A View of Life

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• The Final Exam (150 points)
• Lab 9 -ReproductiveSystems/Development
• Lab 10 Abortion
• Lab 11 Mankind and Biodiversity
• Lab 12 Patterns of Genetic Inheritance (Ch. 20
  in the text)
• DONT FORGET Lab Notebook check. (40 points)

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Chapter 20

• Patterns of Genetic Inheritance

Why do they share their distinctive traits?
Its all in the genes.
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Review

• Genotype and Phenotype
• One- and Two-Trait Inheritance
• Beyond Simple Inheritance Patterns
• Sex-Linked Inheritance

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Introduction

• Genetics?
• the study of heredity. . . .
• the study of how traits are passed from one
  generation to the next.
• Mendelian Genetics is our focus today.
• Gregor Mendel (1859) pea plants Principles
  (Laws) of Inheritance. . . .
• 1. Law of dominant and recessive
• 2. Law of unit characteristics (now called
  genes)

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• 3. Law of segregation
• 4. Law of independent assortment
• Before we examine these concepts, let us examine
  some of the genetic terms in Lab 12
• Chromosomes, genes, and alleles.
• The other terms (definitions) found in the lab
  will be addressed as we examine this chapter (Ch.
  20) in the text.
• You definitely want to know all of these terms
  for the exam.

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Genotype and Phenotype

• Genotype refers to an individuals genes (genetic
  traits, represented by letters).
• Alleles are alternate forms of a gene.
• Dominant alleles are assigned uppercase letters,
  while recessive alleles are assigned lowercase
  letters.
• Homozygous Dominant EE.
• Homozygous Recessive ee.
• Heterozygous Ee.
• Phenotype refers to an individuals physical
  appearance (physical traits or characteristics)

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Genetic Inheritance
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One- and Two-Trait Inheritance

• Two types of cell division
• Mitosis normal cell division (duplication
  division).
• Meiosis reduction division (producing sex
  cells).
• Forming the Gametes.
• Reduction of chromosome number occurs when pairs
  of chromosomes separate as meiosis occurs.
• Spermatogenesis, oogenesis.

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Gametogenesis
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One-Trait Cosses

• Punnett square ?
• A square with 4 squares within it.
• Is used to determine the phenotypic /genotypic
  ratios (the physical and genetic traits and their
  occurrence in the next generation) among the
  offspring when all possible sperm are given an
  equal chance to fertilize all possible eggs.
• If both parents are heterozygous, each child has
  a 25 chance of exhibiting the recessive
  phenotype.

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Heterozygous-Heterozygous Cross

• What phenotypes do you see?
• What genotypes?
• What is the genotypic ratio?
• How would we know an individuals genotype as to
  whether they were heterozygous or homozygous?
• Do a test cross.

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• This was called a monohybrid cross.
• They involved a single trait.
• What would it be called if we were following 2
  traits?
• Dihybrid cross.
• There would be 16 boxes, not 4!
• Three traits?
• Trihybrid cross.
• What are some examples of complete dominance?

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• because a gene is either dominant or recessive.
• Let us go back to the lab and do some genetics
  problems involving complete dominance in Sections
  I and II.
• Now let us return to the text (Ch. 20) and look
  at the topic of Family Pedigrees for Genetic
  Disorders.

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Family Pedigrees for Genetic Disorders

• A pedigree chart (Family tree) shows the pattern
  of inheritance for a particular disorder.
• Males are designated by squares.
• Females are designated by circles.
• Shaded circles or squares are affected
  individuals.
• Vertical line down represents a child, while an
  attached horizontal line across represents more
  children (siblings).

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Genetic Disorders of Interest
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Autosomal Recessive Disorders

• In this pattern, the child is affected but
  neither parent is affected.
• Therefore, since the parents are heterozygous,
  they can be called carriers.
• Recessive disorders can by passed on by parents
  who are unaffected (ie. Albinism).
• Tay-Sachs Disease.
• Allele located on chromosome 15.
• Jewish of central, eastern European descent.
• Lysosome buildup in brain, leads to progressive
  neurological / psychomotor deterioration.

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Autosomal Recessive Pedigree Chart
P1 F1/P2 F2/P3 F3/P4
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• Phenylketonuria (PKU).
• Allele located on chromosome 12.
• Unable to metabolize phenylalanine causing
• severe mental retardation.
• Treatment diet low in until brain develops,
• around age 7.
• Sickle-Cell Disease
• Description ..
• Origin..
• HbA vs. HbS
• Heterozygotes protected from malaria.
• Prognosis

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• Cystic Fibrosis.
• Allele located on chromosome 7.
• Most common lethal genetic disorder among
• U.S. Caucasians.
• Epecially thick mucus in the lungs and pancreas.
• Treatment

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Autosomal Dominant Disorders

• In this pattern, the child and at least one
  parent are affected, due to a dominant allele on
  an autosomal chromosome.
• Dominant disorders are passed on by a parent who
  has, or will develop, the disorder
  (ie. Achondroplasia, brachydactyly,
  hyercholesterolemia, Marfan syndrome).
• Neurofibromatosis (NF)
• Also known as von Recklinghausen disease.
• Allele located on chromosome 17.
• Huntington Disease (HD).
• Allele located on chromosome 4.

