Fundamentals of Genetics

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Fundamentals of Genetics
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Patterns of Inheritance

• The History of Genetics
• Genetics scientific study of heredity
• Trait characteristic that can be passed from
  parents to offspring

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Father of Genetics

• Gregor Mendel (born 1822)
• Austrian Monk
• Studied 7 different pea plant traits that are
  true-breeding
• Produce offspring identical to themselves

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Mendels 1st Conclusion

• Biological inheritance is passed from one
  generation to the next- Genes
• Alleles- different forms of a gene

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Parental Cross

• Cross-pollinated flowers with opposite traits
  (tall, short)
• P generation
• Plants from the first cross were all tall-
  hybrids.
• F1 generation

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F1 Cross

• Allowed plants from P cross to self-fertilize
• The recessive trait had reappeared!!
• About 25 of the offspring (F2 generation) were
  short.

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Mendels 2nd Conclusion

• Principle of Dominance
• Some alleles are dominant
• Capital Letter -R,D
• This trait will be always be seen
• Some alleles are recessive
• Lower case Letter r,d
• This trait will only be seen when a dominant
  allele is NOT present

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Mendels 3rd Conclusion

• Principle of Segregation
• Alleles separate from each other during formation
  of sex cells, or gametes.

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• Purebred organism receives the same genetic
  traits form both of its parents
• Homozygous AA or aa
• Hybrid organism receives different forms of a
  genetic trait
• Heterozygous - Aa

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Important Terms

• Genes sections of a chromosome that code for a
  trait
• Allele distinct form of a gene
• Dominant Allele expressed when two different
  alleles are present represented with capital
  letter
• Recessive Allele form of gene that is not
  expressed when paired with a dominant allele
  represented with lower case letter

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Genes Represent Traits

• Genotype genes that make up an organism
• Includes both genes in a homologous pair
• Phenotype outward expression of the trait
• Homozygous two alleles are identical (AA or aa)
• Heterozygous two alleles are different (Aa)
• Also known as a hybrid organism

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Genetics and Prediction
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Predictions for One Trait

• Probability predict likelihood of an event or
  outcome
• Punnett square grid for organizing genetic
  information
• Can be used to make predictions about a cross
  between two organsims
• Monohybrid Cross cross between two parents and
  one trait

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Monohybrid Cross
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Predictions for Two Traits

• Dihybrid Cross cross between two parents and
  two traits
• Use a 4 x 4 Punnett square
• Sixteen possible outcomes

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Incomplete Dominance

• Heterozygous offspring show a phenotype that is
  in-between the phenotypes of the two homozygous
  parents
• Blending of traits
• Color in snapdragons
• instead of white or red,
• color is pink

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Codominance

• Both alleles are expressed
• Example Blood type
• IA, IB, i(O), or IAIB blood type
• Both A and B are dominant so they are both
  expressed in the IAIB blood type

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Polygenic Trait

• Trait controlled by more than one gene
• Example eye color

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Pleiotropy

• Single gene affects more than one trait
• Example sickle cell anemia
• Effects include blood cell shape, anemia,
  weakness, brain damage, spleen damage, and heart
  damage

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Environmental Effects

• Phenotype is a combination of genetic and
  environmental influences
• Example Himalayan rabbit fur color depends on
  body temperature

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Human Genetics
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Difficulties in Studying Human Heredity

• Controlled experiments are not possible
• Small numbers of offspring per generation
• Long periods between generations

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Sex Determination

• Autosomes body chromosomes first 22 pair
• Same in both male and female
• Sex Chromosomes 1 pair, last pair
• XX Female
• XY - Male

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XX 50 XY 50
You always have a 50 chance of having a girl
and a 50 chance of having a boy!
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Sex Linked Traits

• Traits controlled by recessive genes located on
  sex chromosomes (normally associated with the X
  chromosome)
• Hemophilia blood clotting enzyme
• is absent
• Queen Victorias family affected

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Sex Linked Traits

• Red Green Colorblindness individuals cannot
  distinguish between these two colors

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Sex Linked Traits

• Duchene Muscular Dystrophy wasting away of
  skeletal muscle

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• Females
• XRXR normal
• XRXr carrier
• XrXr disease

• Males
• XRY normal
• XrY disease

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Sex Limited Traits

• Controlled by genes located in the autosomes
• Only expressed in the presence of sex hormone
• Only expressed in one gender
• First seen at puberty (hormones produced in large
  enough quantities

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Sex Limited Traits

• Examples
• Male birds colorful plumage
• Beard growth in males
• Milk production in females

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Sex Influenced Traits

• Traits that are caused by a gene whose expression
  differs in males and females
• Also located on autosomes
• Expressed in the presence of male or female
  hormones
• Example male pattern baldness
• BB normal
• Bb males bald, females normal
• bb males and females bald

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Hereditary Disorders

• Techniques for detecting genetic disorders
• Amniocentesis technique used that removes and
  studies amniotic fluid
• during pregnancy
• identifies only
• chromosomal disorders

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Hereditary Disorders

• Karyotyping an enlarged photo of the chromosome
  pairs (map) to identify any abnormalities in the
  chromosomes

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Chromosomal Disorders

• Chromosomes fail to separate during meiosis
• Nondisjuction-abnormal numbers of chromosomes
  enter gametes

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Pedigree Charts

• Chart which shows how a trait and the genes that
  control it are inherited within a family
• Identifies the presence or absence of particular
  trait in members of each generation

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Pedigree Charts

• Males
• Females
• Generations Roman Numerals
• Individuals Numbered sequentially
• Trait Expressed Filled in
• Non Carriers Empty
• Carrier (not ill) Half filled
• Individual who carries a recessive allele that is
  not expressed