Which enzymes remove RNA primers and join adjacent DNA fragments on the lagging strand?

In bacteria, DNA polymerase I removes the RNA primers (via 5' to 3' exonuclease activity) and replaces them with deoxynucleotides (in eukaryotes, RNase H and FEN1 remove primers and DNA polymerase delta fills the gap); DNA ligase then forms a phosphodiester bond to seal the nick between adjacent Okazaki fragments.

How do telomeres and telomerase protect eukaryotic chromosomal integrity?

Telomeres are non-coding repetitive DNA caps preventing degradation; telomerase is a reverse transcriptase carrying its own RNA template to extend chromosome ends in germ and stem cells.

What differentiates homologous biological structures from analogous biological structures?

Homologous structures share anatomical ancestry despite divergent functions (e.g., human arm and bat wing); analogous structures share similar function due to convergent evolution without common evolutionary origin (e.g., bird wing and butterfly wing).

How is recombination frequency used to construct genetic chromosome linkage maps?

Recombination frequency between linked genes is proportional to physical distance: a 1% frequency of crossing over corresponds to 1 map unit (centimorgan), with a maximum independent assortment ceiling of 50%.

How does alternative RNA splicing generate proteomic diversity from a single gene?

Differential inclusion or exclusion of particular pre-mRNA exons yields distinct mature mRNA isoforms, allowing a single gene locus to code for multiple distinct protein variants.

What occurs at the A, P, and E ribosomal sites during translational elongation?

An incoming aminoacyl-tRNA carrying the next amino acid binds the mRNA codon in the A (aminoacyl) site; the large subunit's rRNA peptidyl transferase center catalyzes peptide bond formation by transferring the growing polypeptide chain from the P-site tRNA onto the amino acid on the A-site tRNA; during translocation, the tRNA with the polypeptide moves from the A site to the P (peptidyl) site while the deacylated tRNA moves from the P site to the E (exit) site for release.

What are the three essential post-transcriptional modifications made to eukaryotic pre-mRNA?

Addition of a 7-methylguanosine cap at the 5' end, addition of a poly-A tail at the 3' end, and spliceosomal excision of non-coding introns with ligation of coding exons.

How does sexual reproduction provide an evolutionary advantage over asexual reproduction in fluctuating environments?

Meiotic crossing over, independent assortment, and random fertilization generate vast combinatorial genetic diversity, providing phenotypes capable of surviving novel environmental pathogens and selective pressures.

What structural and genetic evidence supports the endosymbiotic origin of mitochondria and chloroplasts?

Both possess double membranes, circular prokaryotic-like DNA genomes, autonomous binary fission replication, and 70S bacterial-style ribosomes.

What distinguishes directional, stabilizing, and disruptive natural selection?

Directional selection favors one extreme phenotype, stabilizing selection favors the intermediate phenotype while reducing variation, and disruptive selection favors both extreme phenotypes over intermediate traits.

In cladistics and phylogenetic analysis, what is a synapomorphy?

A shared derived character state that originated in an immediate common ancestor and is present in all its descendant clade members, distinguishing the group from ancestral clades.

What is Mendel's Law of Segregation and during which stage of meiosis does it occur?

The two alleles for a heritable character separate during gamete formation so each gamete carries only one allele; this segregation occurs during Anaphase I when homologous chromosomes separate.

What is the founder effect in evolutionary biology?

A form of genetic drift that occurs when a small group of individuals colonizes a new habitat or becomes isolated from a larger parent population, carrying by chance a small, unrepresentative sample of the parent population's allele frequencies.

What is the fundamental difference between allopatric and sympatric speciation?

Allopatric speciation occurs when a physical geographic barrier splits a population, whereas sympatric speciation occurs within the same geographic territory through polyploidy, habitat differentiation, or sexual selection.

How do histone acetylation and DNA methylation reciprocally influence eukaryotic chromatin structure?

Histone acetylation (on positively charged lysine residues in histone tails) reduces electrostatic attraction to negatively charged DNA, loosening chromatin into transcriptionally active euchromatin, whereas DNA methylation (commonly at cytosine bases in CpG islands) promotes chromatin condensation into heterochromatin and represses transcription.

Why do insertion or deletion mutations of non-multiples of three nucleotides cause devastating frameshifts?

They alter the triplet reading frame downstream of the mutation, altering every subsequent amino acid and typically generating a premature termination codon.

What five baseline conditions must be satisfied for a population to remain in Hardy-Weinberg equilibrium?

