Biology Unit 4 Chapter 8 - Inheritance And Selecti
Biology Unit 4 Chapter 8 - Inheritance and Selecti
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Biology Unit 4 Chapter 8 - Inheritance and Selection Graded A+
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Biology Unit 4 Chapter 8 - Inheritance and Selecti
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Biology Unit 4 Chapter 8 - Inheritance And Selecti
Biology Unit 4 Chapter 8 - Inheritance and Selection Graded A+
Phenotype Definition
Phenotype refers to the observable characteristics of an organism, which result from the interaction
between its genetic makeup (genotype) and environmental influences.
Tay-Sachs Disease and Genetic Evidence...
Biology Unit 4 Chapter 8 - Inheritance and Selection Graded A+
Phenotype Definition
Phenotype refers to the observable characteristics of an organism, which result from the interaction
between its genetic makeup (genotype) and environmental influences.
Tay-Sachs Disease and Genetic Evidence
1. Recessive Allele Evidence:
In the provided family diagram, individuals 3 and 4 are unaffected but have children who are affected
by Tay-Sachs disease. This indicates that both must be carriers of the recessive allele (t), supporting the
conclusion that the allele for Tay-Sachs is recessive.
2. Non-X Chromosome Allele Evidence:
The diagram shows that individual 11 is affected by Tay-Sachs disease while individual 3 is not. If the
Tay-Sachs allele was located on the X chromosome, then individual 11 would inherit the recessive allele
from their father, who does not carry the allele. This suggests that the Tay-Sachs allele is not X-linked.
Population Genetics and Hardy-Weinberg Equation
In a population where Tay-Sachs disease occurs in 1 out of every 1,000 births:
- Calculating Heterozygotes: Using the Hardy-Weinberg principle, where \( q^2 = 0.001 \) (or 1/1000),
we find that \( q \) (frequency of the recessive allele) is approximately 0.0316, leading to \( p \approx
0.9684 \) (frequency of the dominant allele). The formula for heterozygotes (2pq) gives us a percentage
ranging between 5.8% and 6.2%.
Future Heterozygote Percentages
The actual percentage of heterozygous individuals is likely to decrease in future generations, primarily
because individuals affected by Tay-Sachs typically do not reproduce, thus reducing the number of
carriers in the gene pool.
Speciation in the Amazon
Speciation is less common in the reformed Amazon rainforest, likely due to the retention of similar
environmental conditions which do not encourage the development of distinct species.
, Advantages of Using Fruit Flies for Genetic Studies
1. High Reproductive Output: Female fruit flies can lay up to 400 eggs, making it easier to obtain a
significant sample size for genetic studies.
2. Easy Identification of Sex: The physical characteristics (such as size and specific markings) of male and
female fruit flies allow for straightforward identification in genetic experiments.
Expected vs. Observed Ratios
Discrepancies between observed and expected ratios in genetic offspring can occur due to the random
nature of fertilization, where not every gamete has an equal chance of merging.
X-Linked Recessive Alleles in Male Fruit Flies
Male fruit flies are more susceptible to exhibiting phenotypes associated with recessive alleles on the X
chromosome because they only possess one X chromosome. In contrast, females have two X
chromosomes, allowing them to have either a dominant or recessive allele, which affects their
expression.
Dominant Allele Definition
A dominant allele is one that will always manifest in the phenotype of an organism, regardless of the
presence of other alleles.
Genotypes for Brown-Shelled Snails
Brown-shelled snails can have the following genotypes: CBCB (homozygous dominant), CBCP
(heterozygous with pink), and CBCY (heterozygous with yellow).
Shell Banding in Snails and Hardy-Weinberg Calculation
Given that 51% of a snail population has unbanded shells:
- Calculating Heterozygous Percentage: The Hardy-Weinberg equation suggests that if the proportion of
unbanded snails is 0.51, we can derive that approximately 42% of the population would be
heterozygous.
Impact of Land Use Changes on Biodiversity
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