Heredity and Evolution

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Chapter 4

• Heredity and Evolution

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Chapter Outline

• Genetic Principles Discovered by Mendel
• Mendelian Inheritance in Humans
• Non-Mendelian Patterns of Inheritance
• Mitochondrial Inheritance

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Chapter Outline

• Modern Evolutionary Theory
• Definition of Evolution
• Factors That Produce and Redistribute Variation
• Natural Selection Acts on Variation
• Review of Genetics and Evolutionary Factors

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Genetic PrinciplesDiscovered by Mendel

• Gregor Mendel (1822-1884) laid down the basic
  principles of heredity.
• Crossed different strains of purebred plants and
  studied their progeny.
• Worked with common garden peas and considered
  only one trait at a time.
• His work illustrates the basic rules of
  inheritance.

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Principle of Segregation

• Genes occur in pairs because chromosomes occur in
  pairs.
• During gamete production, members of each gene
  pair separate so each gamete contains one member
  of a pair.
• During fertilization, the full number of
  chromosomes is restored and members of a gene or
  allele pairs are reunited.

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Results of Crosses When One Trait at a Time is
Considered
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Principle of Independent Assortment

• The distribution of one pair of alleles into
  gametes does not influence the distribution of
  another pair.
• The genes controlling different traits are
  inherited independently of one another.

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Punnett Square
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Results of Crosses When 2 Traits Are Considered
Simultaneously
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Dominant Mendelian Traits in Humans
Condition Manifestations
Achondroplasia Dwarfism due to growth defects involving the long bones of the arms and legs trunk and head size usually normal.
Brachydactyly. Familial hyper- cholesterolemia Shortened fingers and toes. Elevated cholesterol levels and cholesterol plaque deposition.
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Dominant Mendelian Traits in Humans
Condition Manifestations
Huntington disease Progressive degeneration of the nervous system accompanied by dementia and seizures age of onset commonly between 30 and 40 years.
Cleft chin Dimple or depression in the middle of the chin.
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Recessive Mendelian Traits in Humans
Condition Manifestations
Albinism Inability to produce normal amounts of the pigment melanin.
Sickle-cell anemia Abnormal form of hemoglobin (HbS) that results in collapsed red blood cells, blockage of capillaries, reduced blood flow to organs, and, without treatment, death.
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Recessive Mendelian Traits in Humans
Condition Manifestations
Cystic fibrosis Abnormal secretions of the exocrine glands, with pronounced involvement of the pancreas most patients develop obstructive lung disease.
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Mendelian Inheritance in Humans

• Over 4,500 human trains are known to be inherited
  according to Mendelian principles.
• The human ABO blood system is an example of a
  simple Mendelian inheritance.
• The A and B alleles are dominant to the O allele.
• Neither the A or B allele are dominant to one
  another They are codominant and both traits are
  expressed.

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ABO Genotypes and Associated Phenotypes
Genotype Antigens on red blood cells ABO blood type(phenotype)
AA, AO A A
BB, BO B B
AB A and B AB
OO None O
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Pattern of Inheritance of Autosomal Dominant
Traits
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Inheritance of anAutosomal Dominant Trait
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Partial Pedigree for Albinism
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Discontinuous Distribution of a Mendelian Trait
(ABO Blood Type)
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Inherited Genetic Disorders

• Genetic disorders can be inherited as dominant or
  recessive traits.
• Dominant disorders are inherited when one copy of
  a dominant allele is present.
• Recessive disorders require the presence of two
  copies of the recessive allele.
• Recessive conditions that affect humans cystic
  fibrosis, Tay-Sachs disease, sickle cell anemia,
  and albinism.

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Polygenic Inheritance

• Polygenic traits are continuous traits governed
  by alleles at more than one genetic locus.
• Continuous traits show gradations, there is a
  series of measurable intermediate forms between
  two extremes.
• Skin color is a common example of a polygenic
  trait it is governed by 6 loci and at least 12
  alleles.

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Mendelian Traits Comparedwith Polygenic Traits
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Frequency of the Sickle-cell Allele Distribution
in the Old World
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Malaria Distribution in the Old World
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Genetic and Environmental Factors

• The genotype sets limits and potentials for
  development and interacts with the environment.
• Aspects of the phenotype are influenced by this
  genetic-environmental interaction.
• The environment influences many polygenic traits,
  such as height.
• Mendelian traits are less likely to be influenced
  by the environment.

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Levels of Evolution

• These levels are integrated in a way that
  eventually produces evolutionary change
• Molecular
• Cellular
• Individual
• Population

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Mutation and Evolution

• Mutation is a molecular alteration in genetic
  material
• For a mutation to have evolutionary significance
  it must occur in a gamete (sex cell).
• Such mutations will be carried on one of the
  individual's chromosomes.
• During meiosis the chromosome carrying the
  mutation will assort giving a 50 chance of
  passing the allele to an offspring.

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The Modern Synthesis

• Evolution is defined as a two-stage process
• The production and redistribution of variation
  (inherited differences between individuals).
• Natural selection acting on this variation
  (whereby inherited differences, or variation,
  among individuals differentially affect their
  ability to reproduce successfully).

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Factors That Lead to Increases in Allele
Frequencies

• Genetic drift occurs in small populations where
  random factors cause significant changes.
• Gene flow occurs when individuals migrate and
  mate outside their original population.
• Differential reproduction occurs when individuals
  with particular alleles have more offspring than
  others, leading to changes in allele frequency
  and evolution.

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New Technologies

• Polymerase chain reaction (PCR) makes it possible
  to analyze and identify DNA as small as one
  molecule and produce multiple copies of the
  original DNA.
• Recombinant DNA techniques allow scientists to
  transfer genes from the cells of one species into
  the cells of another.
• Genetic manipulation is controversial due to
  safety and environmental concerns.

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