SOLUTIONS TO EXERCISES, LESSON 14
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)
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
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 loca-
The usual process of cell division is called mitosis. This is the means of pro-
ducing 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)
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.
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.