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76 Cards in this Set
- Front
- Back
primary sex characteristics
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the structures directly involved in reproduction. The uterus and ovaries in
females and the testes in males are examples |
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secondary sex characteristics
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include such human features as
body hair (pubic hair and beards, for example), distribution of muscle and fat, voice quality, and breasts. Deer antlers, lion manes, and peacock tails are examples of secondary sex characteristics in nonhumans. In general, secondary sex characteristics are used to indicate sexual maturity or sexual readiness and to attract or locate mates, or are used by males to compete for females (visual displays and aggression). |
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Ovary
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the organ where ova (singular, ovum), or eggs, are produced. Each female has two ovaries
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Oviduct (or fallopian tube).
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Eggs move from the ovary to the uterus through the oviduct. There are two
oviducts, one for each ovary. |
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Uterus
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A fertilized ovum implants (attaches) on the inside wall, or endometrium, of the uterus. Development of
the embryo occurs here until birth. |
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Vagina.
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At birth, the fetus passes through the cervix (an opening in the uterus), through the vagina, and out of
the body. |
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seminiferous tubules
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for the production of sperm
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interstitial cells
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produce male sex hormones (testosterone and other androgens).
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Epididymis
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This coiled tube, one attached to each testis, is the site for final maturation and storage of the sperm
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Vas deferens
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Each of these two tubes transfers sperm from one epididymis to the urethra.
Sperm exit the penis through the urethra. |
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Seminal vesicles
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During ejaculation, these two glands secrete into the vas deferens mucus (which provides a liquid
medium for the sperm), fructose (which provides energy for the sperm), and prostaglandins (which stimulate uterine contractions that help sperm move into the uterus). |
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Prostate gland
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This gland secretes a milky alkaline fluid into the urethra and serves to neutralize the acidity of
urine that may still be in the urethra, as well as the acidity of the vagina. |
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Bulbourethral glands (or Cowper’s glands)
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These two glands secrete a small amount of fluid of unknown
function into the urethra. |
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Sperm head
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The head of the sperm contains the haploid nucleus with 23 chromosomes (in humans)
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acrosome
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At the tip of
the sperm head is the acrosome, a lysosome containing enzymes which are used to penetrate the egg. The acrosome originates from Golgi body vesicles that fuse to form a single lysosome. |
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Midpiece
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Opposite the acrosome, the flagellum, consisting of the typical 9 + 2 microtubule array, emerges from
the sperm head from one member of a pair of centrioles. The first part of the flagellum, the midpiece, is characterized by mitochondria that spiral around the flagellum and supply ATP for flagellar movement. |
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Tail.
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The remainder of the flagellum, behind the midpiece, is the tail. Sperm are propelled by whiplike motion of
the tail and midpiece. |
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oogonia
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divide by mitosis to produce primary
oocytes |
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primary oocytes
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All primary oocytes, however, progress only to prophase I. They remain at this stage
until puberty, at which time one primary oocyte during each menstrual cycle (averaging 28 days) continues its development through the remainder of meiosis I |
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follicle
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Development occurs within an envelope of encircling cells called a follicle,
which protects and nourishes the developing oocyte. |
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secondary oocyte
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During the remainder of meiosis I, cytoplasm is concentrated in only
one of the daughter cells (unequal cytokinesis). |
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polar body
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the other daughter cell is a polar body with very little cytoplasm
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Ovulation
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marks the release of the secondary oocyte from the follicle. If it is fertilized by a sperm as it moves through
