Biology I - GENETICS

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Biology I - GENETICS

• 1-12 Novak

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Gregor Mendel 1822-1884
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MENDELS PRINCIPLES
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I. ALLELES

• Any organism has two units of heredity (genes)
  for each trait in every body cell

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II. SEGREGATION

• The two units (genes) for a trait are separated
  in the cell one gene is found on a chromosome
  while the other is located in the same place on
  its partner (homologous) chromosome

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III. DOMINANCE

• A. When two genes of a trait are different
  in the cells of the organism, the gene that
  shows up is the dominant while the gene that
  remains hidden is the recessive
• B. Combinations of the two genes
  (genotypes)
• 1. Homozygous (pure) dominant - both genes
  are dominant
• 2. Homozygous (pure) recessive - both genes
  are recessive
• 3. Heterozygous (hybrid) - one gene is dominant
  the other is recessive

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IV. RECOMBINATION - (INDEPENDENT ASSORTMENT)

• In each new generation there is a complete new
  rearrangement of the units of heredity (genes)

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Following the Generations
Cross 2 Pure PlantsTT x tt
Results in all HybridsTt
Cross 2 Hybridsget3 Tall 1 ShortTT, Tt, tt
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Generation Gap

• Parental P1 Generation the parental generation
  in a breeding experiment.
• F1 generation the first-generation offspring in
  a breeding experiment. (1st filial generation)
• From breeding individuals from the P1 generation
• F2 generation the second-generation offspring
  in a breeding experiment. (2nd filial
  generation)
• From breeding individuals from the F1 generation

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Mendels Experimental Results
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Thomas Hunt Morgan 1866-1945
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Incomplete Dominance (blending inheritance)
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• INCOMPLETE DOMINANCE
• A condition in which both alleles for a
  characteristic are partially expressed

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Incomplete Dominance

• F1 hybrids have an appearance somewhat in between
  or a blend of the phenotypes of the two parental
  varieties.
• Example snapdragons (flower)
• red (RR) x white (WW)
• R red flower
• W white flower

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Incomplete Dominance
W
W
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Incomplete Dominance
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• CODOMINANCE
• A condition in which both alleles for a
  characteristic are fully expressed

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Codominant white and pink
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Codominant white and pink
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Homozygous Red
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Hereford Red
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Homozygous white
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Roan hybrid
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Roan hybrid
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Codominant cross
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DIHYBRID INHERITANCE
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Pea Plants
Seed Color
Height
Tall TT, Tt Short tt
Yellow YY, Yy Green yy
Lets cross a homozygous tall (TT), homozygous
yellow seed (YY) plant with a short (tt), green
seed (yy) plant.
TTYY x ttyy
These are the genotypes of the two plants.
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Independent Assortment
Mendels principle of Independent Assortment
states that genes for different traits can
segregate independently during the formation of
gametes (eggs sperm in animals, eggs and pollen
in plants).
TTYY
First T
with first Y
T
Y
Gamete 1 sperm, egg, pollen . . .
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Independent Assortment
Mendels principle of Independent Assortment
states that genes for different traits can
segregate independently during the formation of
gametes (eggs sperm in animals, eggs and pollen
in plants).
TTYY
First T
with second Y
TY
T
Y
Gamete 2
Gamete 1
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Independent Assortment
Mendels principle of Independent Assortment
states that genes for different traits can
segregate independently during the formation of
gametes (eggs sperm in animals, eggs and pollen
in plants).
TTYY
Second T
with first Y
TY
TY
T
Y
Gamete 2
Gamete 3
Gamete 1
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Independent Assortment
Mendels principle of Independent Assortment
states that genes for different traits can
segregate independently during the formation of
gametes (eggs sperm in animals, eggs and pollen
in plants).
TTYY
Second T
with second Y
TY
TY
TY
Y
T
Gamete 2
Gamete 3
Gamete 4
Gamete 1
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Dihybrid Punnett Square - F1
P1 TTYY
TY TY TY TY
ty
ty
ty
ty
Will be F1 Generation
P2 ttyy
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Dihybrid Punnett Square - F1
TY TY TY TY
ty TTYy
ty TTYy
ty TTYy
ty TTYy
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Dihybrid Punnett Square - F1
TY TY TY TY
ty TtYy TtYy TtYy TtYy
ty TTYY TtYY TtYY TTYY
ty TTYY TTYY TTYY TTYY
ty TTYY TTYY TTYY TTYY
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Dihybrid Punnett Square - F1
TY TY TY TY
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
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Dihybrid Punnett Square - F1
TY TY TY TY
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
Genotype ratio TtYy - 16/16
Phenotype ratio Tall, Yellow - 16/16
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Dihybrid Punnett Square F2We need to pair up
the genes which can be given to each gamete (egg
and pollen).Lets cross two of the plants from
the F1 generation
We need to pair up the genes
TY TY TY TY
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
.
x
T
Y
T
y
t
Y
y
t
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Dihybrid Punnett Square F2
TY Ty tY ty
TY
Ty
tY
ty
Both the plants can give the same gene
combinations to their gametes, so the pairs along
the top and down the side are the same.
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Dihybrid Punnett Square F2
When you pair up the gametes from the two plants,
always put like letters together and within the
like letters, put the CAPITAL letter in front of
the lowercase letter.
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Dihybrid Punnett Square F2
TY Ty tY ty
TY TTYY TTYy TtYY TtYy
Ty ???? ???? ???? ????
tY ???? ???? ???? ????
ty ???? ???? ???? ????
Your Turn!!
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Dihybrid Punnett Square F2
TY Ty tY ty
TY TTYY TTYy TtYY TtYy
Ty TTYy TTyy TtYy Ttyy
tY TtYY TtYy ttYY ttYy
ty TtYy Ttyy ttYy ttyy
F2 generation
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Dihybrid Punnett Square F2
Genotype and phenotype ratios?
TY Ty tY ty
TY TTYY TTYy TtYY TtYy
Ty TTYy TTyy TtYy Ttyy
tY TtYY TtYy ttYY ttYy
ty TtYy Ttyy ttYy ttyy
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F2 Genotype Ratio
TTYY - 1 TTYy - 2 TtYY - 2 TtYy - 4 TTyy - 1 Ttyy
- 2 ttYY - 1 ttYy - 2 ttyy - 1
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F2 Phenotype Ratio
TTYY - 1 TTYy - 2 TtYY - 2 TtYy - 4 TTyy - 1 Ttyy
- 2 ttYY - 1 ttYy - 2 ttyy - 1
Tall, Yellow - 9
Tall, Green - 3
Short, Yellow - 3
Short, Green - 1
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Another Mendelian Dihybrid Problem
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Dihybrid F2 Results
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Dihybrid F2 Results
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Sex-Linked Inheritance
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Color Blindness
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normal - trichromatic color vision protanopia
red-green blindness (no red cones) deutanopia
red-green blindness (no green cones) tritanopia
blue-yellow blindness (no blue cones) typical
achromatopsia (no cones rod monochromat)
protanomaly (anomalous red cones) deutanomaly
(anomalous green cones) tritanomaly (anomalous
blue cones) atypical achromatopsia (low cones
cone monochromat)

• TYPES OF COLOR BLINDNESS

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Red Green Color BlindnessMale1.01Female0.02
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Sex-linked Traits

• Traits (genes) located on the sex chromosomes
• Sex chromosomes are X and Y
• XX genotype for females
• XY genotype for males
• Many sex-linked traits carried on X chromosome

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Hemophilia
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Female Carriers
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The effects of hemophilia
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Human Blood Coagulation Cascade
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• The End

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