KEY CONCEPT Genes encode proteins that produce a diverse range of traits.

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KEY CONCEPT Genes encode proteins that produce a
diverse range of traits.
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The same gene can have many versions.

• A gene is a piece of DNA that directs a cell to
  make a certain protein.
• Each gene has a locus, aspecific position, on a
  pair ofhomologous chromosomes.
• Different versions of the same gene are called
  alleles

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• An allele is any alternative form of a gene
  occurring at a specific locus on a chromosome.

• Each parent donates one allele for every gene.
• Homozygous describes two alleles that are the
  same at a specific locus.
• Heterozygous describes two alleles that are
  different at a specific locus.

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Genes influence the development of traits.

• The genome is the collection of all of an
  organisms genetic material.
• All of the genes on all of the chromosomes.
• A genotype refers to the makeup of a specific set
  of genes.
• the alleles of a specific gene
• Bb, BB, bb, where Bbrown eyes, bblue eyes
• A phenotype is the physical expression of a
  trait.
• Blue eyes or brown eyes

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• Alleles can be represented using letters.

• A dominant allele is expressed as the phenotype
  when at least one allele is dominant.
• A recessive allele is expressed as the phenotype
  only when two copies are present.
• Dominant alleles are represented by UPPERCASE
  letters recessive alleles by lowercase letters.

R
r
Rr
r
r
rr
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• Both homozygous dominant and heterozygous
  genotypes yield a dominant phenotype.

• Most traits occur in a range and do not follow
  simple dominant-recessive pattern.
• Height is a good example.

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• Ernest Hemingway had a bunch of cats when he
  lived in Key West, Florida
• When he died he left the house to his cats
• Some of these cats had an extra toe (called
  polydactyly)
• Polydactyly is a dominant trait, so now all the
  cats there have extra toes.
• There is no real advantage to extra toes. It just
  happens to be dominant over the other alleles so
  it is passed on.