- What will be the approximate effective population size in a panmicitic population of 240 with 200 females and 40 polygamous males?
(1) 160 (2) 133
(3) 63 (4)67
Understanding the Scenario
Suppose you have a panmictic population (random mating) of 240 individuals, with 200 females and 40 polygamous males. The question is: What is the approximate effective population size?
Formula for Effective Population Size
For populations with unequal numbers of breeding males ($N_m$) and females ($N_f$), the standard formula is:
Ne=4NmNfNm+Nf
Where:
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$N_m$ = number of breeding males
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$N_f$ = number of breeding females
This formula accounts for the fact that a skewed sex ratio reduces the number of individuals effectively passing genes to the next generation.
Step-by-Step Calculation
Given:
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$N_m = 40$
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$N_f = 200$
Plug these values into the formula:
Ne=4×40×20040+200Ne=4×8,000240Ne=32,000240Ne≈133
Therefore, the effective population size in this scenario is approximately 133.
Why Is Effective Population Size Important?
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Genetic Drift: Smaller $N_e$ means stronger genetic drift, leading to faster loss of genetic diversity.
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Inbreeding: Low $N_e$ increases the risk of inbreeding and expression of harmful recessive traits.
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Conservation: Conservation programs use $N_e$ to assess population health and design breeding strategies to maximize genetic diversity.
Key Takeaways
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Sex ratio matters: Even with a large census size, a skewed sex ratio can dramatically lower the effective population size.
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Polygamous systems: When a few males mate with many females, $N_e$ drops, making the population more vulnerable to genetic drift.
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Conservation planning: Maintaining a balanced sex ratio and larger $N_e$ is crucial for the long-term survival of species.
Correct answer:
(2) 133
