Human Development Ch2

DNA

Long, double-stranded molecules that make up chromosomes.

Chromosomes

Rodlike structures in the cell nucleus that transmit and store genetic information.

Autosomes

The 22 matching pairs of chromosomes in each human cell.

Allele

Each of the 2 forms of a gene located at the same place on corresponding pairs of chromosomes.

Gene

A segment of DNA along the length of the chromosome containing instructions for making proteins that contribute to body growth and functioning.

Gametes

Sex cells or sperm and ovum, which contain half as many chromosomes as normal cells.

Meiosis

The process of cell division through which gametes are formed, halving the normal chromosome number in each cell.

Zygote

The newly fertilized cell when the sperm meets the ovum at conception.

Genotypes

An individual's genetic makeup, distinguished from phenotype.

Phenotypes

A person’s directly observable physical and behavioral characteristics, determined by both genetic and environmental factors.

Fraternal Twins

Twins resulting from the release and fertilization of two ova; genetically no more alike than ordinary siblings.

Identical Twins

Twins resulting from a zygote that duplicates and separates into two clusters of cells with the same genetic makeup.

Homozygous

Having two identical alleles at the same place on a pair of chromosomes.

Heterozygous

Having two different alleles at the same place on a pair of chromosomes.

Cystic Fibrosis

A recessive disease causing lungs, liver, and pancreas to secrete large amounts of thick mucus, leading to breathing and digestive difficulties.

Tay-Sachs Disease

A recessive disease leading to central nervous system degeneration with symptoms including poor muscle tone and blindness.

PKU

A recessive condition causing severe central nervous system damage due to inability to metabolize phenylalanine.

Sickle Cell Anemia

A recessive disease causing abnormal sickling of red blood cells, leading to oxygen deprivation and pain.

Mutations

Changes in the genetic material, some occurring spontaneously and others caused by hazardous environmental agents.

Risk Factor for Down Syndrome

Older maternal age increases the likelihood of the child having abnormalities or Down syndrome.

Genetic Counseling

A communication process designed to help couples assess their risk of having a baby with a hereditary disorder.

Amniocentesis

A prenatal diagnostic method with a small risk of miscarriage.

Chorionic Villus Sampling

A prenatal diagnostic method associated with a slightly greater risk of miscarriage than amniocentesis.

Fetoscopy

A prenatal diagnostic procedure that entails some risk of miscarriage.

Environmental Influences on Gene Expression

Factors that can affect how genes are expressed, including epigenesis and methylation.

Methylation

A biochemical process that reduces or silences gene expression, triggered by certain experiences.

Niche-Picking

A type of gene-environment correlation where individuals choose environments that complement their heredity.