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Key Terms Chapter 28: Development and Inheritance

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    62680
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    acrosomal reaction
    release of digestive enzymes by sperm that enables them to burrow through the corona radiata and penetrate the zona pellucida of an oocyte prior to fertilization
    acrosome
    cap-like vesicle located at the anterior-most region of a sperm that is rich with lysosomal enzymes capable of digesting the protective layers surrounding the oocyte
    afterbirth
    third stage of childbirth in which the placenta and associated fetal membranes are expelled
    allantois
    finger-like outpocketing of yolk sac forms the primitive excretory duct of the embryo; precursor to the urinary bladder
    allele
    alternative forms of a gene that occupy a specific locus on a specific gene
    amnion
    transparent membranous sac that encloses the developing fetus and fills with amniotic fluid
    amniotic cavity
    cavity that opens up between the inner cell mass and the trophoblast; develops into amnion
    autosomal chromosome
    in humans, the 22 pairs of chromosomes that are not the sex chromosomes (XX or XY)
    autosomal dominant
    pattern of dominant inheritance that corresponds to a gene on one of the 22 autosomal chromosomes
    autosomal recessive
    pattern of recessive inheritance that corresponds to a gene on one of the 22 autosomal chromosomes
    blastocoel
    fluid-filled cavity of the blastocyst
    blastocyst
    term for the conceptus at the developmental stage that consists of about 100 cells shaped into an inner cell mass that is fated to become the embryo and an outer trophoblast that is fated to become the associated fetal membranes and placenta
    blastomere
    daughter cell of a cleavage
    Braxton Hicks contractions
    weak and irregular peristaltic contractions that can occur in the second and third trimesters; they do not indicate that childbirth is imminent
    brown adipose tissue
    highly vascularized fat tissue that is packed with mitochondria; these properties confer the ability to oxidize fatty acids to generate heat
    capacitation
    process that occurs in the female reproductive tract in which sperm are prepared for fertilization; leads to increased motility and changes in their outer membrane that improve their ability to release enzymes capable of digesting an oocyte’s outer layers
    carrier
    heterozygous individual who does not display symptoms of a recessive genetic disorder but can transmit the disorder to his or her offspring
    chorion
    membrane that develops from the syncytiotrophoblast, cytotrophoblast, and mesoderm; surrounds the embryo and forms the fetal portion of the placenta through the chorionic villi
    chorionic membrane
    precursor to the chorion; forms from extra-embryonic mesoderm cells
    chorionic villi
    projections of the chorionic membrane that burrow into the endometrium and develop into the placenta
    cleavage
    form of mitotic cell division in which the cell divides but the total volume remains unchanged; this process serves to produce smaller and smaller cells
    codominance
    pattern of inheritance that corresponds to the equal, distinct, and simultaneous expression of two different alleles
    colostrum
    thick, yellowish substance secreted from a mother’s breasts in the first postpartum days; rich in immunoglobulins
    conceptus
    pre-implantation stage of a fertilized egg and its associated membranes
    corona radiata
    in an oocyte, a layer of granulosa cells that surrounds the oocyte and that must be penetrated by sperm before fertilization can occur
    cortical reaction
    following fertilization, the release of cortical granules from the oocyte’s plasma membrane into the zona pellucida creating a fertilization membrane that prevents any further attachment or penetration of sperm; part of the slow block to polyspermy
    dilation
    first stage of childbirth, involving an increase in cervical diameter
    dominant
    describes a trait that is expressed both in homozygous and heterozygous form
    dominant lethal
    inheritance pattern in which individuals with one or two copies of a lethal allele do not survive in utero or have a shortened life span
    ductus arteriosus
    shunt in the pulmonary trunk that diverts oxygenated blood back to the aorta
    ductus venosus
    shunt that causes oxygenated blood to bypass the fetal liver on its way to the inferior vena cava
    ectoderm
    primary germ layer that develops into the central and peripheral nervous systems, sensory organs, epidermis, hair, and nails
    ectopic pregnancy
    implantation of an embryo outside of the uterus
    embryo
    developing human during weeks 3–8
    embryonic folding
    process by which an embryo develops from a flat disc of cells to a three-dimensional shape resembling a cylinder
    endoderm
    primary germ layer that goes on to form the gastrointestinal tract, liver, pancreas, and lungs
    epiblast
    upper layer of cells of the embryonic disc that forms from the inner cell mass; gives rise to all three germ layers
    episiotomy
    incision made in the posterior vaginal wall and perineum that facilitates vaginal birth
    expulsion
    second stage of childbirth, during which the mother bears down with contractions; this stage ends in birth
    fertilization
    unification of genetic material from male and female haploid gametes
    fertilization membrane
    impenetrable barrier that coats a nascent zygote; part of the slow block to polyspermy
    fetus
    developing human during the time from the end of the embryonic period (week 9) to birth
    foramen ovale
    shunt that directly connects the right and left atria and helps divert oxygenated blood from the fetal pulmonary circuit
    foremilk
    watery, translucent breast milk that is secreted first during a feeding and is rich in lactose and protein; quenches the infant’s thirst
    gastrulation
    process of cell migration and differentiation into three primary germ layers following cleavage and implantation
    genotype
    complete genetic makeup of an individual
    gestation
    in human development, the period required for embryonic and fetal development in utero; pregnancy
    heterozygous
    having two different alleles for a given gene
