Chapter 2: Biological and Environmental Foundations

Alleles

A variation of a gene that influences an individual’s characteristics.

Amniocentesis

A prenatal diagnostic procedure in which a small sample of the amniotic fluid is extracted from the mother’s uterus and subject to genetic analysis.

Carrier

An individual who is heterozygous for a particular trait, in which a recessive gene is not expressed in the phenotype yet may be passed on to the carrier’s offspring.

Chorionic villus sampling (CVS)

Prenatal diagnostic test that is conducted on cells sampled from the chorion to detect chromosomal abnormalities.

Chromosomes

One of 46 rod-like molecules that contain 23 pairs of DNA found in every body cell and collectively contain all of the genes.

Crossing-over

The exchange of genes between homologous chromosomes during meiosis, creating new combinations of traits.

DNA

The chemical structure, shaped like a twisted ladder, that contains all of the genes.

Dominant-recessive inheritance

A form of genetic inheritance in which the phenotype reflects only the dominant allele of a heterozygous pair.

Down syndrome

A condition in which a third, extra chromosome appears at the 21st site; also known as trisomy 21. Down syndrome is associated with distinctive physical characteristics accompanied by developmental disability.

Dizygotic (DZ) twins

Occurs when two ova are released and each is fertilized by a different sperm, and the resulting offspring share 50% of the genetic material; also known as a fraternal twin.

Epigenetic framework

A perspective emphasizing that development results from bidirectional exchanges between heredity and all levels of the environment.

Gametes

A reproductive cell; sperm in males and ovum in females.

Genes

The basic unit of heredity; a small section of a chromosome that contains the string of chemicals (DNA) that provide instructions for the cell to manufacture proteins.

Gene-environment correlation

The idea that many of an individual’s traits are supported by his or her genes and environment; there are three types of correlations: passive, reactive, and active.

Gene-environment interactions

Refer to the dynamic interplay between genes and our environment in determining characteristics; behavior; physical, cognitive, and social development as well as health.

Genetic counseling

A medical specialty that helps prospective parents determine the probability that their children will inherit genetic defects and chromosomal abnormalities.

Genome

The complete set of genes or genetic material present in a cell or organism.

Genomic imprinting

The instance when the expression of a gene is determined by whether it is inherited from the mother or father.

Genotype

An individual’s collection of genes that contains instructions for all physical and psychological characteristics, including hair, eye color, personality, health, and behavior.

Heritability

The statistic that indicates the extent to which variation of a certain trait can be traced to genes.

Heterozygous

Alleles of the pair of chromosomes are different

• the trait expressed will depend on the relations among the genes.

Homozygous

Alleles of the pair of chromosomes are alike

• the person will display the inherited trait

Incomplete dominance

A genetic inheritance pattern in which both genes are expressed in the phenotype.

In vitro fertilization

Fertilization, the creation of zygotes, through mixing sperm with ova that have been surgically removed from the woman’s body.

Monozygotic (MZ) twins

Occurs when the zygote splits apart early in development, and the resulting offspring share 100% of their genetic material; also known as an identical twin.

Mutations

A sudden permanent change in the structure of genes.

Niche-picking

An active gene–environment correlation in which individuals seek out experiences and environments that complement their genetic tendencies.

Noninvasive prenatal testing (NIPT)

A prenatal diagnostic that samples cell-free fetal DNA from the mother’s blood for chromosomal abnormalities.

Phenotype

A person's observable physical traits, such as eye color, hair color, or height.

Polygenic inheritance

Occurs when a trait is a function of the interaction of many genes, such as with height, intelligence, and temperament.

Range of reaction

The concept that a genetic trait may be expressed in a wide range of phenotypes dependent on environmental opportunities and constraints.

Ultrasound

Prenatal diagnostic procedure in which high-frequency sound waves are directed at the mother’s abdomen to provide clear images of the womb projected onto a video monitor.

Zygote

A fertilized ovum.

Multifactorial

Characteristics or traits determined by the interaction of multiple genetic and environmental factors.

X chromosome

The sex chromosome present in both sexes, with females typically possessing two copies and males possessing one.

X-linked disorders

Inherited conditions resulting from recessive alleles on the female sex chromosome, making males significantly more susceptible.

Y chromosome

The sex chromosome present only in males.