Transcript Genetic Inheritance

PowerPoint® Lecture Slide Presentation by Robert J. Sullivan, Marist College
Human Biology
Concepts and Current Issues
Second Edition
MICHAEL D. JOHNSON
CHAPTER 19
GENETICS AND INHERITANCE
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.
Alleles
• Different forms of homologous genes: humans
have 23 pairs of chromosomes
• Homozygous: both alleles identical
• Heterozygous: alleles different
• Genotype: complete set of genes and alleles
• Phenotype: observed physical and functional
traits
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.
Punnett Squares
Figure 19.2
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.
Patterns of Genetic Inheritance
• Punnett square analysis: predicts patterns of
inheritance
• Mendel developed basic rules of inheritance
• Law of segregation: reproductive cells carry only
one copy of each gene
• Law of independent assortment: genes for
different traits are separated from each other
independently during meiosis; applies in most
cases
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.
Allelic Interactions
• Genotype and environment affect phenotype
• Dominant alleles: gene always expressed, even if
heterozygous
• Recessive alleles: two copies of gene needed to
be expressed, must be homozygous
• Incomplete dominance: heterozygote is an
intermediate phenotype
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.
Allelic Interactions
(cont.)
• Codominance: both phenotypes equally
expressed
• Polygenic inheritance: multiple genes involved
• Linked genes: may be inherited together if close
on a chromosome
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Pedigree Chart: Inheritance Pattern
for an X-linked Recessive Disease
Figure 19.12
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Sex-Linked Inheritance: X and Y
Chromosomes
• Origin of sex chromosomes
• Chance mutations
• Y determines sex
• Sex-linked genes located on sex chromosomes
• Sex linked or X-linked inheritance
• Characteristics: mostly males with disease, passed
to sons by mother, father cannot pass the gene
• Sex influenced traits: affected by presence of
testosterone, estrogen
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.
Chromosomes May be Altered in
Number and Structure
• Nondisjunction during meiosis
• Examples:
• Down syndrome: trisomy 21
• Alterations of the number of sex chromosomes
• XYY: double-Y syndrome
• XXY: Klinefelter syndrome
• XXX: trisomy-X syndrome
• XO: Turner syndrome, no Y
• Deletions and Translocations: alter chromosome
structure
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.
Inherited Genetic Disorders
• Mechanism
• Most mutations usually involve recessive alleles
• Phenylketonurid
• Tay-Sachs Disease
• Dominant lethal allele: Huntington Disease
• Always expressed, though at midlife
• Always lethal
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.
Genes and Behavior
• Mechanism
• Product from gene-specific proteins
• Proteins have specific functions leading to
phenotypes
• Protein functions: hormones, enzymes, structural,
neurotransmitters
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.
Modifying DNA
• Recombinant DNA technology: cutting, splicing
and copying DNA, polymerase chain reaction
(PCR)
• Genetic engineering
• Microorganisms: factories for human proteins,
vaccines, environmental applications
• New plants for agriculture
• New uses for domestic animals
• Human gene therapy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.