No mutations, random mating, no natural selection, extremely large population size (no genetic drift), and no gene flow (no immigration or emigration).

How does gene flow influence genetic variation between two adjacent populations?

Gene flow introduces new alleles into a local gene pool via migration and reduces genetic divergence between populations, preventing localized speciation.

Why is the lagging strand synthesized discontinuously as Okazaki fragments?

DNA polymerases can synthesize new DNA only in the 5' to 3' direction by adding nucleotides to a free 3'-OH group; because the lagging-strand template runs 5' to 3' toward the opening replication fork, lagging-strand synthesis must proceed discontinuously away from the fork in short RNA-primed Okazaki fragments.

How do molecular clocks estimate the divergence time of evolutionary lineages?

They measure the accumulation of neutral, non-lethal nucleotide or amino acid mutations that accumulate at a relatively constant mutation rate over geological time.

How does phenotype expression differ between incomplete dominance and codominance in heterozygous organisms?

Incomplete dominance produces an intermediate blended phenotype in heterozygotes (e.g., pink snapdragon flowers from red and white parents), whereas codominance simultaneously and distinctly expresses both alleles' phenotypes in heterozygotes (e.g., human AB blood group expressing both IA and IB surface antigens). In both patterns, a cross of two heterozygotes yields a 1:2:1 phenotypic and genotypic ratio.

How does a population bottleneck cause significant evolutionary genetic drift?

A sudden environmental catastrophe or severe population contraction drastically reduces population size largely at random, leaving a surviving gene pool whose allele frequencies differ by chance from those of the original population and has reduced genetic diversity.

In the Hardy-Weinberg formulas p + q = 1 and p^2 + 2pq + q^2 = 1, what does 2pq represent?

In a diploid population at Hardy-Weinberg equilibrium with two alleles (frequencies p and q), 2pq represents the expected frequency of heterozygous individuals (whereas p^2 and q^2 represent the homozygous genotype frequencies).

What is the function of topoisomerase (gyrase) during DNA replication?

Topoisomerase cleaves and rejoins the phosphodiester backbone ahead of the replication fork to relieve severe torsional strain and supercoiling caused by helicase unwinding.

What does it mean that the genetic code is redundant (degenerate) yet unambiguous?

Multiple distinct codons can specify the same amino acid (redundancy), but any single codon specifies only one distinct amino acid (unambiguity).

How does the presence of lactose induce transcription of the bacterial lac operon?

Allolactose acts as an inducer that binds allosterically to the lac repressor protein, causing it to detach from the operator sequence and allowing RNA polymerase to transcribe the genes.

Why is the bacterial trp operon classified as a repressible operon?

It is constitutively active until intracellular tryptophan levels rise; tryptophan acts as a corepressor that binds the inactive repressor, enabling it to bind the operator and halt transcription.

How does glucose level modulate lac operon expression via catabolite repression?

Low glucose triggers adenylyl cyclase to synthesize cAMP; cAMP binds the catabolite activator protein (CAP), which binds the promoter and dramatically stimulates transcription.

What distinguishes a nonsense mutation from a missense mutation?

A missense mutation substitutes a single nucleotide changing one amino acid into another, whereas a nonsense mutation introduces a premature STOP codon (UAA, UAG, UGA) causing truncated nonfunctional protein.

What is Mendel's Law of Independent Assortment and when does it not apply?

Alleles of two or more genes located on different (non-homologous) chromosomes—or far apart on the same chromosome—assort into gametes independently due to the random orientation of homologous chromosome pairs at the metaphase plate during Metaphase I; this law does not hold when genes are closely linked on the same chromosome.

Why do X-linked recessive genetic conditions appear much more frequently in biological males?

Males are hemizygous (XY) and possess only one X chromosome; inheriting a single recessive allele on the maternal X chromosome will express the trait because no homologous allele exists on the Y.

How did the Meselson-Stahl experiment verify the semi-conservative model of DNA replication?

By culturing E. coli in heavy 15N medium and shifting to light 14N medium, CsCl density-gradient centrifugation showed a single intermediate hybrid (15N/14N) DNA band after one generation (ruling out conservative replication) and equal intermediate (15N/14N) and light (14N/14N) bands after two generations (ruling out dispersive replication).

Molecular Genetics, Heredity, Gene Regulation & Natural Selection

Core genetics and evolutionary biology concepts including DNA replication, transcription, translation, prokaryotic and eukaryotic gene regulation, Mendelian and non-Mendelian inheritance, Hardy-Weinberg equilibrium, and speciation.

