Fundamentals of Genetics

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Fundamentals of Genetics

• Genetics field of biology devoted to
  understanding how characteristics are transmitted
  from parents to offspring

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Father of GeneticsGregor MendelAustrian Monk

• Heredity transmission of characteristics from
  parents to offspring
• Garden Peas

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Characteristic Traits

1. Plant Height Tall Short
2. Flower position Axial Terminal
3. Pod appearance Inflated Constricted
4. Seed Texture Smooth Wrinkled
5. Seed Color Yellow Green
6. Flower Color Purple White
7. Pod Color Green Yellow

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Mendels Methods

• Pollination pollen produced in the male
  reproductive parts of the flower (anther) are
  transferred to the female reproductive part of a
  flower (stigma)
• Self-pollination pollen is transferred from an
  anther to a stigma on the same plant
• Cross-pollination involves flowers of two
  separate plants

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Mendels Experiments

• He allowed plants to self-pollinate for several
  generations to obtain 14 pure strains Parental
  Generation (P1)
• Pure - always produce offspring with that trait
• Strain - plants that are pure for a trait
• Cross-pollinated these strains
• one pure for one trait with another pure for the
  contrasting trait
• P1 (tall) X P1 (short) ? First Filial
  Generation (F1)
• Then allowed F1 to self pollinate ? second filial
  generation (F2)

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Mendels Results

• Only one of the two traits in P1 appeared in the
  offspring F1
• The trait then reappeared in F2 in a ratio of 31

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Mendels Conclusions

• Factor something is controlling the traits
• Allele
• Pair of factors controls each trait
• Gene
• Recessive Dominant Traits
• - Dominant Allele masked the other factor
  (appeared in F1)
• - Recessive Allele is masked by the presence
  of another (reappeared in F2)

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Chromosomes and Genes

• Molecular genetics study of the structure and
  function of chromosomes and genes
• Gene segment of DNA on a chromosome that
  controls a particular hereditary trait
• Letters are used to represent alleles of genes
• - capital letters refer to dominant alleles
• T tall
• - lowercase letters refer to recessive alleles
• t short
• Genome - All of an organisms genetic material

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6.4 Traits, Genes, and Alleles

• Genotype genetic makeup of an organism
• TT Tt tt
• Phenotype appearance of an organism as a result
  of its genotype
• Tall or short
• Homozygous both alleles of a pair are alike
• TT or tt
• Heterozygous two alleles in the pair are
  different
• Tt

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6.5 Traits and Probability

• The axes representthe gametes of each parent.
• The boxes show thepossible genotypesof the
  offspring.

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6.5 Traits and Probability

• Genotypic ratio ratio of the genotypes that
  appear in offspring
• 1TT2Tt1tt
• Phenotypic ratio ratio of the offspring's
  phenotypes
• 3 Tall1 short

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A monohybrid cross involves one trait (12 points)

6.5 Traits and Probability
Homozygous Dominant X Homozygous Recessive
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6.5 Traits and Probability
Heterozygous X Heterozygous
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How Mendel's pea plants helped us understand
genetics
6.5 Traits and Probability

• http//ed.ted.com/lessons/how-mendel-s-pea-plants-
  helped-us-understand-genetics-hortensia-jimenez-di
  az

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Testcross
6.5 Traits and Probability

• Determine the genotype of an individual whose
  Phenotype is dominant
• TT or Tt (?)
• Individual of unknown genotype is crossed with a
  homozygous recessive individual
• T? X tt

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Testcross (12 points) Offspring 100 Dom
6.5 Traits and Probability
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7.2 Complex Patterns of Inheritance

• Complete Dominance one allele completely
  dominant over the other
• Incomplete dominance two or more alleles
  influence the phenotype
• results in a phenotype in between the dominant
  and recessive
• R red W white
• RW ? pink

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Incomplete DominanceHomozygous (1st trait)
X Homozygous (2nd trait)
7.2 Complex Patterns of Inheritance
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7.2 Complex Patterns of Inheritance

• Codominance both alleles for a gene are
  expressed in a heterozygous offspring
• neither is dominant or recessive
• R Red W White
• RW ? red white polka dots

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CodominanceHeterozygous X Heterozygous
7.2 Complex Patterns of Inheritance
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Multiple Alleles 3 or more alleles of the same
gene
7.2 Complex Patterns of Inheritance

• IA or
• IB or
• i
• Blood Types
• IAIA or IAi Blood type A
• IBIB or IBi Blood type B
• IAIB Blood type AB
• ii Blood type O

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Blood Type AB X Blood Type O
7.2 Complex Patterns of Inheritance
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Sex-linked Inheritance
7.1 Chromosomes and Phenotype

• Traits controlled by genes located on the sex
  chromosomes (X or Y)
• X-linked traits found on X chromosome
• Y-linked traits found on Y chromosome
• X-linked traits more common in males
• Y-linked traits only in males

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X-LinkedHeterozygous Female X Male with
recessive trait
7.1 Chromosomes and Phenotype
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Y-LinkedFemale X Male with Dominant trait
7.1 Chromosomes and Phenotype
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7.1 Chromosomes and Phenotype

• Female mammals have an XX genotype

• X-inactivation one X chromosome is randomly
  turned off in every cell
• Ex calico cats

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Sex-Influenced traits affected by how much sex
hormones are present
7.1 Chromosomes and Phenotype
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A dihybrid cross involves two traits (12 points)

6.5 Traits and Probability

• Homozygous Recessive/Heterozygous X
• Homozygous Dominant for both

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Heredity patterns can be calculated with
probability.
6.5 Traits and Probability

• Probability is the likelihood that something will
  happen
• Predicts an average number of occurrences, not an
  exact number of occurrences.

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Laws

• Law of Segregation a pair of factors is
  separated during the formation of gametes
• 1 trait Tall from short
• Law of Independent Assortment factors for
  different characteristics are distributed to
  gametes independently
• All characteristics being separated from each
  other
• Ex Tall plant from yellow peas

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7.1 Chromosomes and Phenotype

• Autosomal genetic disorders

• Carrier - A heterozygote for a recessive disorder
  
• Disorders caused by dominant alleles are uncommon.

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Epigenetics study of changes in gene activity
which are not caused by changes in the DNA

•  The changes in gene expression or
   phenotype have other causes
• Ex environment, other genes, etc

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7.2 Complex Patterns of Inheritance

• Genes can interfere with other genes
• Epistatic genes

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Phenotype is a combination of genotype and
environment.
7.2 Complex Patterns of Inheritance

• EX The sex of sea turtles depends on both
  genes and the environment

• EX Height is another example of a phenotype
  strongly affected by the environment.

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Polygenic Inheritance

• Traits controlled by many genes
• 250 genes have been described to control human
  height ? up to 700

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Trihybrid Cross

• Hetero/Homo Rec/Homo Dom X
• Homo Rec/Hetero/Homo Dom