Question 1

Why don't chickens menstruate?

Accepted Answer

Chickens do not have a menstrual cycle because their eggs have all the nutrients the early embryo needs to develop. The yolk serves as the food for the growing embryo and is not connected to a uterus or endometrium like in mammals.

Question 2

The posterior end of the neural tube will develop into the brain.

Accepted Answer

The anterior end of the neural tube develops into the brain, while the posterior end develops into the spinal cord.

Question 3

You are a chemist designing a test to allow women to know when they have ovulated.Choose the best hormone for your test,which will indicate that ovulation has occured when detected at high levels.

Accepted Answer

LH (luteinizing hormone) is the best choice for a test that indicates ovulation. LH levels spike right before ovulation and trigger the release of the egg. Therefore, detecting high levels of LH in the urine can indicate that ovulation has occurred. Estradiol and progesterone levels fluctuate throughout the menstrual cycle and can be less reliable indicators of ovulation. Chorionic gonadotropin is only produced after fertilization and is not useful in detecting ovulation.

Question 4

One type of illegal doping in sports is the abuse of anabolic steroids such as testosterone.Doctors measure the testosterone (T)to LH ratio in athletes' urine to detect such doping.Why is this an effective indicator?

Accepted Answer

Testosterone has negative feedback onto LH production, which means that high levels of testosterone in the body will reduce the production of LH. Therefore, if an athlete is doping with anabolic steroids, they will have an unusually high T/LH ratio, making it an effective indicator for detecting steroid use.

Question 5

Human eggs undergo holoblastic cleavage during development.

Accepted Answer

Human eggs undergo holoblastic cleavage, which means the entire egg is divided during cell division. This is different from meroblastic cleavage, which occurs in eggs with large amounts of yolk, and only a portion of the egg is divided during cell division.

Question 6

A certain drug has a side-effect of disrupting levels of luteinizing hormone (LH).Which patients should be advised that this drug could affect their fertility?

Accepted Answer

Luteinizing hormone (LH) plays a crucial role in the reproductive systems of both men and women. In men, LH stimulates the production of testosterone, which is essential for sperm production. In women, LH is involved in the menstrual cycle and ovulation. Therefore, disrupting LH levels can affect fertility in both men and women.

Question 7

What would happen if the cortical reaction proceeded before the acrosomal reaction was complete?

Accepted Answer

The cortical reaction is important to prevent polyspermy (when multiple sperm fertilize one egg), but it occurs after the acrosomal reaction where the sperm releases enzymes to penetrate the egg's protective layers. If the cortical reaction occurred before the acrosomal reaction was complete, the egg would not have been fully prepared to receive the sperm, and fertilization would not occur.

Question 8

Many small creatures that live in temporary puddles can reproduce asexually at least occasionally.Why might this be a useful strategy for a puddle-dweller?

Accepted Answer

Asexual reproduction allows a single individual to quickly produce many offspring, filling up the small and temporary environment. This can give the offspring a better chance of surviving until the next puddle forms.

Question 9

Under the microscope,you observe the first few cell divisions of an embryo.Instead of dividing the entire ball,the divisions are only separating the top half into smaller and smaller spheres.The bottom half appears to remain as one large cell.What is a likely explanation?

Accepted Answer

This observation is characteristic of meroblastic cleavage, which is common in bird and fish embryos due to the presence of a large yolk in their eggs. The yolk inhibits cytokinesis, leading to partial division of the embryo.

Question 10

Imagine a drug that causes an increase in the signaling pathway activated by nitric oxide (NO).What might be the effect of such a drug?

Accepted Answer

This describes the drug Sildenafil (sold as Viagra).Since it increases nitric oxide signaling,it increases the strength of the male erection.Erection occurs when blood fills spongy erectile tissue located along the length of the penis.Sexual arousal stimulates release of the gaseous neurotransmitter nitric oxide (NO)in the penis,causing vasodilation of arteries.The pressure of the blood flowing into the penis constricts nearby veins,causing a reduction in venous drainage from the penis,engorging it with blood.After ejaculation,NO release is decreased,causing a reversal of the vascular changes responsible for erection.

Question 11

A mutation in mice leads to overgrowth of the Sertoli cells,so they span across the diameter of the seminiferous tubules.What phenotype would you expect to see?

Accepted Answer

If the seminiferous tubules were completely full of Sertoli cells with no space in the middle of the tube,there would be no room for mature sperm to flow through the seminiferous tubules and enter the epididymis.

Question 12

Red blood cells are derived from endoderm.

Accepted Answer

Red blood cells are derived from hematopoietic stem cells, which are derived from the mesoderm layer.

Question 13

Cleavage occurs after implantation into the lining of the uterus.

Accepted Answer

Cleavage occurs before implantation, during the early stages of embryonic development in the fallopian tube. After several cell divisions, the embryo then undergoes implantation into the lining of the uterus.

Question 14

Neurulation begins with the thickening of the ectoderm over the neural tube.

Accepted Answer

Neurulation actually begins with the formation of the neural plate, a thickening of the ectoderm, which then folds to form the neural tube.

Quiz 40: Animal Reproduction and Development