Level: basic
Languages: en → en
Cards: 32
Markdown: Molecular Genetics, Heredity, Gene Regulation & Natural Selection (.md)

Flashcards (32)

#	Front (Term / Question)	Back (Definition / Answer)
1	Which enzymes remove RNA primers and join adjacent DNA fragments on the lagging strand?	In bacteria, DNA polymerase I removes the RNA primers (via 5' to 3' exonuclease activity) and replaces them with deoxynucleotides (in eukaryotes, RNase H and FEN1 remove primers and DNA polymerase delta fills the gap); DNA ligase then forms a phosphodiester bond to seal the nick between adjacent Okazaki fragments.
2	How do telomeres and telomerase protect eukaryotic chromosomal integrity?	Telomeres are non-coding repetitive DNA caps preventing degradation; telomerase is a reverse transcriptase carrying its own RNA template to extend chromosome ends in germ and stem cells.
3	What differentiates homologous biological structures from analogous biological structures?	Homologous structures share anatomical ancestry despite divergent functions (e.g., human arm and bat wing); analogous structures share similar function due to convergent evolution without common evolutionary origin (e.g., bird wing and butterfly wing).
4	How is recombination frequency used to construct genetic chromosome linkage maps?	Recombination frequency between linked genes is proportional to physical distance: a 1% frequency of crossing over corresponds to 1 map unit (centimorgan), with a maximum independent assortment ceiling of 50%.
5	How does alternative RNA splicing generate proteomic diversity from a single gene?	Differential inclusion or exclusion of particular pre-mRNA exons yields distinct mature mRNA isoforms, allowing a single gene locus to code for multiple distinct protein variants.
6	What occurs at the A, P, and E ribosomal sites during translational elongation?	An incoming aminoacyl-tRNA carrying the next amino acid binds the mRNA codon in the A (aminoacyl) site; the large subunit's rRNA peptidyl transferase center catalyzes peptide bond formation by transferring the growing polypeptide chain from the P-site tRNA onto the amino acid on the A-site tRNA; during translocation, the tRNA with the polypeptide moves from the A site to the P (peptidyl) site while the deacylated tRNA moves from the P site to the E (exit) site for release.
7	What are the three essential post-transcriptional modifications made to eukaryotic pre-mRNA?	Addition of a 7-methylguanosine cap at the 5' end, addition of a poly-A tail at the 3' end, and spliceosomal excision of non-coding introns with ligation of coding exons.
8	How does sexual reproduction provide an evolutionary advantage over asexual reproduction in fluctuating environments?	Meiotic crossing over, independent assortment, and random fertilization generate vast combinatorial genetic diversity, providing phenotypes capable of surviving novel environmental pathogens and selective pressures.
9	What structural and genetic evidence supports the endosymbiotic origin of mitochondria and chloroplasts?	Both possess double membranes, circular prokaryotic-like DNA genomes, autonomous binary fission replication, and 70S bacterial-style ribosomes.
10	What distinguishes directional, stabilizing, and disruptive natural selection?	Directional selection favors one extreme phenotype, stabilizing selection favors the intermediate phenotype while reducing variation, and disruptive selection favors both extreme phenotypes over intermediate traits.
11	In cladistics and phylogenetic analysis, what is a synapomorphy?	A shared derived character state that originated in an immediate common ancestor and is present in all its descendant clade members, distinguishing the group from ancestral clades.
12	What is Mendel's Law of Segregation and during which stage of meiosis does it occur?	The two alleles for a heritable character separate during gamete formation so each gamete carries only one allele; this segregation occurs during Anaphase I when homologous chromosomes separate.
13	What is the founder effect in evolutionary biology?	A form of genetic drift that occurs when a small group of individuals colonizes a new habitat or becomes isolated from a larger parent population, carrying by chance a small, unrepresentative sample of the parent population's allele frequencies.
14	What is the fundamental difference between allopatric and sympatric speciation?	Allopatric speciation occurs when a physical geographic barrier splits a population, whereas sympatric speciation occurs within the same geographic territory through polyploidy, habitat differentiation, or sexual selection.
15	How do histone acetylation and DNA methylation reciprocally influence eukaryotic chromatin structure?	Histone acetylation (on positively charged lysine residues in histone tails) reduces electrostatic attraction to negatively charged DNA, loosening chromatin into transcriptionally active euchromatin, whereas DNA methylation (commonly at cytosine bases in CpG islands) promotes chromatin condensation into heterochromatin and represses transcription.
