13
Genetics
Janice Smolowitz and Marybeth Duffy
http://evolve.elsevier.com/Lewis/medsurg/
CONCEPTUAL FOCUS
Cellular Regulation Ethics
LEARNING OUTCOMES
1. Describe common terms related to genetics and genetic 5. Explore the complex ethical and social implications of
disorders. genetic testing.
2. Distinguish between the 2 common causes of genetic 6. Analyze the role of pharmacogenomics and
mutations. pharmacogenetics in personalized drug therapy.
3. Compare and contrast the 3 most common inheritance 7. Discuss your role in assisting the patient and family in
patterns of genetic disorders. dealing with genetic and genomic issues.
4. Describe common classifications of genetic disorders.
KEY TERMS
epigenetics heterozygous, Table 13.1
genes homozygous, Table 13.1
genetics mutation
genome pharmacogenetics
genomics pharmacogenomics
hereditary, Table 13.1
GENETICS AND GENOMICS environmental factors rather than by a single gene. Genomics
Genes are the basic units of heredity. They are composed of may help us understand why some people who eat healthy diets
sequences of deoxyribonucleic acid (DNA) that are arranged and exercise die at a young age of heart disease, while others eat
along a person’s chromosomes. Genes are passed from 1 gen- unhealthy diets and never exercise and live to old age.2 Table
eration to the next. The genome is the complete set of DNA. It 13.1 presents common terms used in genetics and genomics.
includes all the organism’s genes. An organism’s genome has all Advances in genetic and genomic research and technology
the information it needs to build and maintain itself.1 have affected health care delivery.3 In response to these scientific
Genetics is the study of genes and their role in inheritance. advances, nursing organizations have established practice stan-
Genetics determines the way that certain traits or conditions are dards that provide a framework for caring for persons with genetic
passed down through genes. A person’s genes can have a pro- and genomic concerns. Other standards outline competencies and
found impact on health and disease. We think more than 4000 education in relation to professional practice and genetics.3
diseases are related to altered genes. Identifying a genetic basis for many diseases has the poten-
Genomics is the study of all a person’s genes (the genome), tial to influence the care of patients at risk for or diagnosed with
including interactions of these genes with each other and with a disease that has a genetic link. You need to know the basic
the person’s environment. Genomics includes the study of com- genetic principles, be familiar with the impact that genetics has
plex diseases, such as heart disease, diabetes, and cancer. These on health and disease, and be prepared to aid the patient and
diseases are typically caused by a combination of genetic and family with genetic issues.
199
, 200 SECTION 3 Problems Related to Homeostasis and Protection
TABLE 13.1 Glossary of Genetic and Genomic Terms
Term Definition
Allele One of a series of alternative forms (genotypes) at a specific region (locus) of a chromosome
Autosome A chromosome other than X or Y. The human genome has 44 autosomes (22 pairs of autosomes)
Carrier A person who is heterozygous for a gene variant that causes autosomal recessive or X-linked recessive disease. Used to describe
heterozygotes for risk alleles of complex traits with variable penetrance, regardless of inheritance type
Carrier rate Frequency of carriers in a population
Carrier testing Clinical method used to identify at-risk family members of populations who are usually asymptomatic but may have a pathogenic
variant for an autosomal recessive or X-linked disorder
Chromosome Microscopic structures in the cell nucleus composed of chromatin, which contain genetic information. Each cell normally has 46
chromosomes in 23 pairs (22 autosome pairs and 2 sex chromosomes)
Codominance Expression of each pair of alleles when present in the heterozygous state (e.g., AB blood type)
Congenital Present at birth
Consanguineous Reproduction between 2 persons from the same bloodline, such as 1st or 2nd cousins. Consanguineous parentage increases the
probability of a rare recessive disease
Dominant allele Gene that is expressed in the phenotype of a heterozygous person
Familial disorder A trait that appears with higher frequency among close relatives than in the general population
Gene Functional unit of heredity. A gene is a unit of DNA sequence that encodes for a specific functional product, such as RNA
Genetic risk Probability that a trait will occur or recur in a family, based on knowledge of its genetic pattern of transmission
Genetics Study of genes and their role in inheritance
Genome All the DNA contained in a person. A person’s genetic constitution
Genome-wide association study A type of genetic mapping study design that involves scanning complete sets of DNA (genomes) of many people to find genetic
(GWAS) variations associated with a particular disease
Genomics Study of how genes interact and influence people’s biologic and physical characteristics
Genotype Genetic identity of a person, comprised of the entire complex of genes inherited from both parents
Haploid Cells or organisms that have 1 copy of each autosomal chromosome and 1 copy of each sex chromosome. Ova and sperm are
haploid. Fertilization results in an embryo with 1 set of chromosomes from each parent (diploid embryo)
Hereditary Transmission of a disease, condition, or trait from parent to children
Heterozygous Having 2 different alleles for 1 given gene, 1 inherited from each parent
Homozygous Having 2 identical alleles for 1 given gene, 1 inherited from each parent
Locus Position of a gene on a chromosome
Mutation A change in a gene that affects function. Types include nonsense, missense silent, and frameshift. A pathogenic variant is a
mutation associated with a disease. Sometimes parents pass mutations to children.
