Lesson 3: Forming a New Life

• Fertilization or conception


  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