Asked by human
a) Cyprus, a small subtropical island off the coast of Greece, has a population of
1,200,000 people. Calculate how many people in Cyprus you would predict
to carry this trait. Show your work.
(b) Explain how natural selection could influence the frequency of the
thalassemia phenotype in human populations in tropical and subtropical
areas.
All Answers 1
Answered by
GPT-5 mini
AI
I don’t have the trait frequency from your question, so I’ll give (1) the general method you should use, (2) a worked example (two common ways the number is presented), and (3) the explanation for (b).
a) How to calculate the number who carry the trait
- If you are given the carrier (heterozygote) frequency C as a percentage or decimal, multiply by the total population:
number of carriers = C × 1,200,000.
Example: if C = 0.10 (10%), carriers = 0.10 × 1,200,000 = 120,000.
- If you are given the disease (affected homozygote) prevalence q^2 (Hardy–Weinberg), first find q = sqrt(q^2). Then carriers ≈ 2pq = 2(1 − q)q (for small q this ≈ 2q).
Example: if 1 in 250 people are affected, q^2 = 1/250 = 0.004 → q = sqrt(0.004) ≈ 0.0632.
Then carriers ≈ 2(1 − 0.0632)(0.0632) ≈ 0.1183 (11.83%) → 0.1183 × 1,200,000 ≈ 141,960 carriers.
If you tell me the carrier percentage or the affected prevalence given in your problem, I’ll do the exact calculation.
(b) How natural selection can influence thalassemia frequency in tropical/subtropical areas
- Heterozygote advantage (balancing selection): In many malaria-endemic regions, carriers (heterozygotes for thalassemia) have partial resistance to Plasmodium infection or a milder course of malaria compared with non-carriers. That survival/reproductive advantage increases the frequency of the thalassemia allele in those populations.
- Selection against homozygotes: Homozygotes for severe thalassemia often have reduced fitness (illness, early mortality) so there is negative selection against homozygotes. The net result is a balanced polymorphism: the allele is maintained at an intermediate frequency because heterozygotes are favored while homozygotes are disfavored.
- Geographic pattern: Tropical and subtropical regions historically had high malaria pressure, so the protective effect pushed carrier frequencies up in those areas (Mediterranean, parts of Africa, Middle East, South Asia).
- Other factors modifying frequency: founder effects and genetic drift (especially on islands or isolated populations), migration and gene flow, modern medical care (reducing mortality of homozygotes), and public-health measures (malaria control, prenatal screening) can all change allele frequency over time.
If you want, give me the carrier or affected frequency from your worksheet and I’ll compute the exact number for Cyprus.
a) How to calculate the number who carry the trait
- If you are given the carrier (heterozygote) frequency C as a percentage or decimal, multiply by the total population:
number of carriers = C × 1,200,000.
Example: if C = 0.10 (10%), carriers = 0.10 × 1,200,000 = 120,000.
- If you are given the disease (affected homozygote) prevalence q^2 (Hardy–Weinberg), first find q = sqrt(q^2). Then carriers ≈ 2pq = 2(1 − q)q (for small q this ≈ 2q).
Example: if 1 in 250 people are affected, q^2 = 1/250 = 0.004 → q = sqrt(0.004) ≈ 0.0632.
Then carriers ≈ 2(1 − 0.0632)(0.0632) ≈ 0.1183 (11.83%) → 0.1183 × 1,200,000 ≈ 141,960 carriers.
If you tell me the carrier percentage or the affected prevalence given in your problem, I’ll do the exact calculation.
(b) How natural selection can influence thalassemia frequency in tropical/subtropical areas
- Heterozygote advantage (balancing selection): In many malaria-endemic regions, carriers (heterozygotes for thalassemia) have partial resistance to Plasmodium infection or a milder course of malaria compared with non-carriers. That survival/reproductive advantage increases the frequency of the thalassemia allele in those populations.
- Selection against homozygotes: Homozygotes for severe thalassemia often have reduced fitness (illness, early mortality) so there is negative selection against homozygotes. The net result is a balanced polymorphism: the allele is maintained at an intermediate frequency because heterozygotes are favored while homozygotes are disfavored.
- Geographic pattern: Tropical and subtropical regions historically had high malaria pressure, so the protective effect pushed carrier frequencies up in those areas (Mediterranean, parts of Africa, Middle East, South Asia).
- Other factors modifying frequency: founder effects and genetic drift (especially on islands or isolated populations), migration and gene flow, modern medical care (reducing mortality of homozygotes), and public-health measures (malaria control, prenatal screening) can all change allele frequency over time.
If you want, give me the carrier or affected frequency from your worksheet and I’ll compute the exact number for Cyprus.
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