Bacteria. this word has been in the news and textbooks a lot lately. we know that some species of bacteria have evolved a resistance to antibiotics and are difficult if not impossible to kill. instead they are responsible for some potentially deadly illnesses and infections. we also know that recent biochemical discoveries have lead scientists down a path to completely change how life on earth is classified, starting with the bacteria. we have moved from a 5-kingdome system to a 3-domain, 6-kingdom system of classification. all bacteria are still known to be prokaryotes, but we know now that they differ biochemically. this phylogenic tree shows the changes in bacterial species from the ancestral species to the most current split in the modern classification system. this tree supports the theory that a) speciation results in biodiversity. b) natural selection favors the fittest. c) within a population, variation exists. d) extinction is the fate of the species that cannot adapt.

A

Explanation:I just took the test :)

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.

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