Learning Objectives: Heredity
- Define genes
- Distinguish between mitosis and meiosis, genotype and phenotype, homozygous and heterozygous, and dominant and recessive
- Describe some genetic disorders, due to a gene defect, and chromosomal disorders
- Define polygenic and incomplete dominance
- Describe the function of genetic counseling and why individuals may seek genetic counseling
- Define behavioral genetics, describe genotype-environment correlations and genotype-environmental interactions, and define epigenetics
In this chapter, we will begin by examining some of the ways in which heredity helps to shape the way we are. We will look at what happens genetically during conception, and describe some known genetic and chromosomal disorders.
- 2.1: Heredity
- As your recall from chapter one, nature refers to the contribution of genetics to one’s development. The basic building block of the nature perspective is the gene. Genes are recipes for making proteins, while proteins influence the structure and functions of cells. Genes are located on the chromosomes and there are an estimated 20,500 genes for humans, according to the Human Genome Project.
- 2.2: Genotypes and Phenotypes
- The word genotype refers to the sum total of all the genes a person inherits. The word phenotype refers to the features that are actually expressed. Because genes are inherited in pairs on the chromosomes, we may receive either the same version of a gene from our mother and father, that is, be homozygous for that characteristic the gene influences. If we receive a different version of the gene from each parent, that is referred to as heterozygous.
- 2.3: Genetic Disorders
- Most of the known genetic disorders are dominant gene-linked; however, the vast majority of dominant gene linked disorders are not serious or debilitating. For example, Huntington's Disease is a dominant gene linked disorder that affects the nervous system and is fatal, but does not appear until midlife. Recessive gene disorders, such as cystic fibrosis and sickle-cell anemia, are less common but may actually claim more lives.
- 2.4: Chromosomal Abnormalities
- A chromosomal abnormality occurs when a child inherits too many or two few chromosomes. The most common cause of chromosomal abnormalities is the age of the mother. As the mother ages, the ovum is more likely to suffer abnormalities due to longer term exposure to environmental factors. Consequently, some gametes do not divide evenly when they are forming. Therefore, some cells have more than 46 chromosomes.
- 2.5: Behavioral Genetics
- Behavioral Genetics is the scientific study of the interplay between the genetic and environmental contributions to behavior. Often referred to as the nature/nurture debate, Gottlieb (1998, 2000, 2002) suggests an analytic framework for this debate that recognizes the interplay between the environment, behavior, and genetic expression. This bidirectional interplay suggests that the environment can affect the expression of genes just as genetic predispositions can impact a person’s potentials.