Gregor Mendel The Wonder Monk

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Gregor MendelThe Wonder Monk
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Gregor Mendel

• Father of genetics

• studied characteristics of peas
• Normally peas self pollinate male pollen
  fertilizes females egg of same flower
• He cross-pollinated seeds 2 different flowers

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Mendel

• Mendel experimented with pea plants that
  reproduce sexually through pollination
• self-pollination
• cross-pollination

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Genetics - Study of heredity

• Heredity - passing characteristics from parent to
  offspring
• Fertilization-male and female gametes combine to
  form new offspring (children)
• Pollination (in plants) pollen grains fertilize
  female gamete
• Self-pollination
• Cross-pollination

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Genetics Terms

• purebred
• same characteristic from generation to generation
  (ex. Purebred dogs horses)
• hybrid
• crossing parents with different characteristics
  (mut)

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Genes

• Factors (or piece of DNA) that determine a
  characteristic

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Trait

• Characteristic
• Ex eye color, hair color, height, etc

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Alleles

• Different forms of a gene
• Ex blue, brown, green eye color
• Ex tall or short alleles for height
• Organisms have 2 alleles for each gene
• (1 on each chromosome from each parent!)
• Let T tall and t short since same gene
  (only 2 alleles) lets use the same letter

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Genetics Terms

• homozygous
• 2 of the same alleles for a trait
• T tall (TT)
• t dwarf (tt)
• heterozygous
• 2 different alleles for a trait
• Tt

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Dominant

• Trait observed even if another allele is present
  ex TT and Tt both appear tall
• Homozygous dominant or heterozygous
• Capital letter
• Usually more common but not always

Recessive

• NOT seen if other versions are present
• Only expressed if homozygous recessive tt
• designated with a lower case letter

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Genetics Terms

• Phenotype
• Physical, visible characteristics
• Genotype
• Genetic makeup of an organism (capital and
  lowercase letters)

Phenotype Tall Genotype TT
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Questions

• Is TT homozygous or heterozygous?
• What is the phenotype?
• What would the heterozygous genotype be?
• What would be the phenotype for a plant that has
  a heterozygous genotype?
• Can you have a heterozygous recessive?

Tall dominant TT or Tt dwarf recessive tt
ONLY there can never be heterozygous recessive!
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Genetics Terms

• Parental generation
• P1
• parents
• First filial generation
• F1
• Offspring
• Monohybrid cross
• mating between individuals looking at 1 trait

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Product Rule of Probability

• Probability of 2 events happening simultaneously
  the product of the probabilities of the 2
  happening separately
• Ex. Flipping a coin ( ½ heads, ½ tails), rolling
  a die ( 1/6 rolling a 1,2,3,4,5,6)

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Punnett Squares
P generation

• List allele combinations for female on top and
  for male on the side

• Fill in (combine) to get all genotype
  combinations possible for the offspring

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How To Set Up a Punnett Square
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How To Set Up a Punnett Square
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Mendels Findings

• 2 factors controlling each trait
• 1. a dominant (A) and a recessive (a) form
• 2. the presence of the dominant masked the
  recessive
• 3. each of these forms is called an allele
• Law of segregation- a pair of factors separates
  during the formation of gametes (meiosis)
• Law of independent assortment- factors for
  different traits are distributed independently
  from one another (Ex. not all tall people have
  brown eyes and not all short people have blue
  eyes)

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Monohybrid (1 trait) Cross
AA X AA
A
A
AA
AA
A
A
AA
AA
Genotypic ratio all AA
Phenotypic ratio all red
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AA X Aa
A
A
AA
AA
A
a
Aa
Aa
Genotypic ratio 1AA1Aa
Phenotypic ratio all red
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AA X aa
A
A
Aa
Aa
a
a
Aa
Aa
Genotypic ratio all Aa
Phenotypic ratio all red
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Aa X Aa
A
a
AA
Aa
A
a
aa
Aa
aa
Genotypic ratio 1 AA2Aa1aa
Phenotypic ratio 3 red1 white
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Aa X aa
A
a
Aa
aa
Aa
a
Aa
a
aa
Aa
Genotypic ratio 1 Aa1 aa
Phenotypic ratio 1 red 1white
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aa X aa
a
a
aa
aa
a
a
aa
aa
Genotypic ratio all aa
Phenotypic ratio all white
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Dihybrid Cross

• dihybrid cross
• between individuals with 2 pairs of traits

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Dihybrid Cross Rules

• First figure out what the gametes are that the
  parents can make. Use the FOIL (first, outer,
  inner, last) method to do this.
• Parents AaBb X AaBb
• Gametes AB, Ab, aB, ab X AB, Ab, aB, ab
• Then place the gametes along the top and sides of
  the square and do the cross.

