Introduction to

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Introduction to Genetics
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Weve all heard of it, but What is genetics?

• Genetics the study of gene structure and action
  and the patterns of inheritance of traits from
  parent to offspring. 

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Ancient ideas about genetics

• Selective breeding of plants and animals

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Ancient ideas about genetics

• Theories why offspring resemble parents
• Spontaneous generation?
• Miniature pre-formed organisms?
• Blending of vital fluids?

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Then, in 1860

• Gregor Mendel successfully discovered genetic
  principles

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Pea Characteristics

• Mendel studied traits of pea plants one at a time

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Mendel and Plant Breeding

• Mendel examined thousands of crosses and
  offspring
• Mendel analyzed his results mathematically- saw
  patterns no one else saw

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Mendels experiments
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Mendels Principle Findings

• Dominant and Recessive
• Certain characteristics are dominant to others
• The dominant trait will mask another (recessive)
  trait, preventing its expression
• The recessive trait disappears for a generation

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Mendels Principle Findings

• Law of Segregation
• For each trait, organisms have 2 genes
• (which may be different versions or forms of the
  genes, these are called alleles)
• Each pea plant got one gene from each parent
• Genes are segregated from each other during egg
  or sperm formation (meiosis)

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Remember Meiosis?!?The Law of Segregation is the
SAME THING!Mendel just theorized about it before
it was actually discovered.
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Segregation of Genes during Meiosis
B
sperm
B
B
Bb
haploid (n)
b
b
diploid (2n)
b
meiosis II
meiosis I
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Mendels Principle Findings

• Independent Assortment
• Factors for different traits are distributed to
  reproductive cells independently
• Later it was seen that orientation of homologous
  pair to poles during meiosis is random.
• So, for example, genes from the individuals
  mother don't all stay together

Click here for an animation!
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Some terms

• Trait characteristics of an organism passed
  from generation to generation.
• Eye color
• Skin color
• Hair color and type
• Height
• Temperament
• Symptoms for genetic diseases

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Not all traits are easy to predictFor example
polygenic inheritance. (Where have we seen the
prefix poly before?)
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Genotype

• Tells you the genetic makeup of the organism
• The genes the organism carries

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Genotype

• Written using symbols
• Each allele is represented by a letter
• Tall T dominant
• Short t recessive
• Capital letter designates the dominant trait and
  lower case letter designates the recessive trait.
• Capital letter is always written first.

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Homozygous

• An individual which contains one allele for a
  genetic trait
• TT-- homozygous dominant
• tt -- homozygous recessive

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Heterozygous

• An individual which contains different alleles
  for a genetic trait
• Tt heterozygote

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Phenotype

• What the organism looks like
• Controlled by the genotype
• TT---------- tall
• Tt----------- tall
• tt------------ short

TT
Tt
tt
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Remember
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Example
Phenotype
Genotype
This person would have brown eyes (Bb)