➢process by which the diploid germ cells undergo a number of chromosomal and morphological changes to form mature haploid gametes
➢process involved in the maturation of the two highly specialized cells, spermatozoon in male and ovum in the female before they unite to form zygote
GAMETOGENESIS
➢Appears in the wall of the endodermal layer of the yolk sac due to their large size and high content of alkaline phosphatase, and migrate by amoeboid movement toward the hind gut epithelium and then through dorsal mesentery reach to the primordia of the gonads ( primitive sex glands)
PRIMORDIAL GERM CELL
This need for cellular migration causes the cells of the epiblasts to move towards the hypoblasts and with which the third embryonic layer (mesoderm) appears between the two previous layers
GAMETES
Mitotic divisions increase their number during their migration and also when they arrive in the gonad
➢ In preparation for fertilization, germ cells undergo ________, which includes meiosis, to reduce the number of chromosomes and cytodifferentiation to complete their maturation
➢ In preparation for fertilization, germ cells undergo gametogenesis, which includes meiosis, to reduce the number of chromosomes and cytodifferentiation to complete their maturation
(just read)
➢germ cells directed toward the gonads by the mature cellular and non-cellular microenvironment that surround them Or by tissue rearrangement that occur in the early embryos
➢If they fail to reach the ridges, the gonads will not develop
➢So, it has the inductive influence on the development of gonads into ovary and testes
➢Determine sex of the embryo
- tumors of disputed origin
✓contain a variety of tissues, such as bone, hair, muscle, gut epithelia,
✓thought that these tumors arise from pluripotent stem cells that can differentiate into any of the three germ layers or their derivatives
✓_______ that have strayed from their normal migratory paths
✓Another source may be epiblast cells that give rise to all three germ layers during gastrulation
TERATOMAS
-PGCs (Primordial germ cells)
THE ______THEORY OF ______
➢______ genes on ______ chromosomes
➢Genes on the same chromosome tend to be inherited together and so are known as ______
➢In somatic cells, chromosomes appear as __ homologous pairs to form the diploid number of ____
➢ 22 pairs of matching chromosomes - ____
THE CHROMOSOME THEORY OF INHERITANCE
➢23,000 genes on 46 chromosomes
➢Genes on the same chromosome tend to be inherited together and so are known as linked genes
➢In somatic cells, chromosomes appear as 23 homologous pairs to form the diploid number of 46
➢ 22 pairs of matching chromosomes - DIPLOID
➢ __- autosomes, __ pair of sex chromosomes
➢___ - the individual is genetically female
➢___ - the individual is genetically male
➢22- autosomes, 1 pair of sex chromosomes
➢XX - the individual is genetically female
➢XY - the individual is genetically male
➢process whereby one cell divides, giving rise to two daughter cells that are genetically identical to the parent cell
MITOSIS
STAGES OF MITOSIS:
During this replication phase, chromosomes are extremely long, they are spread diffusely through the nucleus, and they cannot be recognized with the light microscope.
prophase
✓ Each chromosome now consists of two parallel subunits, chromatids - joined at a narrow region common to both called the centromere
✓ chromosomes continue to condense, shorten, and thicken , but only at ……. do the ______ become distinguishable
prometaphase
-chromatids
✓The chromosomes line up in the equatorial plane, and their doubled structure is clearly visible
✓ Each is attached by microtubules extending from the centromere to the centriole, forming the mitotic spindle
Metaphase
Centromere of each chromosome divides, marking the beginning of ______, followed by migration of chromatids to opposite poles of the spindle
**The chromosomes have separated and are moving toward the poles
Anaphase
STAGES OF MITOSIS
✓ - chromosomes uncoil and lengthen, the nuclear envelope reforms, and the cytoplasm divides
✓ Each daughter cell receives half of all doubled chromosomes material and thus maintains the same number of chromosomes as the mother cell
**The chromosomes are at poles, and are becoming more diffuse. The nuclear envelope is reforming. The cytoplasm may be dividing
Telophase
➢cell division that takes place in the germ cells to generate male and female gametes, sperm and egg cells
MEIOSIS
➢Meiosis requires two cell divisions, meiosis I and meiosis II, to reduce the number of chromosomes to the haploid number of _____
➢As in mitosis, male and female germ cells (spermatocytes and primary oocytes) at the beginning of meiosis I replicate their DNA so that each of the 46 chromosomes is duplicated into sister chromatids
➢Meiosis requires two cell divisions, meiosis I and meiosis II, to reduce the number of chromosomes to the haploid number of 23
homologous chromosomes then align themselves in pairs, a process called ______
synapsis
➢________- critical events in meiosis I - interchange of chromatid segments between paired homologous chromosomes
➢Segments of chromatids break and are exchanged as homologous chromosomes separate
➢As separation occurs, points of interchange are temporarily united and form an X-like structure, ________
➢Crossovers - critical events in meiosis I - interchange of chromatid segments between paired homologous chromosomes
➢As separation occurs, points of interchange are temporarily united and form an X-like structure, CHIASMA
RESULT OF MEIOTIC DIVISION
➢Genetic variability is enhanced through ______, which redistributes genetic material
➢Random distribution of homologous chromosomes to the daughter cells
*Each germ cell contains a haploid number of chromosomes so that at fertilization, the diploid number of _____ is restored
➢Genetic variability is enhanced through Crossover, which redistributes genetic material
***Each germ cell contains a haploid number of chromosomes so that at fertilization, the diploid number of 46 is restored
CLINICAL CORRELATION
Birth Defects and Spontaneous Abortions: Chromosomal and Genetic Factors
???