16	Why do insertion or deletion mutations of non-multiples of three nucleotides cause devastating frameshifts?	They alter the triplet reading frame downstream of the mutation, altering every subsequent amino acid and typically generating a premature termination codon.
17	What five baseline conditions must be satisfied for a population to remain in Hardy-Weinberg equilibrium?	No mutations, random mating, no natural selection, extremely large population size (no genetic drift), and no gene flow (no immigration or emigration).
18	How does gene flow influence genetic variation between two adjacent populations?	Gene flow introduces new alleles into a local gene pool via migration and reduces genetic divergence between populations, preventing localized speciation.
19	Why is the lagging strand synthesized discontinuously as Okazaki fragments?	DNA polymerases can synthesize new DNA only in the 5' to 3' direction by adding nucleotides to a free 3'-OH group; because the lagging-strand template runs 5' to 3' toward the opening replication fork, lagging-strand synthesis must proceed discontinuously away from the fork in short RNA-primed Okazaki fragments.
20	How do molecular clocks estimate the divergence time of evolutionary lineages?	They measure the accumulation of neutral, non-lethal nucleotide or amino acid mutations that accumulate at a relatively constant mutation rate over geological time.
21	How does phenotype expression differ between incomplete dominance and codominance in heterozygous organisms?	Incomplete dominance produces an intermediate blended phenotype in heterozygotes (e.g., pink snapdragon flowers from red and white parents), whereas codominance simultaneously and distinctly expresses both alleles' phenotypes in heterozygotes (e.g., human AB blood group expressing both IA and IB surface antigens). In both patterns, a cross of two heterozygotes yields a 1:2:1 phenotypic and genotypic ratio.
22	How does a population bottleneck cause significant evolutionary genetic drift?	A sudden environmental catastrophe or severe population contraction drastically reduces population size largely at random, leaving a surviving gene pool whose allele frequencies differ by chance from those of the original population and has reduced genetic diversity.
23	In the Hardy-Weinberg formulas p + q = 1 and p^2 + 2pq + q^2 = 1, what does 2pq represent?	In a diploid population at Hardy-Weinberg equilibrium with two alleles (frequencies p and q), 2pq represents the expected frequency of heterozygous individuals (whereas p^2 and q^2 represent the homozygous genotype frequencies).
24	What is the function of topoisomerase (gyrase) during DNA replication?	Topoisomerase cleaves and rejoins the phosphodiester backbone ahead of the replication fork to relieve severe torsional strain and supercoiling caused by helicase unwinding.
25	What does it mean that the genetic code is redundant (degenerate) yet unambiguous?	Multiple distinct codons can specify the same amino acid (redundancy), but any single codon specifies only one distinct amino acid (unambiguity).
26	How does the presence of lactose induce transcription of the bacterial lac operon?	Allolactose acts as an inducer that binds allosterically to the lac repressor protein, causing it to detach from the operator sequence and allowing RNA polymerase to transcribe the genes.
27	Why is the bacterial trp operon classified as a repressible operon?	It is constitutively active until intracellular tryptophan levels rise; tryptophan acts as a corepressor that binds the inactive repressor, enabling it to bind the operator and halt transcription.
28	How does glucose level modulate lac operon expression via catabolite repression?	Low glucose triggers adenylyl cyclase to synthesize cAMP; cAMP binds the catabolite activator protein (CAP), which binds the promoter and dramatically stimulates transcription.
29	What distinguishes a nonsense mutation from a missense mutation?	A missense mutation substitutes a single nucleotide changing one amino acid into another, whereas a nonsense mutation introduces a premature STOP codon (UAA, UAG, UGA) causing truncated nonfunctional protein.
30	What is Mendel's Law of Independent Assortment and when does it not apply?	Alleles of two or more genes located on different (non-homologous) chromosomes—or far apart on the same chromosome—assort into gametes independently due to the random orientation of homologous chromosome pairs at the metaphase plate during Metaphase I; this law does not hold when genes are closely linked on the same chromosome.
31	Why do X-linked recessive genetic conditions appear much more frequently in biological males?	Males are hemizygous (XY) and possess only one X chromosome; inheriting a single recessive allele on the maternal X chromosome will express the trait because no homologous allele exists on the Y.
32	How did the Meselson-Stahl experiment verify the semi-conservative model of DNA replication?	By culturing E. coli in heavy 15N medium and shifting to light 14N medium, CsCl density-gradient centrifugation showed a single intermediate hybrid (15N/14N) DNA band after one generation (ruling out conservative replication) and equal intermediate (15N/14N) and light (14N/14N) bands after two generations (ruling out dispersive replication).