Chapter 2 Flashcards
Development begins with fertilization, the process by which the male gamete, the ___, and the female gamete, the ___, unite to give rise
to a zygote
sperm - oocyte
There are 22 pairs of matching chromosomes, the ____, and one pair of ____
autosomes - sex chromosomes
Gametes are derived from ___ that are formed in the
epiblast during the second week, move through
the primitive streak during gastrulation, and migrate to the wall of the yolk sac
primordial germ cells (PGCs)
In preparation for fertilization, germ cells undergo _____, which includes meiosis, to reduce the number of chromosomes and ____ to complete their maturation
gametogenesis - cytodiflerentiation
____ are tumors of disputed origin that often contain a variety of tissues, such as bone, hair, muscle, gut epithelia, and others
Teratomas
Genes on the same chromosome tend to be inherited together and so are known as_____
linked genes
In somatic cells, chromosomes appear as 23 ___ to form the ___ number of 46
homologous pairs - diploid
Before a cell enters mitosis, each chromosome replicates its ___
DNA
One chromosome of each pair is derived from the maternal gamete, the __, and one from the paternal gamete, the __
oocyte - sperm
With the onset of mitosis, the chromosomes begin to coil, contract, and condense; these events mark the beginning
of ___.
prophase
___ is the process whereby one cell divides, giving rise to two daughter cells that are genetically identical to the parent cell
Mitosis
Each chromosome now consists of two parallel subunits, ___, that are joined at a narrow region common to both called the ___
chromatids - centromere
Each is attached by ___ extending from the centromere to the centriole, forming the ____
microtubules - mitotic spindle
___ is the cell division that takes place in the ____ to generate male and female gametes, sperm and egg cells, respectively
Meiosis - germ cells
Meiosis requires two cell divisions, ___ and ___, to reduce the number of chromosomes to the haploid number of 23
meiosis I and meiosis II
As in mitosis, male and female germ cells (___ and ___) at the begining of meiosis I replicate their DNA so that each of the 46 chromosomes is duplicated into sister chromatids.
spermatocytes and primary oocytes
____, critical events in meiosis I, are the interchange of chromatid segments between paired homologous chromosomes
Crossovers
In contrast to mitosis, however, ____ then align themselves in pairs, a process called synapsis
homologous chromosomes -
As separation occurs, points of interchange are temporarily united and form an X-like structure, a ___
chiasma
In contrast to mitosis, however, homologous chromosomes then align themselves in ___, a process called __
pairs - synapsis
Only one of these develops into a mature gamete, however, the oocyte; the other three, the ___, receive little cytoplasm and degenerate during subsequent development
polar bodies
Normal somatic cells are __, or 2n
diploid
_____, which may be numerical or structural, are important causes of birth defects and spontaneous abortions
Chromosomal abnormalities
Chromosomal abnormalities account for 10% of major birth defects, and ____ account for an additional 8%
gene mutations
Normal gametes are ___, or n.
haploid
___ refers to any exact multiple of n [e.g., diploid or triploid]. ___ refers t
o any chromosome number that is not euploid. It is usually applied when
an extra chromosome is present [____] or when one is missing [____]
Euploid - Aneuploid - trisomy - monosomy
Such ____ may be balanced, in which case breakage and reunion occur between two chromosomes, but no critical genetic material is lost and individuals are normal; or they may be unbalanced, in which case part of one chromosome is lost, and an altered phenotype is produced.
translocations
Sometimes, however, separation does not occur [____], and both members of a pair move into one cell
nondisjunction
In ____, two members of a pair of homologous chromosomes normally separate during the first meiotic division so that each daughter cell receives one member of each pair
meiosis
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
Such translocations may be ___, in which case breakage and reunion occur between two chromosomes, but no critical genetic material is lost and individuals are normal; or they may be ___, in which case part of one chromosome is lost, and an altered phenotype is produced.
balanced - unbalanced
Down syndrome is caused by an extra copy of _____
chromosome 21 [trisomy 21]
These individuals have __, with some cells having a normal chromosome number and some having trisomy.
mosaicism
Patients with ___ show the following features: intellectual disability, congenital heart defects, low—set ears, and flexion of fingers and hands
trisomy 18
The clinical features of _____, found only in males and usually detected by amniocentesis, are sterility, testicular atrophy, hyalinization of the seminiferous tubules, and usually gynecomastia.