    hindmilk
    opaque, creamy breast milk delivered toward the end of a feeding; rich in fat; satisfies the infant’s appetite
    homozygous
    having two identical alleles for a given gene
    human chorionic gonadotropin (hCG)
    hormone that directs the corpus luteum to survive, enlarge, and continue producing progesterone and estrogen to suppress menses and secure an environment suitable for the developing embryo
    hypoblast
    lower layer of cells of the embryonic disc that extend into the blastocoel to form the yolk sac
    implantation
    process by which a blastocyst embeds itself in the uterine endometrium
    incomplete dominance
    pattern of inheritance in which a heterozygous genotype expresses a phenotype intermediate between dominant and recessive phenotypes
    inner cell mass
    cluster of cells within the blastocyst that is fated to become the embryo
    involution
    postpartum shrinkage of the uterus back to its pre-pregnancy volume
    karyotype
    systematic arrangement of images of chromosomes into homologous pairs
    lactation
    process by which milk is synthesized and secreted from the mammary glands of the postpartum female breast in response to sucking at the nipple
    lanugo
    silk-like hairs that coat the fetus; shed later in fetal development
    let-down reflex
    release of milk from the alveoli triggered by infant suckling
    lightening
    descent of the fetus lower into the pelvis in late pregnancy; also called “dropping”
    lochia
    postpartum vaginal discharge that begins as blood and ends as a whitish discharge; the end of lochia signals that the site of placental attachment has healed
    meconium
    fetal wastes consisting of ingested amniotic fluid, cellular debris, mucus, and bile
    mesoderm
    primary germ layer that becomes the skeleton, muscles, connective tissue, heart, blood vessels, and kidneys
    morula
    tightly packed sphere of blastomeres that has reached the uterus but has not yet implanted itself
    mutation
    change in the nucleotide sequence of DNA
    neural fold
    elevated edge of the neural groove
    neural plate
    thickened layer of neuroepithelium that runs longitudinally along the dorsal surface of an embryo and gives rise to nervous system tissue
    neural tube
    precursor to structures of the central nervous system, formed by the invagination and separation of neuroepithelium
    neurulation
    embryonic process that establishes the central nervous system
    nonshivering thermogenesis
    process of breaking down brown adipose tissue to produce heat in the absence of a shivering response
    notochord
    rod-shaped, mesoderm-derived structure that provides support for growing fetus
    organogenesis
    development of the rudimentary structures of all of an embryo’s organs from the germ layers
    parturition
    childbirth
    phenotype
    physical or biochemical manifestation of the genotype; expression of the alleles
    placenta
    organ that forms during pregnancy to nourish the developing fetus; also regulates waste and gas exchange between mother and fetus
    placenta previa
    low placement of fetus within uterus causes placenta to partially or completely cover the opening of the cervix as it grows
    placentation
    formation of the placenta; complete by weeks 14–16 of pregnancy
    polyspermy
    penetration of an oocyte by more than one sperm
    primitive streak
    indentation along the dorsal surface of the epiblast through which cells migrate to form the endoderm and mesoderm during gastrulation
    prolactin
    pituitary hormone that establishes and maintains the supply of breast milk; also important for the mobilization of maternal micronutrients for breast milk
    Punnett square
    grid used to display all possible combinations of alleles transmitted by parents to offspring and predict the mathematical probability of offspring inheriting a given genotype
    quickening
    fetal movements that are strong enough to be felt by the mother
    recessive
    describes a trait that is only expressed in homozygous form and is masked in heterozygous form
    recessive lethal
    inheritance pattern in which individuals with two copies of a lethal allele do not survive in utero or have a shortened life span
    sex chromosomes
    pair of chromosomes involved in sex determination; in males, the XY chromosomes; in females, the XX chromosomes
    shunt
    circulatory shortcut that diverts the flow of blood from one region to another
    somite
    one of the paired, repeating blocks of tissue located on either side of the notochord in the early embryo
    syncytiotrophoblast
    superficial cells of the trophoblast that fuse to form a multinucleated body that digests endometrial cells to firmly secure the blastocyst to the uterine wall
    trait
    variation of an expressed characteristic
    trimester
    division of the duration of a pregnancy into three 3-month terms
    trophoblast
    fluid-filled shell of squamous cells destined to become the chorionic villi, placenta, and associated fetal membranes
    true labor
    regular contractions that immediately precede childbirth; they do not abate with hydration or rest, and they become more frequent and powerful with time
    umbilical cord
    connection between the developing conceptus and the placenta; carries deoxygenated blood and wastes from the fetus and returns nutrients and oxygen from the mother
    vernix caseosa
    waxy, cheese-like substance that protects the delicate fetal skin until birth
    X-linked
    pattern of inheritance in which an allele is carried on the X chromosome of the 23rd pair
    X-linked dominant
    pattern of dominant inheritance that corresponds to a gene on the X chromosome of the 23rd pair
    X-linked recessive
    pattern of recessive inheritance that corresponds to a gene on the X chromosome of the 23rd pair
    yolk sac
    membrane associated with primitive circulation to the developing embryo; source of the first blood cells and germ cells and contributes to the umbilical cord structure
    zona pellucida
    thick, gel-like glycoprotein membrane that coats the oocyte and must be penetrated by sperm before fertilization can occur
    zygote
    fertilized egg; a diploid cell resulting from the fertilization of haploid gametes from the male and female lines
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