Exam 2 Vocabulary Genetics

• Discontinuous variation: Phenotypes that fall into two or more distinct, nonoverlapping classes.

• Continuous variation: A distribution of phenotypic characters that is distributed from one extreme to another in overlapping, or continuous, fashion.

• Complex traits: Traits controlled by multiple genes, the interaction of genes with each other, and with environmental factors where the contributions of genes and environment are undefined.

• Polygenic traits: Traits controlled by two or more genes.

• Multifactorial traits: Traits that result from the interaction of one or more environmental factors and two or more genes.

• Complex traits: Traits controlled by multiple genes and the interaction of environmental factors where the contribution of genes and environment are undefined.

• Regression to the mean: In a polygenic system, the tendency of offspring of parents with one of the extreme phenotypes to exhibit phenotypes that are closer to the population average.

• Epigenetics: Reversible chemical modifications of chromosomal DNA (such as methylation of bases) and/or associated histone proteins that change the pattern of gene expression without affecting the nucleotide sequence of the DNA.

• Genetic variance: The phenotypic variance of a trait in a population that is attributed to genotypic differences.

• Environmental variance: The phenotypic variance of a trait in a population that is attributed to differences in the environment.

• Heritability: An expression of how much of the observed variation in a phenotype is due to differences in genotype.

• Correlation coefficients: Measures of the degree to interdependence of two or more variables.

• Monozygotic (MZ) twins: Twins derived from a single fertilization event involving one egg and one sperm; such twins are genetically identical.

• Dizygotic (DZ) twins: Twins derived from two separate and nearly simultaneous fertilization events, each involving one egg and one sperm. Such twins share, on average, 50 percent of their genes.

• Concordance: Agreement between traits exhibited by both twins.

• Leptin: A hormone produced by fat cells that signals the brain and ovary. As fat levels become depleted, secretion of leptin slows and eventually stops.

• Intelligence quotient (IQ): A score derived from standardized tests that is calculated by dividing the individual's mental age (determined by the test) by his or her chronologic age, and multiplying the quotient by 100.

• General cognitive ability: Characteristics that include verbal and spatial abilities, memory, speed of perception, and reasoning.

• Centromere: A region of a chromosome to which spindle fibers attach during cell division. The location of a centromere gives a chromosome its characteristic shape.

• Telomere: Short repeated DNA sequences located at each end of chromosomes.

• Metacentric: Describes a chromosome that has a centrally placed centromere.

• Submetacentric: Describes a chromosome whose centromere is placed closer to one end than the other.

• Acrocentric: Describes a chromosome whose centromere is placed very close to, but not at, one end.

• Sex chromosomes: Chromosomes involved in sex determination. In humans, the X and y chromosomes are the sex chromosomes.

• Autosomes: Chromosomes other than the sex chromosomes. In humans, chromosomes 1 to 22 are autosomes.

• Karyotype: A complete set of chromosomes from a cell that has been photographed during cell division and arranged in a standard sequence.

• Amniocentesis: A method of sampling the fluid surrounding the developing fetus by inserting a hollow needle and withdrawing suspended fetal cells and fluid; used in the diagnosing fetal genetic and developmental disorders; usually performed in the 16th week of pregnancy.

• Chorionic villus sampling (CVS): A method of sampling fetal chorionic cells by inserting a catheter through the vagina or abdominal wall into the uterus. Used in diagnosing biochemical and cytogenetic defects in the embryo. Usually performed in the eighth or ninth week of pregnancy.

• Polyploidy: A chromosomal number that is a multiple of the normal haploid chromosome set.

• Aneuploidy: A chromosomal number that is not an exact multiple of the haploid set.

• Monosomy: A condition in which one member of a chromosomal pair is missing; having one less than the diploid number (2n - 1)

• Trisomy: A condition in which one chromosome is present in three copies, whereas all others are diploid; having one more than the diploid number (2n + 1)

• Triploidy: A chromosomal number that is three times the haploid number, having three copies of all autosomes and three sex chromosomes.

