Genetics

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Genetics
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Gregor Mendel

• Father of Genetics
• Austrian monk who discovered the basic laws of
  inheritance in the mid-1800s
• Conducted breeding experiments on pea plants
  worked with 7 clearly contrasting characteristics
  (ex. Seed color, seed texture, plant height,
  etc.)
• Mendels work ignored until after his death in
  the early 1900s, his records were discovered and
  found to be correct

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Genetics Terminology

• P Generation the parental generation the parent
  organisms involved in a genetic cross
• F1 Generation the first filial generation the
  offspring of the P generation
• F2 Generation the second filial generation the
  offspring of the F1 generation

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Genetics Terminology (continued)

• Gene- the basic unit of inheritance located on
  chromosomes represented by letters an
  individual has at least 2 genes for each
  characteristic/trait
• Allele- alternative forms of genes located in
  corresponding positions on homologous chromosomes
• Locus the specific location of a gene on a
  chromosome

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Genetic Terminology (continued)

• Homozygous- pure true-breeding a descriptive
  term for an individual with 2 identical alleles
  for a characteristic/trait
• Heterozygous- hybrid a descriptive term for an
  individual with 2 different alleles for a trait

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Genetic Terminology (continued)

• Dominant- the allele that is expressed in a
  heterozygous individual represented by a capital
  letter
• Recessive- the allele that is hidden, or not
  expressed, in a heterozygous individual
  represented by a lowercase letter

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Genetic Terminology (continued)

• Genotype- the genetic makeup of an individual,
  expressed in letter symbols
• Phenotype- the physical appearance of an organism
  with respect to a trait

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Genetic Terminology (continued)

• Punnett square- the checkerboard chart/table
  used in genetics to determine the possible gamete
  combinations when two individuals are crossed
• Monohybrid cross- a genetic cross between 2
  individuals that differ in the alleles they carry
  for a single trait a true monohybrid cross
  results in a 121 genotypic ratio and a 31
  phenotypic ratio
• Dihybrid cross- a genetic cross between 2
  individuals that differ in the alleles they carry
  for two traits a true dihybrid cross results
  in a 9331 phenotypic ratio

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Sex Determination

• The genotype of a female is XX during oogenesis,
  a female produces eggs, each of which contains a
  single X chromosome
• The genotype of a male is XY during
  spermatogenesis, a male produces sperm, half of
  which contain an X chromosome and the other half,
  a Y chromosome
• If an X sperm fertilizes an egg, a female
  zygote is formed if a Y sperm fertilizes an
  egg, a male zygote is formed

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Sex Determination (continued)

• Occasionally, individuals are born with abnormal
  sex chromosome makeups
• These conditions generally result in individuals
  who are sterile (due to underdeveloped gonads)
• Klinefelters syndrome XXY genetically a male
• Turners syndrome XO genetically a female

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Sex-Linked Characteristics

• Traits controlled by genes located on the X
  chromosome
• If a male has a sex-linked gene, he will have the
  condition it causes
• Examples color blindness, hemophilia

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Sex-Influenced Characteristics

• Traits inherited through autosomal genes, but
  whose expression is affected by the gender of the
  individual
• Example male pattern baldness

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Human Blood Types

• Determined by the type of chemical substances, or
  antigens, found in the plasma membranes of an
  individuals red blood cells
• ABO blood types are determined by the type of
  sugars attached to the the membrane
• Rh blood types are determined by the type of
  proteins in the membrane

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ABO Blood Types

• 4 blood types (phenotypes)
• A contains type A antigens
• B contains type B antigens
• AB contains both type A and type B antigens
• O lacks type A and type B antigens

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ABO Blood Types (continued)

• Inheritance of ABO blood types is based upon
  multiple alleles instead of just 2 types of
  alleles for a trait, there are 3 A, B, and O
• A is dominant to O
• B is dominant to O
• Neither A nor B is dominant to the other

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ABO Blood Types (continued)

• 6 genotypes possible
• AO (type A)
• AA (type A)
• BO (type B)
• BB (type B)
• AB (type AB)
• OO (type O)

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Rh Factor

• Rh positive individuals contain the Rh factor in
  their red blood cells Rh negative individuals do
  not
• An Rh positive individual may contain 2 Rh
  positive genes () or 1 Rh positive gene and 1
  Rh negative gene ( )
• The gene for Rh positive is dominant to the gene
  for Rh negative

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How Common is Your Blood Type?

• O 38.4
• A 32.3
• B 9.4
• O- 7.7
• A- 6.5
• AB 3.2
• B- 1.7
• AB- 0.7
• (Source American Red Cross)

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Blood Transfusions

• During medical emergencies involving blood loss,
  blood transfusions may be given to an individual
• If an individual is given blood containing
  antigens he/she does not normally have, the
  immune system is stimulated to attack the
  transfused cells

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Blood Transfusions (continued)

• Compatible blood types
• Type A can receive A or O
• Type B can receive B or O
• Type AB can receive A, B, AB, or O
• Type O can receive only O
• Rh negative individuals can receive only negative
  blood, but Rh positive individuals can receive
  either Rh positive or Rh negative

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Blood Transfusions (continued)

• Individuals with type O- blood are called
  universal donors
• Individuals with type AB blood are called
  universal recipients

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Human Genetic Abnormalities

• Downs Syndrome (Trisomy 21)three of
  chromosome 21
• Huntingtons Disease/Disorder gene on
  chromosome 4
• Albinism gene on chromosome 11
• Cystic Fibrosis gene on chromosome 7
• Color Blindness gene on an X chromosome
• Hemophilia gene on an X chromosome

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Other Gene Locations

• Chromosome 1Rh blood type
• Chromosome 2colorectal cancer
• Chromosome 3colorectal cancer, lung cancer
• Chromosome 4red hair color
• Chromosome 6dyslexia, schizophrenia, juvenile
  diabetes

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Other Gene Locations (continued)

• Chromosome 7obesity
• Chromosome 9ABO blood type, malignant melanoma
• Chromosome 11sickle-cell anemia
• Chromosome 13breast cancer
• Chromosome 14Alzheimer disease
• Chromosome 17breast cancer

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Other Gene Locations (continued)

• Chromosome 19Alzheimer disease, brown hair
  color
• X Chromosomemuscular dystrophy