Intro to Genetics

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Intro to Genetics

• The genetic variation that the process of meiosis
  provides has undergone a lot of study.
• Genetics branch of biology that focuses on
  heredity
• Mendels breeding experiments with the garden pea
  Pisum sativum illuminated the passing on of
  traits to offspring through the process known as
  heredity.
• Traits the variant for a character (color,
  shape, size)

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.type

• Gene unit of heredity information located on
  the chromosome and consisting of DNA
• Allele alternate form of a gene
• Genotype set of alleles an individual has for a
  specific trait.
• Phenotype physical appearance of a trait

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• Purebred (true breeding) organisms or genotypes
  that are homozygous (when two alleles for a
  particular gene are the same) for a specific
  trait and thus always produces offspring that
  have the same phenotype for that trait
• Hybrid the mating or crossing of two varieties
• Heterozygous having two different alleles for a
  given trait

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• Punnett Squares
• A diagram that predicts the outcome of a genetic
  cross by considering all possible combinations of
  gametes (probability)
• Simplest Punnett squares can predict the outcome
  of a monohybrid cross (a cross of one pair of
  contrasting traits between two individuals)
• Dominant traits are displayed as a capital
  letter, recessive traits are displayed as a lower
  case letter

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• Monohybrid cross homozygous plants
• One parent is homozygous dominant (YY)
• One parent is homozygous recessive (yy)
• Possible outcomes are all Heterozygous (Yy)
• Phenotype 4 Yellow peas
• Genotype 4 Yy

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• Monohybrid cross Heterozygous plants
• Both parents are Heterozygous (Yy) and appear
  yellow in color
• Y- yellow
• y- green
• Possible phenotypic outcomes
• 3 yellow peas, 1 green pea
• Possible genotypic outcomes
• 1 (YY) homozygous dominant
• 2 (Yy) heterozygous
• 1 (yy) homozygous recessive

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• Dihybrid cross
• A cross that involves two pairs of contrasting
  traits
• Determining possible gametes to go on top of the
  columns and beside the rows
• Must include one allele for each trait
• A heterozygous plant for shape and color has the
  following alleles (RrYy)
• R round, r wrinkled, Y Yellow, y - green

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• Types of traits
• Autosomal a trait that appears on a chromosome
  other than the X or Y chromosomes
• Sex-linked a trait whose allele is located on
  the X or Y chromosome
• Most sex-linked traits are recessive, since males
  have only 1 X and 1 Y chromosome males are more
  likely to exhibit the traits
• Females have 2 X chromosomes giving females a
  lower chance of exhibiting the trait

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• Polygenic trait influenced by several genes
• Genes may be scattered on one chromosome or
  located on different chromosomes
• Examples of polygenic traits include hair and eye
  color, skin tone, height, and weight
• Since many genes are involved there are many
  degrees of these conditions
• i.e. Dark brown hair, light brown hair, blonde
• Green eyes, Blue eyes, Brown eyes, Hazel eyes

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Inheritance of traits

• Pedigrees show how a trait is inherited over
  several generations.
• Used to track genetic disorders
• Carriers individuals who are heterozygous but
  do not show symptoms. May pass the disorder to
  their offspring

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Reading a Pedigree

• Squares Males
• Circles Females
• Horizontal lines indicates mating
• Vertical lines indicate offspring 1st born is
  placed on the left
• Blank circles/squares represent individuals
  showing no symptoms
• Dark circles/squares represent affected
  individuals

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Generations on a pedigree

• P generation first two individuals that are
  crossed in a breeding experiment
• F1 generation offspring of the P generation,
  the first filial generation (filial means a son
  or daughter)
• F2 generation offspring of the F1 generation,
  the second filial generation