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Alloploids are produced by crosses involving two different species. Explain why alloploids may be reproductively isolated from the two original species from which they were derived. Explain why alloploids are usually sterile, whereas allotetraploids (containing a diploid set from each species) are commonly fertile.
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Alloploids are sterile. Hence, though they might be fertile between their own cross but cannot interbreed with either of the parent species, thus getting reproductively isolateD.In alloploidy, when two different species interbreed, their chromosomes combine resulting in the formation of a polyploidy hybrid. During meiosis of this polyploidy hybrid, an error occurs due to the absence of homologous pair of chromosomes for each of the chromosome derived from the parent. This thus results to hybrid sterility as the offspring produced by this hybrid would be aneuploid hence rendering it inviable. Thus, alloploids are reproductively isolated from the parent species due to hybrid sterility.
Allotetraploids on the other hand inherit even number of chromosomes from the parents. As a result, during meiosis, they have homologous set of chromosomes that pair up and hence do not from sterile aneuploid cells.
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Prehistoric specimens often contain minute amounts of ancient DNA. What technique can be used to increase the amount of DNA in an older sample Explain how this technique is performed and how it increases the amount of a specific region of DNA.
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The technique that is most commonly used to amplify and increase the amount of DNA (deoxyribonucleic acid) is the PCR (polymerase chain reaction). By this technique, it is possible to create any number of strands from a single strand of DNA.The method of this technique includes several steps:
• Denaturation: This is the first step of the PCR technique. In this step, the strand of DNA is heated to 94 - 98 o C for 20-30 seconds. This process breaks the hydrogen bond present between the bases of two strands of DNA and results in the formation of single stranded DNA molecules.
• Annealing: In this step, the primers are introduced in the reaction. Hence the temperature of the reaction is lowered to 50 - 65 o C that aids in the formation of hydrogen bonds between the primer and single stranded DNA. The DNA polymerase that is present binds to this hybrid template and begins the process of DNA formation.
• Elongation: In this step, the DNA polymerase synthesizes a complementary DNA strand to that of the original single stranded DNA. This process continues until the required length or numbers of DNA strands are produced.
By producing complementary strands of the available DNA strand over and over again until the reaction is stopped, the DNA polymerase along with the primer and original DNA template helps in increasing the amount of a specific region of DNA.
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Two populations of snakes are separated by a river. The snakes cross the river only on rare occasions. The snakes in the two populations look very similar to each other, except that the members of the population on the eastern bank of the river have a yellow spot on the top of their head, whereas the members of the western population have an orange spot on the top of their head. Discuss two experimental methods that you might follow to determine whether the two populations are members of the same species or members of different ones.
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Since the populations of the snakes are separated by a physical barrier, thus there might be a possibility of reproductive isolation amongst them. Thus, some of the best ways to determine, if the two species of snakes are members of the same or different species, are:
• Watching the two populations of snakes in nature, by sitting in a hidden spot, and observing if the eastern and western snakes interbreed in their natural environment.
• The next step could be to breed them in captivity and observe if they mate with each other in captivity.
• The best method of all would be to read and assess the chromosome structure and number for any differences present if any by karyotyping.
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Two diploid species of closely related frogs, which we will call species A and species B, were analyzed with regard to genes that encode an enzyme called hexokinase. Species A has two distinct copies of this gene: A1 and A 2. In other words, this diploid species is A1A1 A 2 A 2. The other species has three copies of the hexokinase gene, which we will call B1 , B2, and B3. A diploid individual of species B would be B1B1 B2B2 B3B3. These hexokinase genes from the two species were subjected to DNA sequencing, and the percentage of sequence identity was compared among these genes. The results are shown here.
Percentage of DNA Sequence Identity
If we assume that hexokinase genes were never lost in the evolution of these frog species, how many distinct hexokinase genes do you think there were in the most recent ancestor that preceded the divergence of these two species Explain your answer. Also explain why species B has three distinct copies of this gene, whereas species A has only two.
