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Genetics

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Gregor Mendel= 1822. 11-1 The Work of Mendel. 1822 Gregor Mendel used purebred pea plants to study the inheritance of traits. ... Mendel's Experiment with Pea Plants ... – PowerPoint PPT presentation

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Title: Genetics


1
Genetics
  • Genetics is the scientific study of heredity.
  • Chapter 11
  • Sections 1-3

2
Gregor Mendel 1822
3
11-1 The Work of Mendel
  • 1822 Gregor Mendel used purebred pea plants to
    study the inheritance of traits.
  • Fertilization the process in sexual
    reproduction in which male female reproductive
    cells join to form a new cell.

4
Review of Meiosis How Gametes (Sex Cells) are
Formed
5
Mendels Experiment with Pea Plants
  • Mendel used the pea flower because they have both
    male female parts.
  • Self-pollinating sperm cell in pollen fertilize
    the egg cells in the same flower. The offspring
    inherit characteristics from a single parent. Ex.
    Pea Plant flowers
  • True-breeding- the pea plants flowers were
    self-pollinating and could produce offspring
    identical to themselves. i.e. they reproduced
    with themselves )

6
Mendels Cross
7
Describing Generations of a Punnett Square
  • Original Parent plants P1 generation
  • 1st set of offspring F1 generation
  • 2nd set of offsprint F2 generation

8
Experiment I Pea Plant
  • Mendel wanted to prevent self-pollination so he
    made a controlled cross between 2 different
    plants.
  • He cut away the male parts dusted pollen from
    another plant on the flower.
  • Cross-pollination seeds produced are the
    offspring of 2 different parents.
  • Accomplished by breeding 2 different plants
    together.
  • Mendel studied specific characteristics of the
    pea plant such as color height.

9
Mendel Studies 7 Traits / Characters pg. 264
  • Seed Shape
  • Seed Color
  • Seed Coat Color
  • Pod Shape
  • Pod Color
  • Flower Position
  • Plant Height

10
The Traits Mendel Crossed
11
Genes and Dominance
  • Mendel crossed 2 different plants that carried
    different forms for the same trait.
  • Ex. 1 tall plant crossed with 1 short plant
  • The plants that grew were hybrid.
  • Hybrid are the offspring of crosses between
    parents with different traits.

12
Experiment I Concluded
  • Traits are inherited through the passing of
    factors from parents to offspring.
  • The hybrid plants looked like only 1 parent and
    the trait of the other parent plant seemed to
    disappear.
  • Each trait is controlled by 1 gene.
  • Genes chemical factors that determine traits.
  • Alleles different forms of a gene.
  • EX Tall plants or Short plants

13
Alleles Different forms of a gene
14
Principle of Dominance
  • States that some alleles are dominant others
    are recessive.
  • Whenever a living thing inherits a dominant
    allele, that trait is visible.
  • The effects of a recessive allele are not seen if
    the dominant allele is present.

15
Experiment II Segregation
  • Mendel crossed a tall plant (dominant) with a
    short plant (recessive),
  • the F1 plant inherited an allele for tallness
    from the tall parent an allele for shortness
    from the short parent. Pg. 265

16
The Law of Segregation in the F1 Generation
17
Now the F2 Generation
18
What happened to the recessive allele?
  • Mendel allowed his hybrid plants to
    self-pollinate.
  • Some showed recessive traits, the recessive
    traits did not disappear.
  • Earlier, the dominant masked the recessive, so it
    was not visible.

19
Experiment II Conclusion
  • Alleles for the same trait can be separated.
  • Segregation When sex cells, or gametes, are
    formed. Each gamete carries only 1 copy of each
    gene.
  • Therefore, each F1 plant produces 2 types of
    gametes (some with an allele for purple flowers
    some with an allele for white flowers). Ex.
    Gametes with P, p, P, p offspring with PP, Pp,
    Pp, pp

20
11-2 Probability Punnett Squares
  • Probability the likelihood that a particular
    event will occur.
  • Ex. Flipping a coin. The probability that it
    will land on tails is ½.

21
The Principles of Probability
  • It is used to predict the traits of the offspring
    produced by genetic crosses.
  • Mendel used a Punnett Square to show the gene
    combinations that might result from a genetic
    cross.

