Answer:
Semi-conservative replication
Explanation:
After the double-helix discovery of Watson and Crick, there were three possible models about the DNI replication:
- The Conservative model stated that the two strands of DNI together were the template of another new molecule. The final product was the original double-stranded molecule and the new molecule.
- The semi-conservative model stated that the original DNI molecule separated into two strands, and each of them served as a template for the synthesis of a new complementary strand. The replication product would be two double-stranded DNA molecules, each carrying an original strand a new one.
- The Dispersive moles stated that the replication product would be two molecules made by a mixture of segments of the original and the new molecules.
Meselson and Stahl joined to discover which of the models was the correct one. To do it they used E. coli and Nitrogen isotopes.
- First, they extracted DNI from bacteria grown in a medium with N¹⁴ and got its density band by centrifugation.
- Then they grew bacteria in a medium with N¹⁵, extracted their DNI molecules, centrifugated them, and got the density band, which was heavier than the firsts ones.
- The researchers then transferred bacteria grown in medium with N¹⁵ to a medium with N¹⁴, and they allowed only one replication process to occur. DNI was extracted and centrifugated again, and a new band appeared. This band was an intermediate form between bands of DNI-N¹⁵ and DNI-N¹⁴.
This event <em>eliminated the conservative model</em>. If this model were correct, the expected result would be to get two bands: one corresponding to the density DNI-N¹⁵ and the other corresponding to the density DNI-N¹⁴.
- Bacteria grown in a medium with N¹⁵ and then transferred to a medium with N¹⁴ were finally allowed to replicate twice. Their DNI was extracted and centrifugated. The result was two bands: one of them coincided with the intermediate band, and the other one with the DNI-N¹⁴.
<u>This result was conclusive</u> because if the dispersal model were correct, these two bands should not appear, as all the DNI strands would have part of the original molecule.
With this experiment, Meselson and Stahl proved that the correct replication model was the semi-conservative one.
An ion is a tiny particle or molecule with a positive or negative charge, meaning that it has either lost or gained electron(s)
something that causes an organism to decay. It could have been eaten, or an air pocket formed as it was fossilizing or basically anything that obstructs the formation of a fossil.... you have to figure the rest out; )
Ok, so I wrote these out just to make it a little bit easier for you to understand what I am about to explain.
So for the first one you have two different traits that can be inherited- having freckles or having no freckles, F and f respectively. The dominant trait (or having freckles) is shown by the capital F, and is almost always expressed over the recessive trait, or the lowercase f. So, for example, if you have a genotype of Ff, the trait having freckles will show up instead of not having freckles. The only way that you could have the trait of no freckles show up is if there are two recessive alleles for having no freckles, or ff. In this case, you have two parents who are both heterozygous for the trait of having freckles, so in other words the mother has Ff and the father has Ff. Each parent passes down one allele to the offspring, so since you are breeding Ff and Ff, you should result in having the possible genotypes of FF, Ff, Ff, and ff. This means that there is a 25% chance that the offspring will be homozygous for having freckles, a 50% chance that the offspring will be heterozygous for having freckles and a 25% chance that they would be homozygous for having no freckles, or a 1:2:1 ratio.
Incomplete dominance is a little bit different that just a normal monohybrid cross. Instead of just the dominant gene showing up in a heterozygous genotype, both traits show up. So like the question says, if a homozygous red flower plant was crossed with a homozygous white flower plant, their offspring would not just be white or red, they would be pink because it is a mixture of white and red. So then if you crossed the heterozygous, or Rr plants, the result would be a 25% chance of getting a homozygous RR red plant, a 50% chance of getting a pink Rr plant, and a 25% chance of getting a white rr plant, or another 1:2:1 ratio.
Sorry for the wordy answer, but hopefully this helps you understand this a little better :)