If we assume that hexokinase genes were never lost in the evolution of these frog species, how many distinct hexokinase genes do you think there were in the most recent ancestor that preceded the divergence of these two species Explain your answer. Also explain why species B has three distinct copies of this gene, whereas species A has only two. Essay
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Distinguish between anagenesis and cladogenesis. Which type of speciation is more prevalent Why
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Explain why molecular techniques were needed as a way to provide evidence for the neutral theory of evolution.
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Describe three or more genetic mechanisms that may lead to the rapid evolution of a new species. Which of these genetic mechanisms are influenced by natural selection, and which are not
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Explain the type of speciation (allopatric, parapatric, or sympatric) most likely to occur under each of the following conditions:
A. A pregnant female rat is transported by an ocean liner to a new continent.
B. A meadow containing several species of grasses is exposed to a pesticide that promotes nondisjunction.
C. In a very large lake containing several species of fish, the water level gradually falls over the course of several years. Eventually, the large lake becomes subdivided into smaller lakes, some of which are connected by narrow streams.
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Would the following examples of reproductive isolation be considered a prezygotic or postzygotic mechanism
A. Horses and donkeys can interbreed to produce mules, but the mules are infertile.
B. Three species of the orchid genus Dendrobium produce flowers 8 days, 9 days, and 11 days after a rainstorm. The flowers remain open for 1 day.
C. Two species of fish release sperm and eggs into seawater at the same time, but the sperm of one species do not fertilize the eggs of the other species.
D. Two tree frogs, Hyla chrysoscelis (diploid) and H. versicolor (tetraploid), can produce viable offspring, but the offspring are sterile.
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Reproductive isolation is the inability of a species to breed
successfully with related species. This is caused due to
geographical, behavioral, physiological, or genetic barriers.
Ernst Mayor has classified the mechanism of reproductive
isolation into two broad categories as isolation before
fertilization (pre-zygotic) and isolation after fertilization
(post-zygotic).
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Sympatric speciation by allotetraploidy has been proposed as a common mechanism for speciation. Let's suppose you were interested in the origin of certain grass species in southern California. Experimentally, how would you go about determining if some of the grass species are the result of allotetraploidy
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A species of antelope contains 20 chromosomes per set. The species is divided by a mountain range into two separate populations, which we will call the eastern and western population. When comparing the karyotypes of these two populations, it was discovered that the members of the eastern population are homozygous for a large inversion within chromosome 14. How would this inversion affect the interbreeding between the two populations Could such an inversion play an important role in speciation
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Compare the forms of speciation that are slow with those that occur more rapidly. Make a list of the slow and fast forms. With regard to mechanisms of genetic change, what features do slow and rapid speciation have in common What features are different
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F 1 hybrids between two species of cotton, Gossypium barbadense and G. hirsutum , are very vigorous plants. However, F 1 crosses produce many seeds that do not germinate and a high percentage of very weak F 2 offspring. Suggest two reasons for these observations.
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The raw material for evolution is random mutation. Discuss whether or not you view evolution as a random process.
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Evolution, which involves genetic changes in a population of organisms over time, is often described as the unifying theme in biology. Discuss how evolution is unifying at the molecular and cellular levels.
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A researcher sequenced a portion of a bacterial gene and obtained the following sequence, beginning with the start codon, which is underlined:
ATG CCG GAT TAC CCG GTC CCA AAC AAA ATG ATC GGC CGC CGA ATC TAT CCC
The bacterial strain that contained this gene has been maintained in the laboratory and grown serially for many generations.
Recently, another person working in the laboratory isolated DNA from the bacterial strain and sequenced the same region. The following results were obtained:
ATG CCG GAT TAT CCG GTC CCA AAT AAA ATG ATC GGC CGC CGA ATC TAC CCC
Explain why these sequencing differences may have occurred.
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