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Dihybrid cross
X
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TtRr X TtRr
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Test Cross

• Used to determine an unknown genotype by crossing
  the unknown with a homozygous recessive
• genotypic ratios of the offspring will tell what
  the unknowns genotype was

Recessive rabbit
Unknown rabbit
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Complete Dominance vs. Incomplete Dominance

• Most traits display complete dominance
• the presence of 1 dominant allele masks the
  recessive allele (all examples thus far)
• Some traits display incomplete dominance
• the heterozygous condition results in a separate
  phenotype, neither allele is completely
  dominant-the traits blend together
• Ex.In some flowers, AA is red, Aa is pink, and aa
  is white

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Codominance

• Some traits are controlled by codominance
• both alleles for a gene are expressed in
  heterozygous offspring
• neither allele is dominant or recessive, nor do
  they blend each is expressed equally
• Ex. horses coat color heterozygous roan color
  where they have both white and red hairs
• AB blood type is another example

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Polygenic Traits

• More than 1 gene determines a trait
• Ex. skin color in humans and height

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Sex Determination

• During embryonic development, the genes on the X
  chromosome turn on first and all sex parts
  begin development as a female
• At some point in men, the X turns off and the Y
  turns on ? the sex parts develop as a male
• Problems in this process can create
  hermaphrodites (persons with both sex parts).
• There are many mutations that arise from the
  segregation of sex chromosomes into gametes
• Klinefelters syndrome (XXY or XXXY) sterile
  male, 47-48 chromosomes
• Turners syndrome (X0) sterile female, 45
  chromosomes
• Triplo X/ Meta-female (XXX) sterile female, 47
  chromosomes

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Sex-Linked Genes

• The presence of a gene on a sex chromosome makes
  the gene sex-linked
• The X chromosome is much larger than the Y, so in
  men there is a difference in the number of genes
  carried on the sex chromosomes.
• There are many disorders that are carried on the
  X chromosome
• if the mother is recessive for these traits she
  can pass the disorder to her son b/c his only X
  is from the mother? that allele is expressed
• there is no corresponding gene on the Y to cover
  the recessive X allele.
• Some of these disorders are muscular dystrophy,
  colorblindness, hemophilia, and baldness

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Sex Chromosomes
XN
Xn
Xn
Site of the gene for colorblindness
No corresponding site on the Y
Y
Colorblind Man-XnY
Non Colorblind Woman-XNXn
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Sex Influenced Traits

• Traits expressed differently in males and females
• Example baldness

BB Bb bb
male
bald bald not bald
bald not bald not bald
female
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Pedigrees

• Females are circles, males are squares
• The recessive trait is shaded, the dominant trait
  is white
• A horizontal line b/w 2 individuals marriage
• A vertical line bracket offspring
• Roman numerals generation

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Rules for Pedigrees

• Label all recessive (shaded) individuals (Ex. aa)
• Label all dominant (non-shaded) individuals (Ex.
  A_)
• Begin at the bottom with the 1st recessive
  individual and work backwards to determine
  whether dominant individuals are AA or Aa
• Note You may not be able to tell if some
  dominant individuals are homozygous or
  heterozygous until they have more kids!

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Rules for Sex-Linked Pedigrees

• Label all females X X and all males X Y
• Fill in all recessive individuals using a
  lowercase superscript (Ex. XnY or XnXn)
• Fill in all dominant individuals using a capital
  superscript (Ex. XNY or XNX-)
• Y will never have an allele (superscript)
• Start with recessive individuals at the bottom
  and work backwards to determine the genotypes of
  the dominant individuals