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Patterns of Inheritance

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Patterns of Inheritance Chapter 9 – PowerPoint PPT presentation

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Title: Patterns of Inheritance


1
Patterns of Inheritance
  • Chapter 9

2
Genetics
  • The science of heredity.
  • A distinct genetic makeup results in a distinct
    set of physical and behavioral characteristics.
  • The DNA you get from your parents determine your
    physical characteristics.

3
History of Genetics
  • Hippocrates (ancient Greek physician) proposed an
    explanation called pangenesis.
  • Particles called pangenes travel from each part
    of the organisms body to the egg or sperm and
    are then passed to the next generation.
  • Also thought that changes that occur during an
    organisms life are passed on in this way.
  • Aristotle (384 B.C.) rejected this idea as
    simplistic, saying that what is inherited is the
    potential to produce body features rather than
    particles of the feature themselves.

4
History of Genetics
  • Biologists in the 19th century observed
    inheritance patterns in plants and concluded that
    offspring inherit traits from both parents.
  • The favored explanation for inheritance then
    became the blending hypothesis.
  • This is the idea that the hereditary materials
    contributed by the male and female parents mix in
    forming the offspring.

5
History of Genetics Gregor Mendel
  • Modern genetics began in the 1860s when a monk
    named Gregor Mendel experimented with breeding
    garden peas.
  • With a history in mathematics, his research
    implemented a great deal of statistics.
  • He stressed that the heritable factors (genes)
    retain their individuality generation after
    generation (no blending).

6
History of Genetics Gregor Mendel
  • He studied pea plants because they had short
    generation times, they produced large numbers of
    offspring, and they came in many varieties.
  • Character flower color, height, seed shape, pod
    color, etc.
  • Traits (each variant for a character)
    purple/white flower, tall/short height,
    round/wrinkled seed, green/yellow pod color.

7
Characters
Traits
Mendel chose to study 7 characters, each of which
occurred in two distinct forms.
8
History of Genetics Gregor Mendel
  • He could strictly control mating of pea plants.
  • Pea plants usually self-fertilize pollen grains
    (carrying sperm) released from the stamens land
    on the egg containing carpel of the same flower.
  • He could also cross-fertilize
  • fertilization of one plant by
  • pollen from a different plant.

9
Cross fertilization
10
History of Genetics Gregor Mendel
  • He worked with plants until he was sure they were
    a true-breed (one that produced offspring all
    identical to the parent if self-fertilized).
  • Example parent plant had purple flowers, and if
    self fertilized it would only produce purple
    flowered plants generation after generation.

11
History of Genetics Gregor Mendel
  • Once he had a true-breed, he then investigated
    what would happen if he crossed true-breeding
    varieties with each other.
  • Example what offspring would result from
    cross-fertilization of true-breeds?
  • purple flowers x white flowers
  • This offspring of two different true-breeds is
    called a hybrid.
  • (the fertilization is called hybridization, or
    cross.)

12
History of Genetics Gregor Mendel
  • P generation the true-breeding parental plants.
  • F1 generation the hybrid offspring.
  • (F stands for filial, Latin for son)
  • F2 generation result self-fertilization of the
    F1 plants.

13
History of Genetics Gregor Mendel
  • Mendel tracked and recorded the inheritance of
    characters, the results lead him to formulate
    several ideas about inheritance.
  • Lets look at his monohybrid-cross (parent plants
    differ in only 1 character).

14
History of Genetics Gregor Mendel
  • He crossed a true-breed purple flower with a
    true-breed white flower.
  • He observed that the F1 generation were all
    purple flowers.
  • Self-fertilizing the F1 generation he found that
    the F2 generation had a ratio of 13. One white
    for every three purple.
  • He concluded that the white trait did not
    disappear, and that they MUST carry two factors
    for the flower color character.
  • He called these alleles alternative versions of
    a gene.

15
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16
Homologous chromosomes
  • Alleles reside at the same locus on homologous
    chromosomes.

17
History of Genetics Gregor Mendel
  • Dominant allele is always expressed if present.
    (like a trump card)
  • PP or Pp
  • Recessive allele is only expressed if the
    dominant allele is NOT present.
  • pp

18
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19
History of Genetics Gregor Mendel
  • A homozygous genotype has identical alleles.
  • PP or pp
  • A heterozygous genotype has two different alleles
  • Pp

20
Law of Segregation
  • A sperm or egg carries only one allele for each
    inherited character.
  • because allele pairs separate from each other
    during the production of gametes.

21
Genetic composition appearance
  • Genotype organisms genetic makeup.
    (Represented by letters)
  • Phenotype organisms expressed or physical
    traits.

22
Genetic composition appearance
  • Carriers organisms that are heterozygous, they
    carry the recessive allele for a trait but
    phenotypically only the dominant trait is
    expressed.

23
Types of hybrid crosses
  • Monohybrid cross the parents differ in only one
    character.
  • Green or Yellow seeds.
  • Dihybrid cross parents differ in two
    characters.
  • (Round or Wrinkled) and (Green or Yellow) seeds.

24
Law of Independent Assortment For Dihybrid
Crosses
  • Each pair of alleles segregates independently of
    other pairs of alleles during gamete formation.
    (Each trait is inherited independently of one
    another.)
  • Which means you could get your moms hair color
    and not get her eye color (or vice versa). The
    two traits are inherited INDEPENDENTLY of one
    another.

25
Law of Independent Assortment
26
Punnett Square
  • Punnett squares are used to show the probability
    of what genotypes the offspring could have.

27
Test Cross
  • Used to determine the genotype of a unknown
    character.
  • Used to verify if organism is in fact a
    true-breed.

B black. The dominant allele. But, is it BB
or Bb? This is unknown.
28
Test Cross
  • Mate organism with unknown genotype, with an
    organism that has a homozygous recessive
    genotype.
  • The appearance of the offspring reveals the
    unknown genotype.
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