Chapter 11: Introduction to Genetics

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Chapter 11Introduction to Genetics

• By Riley Thomas

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11-1 The Work of Gregor Mendel

• Genetics is the scientific study of heredity.
  Genetics, explain every living thing and how it
  has a set of characteristics inherited from its
  parent or parents.

Gregor Mendel, the Father of Genetics
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• Gregor Mendel was very important, because he
  understood biological inheritance.
• Mendel was a so own as the "Father of Genetics "
  He was born in 1822 in what is now the Czech
  Republic. Mendel was a teacher and also took
  charge of the garden duties at the monastery.
  Mendel worked with garden peas.

Pea plants use part of their flowers to
reproduce. The male part produces pollen pollen
is the male sex cell. The female part produces
eggs, which are the female sex cell
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• When Mendel took the part as monastery gardener,
  he had several stocks of pea plants. These peas
  were true breeding. True breeding is a term used
  to describe organisms that produce offspring
  identical to themselves if allowed to
  self-pollinate.
• The true-breeding plants were the basis of
  Mendel's experiment.

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• However, pea plants can also cross-pollinate. In
  cross-pollination, male sex cells in pollen from
  the flower on one plant fertilize the egg cells
  of a flower on another plant. The seeds produced
  from cross-pollination have two plants as
  parents.

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• To perform his experiment, Mendel had to select
  the pea plants that he would mate with each
  other.
• He had to prevent the pea flowers from
  self-pollinating and control their
  cross-pollination.
• Mendel accomplished this task by cutting away the
  male parts of a flower and then dusting the
  flower with pollen from a second flower.

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• Mendel studied seven different pea plants traits.
• A trait is a specific characteristic.
• Mendel studied crossed plants with each of the
  seven contrasting characters and studied their
  offspring.
• Mendel called each original pair of plants the
  P(parental) generation. He called the offspring
  the F1, or first filial' generation.
• The offspring of crosses between parents with
  different traits are called hybrids.

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• Below is a chart of the different crosses Mendel
  did.

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• From his first experiments Mendel drew two
  conclusions
• 1. Biological inheritance is determined by
  factors that are passed from one generation to
  the next.
• 2. The principle of dominance, which states that
  some alleles are dominant and others are
  recessive.

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• Alleles are the different forms of a gene .
• Mendel also had a question he wanted to, answer
• Had the recessive alleles disappeared, or were
  they still present in the F1 plant?
• To answer this question, he allowed all seven
  kinds of F1 hybrid plants to produce an F2
  (second filial) generation by self-pollination.
• The traits controlled by the recessive alleles
  appeared.

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• Segregation means separation.
• Gametes are sex cells
• Ex Pollen is a male sex cell
• Eggs are a feminine sex cell

Magnified Image of flower pollen.
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11-2 Probability and Punnett Squares

• The likelihood that a particular event will occur
  is called probability.
• The principles of probability can predict the
  outcomes of genetic crosses.
• Probabilities predict the average outcome of a
  large number of events. But cannot predict the
  precise outcome of an individual event.

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• A Punnett square is a diagram that shows the
  different gene combinations that might result
  from a genetic cross.
• Below is an example
• TtTt

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• The letters in the Punnett square represent
  alleles
• Capital letters for dominant alleles and
  lowercase letters for recessive alleles.
• In this example, T represents tallness and t
  represent the recessive allele for shortness.

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• Organisms that have two. identical alleles for a
  particular trait TT or tt (for this example) are
  said to be homozygous
• Organisms that have 2 different alleles for the
  same trait are heterozygous.
• Homozygous organisms are true breeding for a
  particular trait.
• Heterozygous organisms are hybrid for a
  particular trait.

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• Phenotype means physical characteristics.
• Genotype means genetic makeup.

A humans genetic makeup.
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11-3 Exploring Mendelian

• The principle of independent assortment, states
  that genes for different traits can segregate
  independent during the formation of gametes.

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• Mendel's principles form the base on which the
  modern science of genetics has been built.
• These principles can be summarized as follows
• Individual units known as genes determine the
  inheritance of biological characteristics.
• In organisms that reproduce sexually, genes are
  passed from parents to their offspring

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• In cases in which two or more forms of the gene
  for a single trait exists, 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 gene-one from each parent.
  These genes are segregated from each other when
  gametes are formed.
• The alleles from different genes usually
  segregate independently of one another.

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• Some alleles are neither dominant nor
  recessive, and multiple alleles or multiple genes
  control many traits.
• Incomplete Dominance
• Cases in which one allele is not completely
  dominant over another are called incomplete
  phenotype is incomplete dominance. In incomplete
  dominance, the heterozygous phenotype is
  somewhere in between the two homozygous
  phenotypes.

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• An example of Incomplete Dominance is when
• RED Flower x WHITE Flower ?PINK Flower
• Codominance is a similar situation (as Incomplete
  Dominance) in which both alleles contribute to
  the phenotype of the organisms.

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• Example
• red x white ---gt red white spotted 
• Multiple Alleles
• Many genes have more than two alleles and are
  therefore said to have multiple alleles.
• This does not mean that an individual can have
  more than two alleles.
• It onlymeans that more than two possible alleles
  exist in a population.

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• Polygenic Traits
• Many traits are produced by the interaction of
  several genes.
• Traits controlled by two or more genes are said
  to be polygenic traits which means, "having many
  genes".

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11-4 Meiosis

• Homologous is a term used to refer to chromosomes
  that each have a corresponding chromosome from
  the opposite sex parent.
• A cell that contains both sets of homologous
  chromosomes is said to be diploid, which means,
  "two sets".
• Haploid is a term used to refer to a cell that
  contains only a single set of chromosomes and
  therefore only a single set of genes.

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• Meiosis is a process of reduction division, in
  which the number of chromosomes per cell is cut
  in half through the separation of homologous
  chromosomes in a diploid cell.
• Meiosis usually involves two distinct stages the
  first meiotic division, called meiosis I, and the
  second meiotic division, meiosis II.

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• Below are the various phases of meiosis and what
  happens during them
• MEIOSIS 1
• Interphase 1 Cells undergo a round of DNA
  replication, forming duplicate chromosomes.
• Prophase 1 Each chromosome pairs with its
  corresponding homologous chromosome to form a
  tetrad.
• Metaphase 1 Spindle fibers attach to the
  chromosomes.
• Anaphase 1 The fibers pull the homologous
  chromosomes toward opposite ends of the cell.

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• MEIOSIS II
• Prophase ll Meiosis I result in two haploid
  daughter cells, each with half the number of
  chromosomes, as the original cell.
• Metaphase ll The chromosomes line up in a
  similar way to the metaphase stage of mitosis.
• Anaphase ll The sister chromatids separate and
  move toward opposite ends of the cell.
• Telophase II Meiosis II results in four haploid
  daughter cells.

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• Mitosis results in the production of two
  genetically identical diploid cells. whereas
  meiosis produces four genetically different
  haploid cells.

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11-5 Linkage and Gene Maps

• Thomas Hunt Morgan did research on fruit flies,
  which led him to the principle of linkage.
• Morgan and his associates observed so many genes
  that were inherited together that before long
  they could group all of the fly's genes into four
  linkage groups.
• The linkage groups assorted independently, but
  all of the genes in one group were inherited
  together.

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• Drosophila has four chromosomes, which led to two
  remarkable conclusions
• 1. Each chromosome is actually a group of linked
  genes
• 2. Mendel's principle of independent assortment
  still hold true.
• (It is the. chromosomes, however, that assort
  independently, not individual genes.)

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• This has been an R-Thom Production.