HELP What Did Scientists Study?
Scientists in one study believed the modern plague and the plague of the 1300s are both
caused by the same bacterium: Yersinia pestis (Y. pestis). They suspected, though, that there
are variants of Y. pestis. There is probably one that caused the very serious plague years
ago and one that causes the less serious plague today.
In the study, the researchers looked at the DNA of Y. pestis from the 1300s and the DNA of Y.
pestis from today. They hoped to discover any differences. Some people carrying Y. pestis
died nearly 800 years ago. Still, researchers could get some DNA from their bones and teeth.
They were able to test the bones and teeth of 100 people who died from the disease in the
1300s.
The researchers did not find any different kinds of Y. pestis. They were disappointed. They
had hoped to find out why the Black Death was so serious.
Researchers plan to continue to look at the DNA of Y. pestis. Understanding ancient
pathogens is important, they say. Doctors might be able to predict the next deadly plague. If
so, they may be more ready to deal with it.

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.

maritime tropical may be your answer.

an individual’s sex (i.e., whether they are a male or female) is determined by the sex chromosomes. most people have two sex chromosomes, one that is inherited from their mother and one that is inherited from their father. typically, females have two x chromosomes (xx) and males have one x chromosome and one y chromosome (xy). conditions caused by changes (“mutations”) in genes located on the x chromosome are considered x-linked.

x-linked recessive inheritance

most x-linked conditions are recessive. this means that in a person with two x chromosomes (most females), both copies of a gene (i.e., one on each x chromosome) must have a change or mutation whereas in a person with one x chromosome (most males), only one copy of a gene must have a mutation. a female with a mutation in one copy of a gene on the x chromosome is said to be a “carrier” for an x-linked condition. a male with a mutation in a gene on the x chromosome is typically affected with the condition. because females have two copies of the x chromosome and males have only one x chromosome, x-linked recessive diseases are more common among males than females. however, x-linked recessive diseases can occur in both males and females.

for x-linked recessive disorders, an unaffected carrier mother who has a mutation in a gene on the x chromosome can transmit either the x chromosome with this mutation or a “normal” x chromosome to her children. if the father is unaffected, none of her daughters will be affected and all of her daughters will be unaffected—since they will inherit at least one normal x chromosome from their father. however, each daughter will have a 50% chance of being an unaffected carrier like her mother and a 50% chance of both x chromosomes being normal.