Klinefelter syndrome
The cells have 47 chromosomes with a sex chromosomal complement of the XXY type, and a ____ is found in 80% of cases
sex chromatin [Barr] body
[____: formed by condensation of an inactivated X chromosome; Is also present in normal females because one of the X chromosomes is normally inactivated].
Barr body
_____, with a 45,X karyotype, is the only monosomy compatible with life. Even then, 98% of all fetuses with the syndrome are spontaneously aborted
Turner syndrome
(Turner syndrome) The few that survive are unmistakably female in appearance and are characterized by the absence of ovaries [____] and short stature
gonadal dysgenesis
(Turner syndrome) In 80% of these females, nondisjunction in the ___ is the cause.
male gamete
Patients with ____ often go undiagnosed because of their mild physical features.
triple X syndrome [47,XXX]
_____, which involve one or more chromosomes, usually result from chromosome breakage.
Structural chromosome abnormalities
In some cases, the broken piece of a chromosome is lost, and the infant with partial ___ of a chromosome is abnormal.
deletion
A well-known syndrome, caused by partial deletion of the short arm of chromosome 5, is the ____.
cri-du-chat syndrome
____, spanning only a few contiguous genes, may result in microdeletion syndrome or contiguous gene syndrome. Sites where these deletions occur, called contiguous gene complexes, are usually identified by fluorescence in situ hybridization
Microdeletions
When the microdeletion occurs on the maternal chromosome, it results in ____, and the children have intellectual disability, cannot speak, exhibit poor motor development, and are prone to unprovoked and prolonged periods of laughter
Angelman syndrome
Microdeletions, spanning only a few _____, may result in microdeletion syndrome or _____. Sites where these deletions occur, called _____, are usually identified by ____
contiguous genes - contiguous gene syndrome - contiguous gene complexes - fluorescence in situ hybridization
If the microdeletion occurs on the paternal chromosome, _____ results. Affected individuals are characterized by hypotonia, obesity, intellectual disability, hypogonadism, and undescended testes
Prader-Willi syndrome
Characteristics that are differentially expressed depending upon whether the genetic material is inherited from the mother or the father are examples of ____
genomic imprinting
Other contiguous gene syndromes may be inherited from either parent, including ____ [lissencephaly, developmental delay, seizures, and cardiac and facial abnormalities resulting from a deletion at 17p13] and most cases of ___ [palatal defects, conotruncal heart defects, speech delay, learning disorders, and schizophrenia—like disorder resulting from a deletion in 22q11]
Miller-Dieker syndrome - 22q11 syndrome
____ are regions of chromosomes that demonstrate a propensity to separate or break under certain cell manipulations.
Fragile sites
Although numerous fragile sites have been defined and consist of ___, only those in the____ gene on
the long arm of the X chromosome [Xq27] have
been correlated with an altered phenotype
that is called the ____
CGG repeats - FMRI - fragile X syndrome
Many birth defects are directly attributable to a change in the structure or function of a single gene, hence the name _____
single gene mutation
If a mutant gene produces an abnormality in a single dose, despite the presence of a normal allele, it is a ___
dominant mutation
With the exception of the X and Y chromosomes in the male, genes exist as pairs, or ____, so that there are two doses for each genetic determinant
alleles
If both alleles must be abnormal [double dose] or if the mutation is X-linked [occurs on the X chromosome] in the male, it is a ______. Variations in the effects of mutant genes may be a result of ____
recessive mutation - modifying factors
If the mutation occurs in a
somatic cell, the individual will have ____ [having more than one genetically distinct cell line] with some cells having the mutation and some not.
mosaicism
In addition to causing congenital malformations, mutations can result in ____
inborn errors of metabolism
_____ is used to assess chromosome number and integrity
Cytogenetic analysis
These diseases, among which ____, ____, and ___ are the best known, may be accompanied by or cause various degrees of intellectual disability if proper diets and medical care are not instituted
phenylketonuria, homocystinuria, and galactosemia
Chromosomes are ____ to reveal light and dark banding patterns unique for each chromosome.
Giemsa-stained
Recently, _____ have been developed that demonstrate greater numbers of bands representing even smaller pieces of DNA, thereby facilitating diagnosis of small deletions.
high-resolution metaphase banding techniques
_____, such as fluorescent in situ hybridization [FISH], use specific DNA probes to identify ploidy for a few selected chromosomes and for detecting microdeletions
Molecular techniques
____ use spots of specific DNA sequences [probes] attached to a solid surface, usually glass or silicon [Affymetrix chips].
