Genetics

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Chapter 11

• Genetics

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Observations

• 1677 Anton van leewenhoek discovers live sperm
  animalcules
• Followers thought little people in sperm
• Followers Spermist
• 1670s Regnier de Graaf describes ovarian
  follicle- (where human egg forms)
• Theory of egg forms even though it is not seen
  for 150 yrs
• Followers called Ovists

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Observations.

• 1850s new data
• Hypothesis Blending Inheritance -
• When sperm and egg (gametes) combine there
  is a mix of hereditary information that cannot be
  separated.

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Mendel

• Gregor Mendel- Austrian Monk
• Began modern genetics
• Discovered elemente (Genes)
• Discrete units that are resorted in each
  generation.
• In the 35 yrs his experiments were ignored
  microscopes improve and chromosomes discovered

www.micro.utexas.edu/.../ genetics/genetics.html
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Mendels Method
Studied first AND second generation
Counted offspring analyzed results
Mathematically
Organized Data to be checked and evaluated

• Planned experiment chose
• clear hereditary traits to
• study

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• Mendel used common garden Pea
• The concept of studying Biology quantitatively is
  NEW

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Segregation

• When a plant with true breeding purple flowers
  crossed with a true breeding white flower the F1
  (first filial generation) all had purple
  flowers thus this was called the dominant trait
• Other trait still in genetic information as it
  shows up in F2 called recessive.
• The law of dominance states that one gene, the
  dominant gene, prevents the appearance of the
  trait controlled by the other gene, the recessive
  gene.

ntri.tamuk.edu/.../ biology/lecture12.html
http//www.physics.unl.edu/fulcrum/resources/Mend
el20Laws20and20Probability.doc
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Principle of Segregation

• Every individual carries pairs of
• factors for each trait and that the
• members of the pair separate during the
  formation of gametes
• Alleles different forms of a gene
• Homozygous 2 of the same allele
• Heterozygous 2 different alleles
• Gametes contain only one allele for each gene

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Phenotype Visual appearance Genotype
Genetic Information
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Alleles

• When the gene for one trait exists as only two
  alleles the alleles play according to Mendel's
  Law of Dominance, there are 3 possible genotypes
  (combination of alleles) 2 possible phenotypes
  (the dominant one or the recessive one).
• If there are only two alleles involved in
  determining the phenotype of a certain trait, but
  there are three possible phenotypes, then the
  inheritance of the trait illustrates either
  incomplete dominance or codominance.

Now, if there are 4 or more possible phenotypes
for a particular trait, then more than 2 alleles
for that trait must exist in the population.  We
call this "MULTIPLE ALLELES". Let me stress
something.  There may be multiple alleles within
the population, but individuals have only two of
those alleles.

• In these situations a heterozygous (hybrid)
  genotype produces a 3rd phenotype that is either
  a blend of the other two phenotypes (incomplete
  dominance) or a mixing of the other phenotypes
  with both appearing at the same time
  (codominance).

http//www.borg.com/lubehawk/multalle.htm
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• GENES
• A gene is a small piece of the genome. It's the
  genetic equivalent of the atom
• As an atom is the fundamental unit
• of matter, a gene is the fundamental
• unit of heredity.
• Genes are found on chromosomes and
• are made of DNA. Different genes
• determine the different characteristics,
• or traits, of an organism.

www.genomenewsnetwork.org/. ../Chp1_3_1.shtml
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Test Cross

• Used to find genotype of parent
• You cross a unknown with a homozygous recessive

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http//www.rit.edu/gtfsbi/IntroBiol/images/CH10/f
igure-10-06.jpg
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Independent Assortment

• Mendel did his next experiment with two
  characteristics
• Green wrinkled seeds (recessive)
• Yellow round seeds (Dominant)
• A cross of these produced F1 all yellow round.
  The F2 were not just green-wrinkled and
  yellow-round they were green-round and
  yellow-wrinkled

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Independent Assortment

• When gametes form alleles of a
• gene for one trait separate
• independently of alleles of a
• gene for another trait

When RRYY x rryy you get 9331 Or when rrYY x
Rryy you get 9331 9 homozygous dominant 33
heterozygous mix 1 homozygous reccessive
ntri.tamuk.edu/.../ biology/lecture12.html
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Dihybrid Test Cross
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Mutations

• Discovered by Hugo de Vries in primroses
• Mutations a characteristic not present in
  earlier generations
• Mutations dont determine direction of evolution
• They are the ultimate, and continual source of
  hereditary variations that make evolution
  possible

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Law of Probability

• Product rule of probability - 2 independent
  events occur simultaneously the probability is
  the independent probability of one times the
  probability of the other
• Sum Rule of Probability When there is more than
  one possible arrangement you add them
• (eg heads first tails second)

http//norskeideer.no/julekalender_2002/images/coi
n_flip.jpg