Biology Unit 4

Gene linkage

The tendency of alleles on a single chromosome to be inherited together because they are located in a fixed order along the chromosome.

Locus

The specific physical location of an allele or gene on a chromosome.

Linkage group

All of the genes located on a single chromosome that tend to be inherited together and do not demonstrate independent assortment.

Recombinant gametes

Gametes containing new combinations of alleles that differ from either parent, produced in reduced proportions when crossing-over occurs between linked genes during meiosis.

Crossing-over

The exchange of genetic material between nonsister chromatids in a tetrad during meiosis, occurring more frequently between genes that are farther apart.

Autosomes

The 22 pairs of chromosomes in human cells that are the same in both males and females and do not determine the sex of the organism.

Sex chromosomes

The pair of chromosomes (XX in human females, XY in human males) that differ between the sexes and control sex-linked traits.

X-linked genes

Genes found exclusively on the X chromosome, containing about 2,000 genes with no matching alleles on the Y chromosome.

Y-linked genes

Genes found exclusively on the Y chromosome, containing approximately 200 genes.

Carrier

A female who is heterozygous for an X-linked recessive trait, meaning she exhibits a normal phenotype but is capable of passing the recessive allele to her offspring.

Color blindness

A common X-linked recessive disorder where an individual cannot distinguish certain colors, such as seeing bright greens as tans and reds as reddish brown.

Duchenne muscular dystrophy

An X-linked recessive genetic disorder characterized by a wasting away of the muscles, caused by the absence of the muscle protein dystrophin.

Fragile X syndrome

The most common cause of inherited mental impairment, associated with some forms of autism and caused by an abnormal number of repeat sequences in the genome.

Hemophilia

An X-linked recessive bleeding disorder in which the blood fails to clot or clots very slowly due to a lack of clotting factor VIII (Hemophilia A) or factor IX (Hemophilia B).

Incontinentia pigmenti

An X-linked dominant disorder that causes severe discoloration of the skin.

Karyotype

A visual display of an individual's chromosomes arranged in pairs according to their size, shape, and general appearance.

Nondisjunction

The failure of homologous chromosomes or sister chromatids to separate properly during meiosis I or meiosis II, resulting in gametes with an incorrect number of chromosomes.

Trisomy

A chromosomal abnormality in which an individual inherits three copies of a specific chromosome instead of the normal two.

Monosomy

A chromosomal abnormality in which an individual inherits only a single copy of a specific chromosome instead of the normal pair.

DNA (Deoxyribonucleic acid)

The stable genetic material that stores information for cell development, structure, and metabolism, capable of high-accuracy replication and transmission across generations.

S Strain (Streptococcus pneumoniae)

A virulent strain of bacteria that forms smooth colonies because it possesses a protective polysaccharide capsule, causing death when injected into mice.

R Strain (Streptococcus pneumoniae)

A nonvirulent strain of bacteria that forms rough colonies because it lacks a polysaccharide capsule, which does not kill mice upon injection.

Transformation

The process by which a cell's genotype and phenotype are altered by taking up foreign genetic material, discovered by Frederick Griffith when dead S strain bacteria transformed live R strain bacteria.

DNase

An enzyme that digests DNA, which was shown by Avery and his coinvestigators to prevent the transformation of bacteria.

Purines

Nitrogen-containing bases with a double-ring chemical structure; in DNA, these are Adenine (A) and Guanine (G).

Pyrimidines

Nitrogen-containing bases with a single-ring chemical structure; in DNA, these are Thymine (T) and Cytosine (C).

Complementary Base Pairing

The precise chemical pairing of nitrogenous bases in a nucleic acid double helix: Adenine pairs with Thymine (via two hydrogen bonds) and Guanine pairs with Cytosine (via three hydrogen bonds).

Antiparallel

The orientation of the two polynucleotide strands in a DNA double helix, where the strands run parallel to each other but in opposite directions (one 5' to 3', and the other 3' to 5').

Semiconservative replication

The mechanism of DNA replication in which each daughter double helix consists of one newly synthesized strand of nucleotides and one conserved template strand from the parent molecule.

DNA helicase

The enzyme that unwinds and "unzips" double-stranded DNA by breaking the hydrogen bonds holding the complementary base pairs together.

DNA polymerase

The enzyme that positions and joins complementary DNA nucleotides along separated template strands during replication, working only in the 5' to 3' direction.

Leading strand

The newly synthesized DNA strand that is built continuously in the direction of the unwinding DNA helicase.

Lagging strand

The newly synthesized DNA strand that is built discontinuously in short segments moving away from the replication fork.

Okazaki fragments

Short segments of DNA synthesized discontinuously on the lagging strand during DNA replication.

DNA ligase

An enzyme that links Okazaki fragments together and seals breaks in the sugar-phosphate backbone during DNA replication and biotechnology cloning procedures.

Gene expression

The process by which a specific gene sequence is utilized to direct the synthesis of a functional protein product, relying on mRNA, tRNA, and rRNA.

