Question

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background:

1. Genes are passed to offspring from parents through both sexual and asexual reproductions. Sexual reproduction provides the opportunity for 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 adults

   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 adultFor this assignment, you are assigned an organism (Black bread mold (Rhizopus stolonifer) which may use either or both sexual and asexual reproduction in their lifecycles.

   1)Describe this organism’s life cycle and where genetic exchange might take place in it.
   • 2)Identify if your organisms match more of a Type 1,2, or 3 life cycle as detailed above.
   • 3)If asexual reproduction is a normal part of this organism’s life cycle, propose why asexual reproduction might be an advantage.
   • 4)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 environment factors might have led to this difference.

Answer 1

Black bread mold is a common name of Rhizopus stolonifer. It belongs to the Zygomycota division of fungi. Bread, cheese is a substrate for the fungi. Rhizopus have extended filaments called hyphae. They have a complex life cycle including asexual and sexual reproduction.

Structure of Rhizopus :-The body of rhizopus consist of 4 parts Sporangium, Spores,Stolon and rhizoids.

The cell wall of fungi is made up of chitin, the cell is multinucleated and consists of other cell organelles such as mitochondria, ER and Golgi apparatus. The spores produced in a sporangium are called sporangiospores. Reproduction in rhizopus takes by all three ways;

1- Vegetative reproduction:

• The rhizopus develops and divides into two daughter cells by fragmentation.

2-Asexual Reproduction

• It takes place by forming spores under favorable conditions as the tip of hyphae enlarges and develops into a round-shaped structure called a sporangium. The sporangium further divides into multinucleated sporoplasm & calculated columellaplasm.
• the sporangium develops and produces non-motile and multinucleated sporangiospores. The formation of sporangiospores takes place in a rapidly dividing nucleus of multinucleated sporoplasm. Upon maturation, the columella region of the sporangium collapses and the sporangiospores(n) are released into the environment. The onset of the favorable condition, these spores germinate to give rise to a new mycelium.
• Under unfavorable condition rhizopus form chlamydospores. they are thick-walled and they remain dormant under the unfavorable conditions and wait till the favorable condition returns.

3-Sexual Reproduction

• Most of the rhizopus stolonifers are heterothallic in nature means they have 2 different steps of mycelium;+and -. Sexual reproduction takes place by fusion hyphae that are compatible with each other.
• The sexual reproduction takes place by the help of gametangia copulation.when two compatible strains. each of the mycelia develops a small projection called progametangia as soon as they come close to each other. Both the gametangia conjugate to form a multinucleated structure leading to the development of a resting spore. The fusion of plasma is followed by nuclei fusion and formation of a zygote having 2n. The fusion of two nuclei is called karyogamy.
• Zygospore enlarges and becomes thick-walled and resistant to environmental stress. under favorable conditions, the zygospores germinate into a new promycelium. It has two distinct regions called as germsporangiospores and germ sporangium. Meiosis takes place to produce haploid spores.

Advantages of asexual reproduction:-It is a uniparental process. The offspring has a genetic identity as of their parents and retain the characters of the parent. A large number of offsprings are produced at one time.

Advantages of sexual reproduction:-Variation induces new characters into the population. Offsprings are more protected and preserved