Cytogenetics and Molecular Genetics Study Flashcards

Comprehensive practice flashcards covering cell division, classical Mendelian genetics, cytogenetic karyotyping and chromosomal abnormalities, DNA structure and replication, gene expression, mutations, recombinant DNA technologies, and genetic disorders based on lecture notes.

How does the human exome compare to the whole human genome in size and composition?

The genome contains approximately $3,200,000,000$ nucleotides comprising both coding and non-coding DNA, whereas the exome consists of about $3,000,000$ nucleotides (about $1\%$ of the genome) containing only protein-coding exons.

What are the seven levels at which genetics can be investigated?

1. Instructions and information from DNA, 2. Genes, 3. Chromosomes, 4. Genomes, 5. Individuals, 6. Families, and 7. Populations.

What was August Weismann's 1883 theory of the continuity of the germ plasm?

It proposed that hereditary factors are transmitted from generation to generation exclusively through the germ plasm located in the sex cells, rather than through somatic cells.

What happens during the Gap 0 ($\text{G}_0$) phase of the cell cycle?

It is a quiet, non-dividing stage in which a cell determines whether to enter DNA synthesis, differentiate into a specialized cell, or undergo apoptosis.

What mechanism drives cytokinesis in animal cells following telophase?

A contractile rim compresses the cell, dividing the replicated organelles and cytoplasm into two nearly equal halves.

What core characteristic defines a stem cell?

Self-renewal, which is the ability to divide to yield another stem cell like itself in addition to producing specialized progenitor cells.

Why is an animal produced via somatic cell nuclear transfer (SCNT) not an exact replica of the donor individual?

Differences arise from premature cellular aging (shorter telomeres), altered gene expression from lack of genomic imprinting, accumulated somatic mutations in the donor nucleus, random X inactivation patterns in females, inheritance of mitochondrial DNA exclusively from the recipient oocyte, and environmental influences.

What is Gregor Mendel's First Law (Law of Gene Segregation)?

Alleles of a gene separate into different gametes during meiosis, meaning each gamete receives only one copy of each gene pair.

What is Gregor Mendel's Second Law (Law of Independent Assortment)?

Two genes located on different chromosomes (or far apart on the same chromosome) assort independently, meaning the inheritance of one trait does not influence the inheritance of the other.

How does the product rule calculate probabilities in genetic crosses?

It states that the probability of simultaneous, independent genetic events equals the product of their individual probabilities.

What molecular mechanism generally differentiates a dominant mutation from a recessive mutation?

Dominant mutations generally confer a gain-of-function (producing altered or increased activity), whereas recessive mutations typically result in a loss-of-function (causing reduced, inactive, or absent protein product).

What repetitive DNA sequence and specialized centromeric protein compose human centromeres?

Centromeres are composed of tandem repeats of a $171\text{-base}$ DNA sequence and centromere protein A (CENP-A), which replicates at the end of S phase and mediates epigenetic continuity between cell divisions.

Based on the position of the centromere shown in the diagram, what are the four structural classifications of chromosomes?

(a) Telocentric (centromere at the tip), (b) Acrocentric (centromere near one end), (c) Submetacentric (centromere off-center creating short p and long q arms), and (d) Metacentric (centromere at the center).

How do amniocentesis and chorionic villus sampling (CVS) differ in timing and diagnostic capacity?

CVS is performed earlier (at $10\text{ to }12\text{ weeks}$ of gestation) and yields faster results, but has a higher risk of spontaneous abortion and cannot detect biochemical/metabolic defects. Amniocentesis is performed later and detects about $1,000$ chromosomal and biochemical problems.

What is a Robertsonian translocation, and which chromosomes are typically involved in translocation Down syndrome?

A structural abnormality where the long arms of two nonhomologous acrocentric chromosomes fuse at their centromeres while their short arms are lost; translocation Down syndrome most commonly results from a Robertsonian translocation between chromosomes $14$ and $21$.

What genetic lesion causes Cri-du-chat syndrome?

A deletion on the short arm of chromosome 5 ($5\text{p-}$).

What famous X-ray diffraction image of B-form DNA is depicted here, and who obtained it in 1952?

Photo 51, obtained by Rosalind Franklin using X-ray diffraction after 100 hours of exposure, which revealed that DNA is a double helix with symmetrically organized subunits.

What are Chargaff's rules regarding DNA base composition?

