Additional Physiology Review Study Guide for McGraw-Hill's ASVAB

Genetics

All characteristics are inherited from genes of the mother and the father. Chromosomes come in pairs. The genes on a chromosome have information about the trait, but the information from the father and the mother is not necessarily exactly the same. Different forms of a gene are called alleles. For example, for the genes that determine hair color, the allele from your mother might be for blond hair and the allele from your father might be for black hair. Some alleles are dominant and some are recessive. The dominant allele will determine what traits actually become part of you.

Sometimes errors in mitosis or meiosis take place, altering a gene or chromosome. Some mutations are harmless, such as a four-leaf clover or a white tiger. Others can be harmful, setting the stage for certain diseases, conditions, or even death.

Determining the Probability of Certain Traits   When describing genetic traits or alleles, a dominant allele is indicated with a capital letter (such as B). A recessive allele is indicated with a lowercase letter (such as b). In the genes, these alleles appear in pairs, such as BB, bb, or Bb. The sum of these genetic codes is the genotype, or genetic makeup of the organism. How the organism looks is called the phenotype. So if you have blond hair, that is your phenotype.

An organism that has two alleles that are the same, such as BB or bb, is called homozygous. An organism that has one allele that is dominant and one that is recessive, such as Bb, is called heterozygous.

To determine the probability that an offspring will have a certain characteristic, you can use a device called a Punnett square.

Suppose a father has black hair with one dominant allele for black hair (B) and one recessive allele for blond hair (b). Then suppose a mother has blond hair with two recessive alleles (bb). The following Punnett square shows the probability that these parents will have a child with black or blond hair.

There is a 2 in 4 (or 50 percent) probability that a child will have black hair (Bb) and a 2 in 4 (or 50 percent) probability that a child will have blond hair (bb). Now suppose the father has two dominant alleles for black hair (BB).

All offspring would have black hair (Bb).

Now suppose that the father and mother each have black hair with one dominant allele for black hair (B) and one recessive allele for blond hair (b).

The probability of having a blond child (bb) would be 1 in 4, or 25 percent.

Determining the Sex of an Offspring   The female carries two X chromosomes, and the male carries an X and a Y chromosome. The female egg contains an X chromosome. A male sperm can contain either an X or a Y chromosome. Depending on which sperm fertilizes the egg, the result can be a female (XX) or a male (XY). The male parent determines the sex of the offspring.

Nutrition

You need to eat for energy and to maintain your biologic functions. Food provides you with the necessary nutrients to survive. There are six types of nutrients: proteins, carbohydrates, fats, vitamins, minerals, and water. Proteins, carbohydrates, fats, and vitamins are all organic nutrients. Minerals and water are inorganic. Organic means the substance contains carbon.

Proteins are used by the body for replacement and repair of body cells and for growth. They are made up of amino acids. Eggs, meat, and cheese are considered protein foods.

Carbohydrates are a good source of energy for your body. Three types of carbohydrates are sugar, fiber, and starch. Sugars are simple carbohydrates. Starches and fiber are complex carbohydrates. Foods like potatoes, pasta, beans, and breads are complex carbohydrates.

Fats provide energy and help to absorb vitamins. Fats contain twice as much energy as carbohydrates. Excess energy from the foods you eat is stored as fat.

Vitamins are nutrients that are needed for certain bodily functions and for preventing some diseases. Water-soluble vitamins, such as B and C, need to be taken in every day. Fat-soluble vitamins are also stored in fat cells. Examples are vitamins A, D, E, and K.

Minerals can regulate the chemical reactions in your body. You need some level of about 14 different minerals. Most minerals are needed only in small (trace) amounts. Others, like calcium and phosphorous, are needed in larger amounts. Perhaps the most important contribution of minerals is the production and maintenance of our bones.

The preceding table lists the most important minerals, their benefits, and the foods that provide each one.

About two-thirds of your body is water. Your cells need water to carry out their work. You would die if you didn't have water for a few days. Some of your water comes from foods, but you must also drink water. Your body loses about four pints of water every day. That needs to be replenished. People who exercise need even more water.