Ch. 14: Mendel + Gene Idea
How did Mendel’s findings disprove the idea of blended inheritance and support the concept of particulate inheritance?
Mendel’s experiments showed that traits are inherited as discrete units (genes) that retain their identity through generations, rather than blending into intermediate forms.
What is the significance of polyploidy, and in which organisms is it most common?
Polyploidy is the presence of more than two complete chromosome sets, common in plants but rare in animals.
What are the levels of DNA packing in a eukaryotic cell, from least to most compact?
DNA → nucleosomes (10-nm fiber) → 30-nm fiber → looped domains → fully condensed chromosome.
What are the key components of the genetic code, and how does it ensure correct translation of mRNA into a polypeptide?
The genetic code is a triplet code of non-overlapping nucleotide triplets called codons, each specifying one amino acid. It is redundant (multiple codons for one amino acid) but not ambiguous (no codon codes for more than one amino acid).
What is one major difference between viruses and living organisms in terms of reproduction and metabolism?
Viruses cannot reproduce or carry out metabolism independently; they require a host cell to replicate, while living organisms can reproduce and metabolize on their own.
What is the difference between the Law of Segregation and the Law of Independent Assortment in Mendelian genetics?
The Law of Segregation states that allele pairs separate during gamete formation.
The Law of Independent Assortment states that alleles of different genes are distributed independently into gametes.
How can recombination frequency distinguish between linked genes and genes on separate chromosomes?
Genes with ≈ 50% recombination are unlinked (independent assortment); those with < 50% are linked on the same chromosome.
How do telomeres and telomerase maintain chromosome stability in eukaryotic cells?
Telomeres are repetitive, noncoding DNA sequences at chromosome ends that protect genes from erosion; telomerase extends these sequences in germ and cancer cells.
Given the mRNA sequence 5′–AUG GGC UAC UAA–3′, what is the corresponding amino acid sequence?
Methionine – Glycine – Tyrosine – Stop.
What are the two main structural components found in all viruses, and what extra structure do some viruses possess?
All viruses have a nucleic acid genome (DNA or RNA) and a protein coat (capsid); some also have a membranous envelope derived from the host cell.
How do complete dominance, incomplete dominance, and codominance differ in their expression of alleles?
Complete dominance: The dominant allele masks the recessive (e.g., purple pea flowers).
Incomplete dominance: The heterozygote shows an intermediate phenotype (e.g., pink snapdragons).
Codominance: Both alleles are fully expressed (e.g., AB blood type).
What process causes one X chromosome to become inactive in female mammals, and what is the result?
X-inactivation occurs early in embryonic development, producing a condensed Barr body and creating a genetic mosaic in heterozygous females.
Explain how proofreading and repair mechanisms maintain DNA replication accuracy.
DNA polymerases proofread newly added bases, removing mismatched nucleotides, while repair enzymes perform mismatch and nucleotide excision repair on damaged
What are the three main components of a eukaryotic pre-mRNA, and how are they modified during RNA processing?
Pre-mRNA has a 5′ cap, a coding region with introns and exons, and a 3′ poly-A tail. During processing, introns are removed and exons are spliced together, while the cap and tail are added.
How does the presence of an envelope in some viruses affect their mode of infection?
Enveloped viruses can enter host cells by membrane fusion or endocytosis and exit by budding, allowing them to avoid immediate host immune detection.
How does epistasis differ from other types of inheritance, and what outcome does it produce?
Epistasis occurs when one gene alters or masks the effect of another gene, changing expected Mendelian ratios.
What was the key discovery made by Thomas Hunt Morgan in his fruit-fly experiments, and why was it important?
Morgan discovered that a specific gene (for eye color) was located on the X chromosome, proving that genes reside on chromosomes.
Identify the major components within a replication bubble and explain their functions.
A replication bubble contains two replication forks, leading and lagging strands, primase, helicase, DNA polymerase, and ligase.
Describe the structure and function of the ribosome during translation.
A ribosome has a large and small subunit, each made of rRNA and protein, with A (aminoacyl), P (peptidyl), and E (exit) sites that hold tRNA during translation.
What occurs during the lytic cycle of a bacteriophage, and what is the outcome for the host cell?
In the lytic cycle, the phage injects DNA, takes over host machinery to produce new viral particles, and then lyses (breaks open) the host cell to release progeny viruses.
How can pedigree analysis be used to identify genotypes and determine whether a trait is dominant or recessive?
Pedigrees trace inheritance through generations; dominant traits appear in every generation, while recessive traits can skip generations and reappear through carriers
How does the behavior of chromosomes during meiosis explain Mendel’s Law of Segregation and Law of Independent Assortment?
The separation of homologous chromosomes in meiosis I explains segregation, and the random orientation of chromosome pairs explains independent assortment.
How did the Hershey and Chase experiment demonstrate that DNA, rather than protein, is the genetic material?
Hershey and Chase used bacteriophages labeled with radioactive phosphorus (DNA) and sulfur (protein) to infect E. coli, showing that only the DNA entered the bacterial cells and directed viral replication.
How does template-driven transcription synthesize RNA, and what is the role of RNA polymerase?
RNA polymerase unwinds DNA and builds RNA in the 5′→3′ direction by matching RNA nucleotides to the DNA template strand.
How does the lysogenic cycle differ from the lytic cycle in bacteriophages?
In the lysogenic cycle, the viral DNA integrates into the host genome as a prophage, replicating with the host cell without destroying it; environmental triggers can later induce the lytic cycle.