Mendelian Genetics

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• An Austrian monk who worked with pea plants
• Provided the foundation for modern genetics
• Scientists understood that traits were inherited
  before they understood the mechanics of
  inheritance

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Traits

• Traits are distinguishing characteristics that
  are inherited.

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Genetics

• Genetics is the study of biological inheritance
  patterns and variations in organisms.

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• Mendel chose pea plants because they were quick
  to reproduce and he could control how they mated
  (model organisms)?
• What is a model organism?

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Purebred pea plants

• Known to have one trait or another, no in
  betweens!!

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Pea plant traits

• He chose 7 traits to follow due to their
  either-or characteristics there were no
  intermediate features
• Pea shape, pea color, pod shape, pod color, plant
  height, flower color, and flower position

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• In genetics, the mating of two organisms is
  called a cross
• The parents in a cross are called the P
  generation (parental generation)?
• The offspring of that generation are called the
  F1 (first filial generation)?
• When Mendel crossed purple flowered pea plants
  with white flowered pea plants, the F1 was all
  purple
• When 2 offspring from the F1 were crossed, the
  resulting plants were purple and white (75
  purple and 25 white)?
• 31 ratio

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• 3 main conclusions from his work
• (1) Demonstrated that traits are inherited as
  discrete units
• Explained why individual traits in the peas did
  not blend or dilute over successive generations

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Law of segregation

• (2 3) Collectively called the Law of
  Segregation
• Organisms inherit 2 copies of each gene.
• Where do those 2 copies come from?
• Organisms donate only one copy of each gene in
  their gametes.

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• A gene is a heritable factor that has a specific
  characteristic.
• Each gene has a specific locus, or location on a
  pair of homologs.

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Alleles

• Alleles are alternative forms of a gene
• Such as round or wrinkled peas, yellow or green
  peas, or purple or white flowers

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• 2 alleles for each gene
• Homozygous two of the same alleles
• Heterozygous two different alleles

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• Dominant allele the allele that is expressed
  usually represented by a capital letter
• The letter B represents brown eyes ? BB or Bb
• Homozygous dominant or heterozygous
• Recessive allele the allele that is only
  expressed if the dominant allele is absent
  usually represented by a lowercase letter
• The letter b represents blue eyes ? bb
• Homozygous recessive
• Are dominant alleles better or stronger than
  recessive alleles? Why or why not?

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• The genome is all of the genetic material in an
  organism
• In genetics, we often only focus on a single
  trait or a set of traits
• 1. Genotype
• 2. Phenotype

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GENOTYPE

• The genotype refers to the genetic makeup of a
  set of genes (what you don't see)?
• Genes that code for flower color, such as PP or Pp

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PHENOTYPE

• The phenotype refers to the physical
  characteristics/traits of the individual organism
  ( what you see)?
• Purple flowers

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• Because some alleles are dominant over others,
  two genotypes could produce the dominant
  phenotype
• Brown hair ? HH or Hh
• In order to express the recessive phenotype, the
  individual must also have the recessive genotype
• Blonde hair ? hh
• There are many factors that play a part in making
  one allele dominant over another

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• Punnett Square a grid system for predicting the
  possible genotypes that result from a cross
• Deals with probability
• The likelihood that a particular event will occur
• The alleles from the gametes of both parents are
  placed on the axes outside the grid while the
  possible genotypes of the offspring are inside
  the grid
• Because segregation and fertilization are random
  events, each combination of alleles is just as
  likely as the next

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• Crosses that examine the inheritance of only one
  specific trait
• Flower color in peas purple (P) is dominant to
  white (p)?
• Cross a purebred purple flower with a purebred
  white flower. Determine the genotypes
  phenotypes of the F1 offspring. What is
  purple? What is white?
• Cross 2 of the F1 offspring together. Determine
  the genotypes phenotypes of the F2 offspring.
  What is purple? What is white? What is the
  genotypic ratio? What is the phenotypic ratio?

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• Still using flower color
• From the F2, cross a heterozygous flower with a
  homozygous recessive flower. Determine the
  genotypes phenotypes of the F3 offspring. What
  is purple? What is white? What is the
  phenotypic ratio? What is the genotypic ratio?
• Testcross a cross between an organism of
  unknown genotype with an organism of the
  recessive genotype allows scientists to
  determine if the organism of unknown genotype is
  homozygous dominant or heterozygous

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• Crosses involving two different traits-what size
  will your grid be?
• One trait does not affect the presence of
  another known as the Law of Independent
  Assortment
• Basically says that allele pairs separate
  independently during meiosis and are, therefore,
  inherited separately
• Flower color and plant height in peas flower
  color is the same as before tall plants (T) are
  dominant to dwarf plants (t)?
• Cross 2 organisms that are heterozygous for both
  traits.

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FOIL

• TtPp x TtPp
• Do one parent at a time, and place all of the
  genotypes on one side of your 16 square box.
• First letter of each trait
• Outside letter of each trait
• Inside letter of each trait
• Last letter of each trait
• Now do the second parent in the same manner.
• What is the probability that the plants will be
  tall and purple?
• tall and white?
• Short and purple?
• Short and white?

