Heredity and gene expression flashcards

Heredity and gene expression describe how genetic information is stored, transmitted, and used to build proteins that determine traits. DNA is organized into genes, which are transcribed into mRNA and then translated into proteins. Mutations in DNA can alter protein structure and function, affecting phenotype. Gene expression is regulated at multiple levels, including transcription factors, promoters, and epigenetic modifications. Mendelian inheritance explains how alleles segregate and assort independently during meiosis, producing predictable ratios in offspring. Non-Mendelian patterns such as incomplete dominance, codominance, and polygenic inheritance add complexity. Understanding how environment interacts with genotype to produce phenotype, and how molecular mechanisms like the lac operon illustrate gene regulation, are essential for mastering this topic.

1. Card 1

   What is the central dogma of molecular biology?

   Genetic information flows from DNA to RNA to protein through transcription and translation, establishing how genes direct the building of functional molecules.

2. Card 2

   What is the difference between a gene's genotype and its expressed phenotype?

   Genotype is the actual allele combination an organism carries; phenotype is the observable trait that results from genotype interacting with the environment.

3. Card 3

   What happens during transcription?

   RNA polymerase reads the template DNA strand and synthesizes a complementary mRNA strand, using uracil instead of thymine, in the nucleus of eukaryotes.

4. Card 4

   What is the role of a codon during translation?

   A codon is a three-nucleotide sequence on mRNA that specifies a particular amino acid or a stop signal, allowing ribosomes to build a polypeptide chain.

5. Card 5

   How does a missense mutation affect a protein?

   A missense mutation changes one nucleotide, substituting a different amino acid in the polypeptide, which may alter protein shape and function depending on location.

6. Card 6

   What is Mendel's Law of Segregation?

   The Law of Segregation states that the two alleles for a trait separate during meiosis so each gamete carries only one allele for that gene.

7. Card 7

   How does incomplete dominance differ from complete dominance?

   In incomplete dominance the heterozygote shows a blended intermediate phenotype, whereas in complete dominance one allele fully masks the other allele's effect.

8. Card 8

   What is codominance and give an example?

   Codominance occurs when both alleles are fully expressed simultaneously, as seen in AB blood type where both A and B antigens appear on red blood cells.

9. Card 9

   What is a transcription factor and why does it matter?

   A transcription factor is a protein that binds near a gene's promoter to increase or decrease RNA polymerase activity, regulating when and how much mRNA is made.

10. Card 10

    How does the lac operon illustrate gene regulation in prokaryotes?

    The lac operon genes are repressed when lactose is absent; lactose acts as an inducer that removes the repressor, allowing transcription of lactose-digesting enzymes.

11. Card 11

    What is epigenetic regulation of gene expression?

    Epigenetic changes like DNA methylation and histone modification alter chromatin structure, making genes more or less accessible to transcription without changing the DNA sequence.

12. Card 12

    What distinguishes polygenic inheritance from single-gene inheritance?

    Polygenic inheritance involves multiple genes each contributing to one trait, producing a continuous range of phenotypes like height rather than discrete Mendelian categories.

• Students often confuse the template strand with the coding strand, forgetting that mRNA has the same sequence as the coding strand (with U replacing T), not the template strand.
• Many students incorrectly assume that a dominant allele is always more common in a population, when dominance refers only to the relationship between alleles, not their frequency.
• A frequent error is thinking that gene regulation occurs only at transcription, overlooking post-transcriptional controls such as mRNA splicing, RNA interference, and translational regulation.

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