Fundamentals of Genetics

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Fundamentals of Genetics
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Introduction to Genetics

• 1. GREGOR MENDEL - Father of Genetics
• Austrian monk, teacher, scientist, gardener
• Formulated basic laws of heredity in the early
  1860s
• Simplified problems was meticulous with data
  collection think quantitatively

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• 2. Worked with garden peas because
• Easy to grow and had a short generation time
• Could be self-pollinated
• 3. Chose true-breeding varieties for his
  experiments
• Means no genetic variation for a trait
• Studied 7 simple traits

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• 4. Mendel cross-pollinated plants
• P1 parental generation
• F1 first-generation (sons/daughters)
• F2 second-generation

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• 5. Principle of Dominance and Recessiveness
• F1 plants resembled only one of the parents
• F1 hybrids contained two factors for each trait
• one dominant (stronger, masks recessive)
• one recessive (seems to disappear)

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• 6. Principle of Segregation
• Organism contains two factors for each trait.
• Factors segregate during formation of gametes.
• Each gamete contains one factor for each trait.

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• 7. Principle of Independent Assortment
• Each trait is independent of another
• Genes of one pair of traits assort independently
• All combinations of genes occur in gametes

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Chromosomes, Genes, and Genetic Crosses

• Homologous Chromosomes contain genes (locations)
  for the same traits
• Traits are controlled by alleles (alternative
  forms of a gene).
• Genotype refers to the alleles an individual
  receives at fertilization
• Phenotype refers to the physical appearance
• of the individual.

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• 5. Homozygous dominant genotypes
• two dominant alleles for a trait. (BB)
• 6. Homozygous recessive genotypes
• possess two recessive alleles for a trait (bb)
• 7. Heterozygous genotypes
• one of each allele for a particular trait (Bb)

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• 8. Punnett Squares
• Show probabilities of future offspring
• Monohybrid crosses crosses between
• individuals that involve one pair of contrasting
  traits.

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9. Monohybrid Crosses (Examples)

• Ex 1 Pure Tall x Pure Short
• TTTall
• tt short F1
  F2

25 pure tall 50 hybrid tall 25 pure short
100 Tall
(Homozygous x Homozygous)
(Heterozygous x Heterozygous)
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10. Test Crosses

• A cross of an individual of unknown genotype with
  an individual of known genotype
• Tells if individual is heterozygous or homozygous
• Very important to breeders

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• OUT Correctly Match the Type of Cross
• Homozygous x Homozygous
• Homozygous x Heterozygous
• Heterozygous x Heterozygous
• Testcross

B.
C.
D.
A.
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Dominance Has Degrees

• 1. Incomplete dominance
• Offspring are intermediate between two parental
  phenotypes
• Neither allele is completely dominant over the
  other
• Both alleles influence phenotype
• 3 phenotypes

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• Ex Japanese Four oclocks
• RR red RR pink RR white

R R
R R
R R
RR
RR
RR
RR
R R
RR
RR
RR
RR
All Pink
1 red 2 pinks 1 white
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• 2. Codominance
• Both alleles of a gene are expressed.
• A person with AB blood has both A and B antigens
  on their red blood cells.
• Neither allele is dominant or recessive

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RED
WHITE
ROAN
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• Ex Red Coat - RR
• White Coat WW
• White Red Mixed RW (roan)

R R
R W
RW
RW
RW
R W
RR
W W
RW
RW
RW
WW
All Roan both red and white hair
1 red 2 roan 1 white
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Dihybrid Cross
 Feather color ORANGE or blue   CREST or no
crest
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• A cross involving two pairs of
• contrasting traits
• Example
• Dominant Recessive
• Yy, YY yellow yy green
• Rr, RR round rr wrinkled

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Example cont.

• P1 RRYY x rryy
• round, yellow wrinkled, green
• (homozygous) (homozygous)

RY
RY
ry
RrYy
RrYy
ry
RrYy
RrYy
Offspring are all heterozygous
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RrYy X RrYy

• Law of Independent Assortment
• Genes for different traits are inherited
  independently
• R, r, Y, y go to sperm/egg independently of each
  other
• Can recombine in four ways
• RY, Ry, rY, ry

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RY Ry rY ry
RY Ry rY ry
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.9 round,yellow 3 round, green 3 wrinkled,
yellow 93311 wrinkled
,green

Ry
rY
ry
RY
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy