ANSC 333 Exam 1

If growth of the gubernaculum were blocked in a male bovine fetus, what would the impact be on male fertility if this bull survived to adulthood?

Bull would be sterile. Sterility results from a failure of testicular thermoregulation, testes must be kept a few degrees below core body temperature for spermatogenesis to occur...testes found in the abdomen would be too warm to sustain spermatogenesis.

Methods of sex determination vary across the animal kingdom. Identify the two general mechanisms of sexual determination we discussed in class and provide a BRIEF and general description of how each mechanism works.

Genetic sex determination. Here, sex is determined by the genes that the embryo possess. For instance, in mammals, females have two X chromosomes, while males have an X and a Y chromosome. The Y chromosome contains a gene known as SRY; SRY is the master regulator that causes the embryo to form a testis.

Environmental sex determination. Here, all animals have the same chromosomal (or genetic) contribution; there are no sex chromosomes, every embryo inherits the same chromosomes and some environmental queue causes an individual to develop into a male or female. In some reptiles, the temperature at which eggs are incubated can dictate which sex develops.

How would fertility be impacted if a genetically male bovine embryo contained a mutation that prevented c-kit from being produced? Assume this embryo could survive to adulthood. As an adult, would this animal be fertile? Explain your reasoning as to why this impact on fertility comes about.

Kit ligand is the ligand that binds to the c-kit receptor; c-kit receptors is expressed on the cell surface of the primordial germ cells (PGCs). The binding of kit ligand to c-kit is the stimulus that leads the PGCs from the yolk sac to the indifferent gonad. A mutation in c-kit would interfere with the binding to kit ligand, therefore PGCs would fail to migrate to the indifferent gonad; PGCs would not be able to differentiate into sperm, therefore this animal would be sterile.

What would happen with regard to the development of the tubular reproductive tracts in a genetically female embryo if the indifferent gonads were removed.

Paramesonephric duct system would develop into a female tubular reproductive tract; mesonephric duct system would regress.

What would happen with regard to the development of the tubular reproductive tracts in a genetically male embryo if the indifferent gonads were removed.

Paramesonephric duct system would develop into a female tubular reproductive tract; mesonephric duct system would regress.

What would happen with regard to the development of the tubular reproductive tracts In a genetically female embryo treated with testosterone and mϋllerian inhibiting hormone (MIH; also known as anti-mϋllerian hormone, AMH).

Mesonephric duct system would develop into a male tubular reproductive tract; paramesonephric duct system would regress.

Explain how the presence of the SRY gene determines maleness in mammals. Be sure to include where the SRY gene is found and how it 'determines' maleness.

Explain how the testes migrate to the scrotum

Occassionally one or both of the testes fail to migrate to the scrotum. What is the impact on fertility of a male in which one or two of the testes fail to descend into the scrotum? Briefly explain your answer.

Primordial germ cells (PGCs) found in mammalian embryos will ultimately develop into either oocytes or spermatozoa.Explain where these cells arise, to where they travel during embryogenesis, how they move, how they are directed to their final destination.

Primordial germ cells (PGCs) found in mammalian embryos will ultimately develop into either oocytes or spermatozoa.How is this different from the way avian PGCs travel to the indifferent gonad?

Primordial germ cells (PGCs) found in mammalian embryos will ultimately develop into either oocytes or spermatozoa.What do you think would happen to PGCs if a mammalian embryo possessed a mutation and

did NOT produce c-kit?

Thermoregulation of the testes is critically important for spermatogenesis to occur properly. Outline the ways that the scrotum and the pampiniform plexus work to regulate the temperature of the testes. Be sure to identify the key structures involved in these two areas AND clearly state how they each work to mediate thermoregulation.

If the vesicular glands were removed from a boar, what affect (if any) would there be on the following:

a. testosterone production

b. spermatogenesis

c. seminal plasma

Define rathe's pouch

Define Cryptorchid

Define Mesonephric (wolffian) Ducts

Acrosomal Cap

In comparing the ejaculates from the ram and the boar, the ejaculate from which

a. have the higher volume

b. have the higher concentration of spermatozoa

c. have a segmented ejaculate

d. take the shorter time to collect (i.e., which animal has the more rapid ejaculation)

Outline the steps of spermatogenesis starting with the Type A spermatogonia through release of spermatozoa from the seminiferous epithelium. Be certain to clearly identify the cell type(s) that undergo meiosis, the cell type(s) that undergo mitosis and the cell type(s) that are haploid

Diagram or describe the hormonal regulation of spermatogenesis. BE CERTAIN that you identify which cell/tissue produces which hormone and on what cell/tissue each hormone acts upon.

Consider the following scenario: A ram is treated with a drug that inhibits the activity of adenylate cyclase in the Leydig cells for a period of 6 months. At the end of the 6 month period, you examine an ejaculate from this boar and find no spermatozoa in the semen. Explain how this result would come about.

Consider the following scenario: A ram is treated with a compound that had NO EFFECT on the type A spermatogonia, but killed ALL other developing germ cells, including the spermatozoa in the seminiferous tubule and epididymis. Following drug treatment you allow the ram to recover, during this recovery period you examine an ejaculate once per week for the next 6 months. The first ejaculate you collected following drug treatment contained only dead, non-motile spermatozoa.What would you expect to detect in the ejaculates you evaluate over 6 months following drug treatment? Would the animal be sterile at the end of the 6 month recovery, why or why not?

A bull is treated daily with LH such that LH levels in circulation are maintained at HIGH levels for a 6 month period. Every week during this treatment, blood is collected to determine the concentration of testosterone and semen is collected to determine sperm concentration.At the end of the 6 month period, do you think the concentration of testosterone in the blood would be lower, higher or unchanged as compared to blood samples taken before LH treatment began? Explain your reasoning (meaning, through what mechanism would your result be reached)?

A bull is treated daily with LH such that LH levels in circulation are maintained at HIGH levels for a 6 month period. Every week during this treatment, blood is collected to determine the concentration of testosterone and semen is collected to determine sperm concentration.At the end of the 6 month period, do you think the concentration of sperm in the bull's ejaculate would be lower, higher or unchanged as compared to an ejaculate collected from that bull before LH treatment? Explain your reasoning (meaning, through what mechanism would your result be reached)?

What is different about the hypothalamus in the male when comparing prepubertal and postpubertal life (HINT, what is different about GnRH secretion and what causes this difference)?

Explain how erection is established in the bull. Be certain to discuss the relevant anatomical structures and how they work in combination to establish erection.