Natural selection is the process by which biological traits either become more or less apparent within a population. There are certain conditions which are the basis for natural
selection. Which of the following examples best represents the adaptation of a species to its
environment?

A. Female Loggerhead turtles lay numerous eggs, about 100, which when hatched produce offspring that must make a mad dash to the ocean before being eaten by predatory sea birds

B. Some members of a species of garter snake are resistant to a toxin produced by one of its food sources; the resistance trait will be passed to their offspring.

C. A species of crab is living and reproducing successfully near hot hydrothermal vents at the bottom of the Pacific Ocean, while other crab species are unable to survive there.

D. Male Birds of Paradise inherit brilliant colors which they display in elaborate poses or dances in order to catch the attention of a female mate.

nucleic acid molecules are incredibly complex, containing the code that guarantees the four different nucleotide units comprise dna, the nucleic acid of interest to the genealogist. and one of four nitrogen-containing molecules called nucleotides

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.