Human Evolution (Ch. 3)

Adenine

One of the nitrogen bases that make up DNA and RNA; it pairs with thymine in DNA molecules and uracil in RNA molecules.

Adenosine Triphosphate (ATP)

An important cellular molecule created by the mitochondria and carrying the energy necessary for cellular functions.

Amino Acids

Organic molecules combined in a specific sequence by ribosomes to form a protein.

Antibodies

Molecules that form as part of the primary immune response to the presence of foreign substances; they attach to foreign antigens.

Anticodons

Sequences of three nitrogen bases carried by tRNA; they match up with the complementary mRNA codons, and each designates a specific amino acid during protein synthesis.

Antigens

Specific proteins, on the surfaces of cells, that stimulate the immune system’s antibody production.

Autosomes

All chromosomes, except the sex chromosomes, that occur in pairs in all somatic cells (not the gametes).

Coding DNA

Sequences of a gene’s DNA (also known as exons) that are coded to produce a specific protein and are transcribed and translated during protein synthesis.

Codominance

The condition in which two different alleles are equally dominant; both alleles are fully expressed in a heterozygote’s phenotype.

Codons

Sequences of three nitrogen bases carried by mRNA that are coded to produce specific amino acids in protein synthesis.

Complementary Bases

The predictable pairing of nitrogen bases in the structure of DNA and RNA, such that adenine and thymine always pair together (adenine and uracil in RNA) and cytosine and guanine pair together.

Crossing-over

The process by which homologous chromosomes partially wrap around each other and exchange genetic information during meiosis.

Cytoplasm

The jellylike substance inside the cell membrane that surrounds the nucleus and in which the organelles are suspended.

Cytosine

One of the nitrogen bases that make up DNA and RNA; it pairs with guanine.

Diploid Cell

A cell that has a full complement of paired chromosomes.

Epigenetic

Refers to chemical changes in the genome affecting how the underlying DNA is used in the production of proteins, but without altering the DNA sequences.

Essential Amino Acids

Those amino acids that cannot be synthesized in the body and, thus, must be supplied by the diet.

Eukaryotes

Multicelled organisms whose cells have a membrane-bound nucleus containing both the genetic material and specialized organelles.

Gametes

Sexual reproductive cells, ova and sperm, that have a haploid number of chromosomes and that can unite with a gamete of the opposite type to form a new organism.

Guanine

One of the nitrogen bases that make up DNA and RNA; it pairs with cytosine.

Haplogroups

A large set of haplotypes, such as the Y chromosome or mitochondrial DNA, that may be used to define a population.

Haploid Cell

A cell that has a single set of unpaired chromosomes, half of the number of chromosomes as a diploid cell.

Haplotypes

A group of alleles that tend to be inherited as a unit due to their closely spaced loci on a single chromosome.

Heteroplasmic

Regarding mitochondrial DNA or other organellar DNA, the quality of being different or varying among the parts of a single organism’s body or even within cells of the same type, usually due to the mutation of the DNA in some organelles but not in others.

Heterozygous

The condition in which the two alleles of a pair of alleles at a single locus on homologous chromosomes are different.

Homeotic (Hox) Genes

The genes responsible for differentiating the specific segments of the body, such as the head, tail, and limbs, during embryological development; also known as homeobox genes.

Homologous

Refers to chromosomes that occur in matching pairs in the genome.

Homoplasmic

Regarding nuclear DNA, the quality of being identical in each cell type (except red blood cells) within an organism.

Homozygous

The condition in which the two alleles of a pair of alleles at a single locus on homologous chromosomes are the same.

Karyotype

The complete set of chromosomes for an individual organism or a species. The karyotype is typically presented as a photograph of an individual’s chromosomes that have been arranged in homologous pairs and put in numerical order by size.

Law of Independent Assortment

Mendel’s second law, which asserts that the inheritance of one trait does not affect the inheritance of other traits.

Law of Segregation

Mendel’s first law, which asserts that the two alleles for any given gene (or trait) are inherited, one from each parent; during gamete production, only one of the two alleles will be present in each ovum or sperm.

Locus

The location on a chromosome of a specific gene.

Matriline

Lineage or inheritance that can be traced from mother to daughter or to son; mitochondrial DNA is matrilineal DNA.

