Hole'sA&P12eChapter24Outline - McGraw-Hill

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Hole'sA&P12eChapter24Outline - McGraw-HillHill

Hole’s Human Anatomy and Physiology

    Shier, Butler & Lewis

    Twelfth Edition

Chapter 24 Outline

24.1 Introduction

     A. Packaged into our cells are instruction manuals

     B. The manual is the human genome

     C. It is written in the language of the DNA molecules

     D. DNA consists of a sequence of nucleotide building blocks A, g, C, and T

     E. Sequences of DNA that encode particular proteins are called genes

     F. A gene has different forms and can vary from individual to individual

     G. Genetics is the study of the inheritance of characteristics

     H. A genome is a complete set of genetic instructions

     I. Genomics is the field in which the body is studied in terms of multiple,

    interacting genes

     Review Figures 24.1 and 24.2

    24.2: Modes of Inheritance

     A. Genetics has the power of prediction

    B. Knowing how genes are distributed in meiosis and the combinations in which

    they join at fertilization makes it possible to calculate the probability that a certain

    trait will appear in the offspring of two particular individuals

    C. These patterns in which genes are transmitted in families are termed modes of


     Chromosomes and Genes Come in Pairs

     A. This normal karyotype shows 23 pairs of chromosomes:

     1. Pairs 1-22 are autosomes (they do not determine sex)

     2. Pair 23 are the sex chromosomes

     Review Figure 24.3

     Chromosomes and Genes Come in Pairs

    A. A gene consists of hundreds of nucleotide building blocks and exists in variant

    forms called alleles that differ in DNA sequence

    B. An individual who has two identical alleles of a particular gene is homozygous

    for that gene

     C. A person with two different alleles for a gene is heterozygous

    D. The particular combination of gene variants (alleles) in a person’s genome

    constitutes the genotype

    E. The appearance or health condition of the individual that develops as a result of

    the ways the genes are expressed is termed the phenotype

     F. Wild type alleles produce mutations

     Dominant and Recessive Inheritance

     A. For many genes, in heterozygotes, one allele determines the phenotype

     B. Dominant allele masks the phenotype of the recessive allele

     C. Recessive allele is expressed only if in a double dose (homozygous)

     D. Autosomal conditions are carried on a nonsex chromosome

     E. Sex-linked conditions are carried on a sex chromosome

     F. X-linked conditions are carried on the X chromosome

     G. Y-linked conditions are carried on the Y chromosome

     Review Figures 24.4 and 24.5

     Different Dominance Relationships

     A. Most genes exhibit complete dominance or recessiveness

     B. Exceptions are incomplete dominance and codominance

    C. Heterozygote has a phenotype intermediate between homozygous dominant

    and homozygous recessive

     D. Familial hypercholesterolemia is an example here

     Review Figure 24.6

     Different Dominance Relationships: Codominance

     A. Different alleles expressed in a heterozygote are codominant

     B. ABO blood type is an example: AB 1. Three alleles of ABO blood typing are I, I, I AAA 2. A person with type A may have the genotype I i or I I BB B 3. A person with type B may have the genotype I i or II AB 4. A person with type AB must have the genotype I I