In double-stranded DNA, the concentration of adenine equals thymine ($A = T$), the concentration of guanine equals cytosine ($G = C$), and the total sum of purines equals pyrimidines ($A + G = T + C$).

What is the function of the CTCF anchor protein in nuclear DNA packaging?

It binds specific sequences to anchor DNA loops together at roughly $10,000$ sites across the genome, creating the organized higher-order chromatin structure termed the 'loop-ome'.

How did Meselson and Stahl demonstrate the semiconservative model of DNA replication in 1957?

They cultured bacteria in heavy nitrogen ($^{15}\text{N}$) followed by light nitrogen ($^{14}\text{N}$); density gradient centrifugation confirmed that daughter DNA molecules contained one heavy parental strand and one newly synthesized light strand.

What are the roles of helicase, primase, and ligase at the replication fork?

Helicase unwinds and separates parental DNA strands, primase synthesizes an RNA primer to provide a free $3'\text{-OH}$ group, and ligase joins Okazaki fragments and seals nicks in the phosphodiester backbone.

What three post-transcriptional modifications produce mature eukaryotic mRNA from pre-mRNA?

1. Addition of a methylated cap at the $5'$ end, 2. Addition of a poly-A tail at the $3'$ end, and 3. RNA splicing to excise non-coding introns and join coding exons.

How do chaperone proteins and proteasomes cooperate in protein quality control?

Chaperone proteins bind partially folded polypeptides to prevent inappropriate intermediates and stabilize correct conformations; irreversibly misfolded proteins are tagged with ubiquitin and transported to proteasomes for destruction.

What distinguishes transition point mutations from transversion point mutations?

A transition replaces a purine with a purine ($A \leftrightarrow G$) or a pyrimidine with a pyrimidine ($C \leftrightarrow T$); a transversion replaces a purine with a pyrimidine or vice versa ($A\text{ or }G \leftrightarrow C\text{ or }T$).

What specific amino acid alteration in the beta-globin chain causes Sickle Cell Disease (Hb S)?

A missense mutation replacing glutamic acid with valine at amino acid position 6 of the beta-globin chain ($\text{Glu} \rightarrow \text{Val}$).

How does the CCR5-delta 32 mutation provide natural protection against HIV?

The 32-base pair deletion prevents the normal formation of the CCR5 co-receptor on the cell membrane of $\text{CD4}^+$ cells, blocking viral gp120 from binding and preventing viral entry into the host cell.

What legal requirements must a biotechnology invention meet to be granted patent protection?

The invention must be new (novel), useful, and non-obvious.

How does RNA interference (RNAi) achieve targeted gene silencing?

The enzyme Dicer cuts double-stranded RNA into $21\text{ to }24\text{-base}$ small interfering RNAs (siRNAs); a single guide strand incorporates into the RNA-induced silencing complex (RISC), binds complementary mRNA transcripts, and an associated nuclease degrades the mRNA to block translation.

What are the essential components of the CRISPR-Cas9 genome editing platform?

A synthetic single-guide RNA (sgRNA) engineered to match a specific genomic target sequence and the Cas9 endonuclease enzyme, which induces double-stranded DNA breaks at the target site.

What three therapeutic approaches are used to manage lysosomal storage disorders at the protein level?

1. Enzyme replacement therapy (infusing recombinant human enzyme), 2. Substrate reduction therapy (oral drugs reducing substrate accumulation), and 3. Pharmacological chaperone therapy (oral molecules binding patient misfolded enzymes to restore native conformation).

What is the primary difference between in vivo and ex vivo somatic gene therapy?

Ex vivo gene therapy removes cells from the patient, introduces the therapeutic gene in the laboratory, and returns the modified cells to the body; in vivo gene therapy delivers the vector-borne therapeutic gene directly into an internal organ or tissue inside the patient.

What gene is mutated in Cystic Fibrosis, and what is its most prevalent clinical mutation?

The Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene located on chromosome $7\text{q}31.2$; the most common mutation is $\Delta \text{F}508$, which accounts for about $70\%$ of CF alleles in Caucasians.

What two neuropathological structures characterize brain tissue in Alzheimer's disease?

Extracellular amyloid plaques (formed from amyloid beta precursor protein) and intracellular neurofibrillary tangles formed from hyperphosphorylated and misfolded tau proteins that cause microtubule collapse.