Chapter 2: Heredity, Prenatal Development, and Birth

Gene

The basic building block of heredity, providing the instructions for making proteins.

Chromosomes

Structures located within cells that contain genetic material; normal human cells have 46 chromosomes.

Genes in Humans

There are approximately 20,500 genes estimated in humans.

Mitosis

The process by which a cell’s nucleus makes an exact copy of all chromosomes and divides into new cells.

Meiosis

The process that results in gametes, where chromosomes duplicate and divide twice, producing four cells with half the genetic material.

Gametes

Reproductive cells (sperm or ova) that contain only 23 chromosomes each.

Genotype

The sum total of all inherited genes.

Phenotype

The observable features expressed by an organism that can be seen.

Homozygous

A person who inherits two identical versions of the same gene.

Heterozygous

A person who has two different versions of the same gene.

Dominant Gene

A gene that is heavily expressed in the phenotype even when paired with a different version.

Recessive Gene

A gene that is expressed only when paired with a similar version.

Alleles

Different versions of a gene.

Polygenic Genes

Characteristics that result from the interaction of several genes.

Monozygotic Twins

Genetically identical twins that develop from one egg that splits.

Dizygotic Twins

Fraternal twins that develop from two different eggs.

Genetic Disorders

Disorders that are most commonly linked to dominant genes.

Trisomy 21

Also known as Down Syndrome, this condition occurs when an individual has an extra 21st chromosome.

Behavioral Genetics

The study of how genetic and environmental factors influence behavior and traits.

Germinal Period

The first 14 days of prenatal development from conception to implantation.

Embryonic Period

Starting the third week of development when the blastocyst has implanted and is referred to as an embryo.

Fetal Period

The stage from the ninth week until birth, during which the developing body parts and functions mature.

Teratology

The study of factors that contribute to birth defects.

Teratogens

Environmental factors that can lead to birth defects.

Maternal Factors

Conditions such as gestational diabetes, high blood pressure, Rh disease, weight gain, stress, and depression that can affect pregnancy.