the oviduct, the secondary oocyte will begin meiosis II and produce an egg that combines with the chromosomes contributed by the sperm. The second daughter cell of meiosis II, again a polar body, disintegrates. |
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spermatogonia
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divide by
mitosis repeatedly to produce primary spermatocytes that begin meiosis |
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secondary spermatocytes
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Meiosis I produces two of
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spermatids
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Meiosis II produces four of
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Sertoli cells
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Sertoli cells in the seminiferous tubules provide
nourishment to the spermatids as they differentiate into mature sperm. The sperm complete their development in the epididymis, where they are stored until needed. |
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initiate the reproductive cycle for female
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The hypothalamus monitors the
levels of estrogen and progesterone in the blood. In a negative feedback fashion, low levels of these hormones stimulate the hypothalamus to secrete GnRH, which, in turn, stimulates the anterior pituitary to secrete FSH and LH. |
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FSH stimulates
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the development of the follicle and the oocyte + the secretion of estrogen from the follicle
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Ovulation occurs by
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Positive feedback from rising levels of estrogen stimulate the anterior pituitary (through GnRH
from the hypothalamus) to produce a sudden midcycle surge of LH. This high level of LH triggers ovulation. |
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The corpus luteum secretes
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estrogen and progesterone. After ovulation, the follicle, now called the corpus
luteum, continues to develop under the influence of LH and secretes both estrogen and progesterone. |
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The endometrium thickens by
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Estrogen and progesterone stimulate the development of the endometrium, the inside
lining of the uterus. It thickens with nutrient-rich tissue and blood vessels in preparation for the implantation of a fertilized egg. |
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The hypothalamus and anterior pituitary terminate the reproductive cycle by
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Negative feedback from high levels
of estrogen and progesterone cause the anterior pituitary (through the hypothalamus) to abate production of FSH and LH. 8. The endometrium disintegrates. In the absence of FSH and LH, the corpus luteum deteriorates |
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The endometrium disintegrates. In the absence of
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FSH and LH, the corpus luteum deteriorates. As a result,
estrogen and progesterone production stops. Without estrogen and progesterone, growth of the endometrium is no longer supported, and it disintegrates, sloughing off during menstruation (flow phase of the menstrual cycle). |
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The implanted embryo sustains the endometrium by
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If implantation occurs, the implanted embryo secretes human
chorionic gonadotropin (HCG) to sustain the corpus luteum. As a result, the corpus luteum will continue to produce estrogen and progesterone to maintain the endometrium. Without HCG, menstruation would begin and the embryo would abort. (Pregnancy tests check for the presence of HCG in the urine.) Later during development, HCG is replaced by progesterone secreted by the placenta. In this way, the embryo directly maintains the pregnancy. |
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menstrual cycle
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thickening of the endometrium of the uterus in preparation for
implantation of a fertilized egg and the shedding of the endometrium if implantation does not occur |
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ovarian cycle
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1. Follicular phase: the development of the egg and the secretion of estrogen from the follicle.
2. Ovulation: the midcycle release of the egg. 3. Luteal phase: the secretion of estrogen and progesterone from the corpus luteum after ovulation. |
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In males LH stimulates
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the interstitial cells in the testes to produce testosterone and
other male sex hormones (androgens) |
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In males FSH and testosterone
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Sertoli cells promote the development
of sperm. |
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metamorphosis
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transforms
the larva into an adult. |
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fetus
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embryo that resembles the infant form
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Fertilization
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Fertilization occurs when the sperm penetrates the plasma membrane of the secondary oocyte
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Recognition
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Before penetration can occur, the sperm secretes a protein that binds with special receptor molecules
that reside on a glycoprotein layer surrounding the plasma membrane of the oocyte |
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vitelline layer (or zona pellucida in humans)
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insures that fertilization occurs only between egg and sperm of the same species.
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Penetration
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The plasma membranes of the sperm and oocyte fuse, and the sperm nucleus enters the oocyte
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Formation of the fertilization membrane
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The vitelline layer forms a fertilization membrane which blocks
the entrance of additional sperm. |
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Completion of meiosis II in the secondary oocyte
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In humans, sperm penetration triggers meiosis II in the
oocyte, producing an ovum (egg) and polar body. The polar body is discharged through the plasma membrane. |
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Fusion of nuclei and replication of DNA
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The sperm and ovum nuclei fuse, forming a zygote nucleus consisting
of 23 pairs of chromosomes (in humans). Each chromosome replicates so that it consists of two identical chromatids. |
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Cleavage
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rapid cell divisions without cell growth
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blastomeres
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resulting cells from cleavage
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animal pole
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upper pole cleaves faster
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vegetal pole
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lower pole cleaves slower due to more yolk
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Polar and equatorial cleavages
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Early cleavages are polar, dividing the egg into segments that stretch from
pole to pole (like sections of an orange). Other cleavages are parallel with the equator (perpendicular to the polar cleavages). |
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Radial and spiral cleavages
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In deuterostomes, early cleavages are radial, forming cells at the animal and
vegetal poles that are aligned together, the top cells directly above the bottom cells. In protostomes, cleavages are spiral, forming cells on top that are shifted with respect to those below them. |
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Indeterminate and determinate cleavages
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A cleavage is indeterminate if it produces blastomeres that, if
separated, can individually complete normal development. In contrast, blastomeres produced by a determinate cleavage cannot develop into a complete embryo if separated from other blastomeres. Instead, their developmental program is limited to the production of definite (or determined) cells that contribute to only a part of a complete embryo. Radial cleavages of deuterostomes are usually indeterminate, while spiral cleavages of protostomes are often determinate |
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Morula
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Successive cleavage divisions result in a solid ball of cells called a morula.
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Blastula
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As cell divisions continue, liquid fills the morula and pushes the cells out to form a circular cavity surrounded
by a single layer of cells. This hollow sphere of cells is called the blastula, and the cavity is the blastocoel. |
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Gastrula
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Formation of the gastrula, or gastrulation, occurs when a group of cells invaginate (move inward) into
the blastula, forming a two-layered embryo with an opening from the outside into a center cavity |
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The following features are associated with the gastrula:
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• Three germ layers. A third cell layer forms between the outer and inner layers of the invaginated embryo.
These three cell layers, the ectoderm, mesoderm, and endoderm (outside, middle, and inside layers, respectively) are the primary germ layers from which all subsequent tissues develop. • Archenteron. The center cavity formed by gastrulation is called the archenteron. It is completely surrounded by endoderm cells. • Blastopore. The opening into the archenteron is the blastopore. It becomes the mouth (in protostomes) or the anus (in deuterostomes). |
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Chorion
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The chorion is the outer membrane. In birds and reptiles it acts as a membrane for gas exchange. In
mammals, the chorion implants into the endometrium. Later, the chorion, together with maternal tissue, forms the placenta. |
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placenta
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The placenta is a blend of maternal and embryonic tissues across which gases, nutrients, and
wastes are exchanged. |
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Allantois
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The allantois begins as a sac that buds off from the archenteron. Eventually, it encircles the embryo,
forming a layer below the chorion. In birds and reptiles, it initially stores waste products (in the form of uric acid). Later in development, it fuses with the chorion, and together they act as a membrane for gas exchange with blood vessels below. In mammals, the allantois transports waste products to the placenta. After subsequent development, it forms the umbilical cord, transporting gases, nutrients, and wastes between the embryo and the placenta. |
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Amnion
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The amnion, for which this group of vertebrates is named, encloses the amniotic cavity, a fluidfilled
cavity that cushions the developing embryo much like the coelom cushions internal organs in coelomate animals. |
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Yolk sac
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In birds and reptiles, the yolk sac membrane digests the enclosed yolk. Blood vessels transfer the nutrients
to the developing embryo. In placental mammals, the yolk sac is empty. Instead, nutrition is obtained through the placenta |
