Introduction to Genetics

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Introduction to Genetics
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Gregor Mendel

• Gregor Mendel is the father of modern genetics
• Austrian monk who did genetic experiments with
  pea plants
• Defined basic units of heredity

1822-1844
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• Mendel used pea plants to conduct experiments. He
  concentrated on petal color and shape of peas.
• Experiments led to basic genetic understandings
  such as
• What happens when two different plants breed?
• How traits are passed from parents to offspring?
• Basic understandings of dominant and recessive
  traits?

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Different traits Mendel observed
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Why Peas?

• Mendel could do two experiments a year
• Lacked modern technology
• Today scientists use organisms that reproduce
  quickly such as drosophila (fruit fly) which
  reproduces in 2 weeks or bacteria such as E. coli
  which reproduces within hours.

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Genetics

• DNA are the blue-prints of all of your genetic
  information.
• DNA is tightly wound into chromosomes
• Your genetic information is on genes
• Genes are located on chromosomes

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Your Genes and DNA

• You are a combination of your parents.
• You have ½ of your moms and ½ of your dads DNA
• Remember Meiosis?
• You have 23 pairs (one from each parent) to make
  a total of 46 chromosomes.

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Human Chromosomes
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Genetic Traits

• Genes you get from your dad are paternal and
  genes you get from your mom are maternal
• These make up your traits.
• Trait characteristic determined by genes
• Example I have the trait for blue eyes

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Alleles

• Each trait is carried on a chromosome stripe.
• These stripes are called alleles.
• Allele form of a gene on a specific region of a
  chromosome

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Alleles for flower color
Maternal Chromosome
Paternal Chromosome
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Which of Your Parents Traits Will You Get?

• Based on probability
• For example, eggs have X chromosomes and sperm
  have either X or Y chromosomes.
• XX girl
• XY boy
• What is the probability offspring will be a girl?

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Boy or Girl

• 50 chance or 1 out of 2
• Only two different combinations!
• XX or XY
• Determining the sex of a baby is one example of
  probability.
• Butit doesnt always work that way

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Dominant Alleles vs. Recessive Alleles

• Certain traits are stronger then others. This
  means that they will more likely be expressed.
• For example If I mix black paint with white
  paint, what color will paint most likely be?
• Black! It is a stronger color.
• Dominant allele one that is expressed physically
  (what organism looks like)

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Dominant Alleles vs. Recessive Alleles

• What about the white paint?
• Recessive allele one that is masked or hidden by
  the dominant allele.
• White paint would be an example of the recessive
  color. There is still white paint in the
  mixture, but it looks black.

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Terms To Know

• Genotype combination of two alleles
• Homozygous When the genes are
• identical
• Heterozygous When the genes are
• different
• Phenotype The observable trait
• (the trait you see)

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Boy XY Girl XX

• What is the genotype for girl?
• XX
• Is boy homo or heterozygous?
• Heterozygous XY (different letters)
• Homozygous XX (same letters)
• What is the dominant allele (X or Y?)
• Y
• How do you know?
• Wherever Y is means a boy will form

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How genes are expressed

• If an organism carries any combination of
  dominant genes, it will be expressed in an
  organism.
• Recessive genes are only expressed when there are
  two recessive genes
• Example XX in girls