✓- any chromosome number that is not euploid; it is usually applied when an extra chromosome is present [trisomy] or when one is missing [monosomy]
Aneuploid
✓estimated that 50% of conceptions end in spontaneous abortion and that 50% of these abortuses have major chromosomal abnormalities
✓approximately 25% of conceptuses shave a major chromosomal defect
✓45,X [Turner syndrome], triploidy, and trisomy 16 ✓Chromosomal abnormalities account for 10% of major birth defects, and gene mutations account for an additional 8%
✓ ________ - one cell receives 24 chromosomes, and the other receives 22 instead of the normal 23 When, at fertilization, a gamete having 23 chromosomes fuses with a gamete having 24 or 22 chromosomes, the
✓ result is an individual with either chromosomes (trisomy) or _____ chromosomes (monosomy)
Nondisjunction
✓ result is an individual with either 47 chromosomes (trisomy) or 45 chromosomes (monosomy)
- extra copy of chromosome 21
✓ **In 95% of cases, the syndrome is caused by trisomy 21 resulting from meiotic nondisjunction, and in 75% of these instances, nondisjunction occurs during oocyte formation.
✓Down syndrome/ Trisomy 21
✓4% of cases of Down syndrome, there is an unbalanced translocation between chromosome 21 and chromosomes ___, ___, ___, and ___
✓1% - ______ resulting from a trisomic conception followed by the loss of the extra
✓4% of cases of Down syndrome, there is an unbalanced translocation between chromosome 21 and chromosomes13,14, 15, or 21
✓1% - mosaicism resulting from a trisomic conception followed by the loss of the extra
✓growth retardation
✓varying degrees of intellectual disability
✓____abnormalities- upward slanting eyes, _______ [extra skin folds at the medial corners of the eyes]
✓ flat facies
✓small ears
✓cardiac defects
✓hypotonia
(Trisomy 21) DOWN SYNDROME
✓craniofacial abnormalities- upward slanting eyes, epicanthal folds [extra skin folds at the medial corners of the eyes]
CLINICAL CORRELATION Birth Defects and Spontaneous Abortions: Chromosomal and Genetic Factors
?????
✓intellectual disability
✓ congenital heart defects
✓ low—set ears, and
✓Flexion of fingers and hands
✓Syndactyly
✓Micrognathia
✓Renal anomalies
✓Malformation of the skeletal system
TRISOMY 18 (Edwards’ syndrome)
????
✓Holoprosencephaly
✓congenital heart defects
✓deafness
✓cleft lip and palate
✓eye defects, such as microphthalmia, anophthalmia and coloboma
TRISOMY 13 (Patau Syndrome)
TRISOMY 13
✓The incidence of this abnormality is approximately 1 in 20,000 live births, and more than 90% of the infants die in the first month after birth
✓Approximately 5% live beyond 1 year
✓ 1 in 5,000
✓ 85 % - lost between 10 weeks of gestation and term
✓ 2 months of age
✓ 5% live beyond 1 year
________ SYNDROME
✓Sterility
✓testicular atrophy
✓hyalinization of the seminiferous tubules
✓Gynecomastia
✓The cells have 47 chromosomes with a sex chromosomal complement of the XXY type, and a sex chrmatin [_____] body is found in 80% of cases
KLINEFELTER SYNDROME (XXY syndrome)
✓The cells have 47 chromosomes with a sex chromosomal complement of the XXY type, and a sex chrmatin [Barr] body is found in 80% of cases
KLINEFELTER SYNDROME
✓incidence is approximately 1 in 500 males ✓Nondisjunction of the ____ homologues - most common causative event
✓incidence is approximately 1 in 500 males ✓Nondisjunction of the XX homologues - most common causative event
_________
✓45,X karyotype
✓only monosomy compatible with life
✓98% of all fetuses with the syndrome are spontaneously aborted
TURNER SYNDROME (45X syndrome)
TURNER SYNDROME
✓55% - monosomic for the X and ______ body negative because of nondisjunction
✓80% of these females nondisjunction in the male gamete is the cause.