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Autosomal Dominant Pedigree Chart
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HEALTH FOCUS

• Preimplantation Genetic Diagnosis !!!!!!

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Beyond Simple Inheritance Patterns

• Unfortunately, life is not so simple as simple
  dominance problems would imply.
• There are complicating factors, other patterns of
  inheritance. . . .
• Polygenic (Multifactorial) Inheritance.
• Polygenic - one trait is governed by two or more
  sets of alleles.
• Continuous variation of phenotypes.
• Skin Color, height, weight, metabolic rate,
  behavior, intelligence.
• Multifactorial - a polygenic trait that is
  particularly influenced by the environment.

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Polygenic (Multifactorial) Inheritance
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Environmental Influences

• The environment can influence the phenotype.
• Human disorders include cleft lip/palate,
  club-foot, hypertension, diabetes, schizophrenia
  
• For example Siamese cats, Himalayan rabbits are
  darker in color at the ears, nose, paws, and
  tail.
• Why?
• Homozygous for allele involved in melanin
  production (ch) via produced enzyme that is
  active only at lower temperature
• Therefore, black fur occurs at the extremities
  where body heat is lost to the environment!
• Polygenic traits seem to be particularly
  influenced by the environment.

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Beyond Simple Inheritance Patterns

• Incomplete Dominance and Codominance.
• Codominance occurs when alleles are equally
  expressed in a heterozygote.
• Example human blood type AB.
• Incomplete Dominance is exhibited when the
  heterozygote has an intermediate phenotype
  between that of either homozygote.
• Familial hyper/cholesterol/emia (FH)
• Sickle Cell Disease.
• HbA vs. HbS
• Heterozygotes protected from malaria.

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Incomplete Dominance

• Note the characteristics
• Two different letters are used for the alleles.
• Usually, both letters are lower case.
• The heterozygote represents an in between trait.

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• Now let us return to the lab and examine some
  problems involving incomplete dominance in
  section III and IV.
• However, there are yet other patterns
  influencing inheritance which complicate the
  process. . . .
• Let us return to the text (Ch. 20) and examine
  these.

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Beyond Simple Inheritance

• Multiple Allele Inheritance.
• Gene exists in several allelic forms, although an
  individual usually only has two of the possible
  alleles.
• ABO Blood Types.
• A - A antigen on red blood cells.
• B - B antigen on red blood cells.
• O - Neither A or B antigen on red blood cells.

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Inheritance of Blood Type
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• Let us now return to the lab problems and do
  section V.
• Note there are 4 pages of practice problems
  which should be completed to get full credit for
  the lab in your notebook check.
• However, again there are yet other patterns of
  inheritance. . . . .
• These involve not the autosomes (the 22 pair of
  non-sex chromosomes) but the sex chromosomes.
• Let us return to the text (Ch. 20) and take a
  look at . . . .

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Sex-Linked Inheritance

• Traits controlled by alleles on the sex
  chromosomes are said to be sex-linked.
• On X chromosome X-linked.
• On Y chromosome Y-linked.
• Most sex-linked alleles are on the X chromosome
  and are recessive.
• Therefore, males demonstrate if get, females
  dont unless homozygous for it.
• Examples of X-linked recessive disorders
• Muscular Dystrophy (Duchenne MD).
• Red-Green Color Blindness.
• Hemophilia

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Color-Blindness Cross
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Pedigree for X-Linked Disorders
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X-Linked Recessive Disorders

• More males than females are affected.
• Examples
• Red-green color blindness.
• Muscular Dystrophy
• Duchenne Muscular Dystrophy which is a muscle
  wasting disease.
• Symptoms include waddling gait, toe walking,
  frequent falls, difficulty rising.
• Become wheel chair bound, usually die by age 20.
• Allele located on chromosome 17.

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• Hemophilia.
• Allele located on chromosome 4.
• Two types.
• Hemophilia A absence of factor VIII.
• Hemophilia B absence of factor IX.
• What are other names associated with this
• disease ?
• Bleeders disease, Kings disease, free
• bleeders.
• Why was Queen Victoria of the British
• Commonwealth of significance concerning this
• disease?

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Royal Hemophilia Pedigree
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BIOETHICAL FOCUS

• Genetic Profiling

1. Should people be encouraged, or even required, to
   have their DNA analyzed so that they can develop
   programs to possibly prevent future illness?
2. Should employers be encouraged, or required, to
   provide an environment suitable to a persons
   genetic profile? Or, should the individual avoid
   a work environment that could bring on an
   illness?
3. How can we balance individual rights with the
   public health benefit of matching genetic
   profiles to detrimental environments?

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Sex-Influenced Traits

• Some traits carried on autosomes can be
  influenced by gender through ones hormones.
• Examples?
• Male-pattern baldness where the male hormone
  (testosterone) is the culprit.
• Acts as dominant trait in males, recessive in
  females.
• Length of index finger (longer than ring finger)

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