16.3 A2 Level

Gene control

10 flashcards to master this topic

Definition Flip

What is the difference between a structural gene and a regulatory gene?

Answer Flip

Structural genes code for proteins that become part of the cell's structure or have metabolic/physiological roles. Regulatory genes control the expression of structural genes by coding for proteins that influence transcription (

Example: repressors, activators).
Definition Flip

Distinguish between repressible and inducible enzymes, referencing their normal state.

Answer Flip

Repressible enzymes are typically synthesized unless a repressor molecule binds, halting production (normally 'on'). Inducible enzymes are typically not synthesized unless an inducer molecule is present, triggering production (normally 'off').

Key Concept Flip

Explain the role of the lac repressor in the absence of lactose.

Answer Flip

In the absence of lactose, the lac repressor protein binds to the lac operator region of the lac operon. This binding physically blocks RNA polymerase from transcribing the structural genes, preventing the production of lactose-digesting enzymes.

Key Concept Flip

How do transcription factors influence gene expression in eukaryotes?

Answer Flip

Transcription factors are proteins that bind to specific DNA sequences, either increasing (activators) or decreasing (repressors) the rate of transcription of a gene. They affect the ability of RNA polymerase to bind to the promoter and initiate transcription.

Key Concept Flip

Describe the mechanism by which gibberellin activates gene expression.

Answer Flip

Gibberellin binds to a receptor, leading to the degradation of DELLA repressor proteins. These DELLA proteins normally inhibit transcription factors. Degradation releases these factors, promoting transcription of the gibberellin-responsive genes.

Definition Flip

What is phenotypic variation, and what are the potential causes?

Answer Flip

Phenotypic variation refers to the differences in observable characteristics within a population. It can be due to genetic factors (different alleles), environmental factors (

Example: diet, temperature), or, most commonly, a combination of both.
Definition Flip

Define discontinuous and continuous variation.

Answer Flip

Discontinuous variation shows distinct categories with no intermediate values (

Example: blood type). Continuous variation shows a range of values between two extremes (. height, weight).
Key Concept Flip

Explain the genetic basis of discontinuous variation.

Answer Flip

Discontinuous variation is typically controlled by a single gene or a small number of genes, with each gene having a major effect on the phenotype. The alleles produce distinct phenotypes, and there is little environmental influence.

Key Concept Flip

Explain the genetic basis of continuous variation.

Answer Flip

Continuous variation is typically controlled by many genes (polygenic inheritance), each having a small additive effect on the phenotype. Environmental factors also play a significant role in determining the final phenotype.

Definition Flip

What is the purpose of using a t-test?

Answer Flip

A t-test is a statistical test used to determine if there is a significant difference between the means of two independent groups or samples. It helps to determine if the observed difference is likely due to a real effect or just random chance.

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16.2 The roles of genes in 17.2 Natural and artificial