• Tetraploidy: A chromosomal number that is four times the haploid number, having four copies of all autosomes and four sex chromosomes.

• Nondisjunction: The failure of homologous chromosomes to properly separate during meiosis or mitosis.

• Trisomy 21: Aneuploidy involving the presence of an extra copy of chromosome 21, resulting in Down syndrome.

• Turner syndrome: A monosomy of the X chromosome (45,X) that results in female sterility.

• Klinefelter syndrome: Aneuploidy of the sex chromosomes involving XXY chromosomal constitution.

• XYY karyotype: Aneuploidy of the sex chromosomes involving an XYY chromosome constitution.

• Cri du chat syndrome: A deletion of the short arm of chromosome 5 associated with an array of congenital malformations, the most characteristic of which is an infant cry that resembles a meowing cat.

• Uniparental disomy (UPD): A condition in which both copies of a chromosome are inherited from one parent.

• Fragile-X syndrome: An X chromosome that carries a gap, or break, at band q27; associated with intellectual disability in males.

Zygote: The fertilized egg that develops into a new individual.

• Sperm: Male gamete.

• Oocyte: Female gamete.

• Gametes: Unfertilized germ cells.

• Gonads: Organs where gametes are produced.

• Testes: Male gonads that produce sperm and male sex hormones.

• Ovaries: Female gonads that produce oocytes and female sex hormones.

• Scrotum: A pouch of skin on the male body that contains the testes.

• Seminiferous tubule: Small, tightly coiled tubes inside the testes where sperm are produced.

• Spermatogenesis: The process of sperm production.

• Spermatocytes: Diploid cells that undergo meiosis to form haploid spermatids.

• Epididymis: A part of the male reproductive system where sperm are stored.

• Vas deferens: A duct connected to the epididymis, which sperm travels through.

• Ejaculatory duct: In males, a short connector from the vas deferens to the urethra.

• Urethra: A tube that passes from the bladder and opens to the outside. It functions in urine transport and, in males, also carries sperm.

• Seminal vesicles: Glands in males that secrete fructose and prostaglandins into semen.

• Prostaglandins: Locally acting chemical messengers that stimulate contraction of the female reproductive system to assist in sperm movement.

• Prostate gland: A gland that secretes a milky, alkaline fluid that neutralizes acidic vaginal secretions and enhances sperm viability.

• Bulbourethral glands: Glands in the male that secrete a mucus-like substance that provides lubrication for intercourse.

• Semen: A mixture of sperm and various glandular secretions, containing 5% sperm.

• Follicle: A developing egg surrounded by an outer layer of follicle cells, contained in the ovary.

• Ovulation: The release of a secondary oocyte from the follicle; usually occurring monthly during a female’s reproductive lifetime.

• Oviduct: A duct with fingerlike projections partially surrounding the ovary and connecting to the uterus. Also called the fallopian, or uterine, tube.

• Uterus: A hollow, pear-shaped muscular organ where an embryo will implant and develop throughout pregnancy.

• Endometrium: The inner lining of the uterus that is shed at menstruation if fertilization has not occurred.

• Cervix: The lower neck of the uterus, opening into the vagina.

• Vagina: The opening that receives the penis during intercourse and also serves as the birth canal.

• Oogenesis: The process of oocyte production.

• Oogonia: Cells that produce primary oocytes by mitotic division.

• Fertilization: The fusion of two gametes to produce a zygote.

• Blastocyst: The developmental stage at which the embryo implants into the uterine wall.

• Trophoblast: The outer layer of cells in the blastocyst that gives rise to the membranes surrounding the embryo.

• Inner cell mass: A cluster of cells in the blastocyst that gives rise to the embryonic body. The inner cell mass contains the embryonic stem cells.

• Chorion: A two-layered structure formed during embryonic development from the trophoblast.

• Teratogen: Any physical or chemical agent that brings about an increase in congenital malformations.

