Chapter 5: Sex Determining and Sex Chromosome Flashcards
True or False. The continuity of a sexually reproducing species depends on an efficient union of gametes during fertilization. In turn, successful fertilization depends on some forms of sexual differentiation.
True
He identified nuclear structure in the sperm of certain insects, which he labeled the X-body.
Hermann Henking
He showed that some of the sperm in grasshoppers contain an unusual genetic structure, called a heterochromosome.
Clarence Mclung
Sex determination in Protenor butterfly.
- Female diploid = 14; gametes = 7 (six somatic and 1 X)
- Males diploid = 13; gametes = either 6 (all somatic) or 7 (6 somatic, 1 X)
- Fertilization by X-bearing sperm results in female offspring, and fertilization by X-deficient sperm results in male offspring.
Sex determination in Lygaeus turcicus.
- Female diploid = 14; gametes = 7 (six somatic and 1 X)
- Males diploid = 14; gametes = 7 (6 somatic 1 X or Y))
- Fertilization by Y-bearing sperm results in female offspring, and fertilization by X-bearing sperm results in male offspring.
The sex that produces unlike gametes. Their gametes determine the sex of the progeny.
Heterogametic sex
Manifestation of secondary characteristics of both sexes in one individual.
Intersexuality
Additional copy of the X chromosome in addition to the normal diploid set (46, XY)
Klinefelter syndrome (47, XXY)
True or False. The presence of at least one Y chromosome is sufficient to express human maleness.
True
Individuals with this syndrome most often have only 45 chromosomes, including just a single X chromosome.
Turner syndrome (45, X)
True or False. Individuals with Klinefelter syndrome are genetically females and individuals with Turner syndrome are genetically male.
False. Klinefelter individuals are males due to the presence of the Y chromosomes and Turner individuals are female due to the absence of the Y chromosome.
Individuals whose somatic cells display two different genetic cell lines, each exhibiting a different karyotype.
Mosaic
Two possible karyotypes of mosaic individuals.
45, X/46, XY
45, X/46, XX
Karyotype of triplo-X individual.
47, XXX
Karyotype of tetra-X individual.
48, XXXX
What condition do mosaic individuals have?
Turner syndrome
Above-normal height, subnormal intelligence, suffered personality disorder.
47, XYY condition
True or False. Additional Y chromosome predisposes males to behavioral problems.
True
Precursor tissue of the gonadal organs.
Gonadal primordia
Gonadal primordia arise as a pair of what structure associated with each embryonic kidney during the fifth week of gestation?
Gonadal ridges
True or False. During the early stages of fetal development, the sex of the embryo is male.
False. The sex of the embryo is hermaphroditic since reproductive structures cannot be distinguished, and the gonadal ridge tissue can develop to form male or female gonads.
As development progresses, primordial germ cells migrate to these ridges forming what structures.
Cortex and Medulla
The outer layer of tissues in an organ.
Cortex
The inner layer of tissues in an organ.
Medulla
The cortex is capable of developing into what structure?
Ovary
The medulla may develop into what structure?
Testis
Which undifferentiated duct differentiates into other organs of the male reproductive tract.
Wolffian ducts
Which undifferentiated duct differentiates into other organs of the female reproductive tract.
Mullerian ducts
Gonadal ridges are called what because they can form either ovaries or testis?
Bipotential gonads
True or False. The presence of the Y chromosome in the cells of the gonadal ridge does not interfere with the development of female reproductive organs.
False.
Whats happens if the cells of the gonadal ridges contain an XY constitution?
- Medulla differentiates into testis
2. Wolffian ducts differentiate into organ organs of the male reproductive tract.
Whats happens if the cells of the gonadal ridges contain an XX constitution?
- Cortex differentiates into the ovaries
- Mullerian ducts differentiate into organs of the female reproductive tract (oviducts, uterus, cervix, and portions of the vagina)
True or False. In females, the oogonia within the ovaries begin meiosis at 12th week of gestation, and primary oocytes can be detected. By the twenty-fifth week of gestation, all oocytes become arrested in meiosis and remain dormant until puberty is reached some 10 to 15 years later.
True.
True or False. In males, primary spermatocytes are not produced until puberty is reached.
True.
How many genes are found in the Y chromosome?
75 genes
How many genes are found in the X chromosome?
900-1400 genes
Which segments of the Y chromosome do undergo crossing over with X during meiosis.
Psuedoautosomal Regions (PARs)
Composes 95 percent of the Y chromosome. Does not synapse or recombine with the X chromosome.
Male-specific region of the Y or Nonrecombining region of the Y
Male-specific region of the Y (MSY) does not synapse or recombine with the X chromosome and is entirely heterozygous to X chromosome.
