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.

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 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 of interdependence of two or more variables.

Monozygotic (MZ) twins

Twins derived from a single fertilization event involving one egg and one sperm; they are genetically identical.

Dizygotic (DZ) twins

Twins derived from two separate and nearly simultaneous fertilization events; they 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, affecting appetite regulation.

Intelligence quotient (IQ)

A score derived from standardized tests that reflects an individual's cognitive abilities.

General cognitive ability

Characteristics including verbal and spatial abilities, memory, speed of perception, and reasoning.

Centromere

A region of a chromosome to which spindle fibers attach during cell division.

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, such as the X and Y chromosomes in humans.

Autosomes

Chromosomes other than the sex chromosomes, specifically chromosomes 1 to 22 in humans.

Karyotype

A complete set of chromosomes from a cell, arranged in a standard sequence.

Amniocentesis

A procedure to sample the fluid surrounding a developing fetus for diagnostic purposes.

Chorionic villus sampling (CVS)

A method of sampling fetal chorionic cells used to diagnose biochemical and cytogenetic defects.

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 where one member of a chromosomal pair is missing.

Trisomy

A condition where one chromosome is present in three copies.

Triploidy

A condition where a chromosome number is three times the haploid number.

Tetraploidy

A condition where a chromosome number is four times the haploid number.

Nondisjunction

The failure of homologous chromosomes to separate properly during cell division.

Trisomy 21

Aneuploidy involving an extra copy of chromosome 21, resulting in Down syndrome.

Turner syndrome

A condition resulting from a monosomy of the X chromosome, leading to female sterility.

Klinefelter syndrome

A condition involving an aneuploidy of sex chromosomes with an XXY configuration.

XYY karyotype

A condition involving an aneuploidy with an XYY chromosome constitution.

Cri du chat syndrome

A deletion of the short arm of chromosome 5 associated with congenital malformations.

Uniparental disomy (UPD)

A condition where both copies of a chromosome are inherited from one parent.

Fragile-X syndrome

An X chromosome that carries a gap at band q27 associated with intellectual disability in males.

Zygote

The fertilized egg that develops into a new individual.

Sperm

The male gamete.

Oocyte

The female gamete.

Gametes

Unfertilized germ cells produced by gonads.

Gonads

Organs where gametes are produced, such as testes and ovaries.

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 that contains the testes in males.

Seminiferous tubule

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

Part of the male reproductive system where sperm are stored.

Vas deferens

The duct that sperm travel through after leaving the epididymis.

Ejaculatory duct

Connector from the vas deferens to the urethra in males.

Urethra

The tube that connects to the outside for urine transport and sperm delivery.

Seminal vesicles

Glands in males that secrete components into semen.

Prostaglandins

Chemical messengers that assist in sperm movement within the female reproductive system.

Prostate gland

Gland that secretes alkaline fluid to enhance sperm viability.

Bulbourethral glands

Glands that secrete a mucus-like substance to lubricate for intercourse.

Semen

A mixture of sperm and glandular secretions.

Follicle

A developing egg surrounded by follicle cells, contained in the ovary.

Ovulation

The release of a secondary oocyte from the follicle.

Oviduct

Duct connecting the ovary to the uterus, involved in transport of oocytes.

Uterus

An organ where an embryo implants and develops throughout pregnancy.

Endometrium

The inner lining of the uterus that is shed if fertilization does not occur.

Cervix

The lower neck of the uterus that opens into the vagina.

Vagina

The female reproductive opening that receives the penis during intercourse.

Oogenesis

The process of producing oocytes.

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 supports embryo development.

Inner cell mass

A cluster of cells in the blastocyst that forms the embryonic body.

Chorion

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

Teratogen

Any agent that increases the risk of congenital malformations.

Fetal alcohol syndrome (FAS)

Birth defects caused by maternal alcohol use during pregnancy.

Sex ratio

The proportion of males to females in a population.

SRY gene

A gene on the Y chromosome that plays a major role in male sex determination.

Testosterone

The primary male sex hormone produced by the testes.

Anti-Müllerian hormone (AMH)

A hormone from the developing testis that affects reproductive system development.

Complete androgen insensitivity (CAIS)

An X-linked genetic condition leading XY individuals to develop as phenotypic females.

Dosage compensation

A mechanism that regulates the expression of sex-linked gene products.

Barr body

An inactivated X chromosome visible in the nuclei of female somatic cells.

Lyon hypothesis

Proposes that one of the two X chromosomes is inactivated in female mammals.

X-inactivation center (Xic)

The region on the X chromosome where inactivation starts.

Sex-influenced traits

Traits controlled by autosomal genes dominant in one sex but recessive in another.

Pattern baldness

A sex-influenced trait characterized differently in males and females.

Sex-limited genes

Loci that produce a phenotype in only one sex.

Transformation

The process of transferring genetic information between cells by DNA.

Transforming factor

The molecular agent of transformation, usually DNA.

Covalent bonds

Bonds formed by the sharing of electrons between atoms.

Hydrogen bond

A weak bond between a hydrogen atom and another atom.

Deoxyribonucleic acid (DNA)

The molecule that carries genetic information, consisting of polynucleotide strands.

Ribonucleic acid (RNA)

A nucleic acid that functions in gene expression and contains uracil.

Nucleotide

The basic building block of DNA and RNA, consisting of a base, sugar, and phosphate.

Nitrogen-containing base

A purine or pyrimidine 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 in nucleic acids.