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90 Cards in this Set
- Front
- Back
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What are chromosomes and what do they transmit?
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- Nuclear structure containing a linear thread of DNA
- Transmit genetic information |
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What two types of chromosomes do humans have?
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- A single pair of sex chromosomes
- 22 pairs of autosomal chromosomes (autosomes) |
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What are the differences between male and female chromosomes?
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F: two X chromosomes
M: one X chromosome and one Y (Y chrom. is acrocentric --> centromer is located at one end of chromosome) F: 8 pairs including two X chromosomes of similar size M: 7 1/2 pairs |
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Where does mitosis occur?
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Somatic cells for growth
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Where does meiosis occur?
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Germ cells for production of male and female gametes
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What does mitosis result in?
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Formation of two identical daughter cells with same number of chromosomes (46 in humans) and same DNA content as the original cell
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What 5 phases make up mitosis?
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Prophase, prometaphase, metaphase, anaphase, and telophase
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What are two reasons for genetic identity?
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i) No exchange of genetic material occurs between homologous chromosomes, so sister chromatids (the two copies of the same DNA on a chromosome) are identical
ii) Sister chromatids of each chromosome split, one going to each daughter cell during anaphase of the single mitotic division |
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How many chromosomes are in Interphase?
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46
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What occurs during prophase?
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Chromosomes double to 92
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What occurs during prometaphase?
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The nucleus dissolves and microtubules attach to centromeres
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What occurs during metaphase?
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Chromosomes align at middle of cell
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What occurs during anaphase?
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Separated chromosomes are pulled apart
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What occurs during telophase?
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Microtubules disappear and cell division begins
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What occurs during cytokinesis?
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Two daughter cells form, each with 46 chromosomes
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What are the germ cells that occur in meiosis specific to males and females?
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- spermatogonia in males
- oogonia in females |
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What occurs during meiosis-1?
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- homologous chromosomes separate
- involves recombination (cross over of genetic material between homologous chromosomes) - involves reduction to the haploid number of chromosomes |
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What occurs during meiosis-2?
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- chromatids separate
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What is established in a zygote at fertilization?
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The genetic sex of a zygote is established, when an X- or Y- bearing sperm fertilizes an oocyte
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What occurs in interphase 2 of meiosis?
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Two cells form, each with 46 chromosomes
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What occurs in metaphase 2 of meiosis?
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Microtubules attach to centromeres
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What occurs in anaphase 2 of meiosis?
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Chromosomes are pulled apart to 23
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What occurs in telophase 2 of meiosis?
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Microtubules disappear and cell division begins
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What is a major difference between male and female gametogenesis?
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One spermatogonium yields four spermatids, whereas one oogonium yields one mature oocyte and two polar bodies
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What does the genotypic sex determine?
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Gonadal sex
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What does the gonadal sex determine?
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Phenotypic sex
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What directs all ontogenetic processes involved in male-female differentiation?
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Sex-determining mechanisms established at fertilization
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What does the Y chromosome exert on the indifferent or developing gonad?
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A powerful testis-determining effect
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What is established during embryogenesis?
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The male sex is established when the primary sex cords differentiate into seminiferous tubules under the influence of the Y chromosome
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In the absence of a Y chromosome, what would the indifferent gonad develop into?
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An ovary
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What is the indifferent gonad composed of?
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An outer cortex and an inner medulla
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What occurs in embryos with XX chromosome?
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The cortex develops into an ovary, and the medulla degenerates
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What occurs in embryos with XY chromosome?
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The medulla differentiates into a testis, and the cortex regresses
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What do differentiated gonads determine?
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The sexual differentiation of the genital ducts and external genitalia
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What is the testis-determining factor (TDF), and what is it necessary for?
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- TDF is a single gene located on the short arm of the Y chromosome
- TDF also known as SRY (Sex-determining Region Y) - TDF is necessary for normal testicular development |
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What occurs during normal male meiosis?
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X and Y chromosomes pair and recombine at the distal end of their short arms
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How do XX males arise?
