Question

What is true about the isolated small tribal populations ?
A) Hereditary diseases like color blindness do not spread in the isolated population.
B) Wrestlers who develop strong body muscles in their lifetime pass this character onto their progeny.
C) There is no change in population size as they have a large gene pool.
D) There is a decline in population as boys marry girls only from their own tribe.

Answer 1

Since the population of the tribal community is small and isolated from other tribal communities , the genes of them will remain in that area and not migrate , also the progeny will be the result of inbreeding.

Complete answer:

Color Blindness is a Mendelian disorder in which the person fails to discriminate between red and green colour due to defect in either red or green cones of the eye and sees an intermediate colour as grey.
It is a sex – linked recessive disorder occurring due to mutation in certain genes present in the X chromosome. The gene pool of small isolated populations will be small , therefore inbreeding in them will cause hereditary diseases like color blindness to spread in the isolated population. Males are more affected and females will act as carriers in most of the cases , therefore due to small gene pool and marriage between close individuals , colour blindness will spread in the population. This fact contradicts the first option.
There are two types of characters :acquired characters and inherited characters. The characters which are acquired in the lifetime and not inherited from the parents are called as acquired characters and the characters which are inherited from the parents to the progeny are called as inherited characters.
Wrestlers acquire strong muscles , acquire this character in their lifetime through their workout and diet and not the genes. These characters are not transmitted to their progeny because genes play no role here. It is an example of acquired character.
In an inbreeding population , the sum total of genes of all the individuals of the population is called a gene pool. This gene pool consists of a large number of genes which will vary in their frequency.
The small isolated tribal population will have a small gene pool and the frequencies in the gene pool depend on the proportion of various genotypes in the total population. Due to isolation of the population , the genes remain confined in that area itself and also no gene from outside enters in. >Therefore they won’t have a large gene pool and hence this is not the correct answer too.
When there is a transfer of genes between the populations differing in genetic constitution , then that phenomenon is known as gene migration or gene flow. If a population is isolated , then there is no possibility of gene flow.
Since this population of tribes is isolated , then there would be no gene flow or gene migration since the boys would marry the girls of their own tribe and hence the population will decline.
The decline in population occurs due to a phenomenon similar to inbreeding depression. Here homozygosity is increased which reduces the reproductive fitness of the individual , therefore reducing the population.
A similar phenomenon is observed in livestock and the phenomenon is called as inbreeding depression. This occurs when there is continued inbreeding or closed inbreeding and as a result reduces fertility or productivity.

Therefore this makes it clear that option (D) is the correct answer.

Note: Inbreeding has many advantages as well. It helps us to evolve a pureline in any animal and increases homozygosity. It helps us to expose harmful recessive genes and simultaneously helps in the accumulation of superior genes and elimination of less desirable genes.