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Types of Reproduction and Which You Think is Better and Why essay

7th grade level of the diferent types of reproduction. Teacher gave them this along wth chapter on her book. paragraphs nee to be of 5 senteces or more. MLA format

Aurora Rayon
Ms. Das 7C

The Pros and Cons of
Asexual Reproduction
Science Daily – Opposite-sex partners: can’t live with ’em, can’t evolve without ’em
Making babies requires a male and a female, a sperm and an egg, right? Well, the wild world of
animals is often more creative. In fact, some animals don’t have sex at all, thank you very much.
Just this month, bug biologists found the first all-female ant species, Mycocepurus smithii. The
queen ant clones herself by making eggs that develop into adult females without fertilization. Some of
those females will then become queens themselves. Apparently the species has been sexless for enough
generations that the ants might not be able to mate even if they wanted to. Dissections showed that a
key female sex part that normally interlocks with a male organ during mating had shrunken to a ghost of
its former self.
Bugs aren’t the only ones that can do without sex. Some lizards and fish reproduce purely
asexually, and a few aquarium sharks have been observed popping out little clones of themselves with
nary a male around. Doing away with males can make a species efficient at making more offspring: 100
percent of kids will be egg-laying (or child-bearing) females instead of 50 percent. Also, why expend all
that energy on mating rituals and copulation? For some species, males just seem to be dead weight.
Although a sexless existence can have these advantages, it’s generally a dangerous lifestyle,
which carries a greater risk of extinction.
Environmental changes are less hazardous to species that have sex. By mixing some momma
chromosomes with some poppa chromosomes, sexual reproduction shuffles genes around, making
individuals of a species more varied. A sexual species will be more resilient in a changing environment,
because a few of their members might randomly have the right traits to survive. If each ant is exactly the
same, adverse conditions, such as a new bacterial infection, could easily wipe them all out.So, in
general, it’s good to keep a few lads around for some gene swapping.
SEXUAL VS. ASEXUAL REPRODUCTION
By Gail Brown
Thursday, October 18, 2001 – 17:00
Santa Barbara, CA
The question of why most species reproduce sexually and others reproduce asexually has stymied
biologists for years (particularly since asexual reproduction has many advantages including
producing more offspring.) Studies by scientists at the University of California, Santa Barbara show
that sexual reproduction wins out, in an evolutionary sense, over asexual reproduction in a major
study that included 34 experiments with the common fruit fly Drosophila melanogaster.
Specifically, they discovered that the rate of progressive evolution (the accumulation of beneficial
mutations) is faster in populations that reproduce sexually.
“However, there is a high cost associated with producing males,” said William R. Rice, first author and
professor of biology at the UC, Santa Barbara. “Just do the math and you will see. The math is simple:
with four asexual adults (females) you get eight offspring, but with two males and two females you
get only four offspring. In other words, the asexual population grows twice as fast as the sexually
reproducing one.
Name: _________________________________________ Date: _________________________
The second part of the mathematical advantage is that the asexual adult female is able to put all of
her genes into the next generation, whereas with sexual reproduction, each individual is responsible
for only half of the genetic information in the offspring. “It’s a dosage cost,” said Rice. “My son only has
half of my genes; the other half are from his mother. Only half of my genome is getting into the
population. However, if I were an asexual female, my offspring would carry all of my genome. I would
put twice as many genes into the next generation. With asexual reproduction you get two times as
many offspring and two times as many genes into the population.”
There is a broad assumption in this scenario that males do not help with the care and feeding of
offspring, although in a small proportion of species they do help: people, wolves, foxes and most
songbirds. In these species it is possible to produce more offspring because of the help of the male.
One hypothesis has been that the process of natural selection is more powerful when you mix genes
in each generation. The UCSB scientists created populations that mixed genes and populations that
didn’t.
For the fruit fly experiments, Rice and Adam K. Chippindale (a post-doctoral fellow soon to be on the
faculty at Queen’s University in Canada), used genetic tools to manipulate the fruit fly so that half
were normal flies and half were asexual, and reproduced asexually (a situation that occurs in nature
in several species, such as certain lizards and insects). “We created 17 populations that mixed genes
and 17 that didn’t,” said Rice. “In other words, we had populations that were sexual and populations
that were asexual.”
They followed a mutation at a gene that coded for eye color, specifically for red eyes versus white.
They found that this beneficial red eye mutation began to accumulate in both the sexual and
asexual populations, but not as much or as fast in the asexual populations.
The researchers found that the efficiency of natural selection is higher because the “signal to
background noise ratio of natural selection is higher in the sexual populations.” This means that in
evolutionary terms the sexually reproducing populations are the winners on average.
“Almost every life form is sexual, but according to theory asexual populations should win out,”
explained Rice. “We knew there must be a big countervailing reason that asexual reproduction loses
out to sexual reproduction.”
Rice and Chippindale knew that they needed a significant number of experiments in order to
discover the average tendency. “Otherwise, it is like looking at whether or not wearing seat belts
helps,” said Rice. “You can’t look at only one accident from which to draw conclusions, you need
large numbers to show the average.”
In the experiments, conducted over a year and a half, the researchers were able to track individual
mutations over time. They found that with sexual reproduction, the gene for red eye color rose rapidly
toward “fixation” or establishment in the population. The proportion of the red eye color gets higher
and higher over time until it is fixed at 100 percent.
With the asexual populations the mutation began to accumulate, but eventually stopped in most
cases.
“We knew that there were advantages to sexual diversity, but it was not clear why,” said Rice. “Now
we have evidence that the rate of progressive evolution (the accumulation of beneficial mutations)
is faster in sexual populations. We simulated that and saw that the sexual population gets the good
gene faster. This is the first time that this has been consistently demonstrated.”
Name: _________________________________________ Date: _________________________
Based on the articles above, write a short essay in which you explain the two
types of reproduction and appropriately justify which method you think is more
advantageous to a population of organisms.