Question

The usual result of an oocyte fertilized by two sperm is A. dizygotic twins. B. partial mole. C. normal pregnancy. D. fetal gigantism.

Short answer

B. Partial mole.

Step-by-step solution

Understand the Question

The question asks for the usual result when an oocyte is fertilized by two sperm. Recognize the key terms: 'oocyte,' 'fertilized by two sperm,' and understand the potential outcomes listed in the options.

Define Key Terms

An 'oocyte' is a female gamete or egg cell. 'Fertilized by two sperm' refers to a condition called 'dispermy,' where two sperm cells enter one egg.

Analyze Each Option

Consider each outcome in the context of dispermy: A. Dizygotic twins: Twins from two different eggs, not from one egg fertilized by two sperms. B. Partial mole: An abnormal pregnancy resulting from one egg fertilized by two sperms, leading to molar tissue and limited fetal development. C. Normal pregnancy: Unlikely with dispermy due to genetic imbalance. D. Fetal gigantism: Often unrelated to genetic situations involving dispermy.

Select the Correct Option

Based on the analysis, the answer is B. Partial mole, as it matches the result of an egg fertilized by two sperms.

Key concepts

oocyte

An oocyte is a female reproductive cell, also known as an egg cell. It plays a crucial role in the fertilization process. When an oocyte matures, it undergoes a series of changes that prepare it for potential fertilization by sperm.
Oocytes are created during fetal development in females and remain dormant until puberty. Each menstrual cycle, one oocyte matures and is released during ovulation. The oocyte waits in the fallopian tube for fertilization.
Understanding the function and journey of an oocyte helps in grasping its role in the reproductive process and what happens when anomalies like dispermy occur.

dispermy

Dispermy occurs when one oocyte is fertilized by two sperm cells. This is an abnormal fertilization process and usually results in complications.
The entry of two sperm into one egg leads to a triploid set of chromosomes (69 chromosomes instead of the normal 46). This genetic imbalance disrupts normal development.
Dispermy can lead to severe genetic disorders and usually does not result in viable pregnancy outcomes. The most common result of dispermy is a partial mole.

partial mole

A partial mole is a type of molar pregnancy resulting from dispermy, where one oocyte is fertilized by two sperm cells.
This leads to abnormal growth of placental tissue and a mix of normal and abnormal cells. The fetus usually does not develop properly, if at all.
Symptoms of a partial mole may include severe nausea, high hCG levels, and abnormal vaginal bleeding. Ultrasound usually reveals a characteristic pattern of molar growth.
Diagnosis and treatment generally involve removal of the molar tissue to prevent complications.

zygote formation

Zygote formation is the initial stage of human development post-fertilization. Normally, one sperm cell fertilizes one oocyte, resulting in a zygote with 46 chromosomes.
The zygote undergoes rapid cell division and differentiation, eventually forming an embryo and then a fetus.
However, in cases of dispermy, the resulting zygote has an abnormal number of chromosomes. This disrupts normal cell division and development, often leading to a partial mole rather than a healthy pregnancy.
Understanding zygote formation is essential to see why dispermy leads to such significant complications and isn't conducive to a normal pregnancy.