Introduction to Genetics

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Introduction to Genetics

• Chapter 11

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• How can two brown rabbits have a white offspring?

• If two white rabbits mated what color would their
  offspring be?

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Gregor Mendel

• The work of Gregor Mendel
• Austrian monk who is the father of Genetics
• Genetics the scientific study of heredity

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http//learn.genetics.utah.edu/content/begin/trait
s/
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Gregor Mendel

• Fertilization when male and female reproductive
  cells join
• Male pollen or sperm
• Female eggs
• Gamete the individual egg or sperm
• Seed fertilized egg or new cell (zygote)

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Gregor Mendel

• True-breeding if they were allowed to
  self-breed they would have identical offspring.
• Experiment
• Cross-pollination
• Mendel took sperm from one plant and fertilized
  eggs from other plants

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Gregor Mendel

• Genes and Dominance
• Traits a specific characteristic (ex. Brown
  hair)
• Seed color
• Plant height
• Parental generation (P) Original pair of
  plants
• Filial generation (F1) offspring, progeny
• Hybrids offspring of crosses between parents
  with different traits

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Gregor Mendel

• Genes chemical factors that determine traits
  (Hair color)
• Alleles different forms of traits (Brown vs.
  blond hair, brown vs. blue eyes)

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Gregor Mendel 2 Principles

• Principle of Inheritance factors are passed
  from one generation to the next.
• Principle of Dominance some alleles are
  dominant and other are recessive
• Dominant traits will always show over recessive
  traits

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Gregor Mendel

• Segregation
• F1 generation self-pollinated
• F1 X F1 F2
• F1 Cross
• ¼ of the F2 plants now show the recessive traits

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Gregor Mendel

• Explaining the F1 Cross
• When each F1 plant flowers and produces gametes,
  the two alleles segregate from each other so that
  each gamete carries only a single copy of each
  gene.
• Therefore, each F1 plant produces two types of
  gametesthose with the allele for tallness and
  those with the allele for shortness.
• Segregation -separation of alleles during gamete
  formation

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Probability and Punnett Square

• Probability and Punnett Square
• Probability in Genetics
• Probability the likelihood that a particular
  event will occur
• Coin flip
• ½ or 50
• Chance that youll end up with heads 3 times in
  a row.
• ½ X ½ X ½ 1/8
• Past outcomes do not affect future ones

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Probability and Punnett Square

• Punnett Square
• A diagram showing the gene combinations that
  might result from a genetic cross
• Letters represent each allele
• Top and left letters are the parents genes
• The four boxes show each possible gene combination

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Probability and Punnett Square

• Homozygous-- two identical alleles for a
  particular trait.

• Heterozygous two different alleles for a
  particular trait

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Probability and Punnett Square

• GG, Gg, gg are all of the possible combinations
  of genes
• GG means homozygous dominant
• gg means homozygous recessive
• Gg means heterozygous

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Probability and Punnett Square

• Phenotype
• Physical characteristics
• Tall or short
• Rolling the tongue
• Genotype
• Genetic makeup
• DD, Dd, or dd

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Probability and Punnett Square

• Probability and segregation
• Each parent only donates one of their two alleles
  to each offspring

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Probability and Punnett Square

• Probabilities predict averages, not exact
  outcomes
• Probability is more accurate when you have more
  chances

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REVIEW

• What is a gamete?
• Sperm or egg cell
• What is a zygote?
• Fertilized egg cell
• What is the genotype?
• Genetic make-up
• What is the phenotype?
• Trait that shows
• What is heterozygous?
• 2 different alleles
• What is homozygous?
• 2 identical alleles

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11-3 Exploring Mendelian Genetics

• Two-factor cross F1
• Crossing true-breeding organisms does not answer
  this question
• They do produce hybrid offspring used for the
  next test
• RrYy

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Exploring Mendelian Genetics

• Two-factor cross F2
• 9331 ratio

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Exploring Mendelian Genetics

• Exploring Mendelian Genetics
• Independent assortment
• States that genes for different traits can
  segregate independently during the formation of
  gametes.
• Accounts for the many genetic variations observed
  in plants, animals, and other organisms.

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Exploring Mendelian Genetics

• Mendels Principles
• The inheritance of biological characteristics is
  determined by individual units known as genes.
  Genes are passed from parents to their offspring.
• In cases in which two or more forms (alleles) of
  the gene for a single trait exist, some forms of
  the gene may be dominant and others may be
  recessive.
• In most sexually reproducing organisms, each
  adult has two copies of each geneone from each
  parent. These genes are segregated from each
  other when gametes are formed.
• The alleles for different genes usually segregate
  independently of one another.

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Exploring Mendelian Genetics

• Beyond dominant and recessive alleles
• Incomplete dominance alleles are not completely
  dominant

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Exploring Mendelian Genetics

• Codominance both alleles contribute to the
  phenotype

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Exploring Mendelian Genetics

• Multiple allele more than two alleles
• Polygenic trait
• Two or more genes control one allele

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Exploring Mendelian Genetics

• Mendels Principles
• Apply to animals as well as plants
• More importantly to humans

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Exploring Mendelian Genetics

• Genetics and the Environment
• Environment affects how genes are displayed

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11-4 Meiosis

• Meiosis
• Chromosome number
• Human
• Body cell 46 Chromosomes
• 23 from mom
• 23 from dad

• Homologous the 2 sets of 23 chromosomes.

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11-4 Meiosis

• Diploid cell that has both sets of homologous
  chromosomes
• 2N
• Body cells
• Haploid cells that have just one set of
  chromosomes
• 1 N
• Sex cells

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11-4 Meiosis

• Phases of meiosis
• A process of reduction and division in which the
  number or chromosomes per cell is cut in half
  through the separation of homologous chromosome
  in a diploid cell

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11-4 Meiosis

• Meiosis I
• Each chromosome lines up with its corresponding
  homologous chromosome making a tetrad
• They exchange genetic information called
  crossing-over
• Homologous chromosomes separate and form two new
  cells with different chromosome and alleles

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11-4 Meiosis

• Meiosis II
• Two new cells divide
• Neither cell makes a copy of the chromosomes
• All four new cells have one set of chromosomes

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11-4 Meiosis

• Gamete formation
• Haploid cells
• Sperm or pollen
• Eggs

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11-4 Meiosis

• Mitosis vs. Meiosis
• Mitosis results in two genetically identical
  diploid cells
• Meiosis results in four genetically different
  haploid cells

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11-5 Linkage and Gene Maps

• Gene linkage
• Chromosomes assort independently, not individual
  genes

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11-5 Linkage and Gene Maps

• Gene maps
• Shows the exact location of each known gene on
  one chromosome