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blsea [12.9K]
3 years ago
9

If 20% of a DNA sample is made up of thymine, T, what percentage of the sample is made vo

Biology
2 answers:
Ksenya-84 [330]3 years ago
6 0

Answer:

B. 30%

Explanation:

DNA has four type of nitrogenous bases in its nucleotides named as adenine, thiamine, cytosine and guanine and the abbreviations for these bases are A, T, C and G respectively. DNA is a double stranded bio molecule and the nucleotides of both the strands of DNA are joined with each other with the help of either double bonds or triple bonds which exist between the nitrogenous bases of its nucleotides. There are two type of bases, purines and pyrimidines. Adenine and guanine are purine bases while cytosine and thiamine are pyrimidine bases.

Chargaff's base pair rule says that the ratio of purine bases with respect to pyrimidine bases must be 1:1 ratio. It can be possible only if a purine base pairs with pyrimidine base of the adjacent DNA helix. So, adenine which is a purine always pairs up with thiamine which is a pyrimidine with the help of two hydrogen bonds while guanine being a purine always pairs up with cytosine which is a pyrimidine with the help of three hydrogen bonds. It simply means that a DNA molecule will have as many adenine as many there are thiamine. Also, for the same reason there will be as many cytosine as many there are guanine.

So, 20% of T means same amount of A which is 20%. Hence, A and T will together form 20% + 20% = 40% of the sample.

In the remaining 60% sample the amount of C and G is equal that means it will have 30% C and 30% G.

So, the answer is 30% C or cytosine.

Brut [27]3 years ago
3 0
B. 30% because it was in the internet and i just gave it to you
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During replication, which sequence of nucleotides would pair with the DNA segment TTACGC? GGACTC AATGCG UUAGCG AACGTG
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Answer:

The Answer would be AATGCG.

Explanation: The reason is because A pairs with T and C pairs with G.

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Consider a species of sparrow that originally lived only in Alaska but recently expanded its range through North America, then C
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Answer:

North America is the one with the highest heterozygosity frequency for most loci, followed by Central America, and finally, South America with the lowest heterozygosity level.  

Explanation:

Some different forces or mechanisms might alter H-W equilibrium and lead to evolution, such as mutation, natural selection, migration, and genetic drift.

In the exposed example, we have a species of sparrow that migrates from Alaska to North America. Migration is unidirectional, which means that the movement occurs in only one direction: from Alaska to North America. We should also consider that the first immigrants colonized the area for the first time, meaning that there was not a receiving population of the same species already established. Finally, we need to consider that Alaska´s environmental conditions are very different from North America´s environmental conditions.

When a species arrives at a new place, it needs to adapt. The establishment and dispersion of the species in the new area depend on previous adaptation. So, when the firsts sparrow individuals arrived in North America, they faced new environmental conditions that acted as selective pressures that drove to the occurrence of mutations. A mutation implicates a stable and inheritable change in the genetic material. A mutation introduces changes, new alleles in the population, variability. But mutation rates are very low and have no evolutive direction, so they need another force to increase or decrease the mutant allelic frequencies. Natural selection benefits new advantageous alleles and transmits them to new generations changing their relative frequencies. <em>So, sparrows arrive in North America, mutated, and natural selection favored the beneficial mutations leading to a better adaptation to the environment.</em> This means that the heterozygosity level in this new recent population is very high.

As animals adapt to the new habitat and have better dispersal genes, they get to disperse even more. So they start new migration south, to Central America and South America. Again, they are moving to new regions with new conditions, and to establish they need to suffer new adaptations. But remember that we are talking about a recent event in time. Probably the animals migrating south are just a few.  They have not spent enough time yet in the new area, to adapt to the new environment and to include new genes into their population. What is even more, as they are a small new population moving south, they are more vulnerable to genetic drift events. Genetic drift acts on a population decreasing the variability between individuals, hence, decreasing the heterozygosity. <em>This small population suffers low mutation, has not enough time to establish, and is more vulnerable to genetic drift events.</em> The heterozygosity level is probably inferior to North America´s one.

Comparing the three areas, we could say that North America is the one with the highest heterozygosity frequency, followed by Central America, and finally, South America with the lowest level of heterozygosity.

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