The process by which sperm and ovum (the male and female gametes or sex cells) meet and an entirely new individual is created from parental genomes
Zygote
One-celled organism resulting from fertilization
Fertile window
The time during which conception is possible
Ovulation
Rupture of a mature follicle in either ovary and expulsion of its ovum that occurs about once every 28 days until menopause
Sperm
Produced in the testicles (testes), or reproductive glands, of a mature male at a rate of several hundred million a day and are ejaculated in the semen at sexual climax
Dizygotic Twins (fraternal twins)
Result of two separate eggs being fertilized by two different sperm to form two unique individuals
Monozygotic Twins (identical twins)
Result from the cleaving of one fertilized egg and are generally identical
Heredity
The genetic transmission of heritable characteristics from parents to offspring
Genetic Code
Sequence of bases within the DNA molecule; governs the formation of proteins that determine the structure and functions of living cells
Deoxyribonucleic Acid (DNA)
Chemical that carries inherited instructions for the development of all cellular forms of life
Chromosomes
Coils of DNA that consist of genes
Genes
The functional units of heredity; small segments of DNA located in definite positions on particular chromosomes
Human Genome
Complete sequence of genes in the human body; the reference point that shows the location of all genes
Meiosis
The sex cells undergo when they are developing, each sex cell ends up with only 23 chromosomes (one from each pair)
Mitosis
A process by which the non–sex cells divide in half over and over again, the DNA replicates itself, so that each newly formed cell has the same DNA structure as all the others
Mutations
Permanent alterations in genes or chromosomes that may produce harmful characteristics
Autosomes
The twenty-two pairs of chromosomes not related to sexual expression
Sex Chromosomes
The 23rd pair that governs the baby's sex; XX in the normal human female and XY in the normal human male (sex of the baby is determined by the male)
Alleles
Two or more alternative forms of a gene that occupy the same position on paired chromosomes and affect the same trait
Homozygous
Possessing two identical alleles for a trait
Heterozygous
Possessing differing alleles for a trait
Dominant Inheritance
When a child receives different alleles, only the dominant one is expressed
Recessive Inheritance
When a child receives identical recessive alleles, resulting in expression of a nondominant trait
Polygenic Inheritance
Interaction of multiple genes at different sites on chromosomes affect a complex trait
Incomplete Dominance
When a child receives two different alleles, resulting in partial expression of a trait
Phenotype
Observable characteristics of a person
Genotype
Genetic makeup of a person, containing both expressed and unexpressed characteristics
Multifactorial Transmission
Illustrates the interaction of nature (genetic factors) and nurture (environmental factors) to produce certain complex traits
Epigenesis or epigenetics
Mechanism that turns genes on or off, and determines functions of body cells
Genome Imprinting
The differential expression of certain genetic traits, depending on whether the trait has been inherited from the mother or the father
Sex-Linked Inheritance of Defects
Pattern of inheritance in which certain characteristics carried on the X chromosome inherited from the mother are transmitted differently to her male and female offspring
Carriers
Heterozygous females who carry one "bad" copy of a recessive gene and one "good" one
Chromosomal Abnormalities
Typically occur because of errors in cell division, resulting in an extra or missing chromosome
Genetic Counseling
Help prospective parents assess their risk of bearing children with genetic or chromosomal defects
Karyotype
A chart that shows chromosomal abnormalities and can indicate whether a person might transmit genetic defects
Behavioral Genetics
A quantitative study of relative hereditary and environmental influences on behavior
Heritability
Statistical estimate of contribution of heredity to individual differences in a specific trait within a given population
Concordant
Describes the tendency of twins to share the same trait or disorder
Reaction Range
Refers to the potential variability, depending on environmental conditions, in the expression of a hereditary trait
Canalization
Limitation on variance of expression of certain inherited characteristics