Types of Heritability: Broad Sense vs Narrow Sense Explained
Heritable Meaning: Heritability refers to how much genetic variations account for differences in people's characteristics. Estimates of heritability vary from zero to one. A heritability close to zero means that environmental factors account for almost all of the variation in a trait among individuals, with genetic variations having very little effect. Religion, spoken language, and political preferences have a heritability of zero since they are not genetically regulated. A heritability close to one means that genetic variations account for almost all of the variability in a trait, with very little input from environmental influences. Mutagenic diseases cause a slew of problems.
Heritability Definition: In scientific terms, heritability (abbreviated as h2) is a mathematical phenomenon that explains how much of a trait's variance can be attributed to genetic variation. Estimation of a trait's heritability is unique to a single population in a single climate, and it can change over time as conditions change.
What are in Heritable Traits?
Heritable Traits Definition - A heritable trait is essentially a trait in a child that is more similar to the parents' corresponding trait than it is to the same trait in a random person in the population. Prior to its inclusion as a central principle within evolutionary theory, inheritance or heredity was the subject of systematic study.
Heritable traits include height, skin colour, and intelligence, as well as conditions like schizophrenia and autism spectrum disorder etc.
Twin experiments have traditionally been used to estimate heritability. Fraternal twins share 50% of their DNA on average, while identical twins have almost no variations in their DNA. If identical twins tend to have more in common than fraternal twins (when they were raised in the same environment), genetic factors are likely to play a role in deciding the trait. Researchers can measure an estimation of a trait's heritability by comparing identical twins to fraternal twins.
Since heritability is a complex concept to grasp, there are many misunderstandings regarding what it can and cannot tell us about a particular trait:
Heritability does not reveal how much of a trait is determined by genes and how much is determined by environmental factors. So, a heritability of 0.7 does not mean that genetic factors are responsible for 70% of a trait's variability in a population; rather, it means that genetic variations among people are responsible for 70% of the trait's variability in a population.
Knowing a trait's heritability does not tell you which genes or environmental factors are involved, or how significant they are in deciding the trait's heritability.
The terms "heritable" and "familial" are not interchangeable. If members of a family share a trait, it is referred to as familial. Traits may occur in families for a variety of reasons other than biology, such as lifestyle and environmental similarities. For example, spoken language is often passed down through families, but it has no genetic component and thus is not heritable.
Heritability provides little insight into how straightforward or difficult it is to alter a trait. Hair colour, for example, has a high heritability but is very easy to alter with dye.
Narrow Sense Heritability and Broad Sense Heritability
Narrow sense heritability (h2) is defined as the proportion of trait variance that is due to additive genetic factors.
The narrow-sense heritability is the ratio of additive genetic variance to the total phenotypic variance.
H2 = \[\frac{V_{a}}{v_{p}}\]
Broad sense heritability (H2) is defined as the proportion of trait variance that is due to all genetic factors including dominance and gene-gene interactions.
Heritability of Intelligence
In differential psychology and behavioural biology, intelligence is a central concept, and it should be in cognitive neuroscience as well. It's one of the most accurate predictors of critical life outcomes like schooling, occupation, mental and physical wellbeing, and mortality. One of the most heritable behavioural characteristics is intelligence.
The heritability of intelligence rises from around 20% in childhood to possibly 80% in later adulthood. Intelligence encompasses hereditary influences on a wide range of cognitive and learning abilities, which correlate phenotypically at around 0.30 but genetically at around 0.60 or higher.
What is Missing Heritability?
Single genetic variants cannot account for much of the heritability of diseases, habits, and other phenotypes, which is known as the "missing heritability" issue. This is a serious problem in medicine, since a person's vulnerability to disease may be determined by "the cumulative impact of all the background genes rather than the disease genes in the foreground," or the function of genes may have been greatly exaggerated.
In 2008, the issue of "missing heritability" was coined (after the "missing baryon problem" in physics). The Human Genome Project led to optimistic predictions that the large genetic contributions to many traits and diseases (identified by quantitative genetics and behavioural genetics in particular) would soon be mapped and pinned down to specific genes and genetic variants using methods like candidate-gene studies, which used small samples with limited genetic sequencing to focus on sp Though there were a lot of hits, they didn't always hold up in other tests.
FAQs on Understanding Heritability in Biology
1. What is heritability in biology?
Heritability is a statistical measure used in genetics to estimate how much of the variation in a specific trait within a population is due to genetic variation among individuals. It does not tell us how much of a trait is determined by genes, but rather how much of the difference in that trait among people is due to differences in their genes.
2. How is heritability calculated?
Heritability (H²) is calculated using the formula: H² = Vg / Vp. In this formula:
- Vg stands for Genetic Variance, which is the variation in a trait caused by different genes.
- Vp stands for Phenotypic Variance, which is the total observable variation of a trait in a population, resulting from both genetic and environmental factors.
3. What is a simple example of heritability in humans?
A good example is human height. While nutrition and health (environmental factors) play a role, much of the variation in height across a population is due to genetic differences inherited from parents. Therefore, height is considered a trait with high heritability. Similarly, eye colour is another trait with very high heritability.
4. What kinds of traits are considered non-heritable?
Non-heritable traits are those that are acquired during an organism's life and are not passed on through genes. Examples include:
- Scars from an injury.
- Muscle development from exercise.
- The language a person speaks.
- Knowledge gained through education.
5. What is the difference between a trait being 'genetic' and having high 'heritability'?
This is a common point of confusion. A trait being 'genetic' means that genes are involved in its development. For example, having two eyes is genetic. However, since almost everyone has two eyes, the variation for this trait in the population is near zero, making its heritability very low. High heritability applies to traits that vary significantly across a population *because* of genetic differences, like height or skin tone.
6. If a trait has 50% heritability, does it mean 50% of that trait comes from genes?
No, this is a common misconception. A heritability of 50% (or 0.5) does not mean that 50% of your personal trait is from your genes and 50% is from your environment. Instead, it means that 50% of the variation we observe in that trait across the entire population can be attributed to genetic differences among individuals in that population.
7. Why can the heritability of a single trait be different in different environments?
Heritability is not a fixed number for a trait. It can change because it depends on both genetic and environmental variation. For example, if a population lives in a very uniform environment with identical nutrition, any remaining differences in height would be more strongly linked to genes, leading to a higher heritability estimate. In a population with widely varying nutrition, environmental factors would cause more variation, leading to a lower heritability estimate for the same trait.
8. Why is heritability an important concept in fields like agriculture and animal breeding?
Heritability is crucial for breeders because it helps predict how effectively they can change a trait through selective breeding. If a desirable trait, like milk production in cows or crop yield in plants, has high heritability, it means that selecting parents with that trait will likely produce offspring with the same trait. If heritability is low, it suggests that changing the environment (e.g., improving feed or soil quality) would be a more effective strategy.
9. What are the two main types of heritability?
The two main types of heritability that students learn about are:
- Broad-sense heritability (H²): This measures the proportion of phenotypic variance that is due to all genetic factors combined.
- Narrow-sense heritability (h²): This measures only the proportion of variance due to additive genetic effects, which are the effects that are reliably passed from parents to offspring. This type is more useful for predicting the outcomes of selective breeding.