Transcription

The first process of gene expression, taking place in the nucleus, where a segment of DNA serves as a template to generate a complementary mRNA molecule.

Translation

The second process of gene expression, taking place in the cytoplasm at a ribosome, where the sequence of codons in mRNA dictates the precise sequence of amino acids in a polypeptide.

RNA polymerase

An enzyme that binds to a promoter region on DNA, opens the double helix, and joins complementary RNA nucleotides together to construct an RNA transcript.

Promoter

A specific sequence of DNA to which RNA polymerase binds to initiate the process of transcription.

Introns

Noncoding, intergenic regulatory segments of pre-mRNA that are excised during mRNA processing in eukaryotic cells.

Exons

The coding portions of a gene within pre-mRNA that remain after splicing and are joined together to form the mature mRNA molecule.

Codon

A three-nucleotide sequence in an mRNA molecule that specifies a particular amino acid or serves as a start or stop signal during translation.

Degenerate code

A property of the genetic code meaning that most amino acids are specified by more than one codon, which helps protect against harmful mutations.

Anticodon

A triplet of three bases on one end of a tRNA molecule that is complementary to a specific codon on an mRNA strand.

Polyribosome

A complex consisting of an mRNA molecule being translated simultaneously by several ribosomes to create multiple copies of a polypeptide.

Initiation

The first step of translation that uses initiation factors and energy to assemble the small ribosomal subunit, mRNA, initiator tRNA, and the large ribosomal subunit together.

Elongation

The second step of translation where the polypeptide chain increases in length one amino acid at a time as tRNAs deliver amino acids to the A site and translocation occurs.

Translocation

The movement of the ribosome along the mRNA molecule during elongation, shifting the mRNA forward by one codon length.

Termination

The final step of translation where the ribosome reaches an mRNA stop codon, causing the completed polypeptide to be released.

Biotechnology

The utilization of natural biological systems, living organisms, or derivatives thereof to create products or achieve specific technological or medical ends.

Genetic engineering

The direct manipulation of an organism's genome using biotechnology to improve characteristics, make products, or treat genetic disorders and cancer.

Genetically Modified Organism (GMO)

An organism whose genome has been modified, typically through the application of recombinant DNA technology.

Transgenic organism

A specific type of GMO that has had a functional gene from an entirely different species permanently inserted into its genome.

Gene cloning

The production of multiple identical copies of a single specific gene.

Recombinant DNA (rDNA)

A DNA molecule that contains genetic material originating from two or more different sources.

Vector

A piece of DNA, such as a bacterial plasmid, into which foreign DNA can be inserted to introduce it into a host cell.

Plasmids

Small, accessory rings of self-replicating DNA found in bacteria that are separate from the main bacterial chromosome and frequently used as vectors.

Restriction enzyme

An enzyme that cuts double-stranded DNA at precise nucleotide sequences, acting as "molecular scissors" to create gaps or sticky ends for gene cloning.

Sticky ends

Single-stranded, complementary ends of two different DNA molecules cleaved by the same restriction enzyme, facilitating insertion via base pairing.

DNA sequencing

A laboratory procedure used to determine the exact order of nucleotides within a specific segment of DNA.

Polymerase Chain Reaction (PCR)

An automated test-tube technique that amplifies a targeted DNA sequence, generating billions of identical copies within hours using a heat-insensitive DNA polymerase.

Denaturation

The first step of PCR where the double-stranded DNA mixture is heated to 95 degrees Celsius to separate it into single strands.

Annealing

The second step of PCR where the mixture is cooled to 50–60 degrees Celsius to allow primers to bind to the ends of the single DNA strands.

Extension

The third step of PCR occurring at 72 degrees Celsius where a temperature-insensitive DNA polymerase synthesizes complementary strands.

Gel electrophoresis

A technique used to separate DNA fragments according to size by migrating them through a gel matrix using an electrical current, where smaller fragments move faster.

DNA fingerprint

A distinctive pattern of bands produced by treating a genome with restriction enzymes and separating the fragments via gel electrophoresis.

Short Tandem Repeat (STR) profiling

A modern method of DNA analysis that measures variations in the number of times a short DNA sequence repeats at specific loci across different individuals.

Genome editing

A group of technologies that enable scientists to target and alter specific sequences in an organism's DNA by removing, adding, or replacing nucleotides.

CRISPR

The most widely used genome editing system, derived from prokaryotic immune defense mechanisms, which uses a guide RNA molecule and the Cas9 enzyme to target and cut specific DNA sequences.

Cas9

An endonuclease enzyme used in the CRISPR system that identifies and breaks both strands of a targeted genomic DNA sequence.

Bioreactors

Large fermentation vats in which transgenic bacteria are grown on a commercial scale to harvest their biotechnology products.

Protoplasts

Plant cells that have had their protective cell walls completely removed, making them accessible for genetic manipulation such as electroporation.