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Practice Problems

• Dihybrid Cross blue eyes and blonde hair are
  recessive
• Bbhh X bbHh
• Probability of offspring with Blue eyes and
  blonde hair?
• Brown eyes and brown hair?

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Patterns of Inheritance

• BIOLOGY

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Mendels Principles

• Mendel came up with certain principles keep
  these in mind with these new patterns of
  inheritance
• Inheritance of biological characteristics is
  determined by genes which are passed from parents
  to offspring
• Some form of a gene may be dominant or recessive
• Each individual has 2 copies of a gene which will
  segregate during gametogenesis (Law of
  Segregation)
• Alleles for different genes segregate
  independently from one another (Law of
  Independent Assortment)

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Incomplete Dominance

• Cases that result in one allele not being
  completely dominant over another allele
• This means that the heterozygous phenotype is
  somewhere between the two homozygous phenotypes
• Blending of phenotypes
• Snapdragons exhibit incomplete dominance with
  flower color
• Red flowers are RR
• White flowers are WW
• When a RR snapdragon is crossed with a WW
  snapdragon, the offspring are RW
• Pink flowers are RW

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Codominance

• Codominance - Cases in which both alleles
  contribute to the phenotype of the organism
• Neither allele is dominant over the other
• So, both phenotypes are expressed
• RED x WHITE?RED AND WHITE

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Multiple alleles

• Multiple alleles Cases in which genes have more
  than 2 alleles that code for a trait
• More than 2 alleles exist in a population, NOT in
  the individual
• Human blood types (ABO) are codominant and have
  multiple alleles

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IAIA or IAi Type A IAIB Type AB IBIB or IBi
Type B ii Type O
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Practice Problem A homozygous type B woman
marries a heterozygous Type A man. Show the
punnett square, genotypes phenotypes
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Sex linked disorders
Sex-linked genes are carried on the sex
chromosomes Males- XY Females-XX Most traits are
on the X-chromosome, which means that the female
has to get two copies of the gene to show a
genetic disorder. Males only have to get one
copy of the bad gene. Some examples of sex
linked genes are baldness, colorblindness,
hemophilia, Duchenne Muscular Dystrophy
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Practice Problem
Cross a white-eyed female fruit fly and red-eyed
male (White eyes are X-linked, recessive)
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Red-green colorblindness
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Polygenic Traits

• Many traits are characterized by the interaction
  of several genes
• Human skin color is determined by the interaction
  of 6 separate genes
• Humans of the same race can have varying skin
  tones due to the interactions of the genes coding
  for skin color
• Human eye color is also determined by 3 separate
  genes
• Brown gt green gt blue
• Only determines the color of the eyes, not the
  varying in eyes of the same color (dark brown
  eyes vs. light brown eyes)

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Epistasis

• A type of polygenic trait
• Certain alleles code for a trait, but other
  alleles on different genes can affect whether or
  not a phenotype is expressed
• Albinism is epistatic
• One allele blocks the others in pigment
  production if it is expressed
• Color of the coat in Labrador retrievers is a
  result of epistasis
• Black coat color (B) is dominant to brown coat
  color (b)
• Yellow coat color (e) is the recessive epistatic
  gene meaning it will block out all other coat
  colors if it is present
• BBEE, BBEe, BbEE, BbEe black lab
• bbEE bbEe chocolate lab
• BBee, Bbee, bbee yellow lab

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Practice Problems

• Incomplete Dominance
• In northeast Kansas there is a creature known as
  a wildcat. It comes in three colors, blue, red,
  and purple. This trait is controlled by a single
  locus gene with incomplete dominance. A
  homozygous (BB) individual is blue, a homozygous
  (RR) individual is red, and a heterozygous (RB)
  individual is purple. What would be the genotypes
  and phenotypes of the offspring if a blue wildcat
  were crossed with a red one?

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Practice Problems

• Codominance
• A cross between a black cat and a tan cat
  produces a tabby cat (black and tan fur)
• What percentage of cats will have tan fur if a
  black cat is crossed with a tabby cat?
• What percentage will have tabby fur if two tabby
  cats are crossed?

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Practice Problems

• Blood Typing
• A male who has AB blood marries a female with
  Type A blood. Their child has type B blood. What
  is the moms genotype? Use a Punnett Square to
  explain your answer.
• A male has type B blood and a female has type AB,
  if their child has type A, what is the dads
  genotype?

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Practice Problems

• Sex-linked Traits
• A female with hemophilia mates with a normal
  male. Create a Punnett Square. What is the
  probability they will have a male with
  hemophilia? A female?
• A female carrier of hemophilia mates with a male
  with hemophilia. Create a Punnett Square. What is
  the probability they will have a male with
  hemophilia? A female?
• If a male is a hemophilic, which parent gave him
  the defective allele?