Question

1. Eggs are structured to prevent multiple sperm from fertilizing it. Discuss what those structures are and how they help prevent extra sperm from getting into the egg.

2. Explain where fertilization occurs in the female reproductive system. How does this lead to the rare ectopic pregnancy?

3. Sometimes people say that the theory of evolution says we humans came from chimpanzees .explain why this argument is flawed.

Answer 1

1. Zona pellucida is the structure in egg that prevents polyspermy. It is a structure that surrounds mammalian eggs. The structure becomes impermeable to sperms by the cortical reactions, after fertilization. In Cortical reactions, enzymes released by cortical granules modify zona pellucida by digesting sperm receptor glycoproteins so that they can no longer bind spermatozoon.

2. Fertilization of an egg by a sperm normally takes place in the fallopian tubes, which connect the ovaries to the uterus. The fertilized egg then moves to the uterus and then burrows into the uterus lining. This is called implantation.

An ectopic pregnancy is an ‘out-of-place pregnancy’. The most common place for an ectopic pregnancy is the Fallopian tube in which the fertilized egg implants and grows in the tube. This is always caused by the damage to the fallopian tubes. The factors like smoking might damage the fallopian tube. A fertilized egg may have trouble passing through a damaged tube. There are many other sites outside the uterus where an ectopic pregnancy can be located.

3. Humans did not evolve from chimpanzees or any of the other primates that live today. Humans instead share a common ancestor with these primates. Phylogenetically close organisms have a higher degree of DNA sequence similarity than organisms that are distant. Human DNA sequences are approximately 1.2% divergent from the chimpanzee, 1.6% from gorillas, and 6.6% from baboons. This closeness in DNA sequences strongly suggests that chimpanzees are most genetically related to humans. It also supports the existence of a common ancestor for all these primates. The chimpanzees has nearly identical DNA sequences to human chromosome 2. The same is true of the more distant gorilla and orangutan. Chromosome 2 thus presents strong evidence to support the common descent of humans and other apes.