• Fetal alcohol syndrome (FAS): A constellation of birth defects caused by maternal alcohol consumption during pregnancy.

• Sex ratio: The proportion of males to females, which changes throughout the life cycle. The ratio is close to 1:1 at fertilization, but the ratio of females to males increases as the population ages.

• SRY: A gene, called the sex-determining region of the Y, located near the end of the short arm of the Y chromosome that plays a major role in causing undifferentiated gonad to develop into a testis.

• Testosterone: A steroid hormone produced by the testis; the male sex hormone.

• Anti-Müllerian hormone (AMH): A hormone produced by the developing testis that causes the breakdown of the Müllerian ducts in the embryo.

• Complete androgen insensitivity (CAIS): An X-linked genetic trait that causes XY individuals to develop into phenotypic females.

• Dosage compensation: A mechanism that regulates the expression of sex-linked gene products.

• Barr body: A densely staining mass found in the somatic nuclei of mammalian females; an inactivated X chromosome.

• Lyon hypothesis: The proposal that dosage compensation in mammalian females is accomplished by partially and randomly inactivating one of the two X chromosomes.

• X-inactivation center (Xic): A region on the X chromosome where inactivation begins.

• Sex-influenced traits: Traits controlled by autosomal genes that are usually dominant in one sex but recessive in the other sex.

• Pattern baldness: A sex influenced trait that acts like an autosomal dominant trait in males and an autosomal recessive trait in females.

• Sex-limited genes: Loci that produce a phenotype that is produced in only one sex.

  • Transformation: The process of transferring genetic information between cells by DNA molecules.

  • Transforming factor: The molecular agent of transformation; DNA.

  • Covalent bonds: Chemical bonds that result from electron sharing between atoms. Covalent bonds are formed and broken during chemical reactions.

  • Hydrogen bond: A weak chemical bonding force between hydrogen and another atom.

  • Deoxyribonucleic acid (DNA): A molecule consisting of antiparallel strands of polynucleotides that is the primary carrier of genetic information.

  • Ribonucleic acid (RNA): A nucleic acid molecule that contains the pyrimidine uracil and the sugar ribose. The several forms of RNA function in gene expression.

  • Nucleotide: The basic building block of DNA and RNA. Each nucleotide consists of a base, a phosphate, and a sugar.

  • Nitrogen-containing base: A purine or pyrimidine that is a component of nucleotides.

  • Purine: A class of double-ringed organic bases found in nucleic acids.

  • Pyrimidine: A class of single-ringed organic bases found in nucleic acids.

  • Adenine and guanine: Nitrogen-containing purine bases found in nucleic acids.

  • Thymine, uracil, and cytosine: Nitrogen-containing pyrimidine bases found in nucleic acids.

  • Sugar: In nucleic acids, either ribose, found in RNA, or deoxyribose, found in DNA. The difference between the two sugars is an OH group present in ribose and absent in deoxyribose.

  • Phosphate group: A compound containing phosphorus chemically bonded to four oxygen molecules.

  • Ribose and deoxyribose: Pentose sugars found in nucleic acids. Deoxyribose is found in DNA, ribose in RNA.

  • Semiconservative replication: A model of DNA replication that provides each daughter molecule with one old strand and one newly synthesized strand. DNA replicates in this fashion.

  • DNA polymerase: An enzyme that catalyzes the synthesis of DNA using a template DNA strand and nucleotides.

  • Chromatin: The DNA and protein components of chromosomes, visible as clumps or threads in nuclei.

  • Histones: DNA-binding proteins that help compact and fold DNA into chromosomes.

  • Nucleosome: A bead-like structure composed of histones wrapped with DNA.

  • Centromere: A regions of a chromosome to which spindle fibers attach during cell division. The location of a centromere gives a chromosome its characteristic shape.

  • Telomere: Short repeated DNA sequences located at each end of chromosomes.

  • Telomerase: An enzyme that adds telomere repeats to the ends of chromosomes, keeping them the same length after each cell division