     5. A person with type O blood must have the genotype ii 24.1 Clinical Application

    24.3: Factors That Affect Expression of Single Genes

    A. Most genotypes vary somewhat from person to person, due to the effects of the

    environment and other genes

     B. Penetrance, expressivity, and pleiotropy describe distinctions of genotype

     Penetrance and Expressivity

     A. Complete penetrance

     1. Everyone who inherits the disease causing alleles has some symptoms

     B. Incomplete penetrance

     1. Some individuals do not express the phenotype even though they inherit

    the alleles

     2. An example is polydactyly

     C. Variable expression

     1. Symptoms vary in intensity in different people

     2. For example, two extra digits versus three extra digits in polydactyly


     A. Pleiotropy

     1. A single genetic disorder producing several symptoms

     2. Marfan syndrome (an autosomal dominant defect) is an example

     3. People affected produce several symptoms that vary

     Genetic Heterogeneity

     A. Genetic heterogeneity

     1. The same phenotype resulting from the actions of different genes

     2. Hereditary deafness is an example

    24.4: Multifactorial Traits

    A. Most if not all characteristics and disorders considered “inherited” actually

    reflect input from the environment as well as genes

     B. Polygenic traits

    1. Determined by more than one gene

     2. Examples include height, skin color, and eye color

     C. Multifactorial traits

     1. Traits molded by one or more genes plus environmental factors

     2. Examples include height and skin color

     3. Common diseases such as heart disease, diabetes mellitus, hypertension,

    and cancers are multifactorial

     Review Figures 24.7, 24.8, and 24.9

    24.5: Matters of Sex

    A. Human somatic (nonsex) cells include an X and a Y chromosome in males and

    two X chromosomes in females

     1. All eggs carry a single X chromosome

     2. Sperm carry either an X or Y chromosome

    B. Sex is determined at conception: a Y-bearing sperm fertilizing an egg

    conceives a male, and an X-bearing sperm conceives a female

     Review Figure 24.10

     Sex Determination

     A. Maleness derives from a Y chromosome gene called SRY

     B. The SRY gene encodes a type of protein called a transcription factor

    C. The SRY activates transcription of genes that direct development of male

    structures in the embryo, while suppressing formation of female structures

    Review Figure 24.11

     Genes of the Sex Chromosomes

     A. X chromosome

     1. Has over 1,500 genes

     2. Most genes on the X chromosome do not have corresponding alleles on the

    Y chromosome

     B. Y chromosome

     1. Has only 231 protein-encoding genes

     2. Some genes are unique only to the Y chromosome


    A. Passed from mother (heterozygote) to son

    B. Each son has a 50% chance of receiving the recessive allele from the mother

    C. Each son with one recessive allele will have the disease

    D. Each son has no allele on the Y chromosome to mask the recessive allele

    E. Each daughter has a 50% chance of receiving the recessive allele from the


    F. Each daughter with one recessive allele will be a carrier

    G. Each daughter with one recessive allele does not develop the disease because

    she has another X chromosome with a dominant allele

     Gender Effects on Phenotype

     A. Sex-limited trait

     1. Affects a structure or function of the body that is present in only males or

    only females

     2. Examples are beards or growth of breasts

     B. Sex-influenced inheritance

     1. An allele is dominant in one sex and recessive in the other

     2. Baldness is an example

     3. Heterozygous males are bald but heterozygous females are not 24.6: Chromosome Disorders

    A. Deviations from the normal chromosome number of 46 produce syndromes

    because of the excess or deficit of genes

    B. Chromosome number abnormalities may involve single chromosomes or entire

    sets of chromosomes

     C. Euploid is a normal chromosome number


     A. Polyploidy

     1. The most drastic upset in chromosome number

     2. This is an entire extra set of chromosomes

     3. Results from formation of a diploid, rather than a normal haploid, gamete

     4. Most embryos or fetuses die, but occasionally an infant survives a few days

    with many abnormalities


     A. Aneuploidy

     1. Cells missing a chromosome or having an extra chromosome

     2. Results from meiotic error called nondisjunction

     3. Here a chromosome pair fails to separate, either at the first or at the second

    meiotic division, producing a sperm or egg that has two copies of a particular

    chromosome or none, rather than the normal one copy

     4. When a gamete fuses with its mate at fertilization, the resulting zygote has

    either 47 or 45 chromosomes, instead of 46

     5. Trisomy is the condition of having an extra chromosome

     6. Monosomy is the condition of missing a chromosome

     Review Table 24.1

    24.2 Clinical Application

     Prenatal Tests Detect Chromosome Abnormalities

     Review Figure 24.13

     Review Figure 24.14

     Review Table 24.2

    24.7: Gene Expression Explains Aspects of Anatomy and Physiology

    A. Gene expression patterns can add to what we know about structure and

    function of the human body

    B. Identifying which genes are active and inactive in particular cell types, under

    particular conditions, can add to our understanding of physiology

     C. Gene expression monitors the proteins that a cell produces

    D. The technology used is termed gene expression profiling, and identifying the

    sets of proteins in a cell is proteomics

     E. DNA microarrays or DNA chips profile gene expression

    F. This is valuable in anatomy and physiology when it allows medical researchers

    see distinctions their eyes cannot detect

     Review Figure 24.15

    Outcomes to be Assessed

    24.1: Introduction

    ; Distinguish among genome, gene, and chromosome.

    ; Define genetics.

    ; Explain how genetic information passes from generation to generation. ; Explain how the human genome is an economical storehouse of information.

    24.2: Modes of Inheritance

    ; State the two bases of genetic predictions.

    ; Define the two types of chromosomes.

    ; Explain the basis of multiple alleles of a gene.

    ; Distinguish between heterozygous and homozygous; genotype and phenotype;

    dominant and recessive.

    ; Distinguish between autosomal recessive and autosomal dominant inheritance.

    24.3: Factors That Affect Expression of Single Genes

    ; Explain how and why the same genotype can have different phenotypes among


    24.4: Multifactorial Traits

    ; Describe how traits determined by genes and the environment are inherited.

    24.5: Matters of Sex

    ; Describe how and when sex is determined.

    ; Explain how X-linked inheritance differs from inheritance of autosomal traits. ; Discuss factors that affect how phenotypes may differ between the sexes.

    24.6: Chromosome Disorders

    ; Describe three ways that chromosomes can be abnormal.

    ; Explain how prenatal tests provide information about chromosomes.

    24.7: Gene Expression Explains Aspects of Anatomy and Physiology

    ; What type of information does gene expression profiling provide? ; Explain how a DNA microarray works.

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