Development Through Life5

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Gene Pool

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The genetic information contained in the genes of the population or culture that providese the ancestry for an individual.

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Chromosomes

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One of the rodlike bodies in a cell nucleus that contains genetic material and that divides when the cell divides. In humans, there are 23 pairs of chromosomes.

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Genes

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The fundamental physical unit of heredity. A gene is as linear sequence of nucleotides along a segment of DNA that carries the coded instructions for the synthesis of RNA, which, when translated into protein, leads to heredityary characteristics.

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Alleles

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The alternate state of a g ene at a given locus.

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Homozygous

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Characterized by the presence of two matched alleles of a particular gene at the same locus.

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Heterozygous

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Characterized by the presence of different alleles of a particular gene at the same locus.

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Genotype

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The hereditary information contained in the cells of an individual. Genotype may or may not be observable in the phenotype. See phenotype.

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Phenotype

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The observable characteristics that result from the interaction of a particular genotype and a particular environment.

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Cumulative Relation

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In heredity, when the allelic states of a gene in a single pair of chromosomes combine to influence a trait.

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Codominance

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A condition in which both alleles of a specific gene contribute to the characteristic that is expressed, as in AB blood type.

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Dominance

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If one allele is present, its characteristic is always observed, whether the other allele of the allelic pair is the same or not.

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Sex-Linked Characteristics

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Characteristics for which the allele is found on the sex chromosomes.

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Zygotes

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The first phase of fetal development, when a single cell is formed from two gametes.

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Autosomal

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Being or pertaining to a chromosome other than a sex chromosome.

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Genetic Counseling

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Recent discoveries make it possible to identify the genes responsible for certain forms of disease and genetic anomalies. Couples who have reason to believe that they may carry genes for one of these disorders can be tested and advised about the probability of having children who may be afflicted.

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Nuclear Transplantation

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A procedure in which the nucleus of an egg cell, which contains its DNA, removed and replaced with the DNA from an adult cell.

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Reaction Range

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The range of possible responses to environmental conditions that is established through genetic influences.

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Zygote

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The first phase of fetal development, when a single cell is formed from two gametes.

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Monozygotic (MZ) Twins

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Twins who develop from a single fertilized egg. These twins have identical genetic characteristics.

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Identical Twins

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Children born at the same time who developed from the same ovum.

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Fraternal Twins

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Children born at the same time who developed from two different ova.

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Dizygotic Twins

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Twins developed from two separate fertilized ova; also called fraternal twins.

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Infertility

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Inability to conceive or carry a fetus through the gestational period.

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Embryo

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The developing human individual from the time of implantation to the end of the eighth week after conception.

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Amniotic Sac

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A thin membrane forming a closed sac around the embryo and containing a fluid in which the embryo is immersed.

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Placenta

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The vascular organ that connects the fetus to the maternal uterus and mediates metaolic exchanges.

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Teratogens

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Agents that produce malformations during the formation of organs and tissues.

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Quickening

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Sensations of fetal movement, usually beginning during the second trimester of fetal growth.

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Labor

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The period of involuntary contractions of the uterine muscles that occurs prior to giving birth.

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Effacement

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The shortening of the cervical canal preceding childbirth.

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Dilation

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The condition of being stretched open beyond normal limits.

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Fetal Alcohol Syndrome

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A condition of the fetus involving central nervous system disorders, low birthweight, and malformations of the face; the condition is associated with heavy use of alcohol by mothers, especially during the last trimester of pregnancy.

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Birth Culture

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A culture's beliefs, values, and guidelines for behavior regarding pregnancy and childbirth.

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Solicitude

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State of caring, attentiveness, and helpfulness.

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Abortion

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Termination of a pregnancy before the fetus is capable of surviving outside the uterus.

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Miscarriage

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Spontaneous termination of a pregnancy.

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Viability

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Reaching the stage of development in which a fetus is capable of living outside the uterus.