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XX males are a result of an abnormal exchange of genetic material between X and Y chromosomes in the father, causing the TDF to be transferred from a Y chromatid to an X chromatid
If the sperm that fertilizes an ovum contains the defective X chromosome with a TDF, the resultant individual will be an XX male |
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Where does the testis develop from?
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The medulla of the indifferent gonad; cortex regresses
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Where does the ovary develop from?
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The cortex of the indifferent gonad; medulla regresses
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What is Tuner Syndrome?
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A disorder of the female sex characterized by short stature, primary amenorrhea, sexual infantilism and other congenital abnormalities
The karyotype is 45, XO |
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What are the characteristics of a true hermaphrodite?
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- no recognizable Y chromosome but have teste
- possess both male and female sex organs - 46, XX |
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What are the characteristics of a pseudohermaphrodite?
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- mixed gonadal dysgenesis
- display morphological characteristics of both sexes, but have only one type of gonadal tissue - have testes and streak ovary - 45, XO |
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What is clearly distinguished in the indifferent duct system?
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The mesonephric or wolffian ducts and the paramesonephric or mullerian ducts
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What occurs in the differentiated male duct system?
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The paramesonephric or müllerian duct degenerates and the mesonephric or wolffian duct develops into the vas deferens, seminiferous tubules and ejaculatory duct
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What occurs in the differentiated female duct system?
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The mesonephric or wolffian duct degenerates and develops into the oviducts (fallopian tube), uterus, and upper third of the vagina
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What is required in the development of wolffian ducts?
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Testosterone produced by adrenal glands
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What does the bilateral removal of the testes deprive the embryo of?
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Testosterone and anti-mullerian hormone (AMH) [also known as mullerian inhibiting substance (MIS)]
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What does the absence of AMH and testosterone cause?
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Absence of AMH causes mullerian ducts to develop in a female pattern
Absence of testosterone causes wolffian ducts to degenerate Thus, genetically male fetus develops female internal and external genitalia |
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What occurs after bilateral removal of the ovaries?
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Mullerian development continues along normal female lines indicating that the ovary is not required for female duct development
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What does unilateral removal of the testis result in?
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Results in female duct (mullerian) development on the same (ipsilateral) side as the castration
Duct develops in a male pattern on the side with the remaining testis Virilazation of the external genitalia proceeds normally |
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In the absence of both testes, what are the effects of administering testosterone?
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Administering testosterone preserves development of the wolffian ducts
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What occurs in the absence of both testes in regards to AMH?
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Because of the absence of AMH (product of testis), no mullerian regression occurs
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In the presence of both ovaries, what does testosterone promote?
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Testosterone promotes development of the wolffian ducts
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What occurs if no AMH is present in regards to the presence of both ovaries?
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Without testes, no AMH is present and so the mullerian ducts develop normally
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What triggers the development of the testis?
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The SRY gene
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What is necessary for the male pattern of sexual differentiation?
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Androgens and antimullerian hormone
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Male pattern of sexual differentiation depends on the presence of which three hormones?
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Testosterone, dihydrotestosterone (DHT), and anti-mullerian hormone (AMH)
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What does the testis directly produce?
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Testosterone and AMH
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What are the mechanisms of peripheral tissues in regards to testosterone?
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Peripheral tissues convert testosterone to DHT
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What does testicular development occur in the presence of?
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TDF (testis-determining factor)
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What is the gene product of the SRY gene before 9 weeks of gestation?
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Testicular development (presence of TDF)
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If TDF is not present of if TDF is present only after the critical window of 9 weeks has passed, what will occur?
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An ovary will develop instead of a testis
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What does the female pattern of sexual differentiation occur in the absence of?
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Testes
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What is the male pattern of sexual differentiation directed by?
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Endocrine and paracrine control mechanisms
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In the absence of all gonadal tissue, what happens to the embryo?
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The embryo still follows the female pattern
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In regards to intercelluar communication, where do hormones / chemical signals of one cell type act on?
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Hormones / chemical signals act on:
Distant tissues (endocrine) Neighbouring cells in the same tissue (paracrine) Same cell that released the signalling molecule (autocrine) |
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What are the two major roles of androgens in male phenotypic differentiation?
