Genetics and Cell Division: Molecular Basis, Inheritance, and Chromosomal Aberrations

What was the significance of Griffith's Transformation Experiment (1928)?

It showed that a 'transforming principle' from heat-killed virulent bacteria could transform non-virulent bacteria into virulent ones, indicating a heritable factor.

What did Avery, McCarty, and MacLeod's Experiment (1944) demonstrate?

They identified DNA as the genetic material by showing that only the degradation of DNA eliminated the transformation ability of the S strain.

What was the main finding of the Hershey and Chase Experiment (1952)?

It provided strong evidence that DNA, not protein, is the genetic material passed from bacteriophages to bacteria.

What are the components of a nucleotide in DNA?

A nucleotide consists of a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C).

Describe the structure of DNA.

DNA has a double helix structure composed of two antiparallel polynucleotide strands with a sugar-phosphate backbone and specific base pairing.

What is Chargaff's rule?

Chargaff's rule states that in DNA, Adenine (A) pairs with Thymine (T) and Guanine (G) pairs with Cytosine (C).

What is the significance of the 5' and 3' ends of a DNA strand?

The 5' end has a free phosphate group, and the 3' end has a free hydroxyl group, which are critical for DNA replication and transcription.

What is the process of DNA replication?

DNA replication is semi-conservative, producing one original parental strand and one newly synthesized daughter strand.

What role does helicase play in DNA replication?

Helicase unwinds and separates the two parental DNA strands by breaking hydrogen bonds between bases.

What is the function of DNA polymerase III?

DNA polymerase III synthesizes new DNA strands by adding nucleotides to the 3' end of a growing strand.

What is the difference between leading and lagging strands during DNA replication?

The leading strand is synthesized continuously towards the replication fork, while the lagging strand is synthesized discontinuously in Okazaki fragments away from the fork.

What is the end replication problem?

The end replication problem occurs because DNA polymerase cannot fully replicate the ends of linear chromosomes, leading to progressive shortening.

What are telomeres?

Telomeres are non-coding, repetitive DNA sequences at the ends of eukaryotic chromosomes that protect essential genes from erosion.

What is the role of telomerase?

Telomerase extends telomeres using an RNA template, counteracting shortening in certain cell types, such as germ cells and some cancer cells.

What are the phases of the cell cycle?

The cell cycle consists of Interphase (G1, S, G2 phases) and the Mitotic (M) phase.

What occurs during the G1 phase of the cell cycle?

During G1, the cell grows and carries out normal metabolic functions.

What happens during the S phase of the cell cycle?

DNA replication occurs, and chromosomes are duplicated.

What is the purpose of the G2 phase?

In G2, the cell continues to grow and synthesizes proteins necessary for mitosis.

What is mitosis?

Mitosis is the specialized nuclear division that produces two genetically identical daughter cells.

What are the functions of cell division?

Cell division is essential for reproduction, growth and development, and tissue renewal and repair.

What role do single-strand binding proteins (SSBs) play in DNA replication?

SSBs stabilize separated single DNA strands to prevent them from re-annealing.

What is the function of primase in DNA replication?

Primase synthesizes short RNA primers that provide a free 3'-hydroxyl group for DNA polymerase to start adding nucleotides.

What does DNA ligase do during DNA replication?

DNA ligase forms phosphodiester bonds to join Okazaki fragments on the lagging strand and seal any remaining nicks in the DNA backbone.

What is the significance of high-fidelity replication?

High-fidelity replication is important because DNA polymerases can proofread and correct incorrectly paired nucleotides, reducing errors.

What is the mitotic (M) phase?

The period of cell division, including mitosis and cytokinesis.

What occurs during mitosis?

Nuclear division where replicated chromosomes are separated into two new nuclei.

What is cytokinesis?

Cytoplasmic division where the cell physically divides into two daughter cells.

What are chromosomes made of?

Chromatin, which is DNA tightly associated with proteins like histones.

What is a chromatid?

A single, linear DNA molecule before DNA replication.

What are sister chromatids?

Identical copies of a chromosome joined at the centromere after DNA replication.

What is the function of the centromere?

It is the constricted region on a chromosome where sister chromatids are attached.

What happens to chromosomes during prophase?

Chromosomes condense and become visible; the mitotic spindle begins to form.

What occurs during prometaphase?

The nuclear envelope fragments, and spindle microtubules attach to kinetochores.

What is the metaphase stage of mitosis?

All chromosomes align along the metaphase plate, ensuring equal tension on sister chromatids.

What happens during anaphase?

Cohesin proteins are cleaved, sister chromatids separate and are pulled to opposite poles.

What occurs during telophase?

Chromosomes decondense, nuclear envelopes reassemble, and the mitotic spindle disassembles.

What is the role of the contractile ring in cytokinesis?

It forms beneath the plasma membrane and contracts to pinch the cell into two daughter cells.

What are centrosomes?

Main microtubule-organizing centers in animal cells that duplicate during interphase.

What is the mitotic spindle?

A complex array of microtubules that orchestrates chromosome movement during mitosis.

What are kinetochores?

Protein structures at centromeres that serve as attachment points for spindle microtubules.

What is the G1 checkpoint?

The most crucial checkpoint that assesses cell size, nutrient availability, and DNA integrity.

What is the G2 checkpoint?

Ensures that DNA replication is complete and undamaged before entering mitosis.

What is the M checkpoint?

Ensures all chromosomes are properly attached to the spindle before anaphase begins.

What are cyclins?

Proteins whose concentrations fluctuate cyclically throughout the cell cycle.

What are cyclin-dependent kinases (CDKs)?

Enzymes that phosphorylate target proteins to activate or inactivate them.

What is MPF?

Maturation-Promoting Factor, a complex of M-phase cyclin and M-CDK that drives the G2 to M transition.