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Organogenesis
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As cells continue to divide after gastrulation, they become different from one another (cell differentiation),
taking on characteristics of specific tissues and organs |
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The formation of the following organs is characteristic of the chordates:
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• Notochord. Cells along the dorsal surface of the mesoderm germ layer form the notochord, a stiff rod that
provides support in lower chordates. The vertebrae of higher chordates are formed from nearby cells in the mesoderm. • Neural tube. In the ectoderm layer directly above the notochord, a layer of cells forms the neural plate. The plate indents, forming the neural groove, then rolls up into a cylinder, the neural tube. The neural tube develops into the central nervous system. Additional cells roll off the top of the developing neural tube and form the neural crest. These cells form various tissues, including teeth, bones, and muscles of the skull, pigment cells in the skin, as well as nerve and other tissues. |
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Frog (an amphibian)
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• Gray crescent. When the sperm penetrates a frog egg, a reorganization of the cytoplasm results in the appearance
of a gray, crescent-shaped region, called the gray crescent. Hans Spemann, in a famous experiment, separated the cells formed during early cleavages and showed that each individual cell could develop into a normal frog only if it contained a portion of the gray crescent. • Gastrulation. During gastrulation, cells migrate over the top edge of the blastopore. The top edge, called the dorsal lip, forms from the same region earlier occupied by the gray crescent. The bottom and sides of the blastopore edge are called the ventral lip and lateral lips, respectively. • Yolk. The yolk material is much more extensive in the frog than in the sea urchin. Cells from the vegetal pole rich in yolk material form a yolk plug near the dorsal lip. |
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Bird
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• Blastodisc. The yolk of the bird egg is very large, and most of it is not involved in cleavages. Instead, the
cleavages occur in a blastula that consists of a flattened, disk-shaped region that sits on top of the yolk. This kind of blastula is called a blastodisc. • Primitive streak. When gastrulation begins, invagination occurs along a line (rather than a circle) called the primitive streak. As cells migrate into the primitive streak, the crevice formed becomes an elongated blastopore (rather than a circular blastopore, as found in sea urchins and frogs). |
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Humans and most other mammals
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Humans and most other mammals
• Blastocyst. The blastula stage, called the blastocyst, consists of two parts—an outer ring of cells, the trophoblast, and an inner mass of cells, the embryonic disc. • Trophoblast. The outer ring of cells, or trophoblast, serves several functions. First, it accomplishes implantation by embedding into the endometrium of the uterus. Second, it produces human chorionic gonadotropin (HCG) to maintain progesterone production of the corpus luteum (which, in turn, will maintain the endometrium). Later, the trophoblast forms the chorion, the extraembryonic membrane that, together with maternal tissue, forms the placenta. • Embryonic disc. Within the cavity created by the trophoblast, a bundle of cells called the inner cell mass (ICM), clusters at one pole and flattens into the embryonic disc. The embryonic disc is analogous to the blastodisc of birds and reptiles. A primitive streak develops, gastrulation follows, and development of the embryo and extraembryonic membranes (except the chorion) ensues. |
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Influence of the egg cytoplasm
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Cytoplasmic material is distributed unequally in the egg (or in subsequent
daughter cells). The gray crescent in frogs and the yolk in bird eggs are examples. Nonuniform distribution of cytoplasm results in embryonic axes, such as the animal and vegetal poles. When cleavages divide the egg, the quality of cytoplasmic substances will vary among the daughter cells. Substances unique to certain daughter cells may influence their subsequent development. |
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Embryonic induction
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the influence of one cell or group of cells over neighboring cells.
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organizers
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Cells that exert this influence are called organizers. Cells act as organizers by secreting chemicals that diffuse
among neighboring cells, influencing their development. Spemann discovered that the dorsal lip of the blastopore induced the development of the notochord in nearby cells. In particular, when a second dorsal lip was grafted into an embryo, two notochords developed. The dorsal lip functioned as an organizer. |
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Homeotic genes
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contribute to the control of development by turning on and off other genes that
code for substances that directly affect development. Mutant homeotic genes in fruit flies are responsible for producing body parts in the wrong places, such as legs where antennae should be. |
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homeobox
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A unique DNA segment, about
180 nucleotides long, has been found in most homeotic genes in numerous species, from fungi to humans. This gene segment, called a homeobox, identifies a particular class of genes that control development. |
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determined cell
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its final form cannot be changed
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lineage map
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By tracing the fates of cells during development, a lineage map can be built. A complete lineage map has been described
for the nematode (roundworm) Caenorhabditis elegans. Every one of the 959 cells in an adult C. elegans can be traced back to the egg, cell division by cell division. |