Oncogene Gene that contributes to the conversion of normal cells to cancer cells. Usually dominant
Pedigree A graphic representation that shows family relationships, gender, age, and presence of diseases for each family member
Pharmacogenetics Study of variability of drug metabolism related to variations in single genes
Pharmacogenomics Study of variability of drug metabolism in relation to variations in and interactions of multiple genes or the person’s genome
Phenotype Observable characteristics of a person. Measured categorically or quantitatively
Protooncogene Genes that can be turned into oncogenes by a dominant activating mutation. Oncogenes produce structurally altered proteins that
result in cancer
Recessive allele Allele that has no noticeable effect on the phenotype in a heterozygous person
Trait Physical characteristics a person inherits, such as hair or eye color
X-linked gene Gene found on the X chromosome rather than an autosome. In general, sex-linked disorders occur in males
Basic Principles of Genetics Genes
Chromosomes We think there are around 30,000 genes in each person’s genome.
Chromosomes are found in the cell nucleus. They occur in pairs. Genes carry the instructions (encode) for making proteins that
Humans have 23 pairs of chromosomes. Twenty-two of the 23 direct the activities of cells. Genes control how a cell functions,
pairs of chromosomes are homologous autosomes. This means including how quickly it grows, how often it divides, and how
the pair of chromosomes has corresponding DNA sequences. long it lives. To control these functions, genes make proteins
Autosomes are the same in both males and females. The sex that perform specific tasks and act as messengers for the cell.
chromosomes make up the 23rd pair. A female has 2 X chromo- Each gene must have the correct instructions, or “code,” for
somes, and a male has 1 X and 1 Y chromosome. One chromo- making its protein so that the protein can perform the proper
some of each pair is inherited from the mother and one from function for the cell.
the father. Half of each child’s chromosomes (and therefore the Genes are arranged in a specific linear formation along a
genetic makeup) come from their father and half from their chromosome (Fig. 13.1). Each gene has a specific location on
mother. a chromosome, called the locus. An allele is 1 of 2 or more
Genetics
Janice Smolowitz and Marybeth Duffy
http://evolve.elsevier.com/Lewis/medsurg/
CONCEPTUAL FOCUS
Cellular Regulation Ethics
LEARNING OUTCOMES
1. Describe common terms related to genetics and genetic 5. Explore the complex ethical and social implications of
disorders. genetic testing.
2. Distinguish between the 2 common causes of genetic 6. Analyze the role of pharmacogenomics and
mutations. pharmacogenetics in personalized drug therapy.
3. Compare and contrast the 3 most common inheritance 7. Discuss your role in assisting the patient and family in
patterns of genetic disorders. dealing with genetic and genomic issues.
4. Describe common classifications of genetic disorders.
KEY TERMS
epigenetics heterozygous, Table 13.1
genes homozygous, Table 13.1
genetics mutation
genome pharmacogenetics
genomics pharmacogenomics
hereditary, Table 13.1
GENETICS AND GENOMICS environmental factors rather than by a single gene. Genomics
Genes are the basic units of heredity. They are composed of may help us understand why some people who eat healthy diets
sequences of deoxyribonucleic acid (DNA) that are arranged and exercise die at a young age of heart disease, while others eat
along a person’s chromosomes. Genes are passed from 1 gen- unhealthy diets and never exercise and live to old age.2 Table
eration to the next. The genome is the complete set of DNA. It 13.1 presents common terms used in genetics and genomics.
includes all the organism’s genes. An organism’s genome has all Advances in genetic and genomic research and technology
the information it needs to build and maintain itself.1 have affected health care delivery.3 In response to these scientific
Genetics is the study of genes and their role in inheritance. advances, nursing organizations have established practice stan-
Genetics determines the way that certain traits or conditions are dards that provide a framework for caring for persons with genetic
passed down through genes. A person’s genes can have a pro- and genomic concerns. Other standards outline competencies and
found impact on health and disease. We think more than 4000 education in relation to professional practice and genetics.3
diseases are related to altered genes. Identifying a genetic basis for many diseases has the poten-
Genomics is the study of all a person’s genes (the genome), tial to influence the care of patients at risk for or diagnosed with
including interactions of these genes with each other and with a disease that has a genetic link. You need to know the basic
the person’s environment. Genomics includes the study of com- genetic principles, be familiar with the impact that genetics has
plex diseases, such as heart disease, diabetes, and cancer. These on health and disease, and be prepared to aid the patient and
diseases are typically caused by a combination of genetic and family with genetic issues.
