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I am an Indian with a small thin stature with some deposition of fat around my belly.I was wondering if genes play a role in fat deposition in the body for Indian, Chinese, European or African people. Fat deposition may differ among all these people around the belly, thighs etc. These people also differ in their stamina and speed naturally.

For example here in India in the game of cricket there has been no fast bowler out of 1.2 billion people who can do fast bowling because it requires a lot of strength and stamina.Also on field athleticism is also very bad compared to Australian or South African players.I assume that may be its because of some cultural or genetic problem.

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possible duplicate biology.stackexchange.com/questions/3165/… –  GriffinEvo Nov 26 '13 at 15:52
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up vote 2 down vote accepted

All these characteristics you observe (speed, ability to play cricket, belly size, height, etc…) are what what we call in biology a list of phenotypic traits. So basically speaking, the phenotype is a characteristic of the organism that we can measure or describe (physiological, behavioural, morphological, and life history are four common classes).

In a given population the phenotypic variance (the variance in height for example) can be expressed as the sum of the genetic variance, the environmental variance and the variance due to the interactions between genes and environment.

Mathematically expressed it gives:

$$V_{phenotype} = V_{genetic}+V_{environment} + V_{gen X env}$$

Therefore, for each trait there is a given part of the variance that is explained by the environment and a given part that is explained by the genes. We might go a bit further and defined the concept of heritability (in the narrow sense, see wikipedia article for more info). The heritability (in the narrow sense) is the ratio of the phenotypic variance to the additive genetic variance. Mathematically expressed it gives:

$$h^2 = \frac{V_{additive}}{V_{phenotype}}$$

Each trait has it's given heritability. The heritability can be defined only for a trait in a population (which defines $V_{genetic}$) and its environment (which defines $V_{environment}$).

For example, the heritability of height in human is around 0.8. Which means that 0.8 of the variance in height in the world-wide population is explained by the genetic variance.

In your question, you also used (before your question was re-edited!) the word fitness (also it is not really present in your question). The fitness is a very important concept in biology, it is the ability of an individual to survive and sire offsprings. Our phenotypic traits influence our ability to sire offsprings and therefore our genes influence our fitness. If the whole phenotypic variance is explained by the environmental variance only, then, even the the trait is under selection, there will be no change in allele frequency due to selection. Note: an allele is a gene variant. If eye color is a gene, brown eyes and blue eyes are alleles (to make it easy). This change in allele frequency is called a response $R$ to selection $S$. This link between selection, the response and the narrow sense heritability $h^2$ is given by:

$$R=S\cdot h^2 $$

So to answer your question. Yes, part of the variance in height, belly size, cricket playing ability, etc… is genetically coded. As the fitness depends on phenotypic traits, Yes, the fitness is genetically coded (otherwise there would have no response to selection). Therefore we're not all equal to playing crickets!

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