Introduction to Genetic Terminology

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Introduction to Genetic Terminology
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Introduction to Genetics

• Every living thing- plant or animal, microbes,
  human beings- has a set of characteristics
  inherited from its parent or parents
• Genetics is the key to understanding this
  heredity and what makes each species unique.

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What is a genome?

• All of an organisms genetic
• material is called the genome.
• You may have heard about the Human Genome
  Project, its goal was to find out the sequence
  of the 3 billion nucleotide pairs that make up a
  human's genome.
• Unless you have an identical twin, you have a
  unique genome that determines all of your traits

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• A Gene!
• 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 of homologous chromosomes.
• Think of the locus as the address that tells
  where a gene is located on a chromosome.

• What did Mendel call his discrete units of
  heredity?

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• Yes
• In Mendels experiments, the effects of these
  different forms were easy to see yellow or
  green round or wrinkled.
• Alleles
• Your cells have 2 alleles for each gene, because
  each parent donates on allele for every gene.
• Remember your alleles are representing your
  different traits!!!

• Do genes exist in many forms?
• What do we call these alternative forms of genes?

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• Even though you have 2 alleles, only one is
  usually expressed because it is either Dominant
  or Recessive.

• A dominant allele is the allele that is expressed
  when two different alleles or dominate alleles
  are present.
• A recessive allele is the allele that is only
  expressed when two copies are present
• Dominant alleles are represented by uppercase
  letters recessive alleles by lowercase letters.
• TT, Tt, or tt
• A dominate allele is not necessarily better or
  stronger than a recessive, its just the one
  expressed.

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• The two alleles may be the same, or they may be
  different.
• Homozygous describes two alleles that are the
  same at a specific locus.
• TT, tt
• Heterozygous describes
• two alleles that are different
• at a specific locus.
• Tt

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• Genotype - gene combination for a trait
• (e.g. RR, Rr, rr)
• Phenotype - the physical feature resulting from a
  genotype (e.g. red, white)

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Genotypes

• Homozygous genotype - gene combination involving
  2 dominant or 2 recessive genes
• (e.g. RR or rr)
• also called pure bred 
• Heterozygous genotype - gene combination of one
  dominant one recessive allele   
• (e.g. Rr)
• also called hybrid

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Genotype Phenotype in Flowers
Genotype of allelesR red flowerr yellow
flower All genes occur in pairs, so 2 alleles
affect a characteristic Possible combinations are
Genotypes RR Rr rr Phenotypes RED RED
YELLOW