What is the role of environmental factors at the G1/S transition?

They regulate cell division through signals like mitogens and anchorage dependence.

What characterizes cancer cells?

Uncontrolled proliferation, invasiveness, and the ability to metastasize.

What is aneuploidy?

An incorrect number of chromosomes, which can lead to cell death or disease.

What happens if a kinetochore is not properly attached?

The M checkpoint remains active, preventing the activation of separase and halting anaphase.

What is metastasis?

The spread of cancer to distant parts of the body, forming secondary tumors.

What is the monoclonal origin of most cancers?

Most cancers originate from a single cell that has accumulated a series of genetic mutations.

Define carcinogenesis.

A multi-step process involving the accumulation of multiple mutations over time that disable cell cycle controls.

What are proto-oncogenes?

Normal genes that promote cell growth and division; when mutated, they become oncogenes.

What happens when proto-oncogenes mutate?

They become oncogenes, which are hyperactive or overexpressed, promoting cancer.

Give an example of a proto-oncogene.

The Ras gene, which encodes a protein involved in growth factor signaling.

What are tumor suppressor genes?

Normal genes that inhibit cell division, repair DNA damage, or induce apoptosis.

What occurs when tumor suppressor genes are mutated?

They lose function, removing the 'brakes' on cell division, which can lead to cancer.

What is the role of the p53 gene?

It is a crucial tumor suppressor that detects DNA damage and can halt the cell cycle or trigger apoptosis.

What is meiosis?

A specialized type of cell division that produces haploid gametes from diploid cells, essential for sexual reproduction.

What is the difference between haploid and diploid cells?

Haploid (n) cells contain a single set of chromosomes, while diploid (2n) cells contain two sets.

What are somatic cells?

All body cells except gametes; they divide by mitosis.

What are germ cells?

Cells that produce gametes (sperm and egg) through meiosis.

What is a karyotype?

An ordered display of an organism's full set of chromosomes, arranged in homologous pairs.

What are homologous chromosomes?

A pair of chromosomes that are of the same length and carry genes for the same traits at the same loci.

What occurs during Prophase I of meiosis?

Chromosomes condense, homologous chromosomes pair up, and crossing over occurs.

What is independent assortment?

The random orientation of homologous pairs at the metaphase plate during Meiosis I.

What happens during Anaphase I of meiosis?

Homologous chromosomes separate and move towards opposite poles, while sister chromatids remain attached.

What is the outcome of Meiosis II?

It results in four genetically distinct haploid daughter cells.

What is the purpose of meiosis?

To produce gametes for sexual reproduction and ensure genetic diversity.

How does meiosis contribute to genetic variation?

Through crossing over, independent assortment, and random fertilization.

What is the difference between mitosis and meiosis regarding the number of divisions?

Mitosis involves one division, while meiosis involves two divisions (Meiosis I and Meiosis II).

What is the significance of crossing over?

It increases genetic variation by exchanging genetic material between homologous chromosomes.

What is the result of mutations in oncogenes?

They lead to uncontrolled cell division and contribute to cancer development.

What is the role of the synaptonemal complex?

It facilitates the pairing of homologous chromosomes during Prophase I.

What happens during Telophase I and Cytokinesis?

Chromosomes arrive at the poles, and two haploid daughter cells are formed.

What is the role of kinetochores during meiosis?

They attach to microtubules from the spindle apparatus to facilitate chromosome movement.

What is the difference in daughter cells produced by mitosis and meiosis?

Mitosis produces two genetically identical diploid cells, while meiosis produces four genetically different haploid cells.

What is independent assortment of chromosomes?

The random orientation of homologous pairs at the metaphase plate during Meiosis I, resulting in independent sorting of maternal and paternal homologs.

How many possible combinations of chromosomes can humans produce through independent assortment?

Approximately 8.4 million combinations.

What is crossing over in genetics?

The exchange of genetic material between non-sister chromatids of homologous chromosomes during Prophase I, creating recombinant chromosomes.

What is random fertilization?

The fusion of any one of millions of sperm with any one of millions of eggs, leading to unique zygotes and increased genetic diversity.

Who is Gregor Mendel?

An Austrian monk known for establishing the principles of heredity through experiments with pea plants.

What did Mendel's experiments with pea plants demonstrate?

Traits are inherited as discrete units (genes) rather than through blending inheritance.

What is blending inheritance?

The outdated idea that parental traits mix to produce intermediate offspring phenotypes.

Why did Mendel choose pea plants for his experiments?

They are easy to cultivate, have a short generation time, and exhibit distinct heritable traits.

What is a true-breeding organism?

An organism that produces offspring identical to itself when self-pollinated, being homozygous for the traits.

What is hybridization?

The mating or crossing of two true-breeding individuals with contrasting traits.

What is a monohybrid cross?

A genetic cross between two individuals that are heterozygous for one particular gene.

What does the P generation refer to?

The true-breeding parents used in an initial genetic cross.

What is the F1 generation?

The first generation of offspring resulting from the P generation cross.

What is the F2 generation?

The offspring produced by self-pollination or crossing of F1 individuals.

What is an allele?

A specific variant or form of a gene.

What is a dominant allele?

An allele whose phenotypic effect is fully expressed in a heterozygote.

What is a recessive allele?

An allele whose effect is masked in a heterozygote and expressed only when homozygous.

What does homozygous mean?

Having two identical alleles for a particular gene.

What does heterozygous mean?

Having two different alleles for a particular gene.

What is genotype?

The genetic makeup of an individual, specifically the combination of alleles for a gene.

What is phenotype?

The observable physical or biochemical characteristics of an individual.

What is Mendel's Law of Segregation?

The principle that alleles for a single gene segregate from each other during gamete formation.