✓55% - monosomic for the X and chromatin body negative because of nondisjunction
_______ SYNDROME
✓Patients with _______ [aka _______] often go undiagnosed because of their mild physical features.
TRIPPLE X SYNDROME
✓Patients with triple X syndrome [47,XXX] often go undiagnosed because of their mild physical features.
gametocytosis
➢The process involved in the development of a mature ovum
➢From yolk sac – Primitive germ cells at 3rd week
OOGENESIS
MATURATION OF THE OOCYTE
➢Once PGCs have arrived in the gonad of a genetic female, they differentiate into oogonia
➢These cells undergo a number of mitotic divisions, and by the end of the third month, they are arranged in clusters surrounded by a layer of flat epithelial cell.
➢The majority of oogonia continue to divide by mitosis, but some of them arrest their cell division in _____ of meiosis ___ and form primary oocytes
➢The majority of oogonia continue to divide by mitosis, but some of them arrest their cell division in prophase of meiosis I and form primary oocytes
➢Near the time of birth, all primary oocytes have started prophase of meiosis I, but instead of proceeding into metaphase, they enter the ______ stage, a resting stage during prophase that is characterized by a lacy network of chromatin
➢Primary oocytes remain arrested in _____ and do not finish their first meiotic division before puberty is reached.
➢Near the time of birth, all primary oocytes have started prophase of meiosis I, but instead of proceeding into metaphase, they enter the diplotene stage, a resting stage during prophase that is characterized by a lacy network of chromatin
➢Primary oocytes remain arrested in prophase and do not finish their first meiotic division before puberty is reached.
✓This arrested state is produced by _______ - small peptide secreted by follicular cells
✓This arrested state is produced by oocyte maturation inhibitor (OMI) - small peptide secreted by follicular cells
➢The total number of primary oocytes at birth is estimated to vary from 600,000 to 800,000
➢During childhood, most oocytes become atretic
➢ only approximately 40,000 are present by the beginning of puberty, and fewer than 500 will be ovulated.
✓At puberty, a pool of growing follicles is established and continuously maintained from the supply of primordial follicles
✓Each month, 15 to 20 follicles selected from this pool begin to mature
________or ______ stage —> Mature Follicles or __ Follicles
Antral or Vesicular stage —> Mature Follicles or Graafian Follicles
➢As follicles continue to grow, cells of the _____ folliculi organize into an inner layer of secretory cells - _________,
➢outer fibrous capsule - _________
➢As follicles continue to grow, cells of the theca folliculi organize into an inner layer of secretory cells - theca interna,
➢outer fibrous capsule - theca externa.
➢Fluid-filled spaces appear between granulosa cells ➢Coalescence of these spaces forms the______ , and the follicle is termed a ______ or an ______
➢______ - consists of a cluster of granulosa cells that surround and support the oocyte
➢Fluid-filled spaces appear between granulosa cells ➢Coalescence of these spaces forms the ANTRUM , and the follicle is termed a VESICULAR or an ANTRAL follicle ➢Cumulus oophorus - consists of a cluster of granulosa cells that surround and support the oocyte
✓ The _____ stage is the longest, whereas the mature vesicular stage encompasses approximately 37 hours prior to ovulation
✓ The antral stage is the longest, whereas the mature vesicular stage encompasses approximately 37 hours prior to ovulation
➢At maturity, the mature vesicular (______) follicle may be 25 mm or more in diameter
➢It is surrounded by the _______ which is composed of cells having characteristics of steroid secretion, rich in blood vessels, and theca externa
➢At maturity, the mature vesicular (graafian) follicle may be 25 mm or more in diameter
➢It is surrounded by the THECA INTERNA which is composed of cells having characteristics of steroid secretion, rich in blood vessels, and theca externa
➢When the secondary follicle is mature, a surge in _____ induces the pre ovulatory growth phase
➢Meiosis I is completed, resulting in formation of two daughter cells of unequal size, each with 23 double structured chromosomes
➢When the secondary follicle is mature, a surge in luteinizing hormone (LH) induces the pre ovulatory growth phase
✓ ______ - receives most of the cytoplasm; the other, the first polar body, receives practically none
✓ The first polar body lies between the _____ and the cell membrane of the secondary oocyte in the ______ space
✓ Secondary oocyte - receives most of the cytoplasm; the other, the first polar body, receives practically none
✓ The first polar body lies between the zona pellucida and the cell membrane of the secondary oocyte in the perivitelline space
_____ —> ___ —> _____
LH SURGE —> OVULATION —> SECONDARY OOCYTE
➢The cell then enters meiosis II but arrests in ______ approximately 3 hours before ovulation.