Meiosis

The production of gametes through one DNA replication and two cell (and nuclear) divisions, creating four haploid gametic cells.

Messenger RNA (mRNA)

The molecules that are responsible for making a chemical copy of a gene needed for a specific protein—that is, for the transcription phase of protein synthesis.

Methylation

The attachment of a methyl group, a simple chemical, to DNA at certain sites throughout the genome.

Microsatellites

Also called short tandem repeats (STRs); sequences of repeated base pairs of DNA, usually no more than two to six. If repeated excessively, they are often associated with neurologic disorders, such as Huntington’s chorea.

Mitochondria

Energy-producing (ATP-producing) organelles in eukaryotic cells; mitochondria possess their own independent DNA.

Mitosis

The process of cellular and nuclear division that creates two identical diploid daughter cells.

Monosomy

The condition in which only one of a specific pair of chromosomes is present in a cell’s nucleus.

Noncoding DNA

Sequences of a gene’s DNA (also known as introns) that are not coded to produce specific proteins and are excised before protein synthesis.

Nondisjunctions

Failures of chromosomes to properly segregate during meiosis, creating some gametes with abnormal numbers of chromosomes.

Nucleotide

The building block of DNA and RNA, composed of a sugar, a phosphate group, and one of four nitrogen bases.

Nucleus

A membrane-bound structure in eukaryotic cells that contains the genetic material.

Omnigenic

Refers to complex traits that involve various parts of the genome and the interconnections among those parts.

Patriline

Lineage or inheritance that can be traced from father to son via the Y chromosome.

Peptide Bond

A chemical bond that joins amino acids into a protein chain.

Personal Genomics

The branch of genomics focused on sequencing individual genomes.

Phenome

The total set of phenotypic traits in an organism.

Pleiotropy

The phenomenon of a single gene having multiple effects.

Polygenic

Refers to one phenotypic trait that is affected by two or more genes.

Polymorphism

The presence of two or more alleles at a locus and such that the frequency of the alleles is greater than 1% in the population.

Polypeptide

Also known as a protein, a chain of amino acids held together by multiple Peptide bonds.

Prokaryotes

Single-celled organisms with no nuclear membranes or organelles and with their genetic material as a single strand in the cytoplasm.

Recombination

The exchange of genetic material between homologous chromosomes, resulting from a crossover event.

Regulatory Genes

Those genes that determine when structural genes and other regulatory genes are turned on and off for protein synthesis.

Regulatory Proteins

Proteins involved in the expression of control genes.

Replication

The process of copying nuclear DNA prior to cell division, so that each new daughter cell receives a complete complement of DNA.

Ribonucleic Acid (RNA)

A single-stranded molecule involved in protein synthesis, consisting of a phosphate, ribose sugar, and one of four nitrogen bases.

Ribosomal RNA (rRNA)

A fundamental structural component of a ribosome.

Ribosomes

The organelles attached to the surface of the endoplasmic reticulum, located in the cytoplasm of a cell; they are the site of protein synthesis.

Sex Chromosomes

The pair of chromosomes that determine an organism’s biological sex.

Single Nucleotide Polymorphisms (SNPs)

Variations in the DNA sequence due to the change of a single nitrogen base.

Somatic Cells

Diploid cells that form the organs, tissues, and other parts of an organism’s body.

Structural Genes

Genes coded to produce particular products, such as an enzyme or hormone, rather than regulatory proteins.

Structural Proteins

Proteins that form an organism’s physical attributes.

Thymine

One of four nitrogen bases that make up DNA; it pairs with adenine.

Transcription

The first step of protein synthesis, involving the creation of messenger RNA (mRNA) based on the DNA template.

Transfer RNA (tRNA)

The molecules that are responsible for transporting amino acids to the ribosomes during protein synthesis.

Translation

The second step of protein synthesis, involving the transfer of amino acids by transfer RNA (tRNA)to the ribosomes, which are then added to the protein chain.

Translocations

Rearrangements of chromosomes due to the insertion of genetic material from one chromosome to another.

Triplets

Sequences of three nitrogen bases each in DNA, known as codons in mRNA.

Trisomy

The condition in which an additional chromosome exists with the homologous pair.

Uracil

One of four nitrogen bases that make up RNA; it pairs with adenine.

Zygote

The cell that results from a sperm’s fertilization of an ovum.