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They trigger conversion of the wolffian ducts to the male ejaculatory system
They direct the differentiation of the urogenital sinus and external genitalia |
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During male differentiation, what does testosterone regulate?
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The wolffian phase
*Does not require conversion of testosterone to DHT by 5alpha reductase |
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During male differentiation, what requires DHT?
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Virilization of the urogenital sinus, the prostate, the penile urethra, and the external genitalia during embryogenesis
Sexual maturation at puberty |
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What is the function of the Sertoli cells after formation of the testicular cords?
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The Sertoli cells produce anti-mullerian hormone (AMH), which causes the mullerian ducts to regress
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What occurs shortly after initiation of AMH production?
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The fetal Leydig cells begin producing testosterone
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What does the embryonic mesenchyme contain and what is it the first site of?
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Androgen receptors and is the first site of androgen action during formation of the male urogenital tract
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What happens in the absence of adequate androgen production or functioning androgen receptors?
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Sexual ambiguity occurs
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What is androgen-binding protein (ABP) produced by?
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Sertoli cells
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What is the function of ABP?
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To bind and maintain a high concentration of testosterone locally for the stimulation of growth and differentiation of the wolffian ducts into the epididymis, the vas deferens, the seminal vesicles, and the ejaculatory duct as well as differentiation of the medulla of the gonad into the rete testes
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What promotes the development of the prostate?
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Testosterone
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What do cells of the wolffian ducts lack? What does this imply?
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Lack 5alpha-reductase and therefore cannot convert testosterone to DHT
Internal male ducts respond to testosterone per se and do not require the conversion of testosterone to DHT |
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What occurs in the absence of testosterone in regards to the duct system?
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The wolffian system remains rudimentary (underdeveloped), and normal male internal ductal development does not occur
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What is required for normal male development of the external genitalia?
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The conversion of testosterone to DHT is required
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What is the congenital absence of 5alpha-reductase associated with?
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Associated with normal development of the wolffian duct system but impaired virilization of the external genitalia
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What are the effects of congenital adrenal hyperplasia?
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People with congenital adrenal hyperplasia lack an enzyme the adrenal gland needs to make cortisol and aldosterone.
At the same time, the body produces more androgen, a type of male sex hormone. This causes male characteristics to appear early (or inappropriately). |
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Deficiencies in which enzymes lead to virilization in females, and thus ambiguous genitalia as a result of the hypersecretion of adrenal androgens?
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21α-hydroxylase
11β-hydroxylase 3β-hydroxysteroid dehydrogenase |
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What is the most common enzyme deficiency in congenital adrenal hyperplasia?
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21α-hydroxylase deficiency
accounts for ~95% of cases |
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What are the effects of 21α-hydroxylase deficiency?
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Reduces conversion of progesterone to 11-deoxycorticosterone, which goes on to form aldosterone
Reduces conversion of 17α-hydroxyprogesterone to 11-deoxycortisol which is the precursor of cortisol As a result, adrenal steroid precursors are shunted into androgen pathways |
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What are the symptoms of adrenogenital syndrome?
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External genitalia are difficult to distinguish from male genitalia on visual inspection
The clitoris is enlarged and resembles a penis, and the labioscrotal folds are enlarged and fused and resemble a scrotum The genitalia thus have a male phenotype in an otherwise normal female infant |
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What is testicular descent dependent on?
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Androgen-dependent process (testosterone)
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What are testosterone-deficient states caused by?
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Inadequate secretion or disordered androgen action
Cause failure of testes to descend in genetic males |
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What is the cause of testicular feminization syndrome?
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5α- reductase deficiency and complete androgen resistance
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What is the cause of male pseudohermaphroditism?
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Any defect in the mechanisms by which androgens act on target tissues in genotypic males may lead to a syndrome of male pseudohermaphroditism
Affected individuals have a normal male karyotype (46, XY) and unambiguous male gonads but ambiguous external genitalia or may phenotypically appear as females |
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What are the effects of 5α-reductase deficiency?
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The activity of 5α-reductase is necessary for the conversion of testosterone to dihydrotestosterone (DHT) This may lead to ambiguous genitalia in males
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