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Chapter 21

Alleles One of two or more different genes for a particular characteristic
Amnion An embryonic membrane that holds the fetus suspended in amniotic fluid; fuses with the chorion by the end of the third month ofgestation
Amniotic fluid The fluid contained within the amnion; cushions the fetus and absorbs shock
Autosomes Chromosomes other than the sex chromosomes; for people there are 22 pairs of autosomes in each somatic cell
Cleavage The series of mitotic cell divisions that take place in a fertilized egg; forms the early multicellular embryonic stages
Embryo The developing human individual from the time of fertilization until the eighth week of gestation
Genotype The genetic makeup of an individual; the genes that are present
Gestation The length of time from conception to birth; the human gestation period averages 280 days
Heterozygous Having two different alleles for a trait
Homologous pair A pair of chromosomes, one maternal and one paternal, that contain genes for the same characteristics
Homozygous Having two similar alleles for a trait
Implantation Embedding of the embryonic blastocyst in the endometrium of the uterus 5 to 8 days after fertilization
Labor The process by which a fetus is expelled from the uterus through the vagina to the exterior of the body
Parturition The act of giving birth
Phenotype appearance of the individual as related to genotype; the expression of the genes that are present
Sex chromosome The pair of chromosomes that determines the gender of an individual; designated XX in females and XY in males
Created by: HannahJaneC