【PEP】High School Biology, Compulsory Book 2: Understanding Gene Mutation Through Sickle Cell Anemia

Phenotypic differences in life often originate from a single "letter" change deep within the molecule.Sickle Cell Anemia(Sickle Cell Anemia) was the first genetic disease whose cause was clearly identified at the molecular level. Its root lies in a subtle change in the gene responsible for hemoglobin synthesis.

Core Logic: From Molecule to Trait

Principle of Complementary Base Pairing: During DNA replication or transcription, a T-A base pair is erroneously substituted with A-T.
Codon Effect: The change in the DNA sequence causes the codon on the mRNA to change from GAA to GUA.
Abnormal Protein Function: The hydrophilic glutamic acid is replaced by hydrophobic valine, causing hemoglobin molecules to polymerize under deoxygenated conditions, deforming red blood cells into a sickle shape.

Key Takeaway: The Creation of New Genes

Gene mutation is a variation caused by changes in the structure of the DNA molecule. This variation producesalleles of existing genes, meaning it creates "new genes." This is the fundamental difference between it and genetic recombination (the reassortment of existing genes).

QUESTION 1

[Multiple Choice] Changes in base sequences during DNA replication can lead to the creation of new genes. Which of the following can produce new genes?

A. Genetic Recombination

B. Gene Mutation

C. Gene Segregation

D. Chromosome Doubling

QUESTION 2

[Short Answer] According to the molecular logic chain in Figure 5-2 of the textbook, describe the specific change in amino acids during the development of sickle cell anemia. What effect does this have on protein function?

QUESTION 3

[Reading Comprehension] The watermelons we commonly eat are diploid. In polyploidy breeding, colchicine is often used to treat germinating seeds or seedlings to produce triploid seedless watermelons. The diagram shows the process of chromosome doubling. Based on this lesson, which of the following descriptions of the type of variation is correct?

Watermelon chromosome doubling is a type of gene mutation because it produces new traits

Watermelon chromosome doubling is a type of chromosomal variation, while sickle cell anemia is a type of gene mutation

Both are microscopic variations at the molecular level

Neither can be inherited by offspring

QUESTION 4

[Multiple Choice] In the case of sickle cell anemia, during which process of DNA is base pair substitution most likely to be inherited?

A. Cellular Respiration

B. Protein Synthesis

C. DNA Replication

D. Cell Growth

QUESTION 5

[Short Answer] Briefly summarize the concept of gene mutation and its relationship with biological traits.

Case Study: Family Tracing and Molecular Significance of Genetic Diseases

Family Investigation Analysis Based on Sickle Cell Anemia

In a malaria-endemic region of Africa, doctors identified a family with sickle cell anemia. The disease follows an autosomal recessive inheritance pattern. Genetic testing revealed that some family members, while not showing symptoms of anemia, carry one mutated gene. Environmental surveys also found that these carriers are more resistant to malaria than normal individuals.

[Short Answer] 1. Does the genetic disease you investigated show a pattern of familial inheritance? (Answer based on molecular principles, at least 100 words)

Answer:
In investigating sickle cell anemia, we found that the disease shows a clear tendency for familial inheritance. This is because when a gene mutation occurs in a germ cell, it is passed to offspring following Mendel's laws of inheritance. At the molecular level, once a base substitution occurs in the DNA sequence of a parent, this altered new sequence (the recessive disease-causing gene) becomes genetically stable. When offspring inherit the mutated gene from both parents simultaneously, the amino acid sequence of their hemoglobin changes, exhibiting anemia traits similar to the parents. Therefore, investigating family history is an important method for identifying genetic diseases caused by gene mutations.

[Short Answer] Based on this case, discuss the significance of gene mutation for biological evolution and population adaptation.

Answer:
Gene mutation is a pathway for generating new genes and is the fundamental source of biological variation, providing rich raw material for evolution. In this case, although the mutation causes anemia, heterozygous carriers gained a survival advantage in the special context of a malaria-endemic environment. This shows that whether a mutation is beneficial or harmful depends on environmental selection, and it forms the basis for a population's adaptation to environmental changes.