Question

Instructions Genes are passed to offspring from parents through both sexual and asexual reproductions. Sexual reproduction provides the opportunity for a genetic exchange to take place whereas asexual reproduction on provides for the same genes that were in the parent to be passed on to the offspring. In general, sexual reproduction is a good thing for a species as it allows for genetic exchanges which typically strengthens species. Although as we saw in the first discussion of this module that is not always true. There are three general types of lifecycles. Type 1 Haploid (1N) adult organism produces haploid gametes -> gametes from different adults fuse to form a diploid zygote ->meiosis occurs -> resulting haploid cells -> haploid adultsOverview The first step in understanding how information is passed from one generation to the next is understanding how cells divide, particularly how the DNA is passed on to the resulting cells. In this discussion you will describe the life cycle of an animal or plant assigned to you (see table at the end of the instructions for assigned organism). During this discussion we will focus on the processes and function of mitosis and meiosis. You should spend approximately 3 hours on this assignment. Type 2 diploid (2n) adult has cells that undergo meiosis to produce haploid gametes -> haploid gametes from different adults fuse ->diploid zygote -> diploid adult Type 3 Diploid adult ->meiosis -> haploid cell (spores) -> haploid adults -> haploid adults produce gametes (sperm and egg) -> gametes fuse to produce -> diploid zygote -> diploid adult For this discussion, you will be assigned an organism (see table at the end of these instructions) which may use either or both sexual and asexual reproduction in their lifecycles. In your initial post you should do the following: Describe this organism’s life cycle and where genetic exchange might take place in it. Identify if your organisms match more of Type 1,2, or 3 life cycle as detailed above. If asexual reproduction is a normal part of this organism’s life cycle, propose why asexual reproduction might be an advantage. If the organism does not have an asexual phase in the lifecycle explain why this might be an advantage for this organism. If your organism has a different type of lifecycle from the expected such as males may become females, females many more than males in the population, etc., then explain what environmental factors might have led to this difference.

 

Answer 1

•Volvox is colonial a chlorophycean algae and a member of family Volvocaceae.

•The sexual reproduction in Volvox is oogamous type.- that means female gamete is stable , non motile and large in size and few in number. Whereas, male gametes are motile large in number and smaller in size.

• Some species of Volvox are monoecious or homothallic:- it means the antheridia and oogonia develop on same colony.

•Other Volvox species are dioecious or heterothallic:- i.e., antheridia and oogonia develop on different colonies.

•Volvox is haploid (n) algae, the haploid gametes fertilize to make diploid zygote (2n) which divides by meiosis to make haploid cells (n) which mature into haploid Volvox colony.

•So in volvox we see type 1 life cycle [i.e. Haploid parent]. During this process-

1.As the parent is haploid the gametes are formed by the process of mitosis [as you know it is an equational division] and maintain the single set of chromosome [n].

2.When the male gamete [n] and female gamete[n] are produced and fussed during fertilization , the resulted zygote is diploid cell [2n].

3.Here the zygote is not divided mitotically and grow into new Volvox colony.

4.The meiosis is going on in the zygote ‘because zygote is diploid and our adult plant body is haploid’. [as meiosis going on the crossing over and recombination is there so each zoospore having different genetic combination as that of parent].

5.So zygotic meiosis process going on which results in haploid spores [biflagelated motile ] on germination they form a new Volvox colony.

6.See the photo of haplontic life cycle of Volvox.

•As the see that the Volvox is monoecious or dioecious .

•Monoecious species are usually protandrous i.e., antheridia mature before oogonia but some species are protogynous i.e., oogonia develop before antheridia. Due to this the fertilization occurs between two different colonies , so even the species might be monoecious or dioecious there is 100 % chance of hybrid formation and 100 % chance of genetic exchange during meiosis for spore formation.

•Asexual reproduction produces genetical clones of parents. The main advantage of asexual reproduction to to propagation of species at faster rate. During favorable condition the species propagate vegetatively / asexually.

•In the absence of asexual reproduction the population of that species not grow as much faster, and clones are not formed.

•If we focused on the number of egg and anthrozoids in Volvox , we noticed that number of male gametes are more than female. Because male gametes have to swim and reach to female gamete [by chaemotactic attraction], it causes loss of male gametes.

• if the scenario is changed and we reduce the number of male gametes , the chances of fertilization will less.