Chapter 12 Section 3-Complex Inheritance of Human Traits

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Chapter 12Section 3-Complex Inheritance of Human
Traits
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I) Codominance in Humans

• Note phenotypes of both homozygotes are
  produced in heterozygotes ? ex/sickle cell anemia
• B) Sickle Cell Anemia (SCA)
• i) Basics of SCA
• Major health problems in US Africa
• Most common among in black Americans w/ origins
  in Africa white Americans with origins in the
  countries that surround the Med. Sea
• 1/12 African American is heterozygote for SCA

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I) Codominance in Humans

• Basics of SCA
• Hemoglobin is a protein that carries O2 in red
  blood cells (RBC)
• Individuals who are homozygotes for SCA have
  defective hemoglobins which form crystal-like
  structures that cause shape changes in RBC

Sickle Cell RBC Half-moon or sickle shaped
Normal RBC Disc Shaped
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I) Codominance in Humans

• ii)How sickle cell works?
• Gene for hemoglobin produces protein that differs
  from normal hemoglobin by 1 AA
• SCA hemoglobin crystallizes when O2 levels are
  low after hemoglobin delivers O2 to cells in
  narrow capillaries
• Causes change in RBC from disc shaped ? sickle
  shape (see Fig.12.16)
• Sickle shaped RBC slow blood flow and block small
  vessels
• Can result in
• Pain
• Tissue damage
• Short life span of RBC

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I) Codominance in Humans

• iv) Codominance of SCA
• Individuals who are heterozygotes for SCA means
  that they produce both
• normal hemoglobin
• SCA hemoglobin (ex/ of codominance) and they have
  the SCA trait
• These individuals produce enough normal
  hemoglobins to prevent serious health problems
  and can live relatively normal lives
• These individuals can show signs of SCA related
  to disorders if O2 availability reduced

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II) Multiple Alleles govern blood type

• ABO blood type grp classic example of single gene
  with multiple alleles in humans
• i) Human Blood Types
• Human blood types determined by presence or
  absence of certain molecules on surface of RBC
• Blood Type Gene I
• (3) alleles that can be present on I gene
• IA surface molecule A
• IB surface molecule B
• i no surface molecule

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GENOTYPES Type A_____ Type B____ Type
AB_______ Type O___ Possibilities Type
A_____ Type B_____
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II) Multiple Alleles govern blood type

• B) Importance of Blood typing (B.T.)
• Blood typing important b/c
• Incompatible blood type given through blood
  transfusion can cause other blood types to clump
  causing death
• Can be used to solve parentage
• Ex/ Child has blood type AB, Mother has blood
  type A, what must the fathers blood type be?

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II) Sex-linked traits in Humans

• Many human traits are determined by genes carried
  on sex chromosomes
• Most genes carried on the X chromosome
• A) How sex chromosomes are passed on?
• Males Females

Can be passed to either sons or daughters
Passed on to Daughters only
Passed on to Sons only
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II) Sex-linked traits in Humans

• If son receives allele on X chromosomes it will
  be expressed b/c males have only 1 chromosome
• 2 traits that are X-linked disorders are
• Red-green blindness
• Hemophilia
• B) Red-green colorblindness
• Individual cant distinguish between red green
• Caused by recessive allele found at 1 of (2) gene
  sites on X chromosome
• Both genes affect red green receptors in eye
  cells
• Can cause problems w/ driving ? traffic lights

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Color Blindness Tests
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II) Sex-linked traits in Humans

• C) Hemophilia An X-linked Disorder
• Clotting ability necessary human adaptation
• If clotting ability not present, could result in
• Excess blood loss due to minor injury
• Serious blood loss due to internal injury
• Major blood loss due to bruising
• Hemophilia A
• X-linked disorder causing a blood clotting
  problem
• 1/10,000 males have hemophilia
• 1/100 million female have hemophilia

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II) Sex-linked traits in Humans

• C) Hemophilia An X-linked Trait
• Hemophilia A
• Males receive hemophilia allele from carrier
  mothers on X chromosome
• 1 recessive allele hemophilia in males
• 2 recessive alleles hemophilia in females
• Treatment of hemophilia
• Blood transfusions
• Injections of Factor VIII (this is a blood
  clotting enzyme that is absent in hemophilic
  patients

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III) Polygenic Inheritance in Humans

• Many human traits are determined by polygenic
  inheritance
• Ex/ variations in eye color (humans)
• Ex/variations in skin color (humans)
• i) Skin Color A polygenic trait
• 1900s-skin color data used to test polygenic
  inheritance theory
• Light skinned individual x Dark Skinned
  individual
• Intermediate skin color

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III) Polygenic Inheritance in Humans

• F2 generation
• results in range of skin colors from light
  skinned ?dark skinned like P1 generation w/ most
  having intermediate skin color
• Variation led to skin color being polygenic has
  3-4 genes involved

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III) Changes in Chromosome Numbers

• Remember abnormal chromosomes usually happens
  b/c of meiosis accidents
• (Process Called _________________)
• Human chromosome
• Pairs of chromosomes 23
• Total chromosomes 46
• A) Abnormal numbers of Autosomes
• Trisomic Humans-those individuals who have either
  partial/whole extra chromosome
• Trisomy usually caused by nondisjunction

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III) Changes in Chromosome Numbers

• i) How abnormal chromosomes are IDed?
• Sample of cells obtained from fetus or individual
• Metaphase chromosomes photographed images are
  enlarged arranged by length location of
  Centromere
• Chart of chromosomes is called a karyotype
• Karyotype-def-pg329-chart of metaphase chromosome
  pairs arranged according to length location of
  the Centromere used to pinpoint unusual
  chromosome s in cells
• Karyotypes valuable in IDing unusual chromosome
  s in cells

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III) Changes in Chromosome Numbers

• B) Down Syndrome Trisomy 21
• Most embryo w/abnormal chromosome result in
  death of the embryo
• Down syndrome only autosomal trisomy that results
  in embryo surviving to birth and adulthood.
• Down syndrome happens in 1/700 live births
• ii) Symptoms of Down Syndrome
• Some degree of mental retardation
• Short stature
• Weak muscles through out body
• Short, wide neck with excess skin
• Short/stocky arms legs
• Facial features sm. Low set ears/nasal bridge
  pushed in/ irregular mouth tongue
• Incident of Down Syndrome births is ?er in older
  mothers (especially over 40)

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III) Changes in Chromosome Numbers

• C) Abnormal numbers of sex chromosomes
• Many abnormalities in of sex chromosomes
• Any individuals w/ at least one Y chromosome is
  male
• Most individuals w/abnormal of sex chromosomes
  lead normal lives, but some may result in
• Klinefelter syndrome (XXY)-sm testes, usually
  sterile
• XYY-may be taller than normal
• Turners syndrome (XO)- monosomy X-have sex
  organs which dont mature/women
  sterile/short/heart defects common