1. Heredity depends upon the passage of materials called genes from one generation to the next. Due to genes, all human beings resemble each other but also have individual differences.
Overall, genes determine the range of potentiality of an individual, and the environment develops it. For example, good nutrition will help a person to attain his full body height and weight within the limitations determined by his genes. (para 14-1)
2. DNA is a large molecule consisting of two strands in a double-helix arrangement. Along each strand are specific chemical elements call nucleotides. Each gene consists of a portion of a strand including a number of nucleotides. Through the arrangement of its nucleotides, the gene provides coded information for the construction of proteins. As these proteins are assembled, they serve as building blocks and as enzymes to promote the life processes of the cell. (para 14-3)
3. A chromosome is a very long double-helix thread of DNA. Thus, each chromosome consists of a large number of genes. The genes have very specific locations along the length of each chromosome. (para 14-4a)
4. The usual process of cell division is called mitosis. This is the means of producing new cells for replacement of worn-out cells and growth and development of the individual. The two daughter cells have 46 chromosomes. (para 14-5a)
5. Meiosis is a type of cell division occurring only in the gonads. It results in the formation of the gametes, or sex cells. Each gamete has 23 chromosomes.
6. The zygote has 46 chromosomes. (para 14-6a)
7. The actual genetic makeup of an individual is the genotype. The physical and functional makeup of an individual is the phenotype, determined both by the genotype and the environment.
If one of the genes of a pair can produce by itself a characteristic of the phenotype, the gene is said to be dominant. If both genes must be the same to produce a characteristic, the genes are recessive. If an individual has one recessive and one dominant gene in a pair, the ultimate characteristic is determined by the dominant gene.
If the two genes for a trait are the same, we say that the individual is homozygous for that trait. If the two genes are different, the individual is heterozygous for that trait.
If two twins in a set are different, they are called fraternal twins. If two twins in a set resemble each other very closely, they are called identical twins and have the same genetic makeup. (para 14-7)
8. In this imaginary situation, 75% of the children will have antennae. (para 14-8a, figure 14-2)
9. In this imaginary situation, 9/16 will have both antennae and four upper members, 3/16 will have antennae and two upper members, and 3/16 will have four upper members but no antennae. (figure 14-3)
10. See paragraph 14-9a for an explanation of this relationship.
11. In complementary inheritance, two independent pairs of genes affect a trait. (para 14-9b)
12. In multifactorial inheritance, a number of gene pairs affect a trait. (para 14-9c)
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.