199
, 200 SECTION 3 Problems Related to Homeostasis and Protection
TABLE 13.1 Glossary of Genetic and Genomic Terms
Term Definition
Allele One of a series of alternative forms (genotypes) at a specific region (locus) of a chromosome
Autosome A chromosome other than X or Y. The human genome has 44 autosomes (22 pairs of autosomes)
Carrier A person who is heterozygous for a gene variant that causes autosomal recessive or X-linked recessive disease. Used to describe
heterozygotes for risk alleles of complex traits with variable penetrance, regardless of inheritance type
Carrier rate Frequency of carriers in a population
Carrier testing Clinical method used to identify at-risk family members of populations who are usually asymptomatic but may have a pathogenic
variant for an autosomal recessive or X-linked disorder
Chromosome Microscopic structures in the cell nucleus composed of chromatin, which contain genetic information. Each cell normally has 46
chromosomes in 23 pairs (22 autosome pairs and 2 sex chromosomes)
Codominance Expression of each pair of alleles when present in the heterozygous state (e.g., AB blood type)
Congenital Present at birth
Consanguineous Reproduction between 2 persons from the same bloodline, such as 1st or 2nd cousins. Consanguineous parentage increases the
probability of a rare recessive disease
Dominant allele Gene that is expressed in the phenotype of a heterozygous person
Familial disorder A trait that appears with higher frequency among close relatives than in the general population
Gene Functional unit of heredity. A gene is a unit of DNA sequence that encodes for a specific functional product, such as RNA
Genetic risk Probability that a trait will occur or recur in a family, based on knowledge of its genetic pattern of transmission
Genetics Study of genes and their role in inheritance
Genome All the DNA contained in a person. A person’s genetic constitution
Genome-wide association study A type of genetic mapping study design that involves scanning complete sets of DNA (genomes) of many people to find genetic
(GWAS) variations associated with a particular disease
Genomics Study of how genes interact and influence people’s biologic and physical characteristics
Genotype Genetic identity of a person, comprised of the entire complex of genes inherited from both parents
Haploid Cells or organisms that have 1 copy of each autosomal chromosome and 1 copy of each sex chromosome. Ova and sperm are
haploid. Fertilization results in an embryo with 1 set of chromosomes from each parent (diploid embryo)
Hereditary Transmission of a disease, condition, or trait from parent to children
Heterozygous Having 2 different alleles for 1 given gene, 1 inherited from each parent
Homozygous Having 2 identical alleles for 1 given gene, 1 inherited from each parent
Locus Position of a gene on a chromosome
Mutation A change in a gene that affects function. Types include nonsense, missense silent, and frameshift. A pathogenic variant is a
mutation associated with a disease. Sometimes parents pass mutations to children.
Oncogene Gene that contributes to the conversion of normal cells to cancer cells. Usually dominant
Pedigree A graphic representation that shows family relationships, gender, age, and presence of diseases for each family member
Pharmacogenetics Study of variability of drug metabolism related to variations in single genes
Pharmacogenomics Study of variability of drug metabolism in relation to variations in and interactions of multiple genes or the person’s genome
Phenotype Observable characteristics of a person. Measured categorically or quantitatively
Protooncogene Genes that can be turned into oncogenes by a dominant activating mutation. Oncogenes produce structurally altered proteins that
result in cancer
Recessive allele Allele that has no noticeable effect on the phenotype in a heterozygous person
Trait Physical characteristics a person inherits, such as hair or eye color
X-linked gene Gene found on the X chromosome rather than an autosome. In general, sex-linked disorders occur in males
Basic Principles of Genetics Genes
Chromosomes We think there are around 30,000 genes in each person’s genome.
Chromosomes are found in the cell nucleus. They occur in pairs. Genes carry the instructions (encode) for making proteins that
Humans have 23 pairs of chromosomes. Twenty-two of the 23 direct the activities of cells. Genes control how a cell functions,
pairs of chromosomes are homologous autosomes. This means including how quickly it grows, how often it divides, and how
the pair of chromosomes has corresponding DNA sequences. long it lives. To control these functions, genes make proteins
Autosomes are the same in both males and females. The sex that perform specific tasks and act as messengers for the cell.
chromosomes make up the 23rd pair. A female has 2 X chromo- Each gene must have the correct instructions, or “code,” for
somes, and a male has 1 X and 1 Y chromosome. One chromo- making its protein so that the protein can perform the proper
some of each pair is inherited from the mother and one from function for the cell.
the father. Half of each child’s chromosomes (and therefore the Genes are arranged in a specific linear formation along a
genetic makeup) come from their father and half from their chromosome (Fig. 13.1). Each gene has a specific location on
mother. a chromosome, called the locus. An allele is 1 of 2 or more
