypic variation that is due to total genetic variation, while narrow-sense heritability (h²) is the proportion of phenotypic variation that is due to additive genetic variation.

What does a breeder need to know to predict how much a trait will change in response to selection?

A breeder needs to know the heritability of the trait and the selection differential. The selection differential is the difference between the mean of the selected parents and the mean of the starting population. The heritability of the trait is a measure of how much of the variation in the trait is due to genetics. The breeder can then use the breeder's equation (R = h²S) to predict the response to selection.

Heritability is a fixed value for a particular trait.

False

What is heterosis and how is it relevant to agriculture?

Heterosis is the phenomenon where the offspring of two different inbred lines have a higher phenotype than either parent. It is a result of hybrid vigor and is often observed in crops and livestock. Heterosis can be exploited in agriculture to improve crop yields and livestock production. Signup and view all the answers

What is transgressive segregation and how is it relevant to agriculture?

Transgressive segregation is the phenomenon where the offspring of two different inbred lines have phenotypes that are outside the range of either parent. It is a result of the recombination of alleles that were not present in either parent. Transgressive segregation can be exploited in agriculture to create new varieties of crops and livestock that have desirable traits that are not present in either parent. Signup and view all the answers

What are quantitative trait loci (QTLs) and how can they be mapped?

Quantitative trait loci (QTLs) are regions of the chromosome that contain genes that contribute to quantitative traits. They can be mapped by using linkage analysis to identify markers that are associated with the trait of interest. QTL mapping is a powerful tool that can be used to identify genes that contribute to complex traits. Signup and view all the answers

What are genome-wide association studies (GWAS) and why would they be relevant?

Genome-wide association studies (GWAS) are a type of genetic association study that looks for associations between genetic variation and disease or traits. GWAS can be used to identify genes that contribute to disease or traits, and they can also be used to develop new therapeutic agents. Signup and view all the answers

What is the role of genetics and environment in disease?

Many diseases are caused by a combination of genetic and environmental factors. Genetic factors can increase an individual's susceptibility to disease, while environmental factors can trigger the development of disease. For example, an individual may inherit a genetic predisposition to heart disease, but they may not develop heart disease if they live a healthy lifestyle. Signup and view all the answers

How can quantitative genetics data be used in conservation?

Quantitative genetics data can be used in conservation to identify species that are at risk of losing genetic diversity and to develop strategies for managing these species. For example, quantitative genetics data can be used to identify populations that have low genetic diversity, to assess the risk of inbreeding, and to develop breeding programs to increase genetic diversity. Signup and view all the answers

Which of the following factors can affect the heritability of a trait?

All of the above Signup and view all the answers

Study Notes

Quantitative Genetics

Quantitative traits are contrasted with qualitative traits. Qualitative traits are discrete, while quantitative traits are continuous.
Quantitative traits are influenced by many genes and environmental factors.
Experimental results illustrate the impact of genetic and environmental factors on a trait.
Phenotype descriptions can be complex. Categorisation might not be appropriate. For example, height could be tall, less tall, medium, short, very short etc. and many genes/alleles may affect height.
Multiple interacting genes influence quantitative traits.
Each additional gene may result in one more unit of trait.
The number of phenotypes increases rapidly as the number of loci increases.
Quantitative traits result in a continuous distribution of phenotypes. Continuous distribution example: flower length.
Genetics and environment work together to shape quantitative traits.
The combined effect of genes results in a continuous spectrum of phenotypes, rather than just a few distinct types.

One Locus

Each uppercase allele contributes to trait increase (e.g. ladybug spots)
Example: ladybug spot count, one allele = 1 more spot

Multiple Loci

In this case, the number of loci will increase. Phenotypes, such as kernel colour in wheat, can be inherited with respect to multiple alleles at multiple loci.

Real Example: Kernel Colour of Wheat

Nilsson-Ehle's experiment.
Cross-breeding wheat with white and purple kernels revealed additive gene action in determining kernel colour

Edward East's Experiment

Experiment: Flower length in Nicotiana longiflora.
The experiment involved two pure-breeding lines of different lengths.
The F1 generation had intermediate lengths.
The F2 generation exhibited increased variation in lengths.
Selecting individuals with extreme lengths over several generations produced parental-like phenotypes, showing they were genetically similar

Phenotypic & Environmental Variance (Vp, VG, VE)

Environmental factors influence phenotype, even with identical genotypes.
Environmental variance (VE) is the component of phenotypic variation due to environmental factors (e.g., differences in nutrition, temperature).
Genetic variance (VG) is the component of phenotypic variation due to genetic factors.
Phenotypic variance (VP) is a composite value of both environmental and genetic variances (VP = VG + VE).

Genetic-Environmental Interaction

The effect of the environment may differ depending on the genotype.
e.g., one genotype may grow larger in dry environments, while a another may be larger in wet environments.

Quantitative Trait Loci (QTL)s

QTLs are chromosomal regions containing loci correlated with quantitative traits.
Mapping QTLs involves breeding strains that differ substantially in the trait of interest, and assessing the inheritance patterns.
QTLs are associated with a particular trait.

Heritability (H²)

Heritability (H²) is the proportion of phenotypic variation due to genetic variation.
Heritability varies depending on the population in question.
Heritability estimates are context-dependent (e.g. particular population, in a specific environment).
Using heritability, breeding can be more effective.
Estimates of the proportion of phenotypic variance due to additive genetic variance are useful in selective breeding. Higher estimates indicate greater resemblance between parents and offspring.
For conservation work, low heritability for survival traits indicate more influence from the environment and can be important for survival in different environments.

Response to Selection

Heritability estimates help predict how much a trait will change in response to selection programs.
Selection differential (S) is the difference in the mean phenotype between the selected individuals and the average population.
Response to selection (R) is the difference between the mean phenotype of the offspring and the average population.
Heritability (h2) = Response to selection (R) / Selection Differential (S)

Heterosis

Also called hybrid vigour
Can lead to higher values in F1 offspring

Transgressive Segregation

Result in offspring with trait values outside the range of parental values in F2 and later generations.
Extremely useful in selective breeding

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the concepts of quantitative traits and their distinction from qualitative traits. This quiz delves into the influence of multiple genes and environmental factors on phenotypes, illustrating how they contribute to continuous distributions. Test your understanding of how genetics shapes quantitative traits in various organisms.