False. Some portions of the MSY share homology with genes on the X chromosome, and others do not.
Portions of the male-specific region of the Y that contains coding genes are called?
Euchromatic regions
Portions of the male-specific region of the Y that contains nonfunctional genes are called?
Heterochromatic regions
The sex-determining region of Y is found between which regions of the Y chromosome?
Found adjacent to the psudoautosomal region and euchromatic region of the p arm.
At which time of development the SRY becomes active in XY embryos?
8th week of gestation
This region is not found in the X chromosome and encodes a protein that causes the undifferentiated gonadal tissue of the embryo to form testes.
Sex-determining region of Y
This protein is encoded by SRY gene which functions as a transcription factor.
Testis-determining factor (TDF)
A DNA- binding protein that interacts directly with the regulatory sequences of other genes to stimulate their expression.
Transcription factor
Behaves as a master switch that controls other genes downstream in the process of sexual differentiation.
Testis-determining factor (TDF)
Reflects the proportion of males to females conceived in a population.
Primary Sex Ratio (PSR)
Reflects the proportion of each sex that is born.
Secondary Sex Ratio (SSR)
True or False. Having an SSR greater than 1 means there is a larger fetal and post-natal mortality in males.
False.
This phenomenon balances the dose of X chromosome gene expression in females.
Dosage compensation
An inactivated X chromosome.
Barr body
True or False. Chromosome inactivation does not normally occur in the very early stages of development of those cells destined to form gonadal tissues.
True.
True or False. All genes on each X chromosome forming a Barr body are inactivated.
False. Not all genes are inactivated.
The theory that states that the inactivation of X chromosomes occurs randomly in somatic cells at a point early in embryonic development.
Lyon hypothesis
True or False. Once inactivation has occurred, all descendant cells have the same X chromosome inactivated as their initial progenitor cell.
True
Relate the Lyon hypothesis to red-green colorblindness.
- Males with the gene for colorblindness are totally colorblind because only one X chromosome is present and no formation of the Barr body occurred.
- Heterozygous females display mosaic retinas, with patches of defective color perception and surrounding areas with normal color perception.
A process, whereby the expression of genes on one homolog, but not the other, is affected.
Imprinting
Major control unit for the inactivation of one of the X chromosomes in females.
X inactivation center (Xic)
Composed of several regulatory units and four genes that include X-inactive specific transcript, Tsix gene, and the Xite.
X inactivation center (Xic)
Its RNA products spread over and coat the X chromosome bearing the gene that produced them.
X-inactive specific transcript
Apart from X-inactive specific transcript, what other genes found in the X inactivation center play important roles in X-inactivation?
Tsix and Xite genes
Two mechanisms of inactivation.
- RNA products of Xist spread over and coat the X chromosome bearing the gene that produced them.
- That transcription of Xist initially occurs at low levels on all X chromosomes. As the inactivation process begins, however, transcription continues, and is enhanced, only on the X chromosome that becomes inactivated.
True or False. In some animals, the ratio of X chromosome to Sets of Autosomes can Determine Sex.
True. e.g, D. melangonaster
True or False. According to genic balance theory, a threshold for maleness is reached when the X:A ratio is 1:2 (X:2A), but that the presence of an additional X (XX:2A) alters the balance and results in female differentiation.
True.
Plays a critical role, serving as a “master switch” in sex determination in D. melangonaster.
Sex-lethal gene
Process whereby portions of the RNA are removed and the remaining fragments are “spliced” back together prior to translation into a protein.
RNA splicing
The RNA transcript may be spliced in different ways. This phenomenon is called?
Alternative splicing
If a hermaphrodite Caenorhabditis elegans is selfed, the resulting progeny is?
99 percent hermaphrodite
1 percent male
If a male and a hermaphrodite Caenorhabditis elegans are crossed, the resulting progeny is?
50 perent male
50 percent hermaphrodite
A ratio of one is to one (2X:2A) between the X and the autosomal chromosomes make Caenorhabditis elegans a?
Hermaphrodite
A ratio of one is to two between the X and the autosomal chromosomes makes Caenorhabditis elegans a?
Male
A phenomenon where sex is determined genetically.
Chromosomal sex determination
Sex determination is achieved according to the incubation temperature of eggs during a critical period of embryonic development.
Temperature-dependent sex determination
Thermosensitive factor mediates the transcription of this gene in reptiles leading to temperature-dependent sex determination.
Aromatase gene
A gene product that converts androgens (male hormones such as testosterone) to estrogens (female hormones such as estradiol) in animals that undergo Temperature-dependent sex determination.
Aromatase