Microarrays
_____ represents a new approach to finding mutations and polymorphisms [single nucleotide changes [SNPs] in a DNA sequence] responsible for birth defects and diseases
Exome sequencing
Exome sequencing represents a new approach to finding ____ and ___ [single nucleotide changes [SNPs] in a DNA sequence] responsible for birth defects and diseases
mutations - polymorphisms
Together, these coding regions make up the ___ and represent only 1% of the entire human genome,
thereby making sequencing them more practical than trying to sequence all of the genome
exome
This arrested state is produced by ____, a small peptide secreted by follicullar cells
oocyte maturation inhibitor (OMI)
Once ____ have arrived in the gonad of a genetic female, they differentiate into oogonia
PGCs
Once PGCs have arrived in the gonad of a genetic female, they differentiate into___
oogonia
Whereas all of the oogonia in one cluster are probably derived from a single cell, the flat epithelial cells, known as ____, originate from surface epithelium covering the ovary
follicular cells
The majority ofoogonia continue to divide by mitosis, but some of them arrest their cell division in prophase of meiosis I and form ____
primary oocytes
Cell death begins, and many oogonia as well as primary oocytes degenerate and become ____
atretic
A primary oocyte, together with its surrounding flat epithelial cells, is known as a ____
primordial follicle
Near the time of birth, all primary oocytes have started prophase of meiosis I, but instead of proceeding into metaphase, they enter the ___, a resting stage during prophase that is characterized by a lacy network of chromatin
diplotene stage
Some of these die, whereas others begin to accumulate fluid in a space called the ___, thereby entering the antral or vesicular stage
antrum
Some of these die, whereas others begin to accumulate fluid in a space called the antrum, thereby entering the ____
antral or vesicular stage
Fluid continues to accumulate such that, immediately prior to ovulation, follicles are quite swollen and are called ___ or ___
mature vesicular follicles or graafian follicles
As primordial follicles begin to grow, surrounding follicular cells change from flat to cuboidal and proliferate to produce a stratified epithelium of ___, and the unit is called a primary follicle
granulosa cells
Granulosa cells surrounding the oocyte remain intact and form the ____. At maturity, the _____ may be 25 mm or more in diameter
cumulus oophorus - mature vesicular (graafian) follicle
As primordial follicles begin to grow, surrounding follicular cells change from flat to cuboidal and proliferate to produce a stratified epithelium of granulosa cells, and the unit is called a ___
primary follicle
Granulosa cells rest on a basement membrane separating them from surrounding ovarian connective tissue (stromal cells) that form the ____
theca folliculi
Also, granulosa cells and the oocyte secrete a layer of glycoproteins on the surface of the oocyte, forming the ____
zona pellucida
Coalescence of these spaces forms the___, and the follicle is termed a ____
antrum - vesicular or an antral follicle
As follicles continue to grow, cells of the theca folliculi organize into an inner layer of secretory cells, the ____, and an outer fibrous capsule, the ____
theca interna - theca externa
When the secondary follicle is mature, a surge in _____ induces the preovulatory growth phase
luteinizing hormone (LH)
Spermatogenesis, which begins at puberty, includes all of the events by which spermatogonia are transformed into ____
spermatozoa
One cell, the ____, receives most of the cytoplasm; the other, the ___ body, receives practically none
secondary oocyte - first polar
____, which begins at puberty, includes all of the events by which spermatogonia are transformed into spermatozoa
Spermatogenesis
Shortly before puberty, the sex cords acquire a lumen and become the ___
seminiferous tubules
Spermatogenesis, which begins at puberty, includes all of the events by which ___ are transformed into spermatozoa
spermatogonia
The last cell division produces ___, which
then divide to form primary spermatocytes
type B spermatogonia
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
At regular intervals, cells emerge from this stem cell population to form ____, and their production marks the initiation of spermatogenesis
type A spermatogonia
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 spermatocytes
During the second meiotic division, these cells immediately begin to form haploid ____
spermatids
____ is also essential because its binding to Sertoli cells stimulates testicular fluid production and synthesis of intracellular androgen receptor proteins
Follicle-stimulating hormone (FSH)
The series of changes resulting in the transformation of spermatids into spermatozoa is ____
spermiogenesis
Every month, 15 to 20 follicles begin to grow, and as they mature, they pass through three stages:
(1) primary or preantral
(2) vesicular or antral
(3) mature vesicular or graafian follicle
Spermatids go through a series of changes (spermiogenesis), including;
(1) formation of the acrosome
(2) condensation of the nucleus
(3) formation of neck, middle piece, and tail
(4) shedding of most of the cytoplasm
