Intro to Genetics

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Intro to Genetics

• Mendel

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What is genetics?

• the study of how traits and diseases are
  inherited from one generation to the next
• through genes.
• Every living thing including plants, animals,
  microbes, etc., has a set of characteristics
  inherited from its parent(s).

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Mendel (Father of Genetics)

• Studied the inheritance of traits in pea plants
• Developed the laws of inheritance
• Mendel's work was not recognized until the turn
  of the 20th century

Gregor Mendel (1822-1884)
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• Mendel notices that there were tall plants and
  short plants.
• -Tall parents produced tall offspring
• -Short produced short offspring.
• He decided to cross pollinate, meaning the pollen
  from one flower fertilized the egg of another.
  This way they would get different traits from
  each parent.

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• A trait is a specific characteristic such as
  height or eye color that makes organisms vary
  from one another.
• Mendel called the parents the P (parental)
  generation.
• The offspring were called F1 or first filial.
  Filius is the Latin word for son.
• The offspring F1 generation are now called
  hybrids since they are a cross of parents with
  different traits.
• Mendel crossed the tall plant with the short
  plant.

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What do you think happened?

• All offspring were tall in the F1 generation.
• Biological inheritance is determined by factors
  passed from one generation (parents) to the next
  (babies).
• Today, these factors are called genes. Different
  genes of the same trait are called alleles. Ex.
  Tall and shorts are alleles for height. (T t)
• 2. Mendel discovered the Law of Dominance - some
  genes can overpower other genes, these genes are
  called the dominant genes. The "weaker genes" are
  called recessive genes.
• Any time a dominant gene is present the dominant
  trait will be expressed.

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• 
  Parents (tall and short)
• 
  F1 generation all tall
• 
  F2 generation 3 tall, one short

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Inheritance

• Mendel stated that physical traits are inherited
  as particles
• Mendel did not know that the particles were
  actually Chromosomes DNA

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Vocabulary

• Trait- any characteristic that can be passed
  from parent to offspring
• Heredity - passing of traits from parent to
  offspring
• Genetics - study of heredity
• Purebred one that always produces offspring
  with the same form of a trait as the parent.
  (homozygous)
• Hybrid has both forms of a trait (heterozygous)
• Gamete - A sex cell, either and egg or a sperm.

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More Vocabulary

• Alleles - two forms of a gene (dominant
  recessive)
• Dominant - stronger of two genes expressed in the
  hybrid represented by a capital letter (R)
• Recessive - gene that shows up less often in a
  cross represented by a lowercase letter (r)
• Homozygous and purebred BB
• Heterozygous and hybrid Bb

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Eight Pea Plant Traits

• Seed shape --- Round (R) or Wrinkled (r)
• Seed Color ---- Yellow (Y) or  Green (y)
• Pod Shape --- Smooth (S) or wrinkled (s)
• Pod Color ---  Green (G) or Yellow (g)
• Seed Coat Color ---Gray (G) or White (g)
• Flower position---Axial (A) or Terminal (a)
• Plant Height --- Tall (T) or Short (t)
• Flower color --- Purple (P) or white (p)

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Generations

• P-Generation (Parents)
• F1 Generation (1st Generation of Offspring)
• F2 Generation (2nd Generation of Offspring)

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Probability

• The likelihood that a particular even will occur
  is call probability.
• For example toss a coin and it will either land
  on heads or tails. The probability that the coin
  will land on heads is ½.
• The probability that it will land on tails is
  also ½.

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• If you flip a coin three times, what is the
  probability that all three will be heads?
• ½ x ½ x ½ 1/8
• The principles of probability can be used to
  predict the outcomes of genetic crosses as well.
  
• A Punnett square is used to do this.

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Punnett Squares

• The gene combinations that might result from a
  genetic cross can be determined by drawing a
  diagram known as the punnett square.

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Parent 1





Parent 2
Try these Tt x TT, Bb x bb, TT x tt , and Bb
x Bb
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Genotype and Phenotype

• Genotype is an organisms genetic makeup. For
  example Bb or BB or bb
• Phenotype is the physical characteristics or what
  they look like. For example if we were talking
  about eye color, the phenotype would be blue or
  brown eyes.
• If B brown eyes and b blue eyes
• Bbwould have brown eyes
• BB brown eyes
• bb blue eyes

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Lets PracticeGenotype or phenotype

• Blue
• Tt
• Tall
• Tt
• Short

• BB
• Brown
• Blonde
• Bb
• bb

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Beyond Dominant and Recessive Alleles

• Some alleles are neither dominant or recessive,
  and many traits are controlled by multiple
  alleles or multiple genes.
• Incomplete dominance one allele is not
  completely dominant over another. A red flower
  crossed with a white flower, produce pink
  flowers. (blending)
• Codominance Both alleles contribute to the
  phenotype of the organism. Black chicken crossed
  to a white chicken produce a black and white
  chicken

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Incomplete Dominance
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Polygenic traits

• Unfortunately, not all traits are as easily
  predicted as plant height.
• Many traits living organisms have are polygenic
  traits.
• Polygenic traits are traits that are controlled
  by two or more genes. Poly means many. Genic
  refers to genes. Polygenic means many genes.

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For example

• There are at least three genes involved in the
  reddish brown pigments in the eyes or fruit
  flies.
• Also, skin color in humans is controlled by at
  least four different genes.
• Mendels principals of probability could not be
  used to predict these traits.
• However they can be used in some human and fruit
  fly traits.