Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
Ooplasmic Determinants and Somatic Cell Determination
Eggs of tunicates go through typically mosaic development in which the various blastomeres become determined to follow their particular paths of differentiation very early after fertilization. The determination is signaled through determinants present in the egg cytoplasm which become segregated in particular blastomeres during the first three cleavage divisions. Intensive descriptive, experimental and biochemical studies on some type of tunicate species like Styela and Ciona have confirmed that determination is brought about under the affect of intrinsic cytoplasmic (ooplasmic) determinants and not by interaction among the blastomeres or alteration in the genome in the nuclei of different blastomeres. This is particularly true for the determination of blastomeres which give rise to muscle cells of the tadpole that hatches from the egg. You have studied determination of germ cells in the mosaic eggs of Ascaris through cytoplasmic determinants. Now muscle cell determination in tunicates based upon the studies on Styela and Ciona.
This is a good instance of determination of a somatic cell type (muscle) by cytoplasmic determinants in mosaic eggs. Eggs of tunicates consist of colored cytoplasmic regions. For instance, Styela eggs contain a yellow colored region, the myoplasm. In another tunicate Boltenia the myoplasm region is orange colored. Besides, the egg contains ectoplasm and endoplasm regions as well. Cytoplasmic movements known as ooplasmic segregation localise these regions in eggs after fertilisation. In Styela and Boltenia the ooplasmic segregation is obvious due to the colored regions of the cytoplasm. In the unfertilised egg of Styela the clear ectoplasm is present in the type of germinal vesicle near the animal pole. The grey yolky endoplasm occupies the entire vegetal half and the yellow myoplasm is confined to the peripheral conical region. Instantaneously after fertilisation there occurs displacement of the three materials (plasmas) in the zygote. The yellow myoplasm flows down to the vegetal pole.
The germinal vesicle breaks and the clear ectoplasm moves into the vegetal hemisphere. At similar time the endoplasm is displaced into the animal half of the egg. This arrangement of cytoplasmic contents of the zygote does not last for much time and soon by a second phase of segregation the three cytoplasmic materials are rearranged again. The myoplasm moves to a position below the equator of the egg and forms a crescentic region on the future posterior side of the egg. It is known as the yellow crescent. Most of the grey yolky endoplasm moves to the future anterior half and the ectoplasm to the animal half of the egg simultaneously. Opposite to the yellow crescent. a fourth cytoplasmic region, the chordoplasm is formed. This is also a crescent located beneath the equator on the anterior side of the vegetal half of the egg. This arrangement of various cytoplasmic regions clearly shows the bilateral organisation of zygote contents.
plese help for an assignment of topic parasitic flat worms for a first year zoology student.
Are dogs colour blind
Michael eats steak & cheese sub sandwiches every day of the week. Explain the types of fats that are found in steak & cheese subs and the properties of each type. Jillian eats
Q. What are the main human diseases caused by prions? The major known human diseases of such type are the Creutzfeldt-Jacob disease (CJD), the kuru and the Gerstmann-Sträussle-
Which of the following serves as an effector, or as part of an effector, that functions in a negative feedback system? A. Glycogen Receptors in the plasma membranes of liver ce
Define the interaction of vitamin c with lead and mercury? Vitamin C, lead and mercury: Iron alleviates lead toxicity but ascorbic acid is ineffective. Ascorbic acid alleviat
Calculate a 95% confidence interval for the difference among the average numbers of ant species in the two regions. Compare your results to SPSS output and interpret the confidence
Q. What is the name of the molecule that transports oxygen in red blood cells? The respiratory pigment of the red blood cells is hemoglobin.
Characteristic of Ecotone A general characteristic of ecotone is that it has sufficiently greater number of species and the diversity of most of the species at times is higher
Applications of microbiology in different fields
Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd