Which of the following statements about the cladogram of animals is true? a) backbones evolved before segmentation. b) radial symmetry appears only once in the cladogram. c) segmentation evolved more than once in different branches of the cladogram. d) all deuterostomes have bilateral symmetry and cephalization.

The correct option is c. Segmentation evolved more than once in different branches of the cladogram.

Phylogenetic studies help to identify and understand evolutionary relationship between different life forms. It uses a diagram called as Cladogram to represent the branching of the evolutionary relationships. In cladogram studies each branching point tells a fundamental character of the evolutionary significance. Cladogenesis separates the gene pool by splitting into two or more than two separate pools each of which gives rise to one or more new species. Segmentation implies repeated parts and many animals consist of such repeated parts. Therefore, segmentation appears more than once in different cladogram branches.

lipid

explanation:

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.