Genetics and Cell Division: Key Concepts for Biology Students

What is genome?

The complete set of genetic material in a cell.

What is chromatin?

DNA plus proteins in a loosely packed form.

What is chromosome?

A single continuous DNA molecule with associated proteins.

What are homologous chromosomes?

Chromosome pairs with the same genes but possibly different alleles.

What is a gene?

A segment of DNA that codes for a protein.

What is an allele?

A version of a gene.

What is a locus?

The location of a gene on a chromosome.

What does diploid mean?

Two sets of chromosomes (2n).

What does haploid mean?

One set of chromosomes (n).

What are sister chromatids?

Identical copies of a chromosome held together by cohesin.

When does DNA replication occur?

Occurs during S phase of interphase.

What is the purpose of mitosis?

To produce genetically identical cells.

What happens in prophase?

Chromosomes condense and the spindle begins to form.

What happens in prometaphase?

Nuclear envelope breaks down and spindle fibers attach to kinetochores.

What is a kinetochore?

A protein complex where spindle fibers attach.

What happens during metaphase?

Chromosomes line up at the metaphase plate.

What happens during anaphase?

Sister chromatids separate and move to opposite poles.

What happen during telophase?

Nuclear envelopes reform and chromosomes decondense.

What happens during cytokinesis?

Division of the cytoplasm.

What is MPF?

Mitosis Promoting Factor, a cyclin-CDK complex.

What are the cell cycle checkpoints?

Control points ensuring proper DNA replication and division.

What is the purpose of meiosis?

To produce haploid gametes and increase genetic variation.

How many divisions occur in meiosis?

2

What seperates in Meiosis I?

Homologous chromosomes separate.

What seperates in Meiosis II?

Sister chromatids separate.

What is synapsis?

Pairing of homologous chromosomes in Prophase I.

What is crossing over?

Exchange of DNA between non-sister chromatids.

What is a chiasma?

The physical site of crossing over.

What is independent assortment?

Random alignment of homologous chromosomes in Metaphase I.

How many gamete combinations are possible from independent assortment in humans?

2^23 (about 8.4 million)

What is nondisjunction?

Failure of homologous chromosomes or sister chromatids to separate.

What is aneuploidy?

An abnormal number of chromosomes.

What is trisomy?

An extra chromosome.

What is monosomy?

A missing chromosome.

Why are sex chromosome aneuploidies often less severe?

Often less severe due to X-inactivation and fewer Y genes.

What defines cancer cells?

Uncontrolled division and loss of differentiation.

What is metastasis?

Spread of cancer to other locations.

What is angiogenesis?

Formation of new blood vessels that feed tumors.

What are proto-oncogenes?

Normal genes that promote cell cycle progression.

What are oncogenes?

Mutated proto-oncogenes that are permanently activated.

What are tumor suppressor genes?

Genes that inhibit cell division or trigger apoptosis.

What is the p53 gene?

A tumor suppressor protein that regulates DNA repair and apoptosis.

What are mutator genes?

Genes responsible for DNA repair; when mutated, mutation rates rise.

What is a multi-hit model of cancer?

Several mutations must accumulate before cancer develops.

What do restriction enzymes do?

Cut DNA at specific sequences.

What are sticky ends?

Single-stranded overhangs created by restriction enzymes.

What is PCR?

A technique that rapidly amplifies DNA.

What enzyme does PCR use?

Taq polymerase

What are the steps of PCR?

Denaturation, annealing, extension.

What is gel electrophoresis?

A method for separating DNA fragments by size.

What is a plasmid?

A small circular DNA molecule used in gene cloning.

What is transformation?

When bacteria take up foreign DNA.

What is a transgenic organism?

An organism containing DNA from another species.

What is CRISPR-Cas9?

A gene editing technology that uses guide RNA and Cas9 to cut DNA.

What is guide RNA?

A RNA sequence that directs Cas9 to a specific DNA target.

What is NHEJ?

A rapid but error-prone repair mechanism that creates mutations.

What is HDR?

A precise DNA repair pathway that uses a template.

What is gene therapy?

Treating disease by modifying genes.

What is a phenotype?

The observable traits of an organism.

What is a genotype?

The genetic makeup of an organism.

What is a dominant allele?

An allele expressed when at least one copy is present.

What is a recessive allele?

An allele expressed only when two copies are present.

What is a monohybrid cross?

A cross involving one trait.

What is a dihybrid cross?

A cross involving two traits.

What is the 9:3:3:1 ratio?

The phenotypic ratio of a dihybrid cross with independent assortment.

What is the Law of Segregation?

Alleles separate during gamete formation.

What is the Law of Independent Assortment?

Genes on different chromosomes are inherited independently.

What is a test cross?

A cross with a homozygous recessive individual to determine an unknown genotype.

Why are males more affected by X-linked traits?

Males are more affected because they have only one X chromosome.

What is a carrier?

Someone who has one recessive allele but does not express the trait.

What is incomplete dominance?

When heterozygotes show an intermediate phenotype.

What is codominance?

When both alleles are fully expressed.

What is polygenic inheritance?

When multiple genes influence one trait.

What is pleiotropy?

When one gene affects multiple traits.

What is epistasis?

When one gene masks the expression of another gene.

What is penetrance?

The proportion of individuals with a genotype who show the phenotype.

What is expressivity?

The degree to which a phenotype is expressed.

What is a recombinant plasmid?

A plasmid containing DNA from another species.

What is a genetic marker?

A known DNA sequence used to identify individuals or alleles.

What is a DNA probe?

A labeled DNA strand used to detect the presence of specific DNA sequences.

What is gene cloning?

Making identical copies of a DNA segment using bacteria or plasmids.

What is a somatic mutation?

A mutation in body cells that cannot be inherited.

What is a germ-line mutation?

A mutation in egg or sperm cells that can be passed to offspring.

What is apoptosis?

Programmed cell death that removes damaged or unnecessary cells.

What is a stem cell?

A cell capable of self-renewal and differentiation into multiple cell types.

What is a mutagen?

Any agent (chemical, radiation, etc.) that increases the rate of DNA mutations.

What is gene regulation?

The control of when, where, and how much a gene is expressed.