➢Meiosis II is completed only if the oocyte is ______; otherwise, the cell degenerates approximately 24 hours after ovulation.
➢The cell then enters meiosis II but arrests in metaphase approximately 3 hours before ovulation.
➢Meiosis II is completed only if the oocyte is fertilized; otherwise, the cell degenerates approximately 24 hours after ovulation.
PHASES OF SPERMATOGENESIS (2)
1. SPERMATOCYTOGENESIS
2. SPERMIOGENESIS
➢Spermatogenesis, which begins at _______, includes all of the events by which spermatogonia are transformed into spermatozoa
➢Spermatogenesis, which begins at puberty, includes all of the events by which spermatogonia are transformed into spermatozoa
➢At birth, germ cells in the male infant can be recognized in the seX cords of the testis as large, pale cells surrounded by supporting cells
➢Supporting cells, which are derived from the surface epithelium of the testis in the same manner as follicular cells, become _____ cells or _____ cells
➢Supporting cells, which are derived from the surface epithelium of the testis in the same manner as follicular cells, become sustentacular cells or Sertoli cells
➢PGCs give rise to spermatogonial stem cells. At regular intervals, cells emerge from this stem cell population to form type_____, and their production marks the initiation of _______.
➢Type A cells undergo a limited number of mitotic divisions to form clones of cells
➢The last cell division produces type B spermatogonia, which then divide to form __________
➢PGCs give rise to spermatogonial stem cells. At regular intervals, cells emerge from this stem cell population to form type A spermatogonia, and their production marks the initiation of spermatogenesis.
➢The last cell division produces type B spermatogonia, which then divide to form primary spermatocytes
➢Primary spermatocytes then enter a prolonged ______ prophase (22 days) followed by rapid completion of meiosis I and formation of secondary spermatocyte
➢During the second meiotic division, these cells immediately begin to form haploid spermatids
➢Primary spermatocytes then enter a prolonged prophase (22 days) followed by rapid completion of meiosis I and formation of secondary spermatocyte
➢Throughout this series of events, from the time type A cells leave the stem cell population to formation of spermatids, cytokinesis is incomplete so that successive cell generations are joined by _______
➢Thus, the progeny of a single type A spermatogonium form a clone of germ cells that maintain contact throughout differentiation
➢Throughout this series of events, from the time type A cells leave the stem cell population to formation of spermatids, cytokinesis is incomplete so that successive cell generations are joined by cytoplasmic bridges
➢Spermatogonia and spermatids remain embedded in deep recesses of ______ throughout their development
➢In this manner, ___support and protect the
germ cells, participate in their nutrition, and assist in
the release of mature spermatozoa.
➢Spermatogonia and spermatids remain embedded in deep recesses of Sertoli cells throughout their development
➢In this manner, Sertoli cells support and protect the
➢Spermatogenesis is regulated by _____ production by the ______
➢LH binds to receptors on ______ and stimulates testosterone production, which in turn binds to______ to promote spermatogenesis
➢____ is also essential because its binding to Sertoli cells stimulates testicular fluid production and synthesis of intracellular ______ receptor proteins.
➢Spermatogenesis is regulated by LH production by the pituitary gland
➢LH binds to receptors on Leydig cells and stimulates testosterone production, which in turn binds to Sertoli cells to promote spermatogenesis
➢Follicle-stimulating hormone (FSH) is also essential because its binding to Sertoli cells stimulates testicular fluid production and synthesis of intracellular androgen receptor proteins.
The series of changes resulting in the transformation of spermatids into spermatozoa
a) formation of the _____, which covers half of the nuclear surface and contains enzymes to assist in penetration of the egg and its surrounding layers during fertilization
b) Condensation of the nucleus
c) formation of neck, middle piece, and tail
d) shedding of most of the cytoplasm as residual bodies that are phagocytized by _____
SPERMIOGENESIS
a) formation of the acrosome, which covers half of the nuclear surface and contains enzymes to assist in penetration of the egg and its surrounding layers during fertilization
d) shedding of most of the cytoplasm as residual bodies that are phagocytized by Sertoli cells
In humans, the time required for a spermatogonium to develop into a mature spermatozoon is approximately ___ days,and approximately __ million sperm cells are produced ___.
In humans, the time required for a spermatogonium to develop into a mature spermatozoon is approximately 74 days, and approximately 300 million sperm cells are produced daily.
➢When fully formed, spermatozoa enter the lumen of ________
➢pushed toward the ______ by contractile elements in the
wall of the ______
➢Although initially only slightly motile, spermatozoa obtain full motility in the ______
➢When fully formed, spermatozoa enter the lumen of seminiferous tubules
➢pushed toward the epididymis by contractile elements in the wall of the seminiferous tubules
➢Although initially only slightly motile, spermatozoa obtain full motility in the epididymis.
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