Patterns of Inheritance

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Patterns of Inheritance

• Chapter 10

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Genetics developed from curiosity about
inheritance

• Gregor Mendel
• Late 1800s
• Pea plants

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Genetics developed from curiosity about
inheritance

• Trait a variation of a particular character
• Genetics study of heredity
• Self-fertilization fertilization of an ovum of
  a plant by a male gamete from the same flower
• True breeding
• Cross-fertilization sperm from the pollen of
  one flower fertilizes the eggs in the flower of a
  different plant

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Mendel discovered that inheritance follows rules
of chance

• Hybrids the offspring of two different
  true-breeding varieties
• P generation P for parent
• F1 generation F for filial (Latin for son)
• F2 generation offspring of the F1
  generationgrandchildren
• Monohybrid cross a pairing in which the parent
  plants differ in only one (mono) character
• Mendel crossed purple-flowered pea plants with
  white-flowered pea plants

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Mendel discovered that inheritance follows rules
of chance
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Mendel discovered that inheritance follows rules
of chance

• Mendel not only used flower color, he also used
  flower position, seed color, seed shape, pod
  shape, pod color, and stem length
• He used monohybrid crosses to study the heredity
  of these traits

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Mendel discovered that inheritance follows rules
of chance

• Mendels 4 hypotheses
• There are other forms of genes.
• Such as the gene for flower color
• One form for purple flowers
• Another for white flowers
• Alternative forms of genes are called alleles
• For each inherited trait, an organism has two
  alleles for the gene controlling that traitone
  from mom and one from dad.
• Heterozygous two alleles for a trait are
  different
• Homozygous two alleles for a trait are the same

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Mendel discovered that inheritance follows rules
of chance

• 3. When only one of the two different alleles
  appears to affect the trait, that allele is
  called the dominant allele. The other allele
  that does not appear is called the recessive
  allele.
• Flower color- Purple
• P dominant
• p recessive
• 4. The two alleles for a trait separate during
  the formation of gametes (remembermeiosis!).
  Each gamete has only one allele for each trait.
  The union of sex cells, during fertilization,
  reunites the alleles to form pairs again.

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Mendel discovered that inheritance follows rules
of chance

• You can calculate the probabilities for different
  combinations of alleles resulting from a genetic
  cross
• Punnett square a diagram that shows all
  possible outcomes of a genetic cross

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Mrs. Bs QUICK QUIZ

• The father of genetics is
• Friar Tuck
• Gregor Mendel
• Anton van Leeuwenhoek
• Bill Nye
• Gregor Mendel

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• 2. _____________ is the fertilization of an ovum
  of a plant by a male gamete from the same flower.
• True breeding
• Cross fertilization
• Self fertilization
• Genetics
• Self fertilization

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• 3. A hybrids is the offspring of one true
  breeding plant.
• True
• False
• False
• Hybrids the offspring of two different
  true-breeding varieties

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Mendel discovered that inheritance follows rules
of chance

• The genetic makeup , or combination of alleles is
  called the genotype
• The genotypic ratio is 1PP2Pp1pp
• The observable trait is called the phenotype
  (purple flowers)
• The 31 ratio is called a phenotypic ratio

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Mendel discovered that inheritance follows rules
of chance

• Testcross breeds an individual of unknown
  genotype, but dominant phenotype with a
  homozygous recessive individual
• The appearance of the phenotype of the offspring
  will reveal the mystery plant

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Mendel discovered that inheritance follows rules
of chance

• Dihybrid cross crossing individuals that differ
  in two characters
• Mendel used this when studying peas with
• different colors (yellow dominant)
• different shapes (round dominant)
• RRYY
• RrYy
• Rryy
• A punnett square can be used in the same way

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Mendel discovered that inheritance follows rules
of chance

• Mendel used dihydrid crosses to study all seven
  characteristics of pea plants
• Proposed his principle of independent assortment,
  which states that during gamete formation in an
  F2 cross, a particular allele for one character
  can pair up with a particular allele of another
  character
• R can end up with Y or y
• r can end up with Y or y
• The alleles are sorted into gametes independently
  of one another

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There are many variations of inheritance patterns

• For some characters of organisms, neither allele
  is dominant
• The heterozygotes have a phenotype that is
  intermediate between the phenotypes to the two
  parents
• This is called incomplete dominance
• Ex Andalusian chickens
• A heterozygote chickenCBCW
• This is NOT blending, because the parent
  phenotypes can reappear in the F2 generation

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There are many variations of inheritance patterns

• Many genes have multiple alleles, instead of just
  two
• Ex human blood type
• A, B, AB, O
• IA and IB display codominance, meaning that a
  heterozygote expresses both traits
• This is NOT intermediate, due to the fact that
  the phenotype shows the separate traits of both
  alleles

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There are many variations of inheritance patterns

• When multiple genes affect a character, the
  variation in phenotypes can increase
• When two or more genes affect a single character,
  it is called polygenic inheritance
• ex height in humans
• 3 tall alleles A, B, C
• 3 short alleles X, Y, Z
• Intermediate inheritance
• AABBCC very tall
• AZBBCC slightly shorter, etc.
• Some characters are affected by dozens of genes,
  which lead to numerous combinations of alleles

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There are many variations of inheritance patterns

• An individuals phenotype depends on environment
  as well as on genes
• Ex tree
• Temperature
• The product of a genotype is generally a range of
  possibilities influenced by the environment

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Meiosis explains Mendels principles

• Chromosome theory of inheritance genes are
  located on chromosomes, and the behavior of
  chromosomes during meiosis and fertilization
  accounts for inheritance

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Meiosis explains Mendels principles

• Gene locus
• When genes are located on separate chromosomes,
  they sort independently of each other during
  meiosis
• Crossing over allows genes on the same chromosome
  to sort independently
• The tendency for alleles on one chromosome to be
  inherited together is called genetic linkagethe
  closer the 2 genes are on a chromosome, the
  greater the genetic linkagethe farther apart
  they are, the more likely a cross over will occur

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Sex-linked traits have unique inheritance patterns

• Eggs contain what kind of chromosome?
• X
• Sperm contain what kind of chromosome?
• Half have X and half have Y
• An offsprings sex is determined by whether or
  not the sperm cell carries an X or a Y
• Any gene that is located on a sex chromosome is
  called a sex-linked gene
• In humans, most are on the X chromosome

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Sex-linked traits have unique inheritance patterns

• Thomas Morgan
• Fruit flies
• Sex-linked disorders
• Red-green colorblindness
• X-linked recessive
• Recessive sex-linked traits are
• much more common in men than
• in women
  
  

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Pedigrees

• Family tree that records and traces the
  occurrence of a trait in a family
• Circles females
• Squares males
• Horizontal lines connecting a square to a circle
  means the couple had children

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Pedigrees

• If shape has two colors the person in a carrier