22
Punnett Squares
  • The F1 parent is shown along the top left
    sides.
  • The possible F2 offspring are in the 4 boxes that
    make up the square.
  • Letters represent alleles.
  • T is dominant allele for tallness.
  • t is recessive allele for shortness.
  • Pg. 268

23
The Punnett Square show
  • All the possible results of a genetic cross.
  • The genotypes of the offspring.
  • The alleles in the gametes of each parent.

24
Punnett Squares
  • Homozygous organisms that have 2 identical
    alleles for a particular trait they are
    true-breeding. Ex. TT or tt
  • Heterozygous organisms that have 2 different
    alleles for the same trait they are hybrid. Ex
    Tt
  • Genotype genetic make up.
  • Phenotype Physical characteristics dont have
    the same genotype.

25
Homozygous Vs. Heterozygous Genotype Vs.
Phenotype
26
Probability of SegregationPg. 268-269
  • ¼ (25) of F2 plants have 2 alleles for tallness
    (TT).
  • ½ (50) of F2 plants have 1 allele for tallness
    1 allele for shortness (Tt).
  • ¾ (75) of F2 plants are tall because the allele
    for tallness is dominant over allele for
    shortness.
  • Overall, there are 3 tall for every 1 short plant
    in F2 generation Ratio of 31

27
11-3 Independent Assortment 2 Factor Crosses
  • states that during gamete (sex cell) formation,
    genes for different traits separate independently
    with out influencing each others inheritance.
  • Helps account for genetic variations.
  • Ex. Pea shape pea color are separate traits
    controlled by separate genes.

28
Experiment III The Two-Factor Cross F1
  • Mendel crossed true-breeding plants - round
    yellow peas (RRYY) with wrinkled green peas
    (rryy)
  • The F1 offspring were all round yellow showing
    that both were dominant alleles. The genotype is
    RrYy. Pg. 270

29
Experiment IIIThe Two-Factor Cross F2
  • The F1 plants were all heterozygous with a
    genotype of RrYy.
  • The F1 plants were segregated to each other to
    produce an F2 generation.
  • Mendel compared the variations in the seeds.

30
2- Factor (Trait) Crosses
31
Experiment III Conclusion
  • Mendel found some offspring that were
  • Round / yellow (P phenotype)
  • Wrinkled / green (P phenotype)
  • Many with combinations of alleles (not found in
    either parent)
  • This showed that the alleles for seed shape
    segregated independently of those for seed color
    (independent assortment). Pg. 271

32
Summary of Mendels Principles
  • Genes are passed from parents to their offspring.
  • Some forms of the gene may be dominant and others
    may be recessive.
  • Each adult has 2 copies of each gene one from
    each parent. The genes are segregated from each
    other when gametes are formed.
  • Alleles for different genes usually segregate
    independently of one another.

33
Different Patterns of Dominant Recessive
  • Incomplete Dominance 1 allele is not completely
    dominant over another. Ex. Red flower (RR)
    white flower (WW), F1 is a pink flower (RW). Pg.
    272
  • Codominance both alleles contribute to the
    phenotype.
  • Ex. A cross of a black chicken (BB) with a
    white chicken (WW) will produce all speckled
    offspring (BBWW) colors appear separately.

34
Incomplete Dominance a blend of 2 taits
35
CoDominance Both Forms of the Trait are Expressed
36
Different Patterns of Dominant Recessive
  • Multiple Alleles have more than 2 alleles. Ex.
    Coat color in rabbits.
  • Polygenic Traits traits controlled by 2 or more
    genes having many genes. Ex. Variation in
    human skin color.

37
Human Blood Type has Multiple Alleles
38
Skin Color Polygeneic Trait (More than one gene
controls the pheonotype
39
Thomas Hunt Morgan
  • Geneticist who looked for a model organism to use
    in studying genetics
  • He chose the fruit fly because it produces large
    numbers of offspring.

40
Genes the Environment
  • Mendels principles apply to all organisms not
    just plants.
  • Characteristics of any organism are not
    determined solely by genes it inherits.
  • Characteristics are determined by interaction
    between genes and the environment.
  • Ex. Genes affect the height and color of a
    sunflower but the same characteristics are
    influenced by climate, soil, conditions, and
    availability of water.
  • Genes provide a plan for development, but how the
    plan unfolds depends on the environment.
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