Questions and Answers
What is the estimated frequency of carriers in a population where the frequency of the disease allele is 0.1?
In the case of autosomal dominant diseases, what can be inferred about the affected individuals in a population when there are many heterozygotes?
What does the term q2 represent in the context of recessive diseases?
When applying Hardy-Weinberg equilibrium to X-linked recessive diseases, what does the frequency q correspond to?
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What is the expected frequency of homozygous affected individuals if the prevalence of an autosomal dominant disease is 1/500?
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What genetic condition must be met for the Hardy-Weinberg equilibrium to be applicable in a population?
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Which of the following conditions could disrupt the Hardy-Weinberg equilibrium?
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What role do females play in the expression of recessive alleles according to the information provided?
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What is necessary for the Hardy-Weinberg equilibrium to maintain consistent genotype proportions in a population?
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How does gene flow impact the Hardy-Weinberg equilibrium?
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Study Notes
Autosomal Recessive Diseases
- Asymptomatic carriers are heterozygotes (Aa).
- Frequency of diseased individuals represented as f(aa) = q².
- If q² = 0.01, then q = 0.1, leading to p (f(A)) = 0.9 since p + q = 1.
- Carrier frequency (f(Aa)) calculated using 2pq: 2(0.9)(0.1) = 0.18, indicating 18% of the population are carriers.
Genotype Frequencies for Autosomal Dominant Diseases
- Most affected individuals are heterozygotes (2pq).
- If allele frequencies approximate p to be close to 1, use 2q for calculations.
- For a population with 1/500 affected, 2q = 1/500 (q = 0.001).
- q² indicates homozygous affected individuals, calculated as 1/10,000.
- Conditions like LDL-receptor deficiency can lead to severe symptoms and increased cardiovascular risk.
X-Linked Recessive Diseases
- Males are hemizygous for the X chromosome; q equals prevalence of affected males.
- A hemophiliac prevalence of 1/10,000 means q = 0.0001.
- Female prevalence calculated as q² (1/100,000,000) and female carrier prevalence as 2q (1/5,000).
- Many recessive alleles remain concealed in female heterozygotes.
Hardy-Weinberg Equilibrium Conditions
- Requires only two alleles and several assumptions:
- No new mutations.
- No selection pressures.
- No genetic drift.
- No gene flow.
- Deviations from these assumptions disturb allele frequencies.
Evolutionary Factors Affecting Genetic Variation
- Key factors include mutation, natural selection, genetic drift, and gene flow.
Natural Selection and Genetic Frequencies
- Negative selection reduces frequency of deleterious alleles if affected individuals don't reproduce.
- Heterozygote advantage can maintain or increase frequency of certain alleles.
- Dominant diseases typically have lower allele frequencies than recessive diseases due to exposure to natural selection.
Gene Flow in Populations
- Migration alters allele frequencies within populations, particularly affecting small populations.
- Balances genetic similarities over time.
Consanguinity and Genetic Diseases
- Consanguinity increases risks for recessive diseases due to shared ancestry.
- Siblings share approximately 1/2, first cousins 1/8, and second cousins 1/32 of their genes.
- Higher risks of genetic diseases in offspring from consanguineous unions.
Health Consequences of Consanguinity
- Offspring of first cousins are about twice as likely to present with genetic diseases compared to unrelated unions.
- Risk increases for closer familial relationships (e.g., uncle-niece, brother-sister).
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Description
This quiz delves into the concepts of autosomal recessive diseases, focusing on carrier genetics and the Hardy-Weinberg principle. Participants will explore calculations related to the frequencies of alleles and the implications for heterozygote carriers. Expand your understanding of genetic inheritance patterns through practical problems.
