Genetics:

1
Genetics

• Mendel Beyond

2
Genetics the foundations

• most early studies were done with plants
  animals of economic importance
• evidence has been found that crossbreeding of
  palm trees and horses began as early as 5,000
  years ago

3
Genetics the foundations

• notion of blending
• Josef Gottlieb Kolreuter (late 18th century) did
  experiments of reciprocal crossing in plants
  found that if a plant had one form of a
  characteristic (i.e. red flowers) was crossed
  with a plant with another form (i.e. blue
  flowers), the offspring would show a blending of
  the two forms (i.e. purple flowers)
• once forms of a characteristic were blended, they
  could no longer be seen in their separate forms
  in subsequent offspring
• Mendel came along a century later

4
Genetics the foundations

• advantage of using of plants in genetic studies
• easily grown in large quantities
• produce large numbers of offspring (from seeds)
• have short generation times
• breeding be easily controlled and manipulated

5
(No Transcript)
6
Gregor Mendel father of genetics

• was an Austrian monk, but intensively studied
  physics, chemistry, mathematics, and biology at
  the University of Vienna
• failed the test for teacher certification
• Biology was his weakest subject
• he used knowledge of physics mathematics to get
  quantitative results and apply experimental
  methods to genetics

7
Gregor Mendel father of genetics

• researched basic inheritance patterns in plants
  for about 9 years
• 1865 public lecture of findings
• 1866 detailed, written publication
• printed in 120 library journals sent 40 copies
  to scholars
• theories were not accepted (for approx. 30 years)

8
Why was Mendel ignored?

• most biologists of his time did not think in
  mathematical terms, including Charles Darwin
• Darwin did almost the exact same experiments as
  Mendel, using snapdragon plants believed in
  concept of blending
• Mendel had little credibility as a biologist

9
Mendels theories accepted

• in 1900 meiosis chromosomes had been observed
  and described
• Mendels work was cited as a source became
  prominently accepted
• Mendels theories provided an explanation of how
  chromosomes meiosis work, and vice versa

10
Mendels methods

• used garden peas
• controlled pollination, thus fertilization
• chose characteristics to observe that had
  well-defined, contrasting alternates (purple vs.
  white flowers)
• began with plants that were true-breeding
• observed character was present for many
  generations
• used self-pollination inbreeding to achieve this

11
Mendels methods

• Mendels terms
• character observed feature, such as flower color
• trait particular form of a character, such as
  white flowers
• heritable character trait that is passed to
  offspring

12
Mendels methods

• cross-pollinated true-breeding plants
• collected pollen from one strain and placed it on
  the stigma of another
• concentrated on seven pairs of contrasting traits

13
(No Transcript)
14
Mendels methods

• P generation (parental) true-breeding plants
  that provided and received pollen
• F1 generation (filial) seeds and resulting new
  plants from the cross of the P generation
• F2 generation (filial) seeds and resulting
  plants from the self-pollination of the F1 plants

15
Mendels methods

• Characteristics of all F1 F2 plants were
  counted and recorded
• Quantitative Data
• described relative proportions of the
  different kinds of progeny

16
Mendels 1st Experiment

• monohybrid cross one trait
• P generation
• true-breeding spherical seeds
• x
• true-breeding wrinkled seeds
• F1 all had spherical seeds

17
Mendels 1st Experiment

• Mendel allowed F1 plants to self-pollinate
• spherical seeds x spherical seeds
• F2 7, 324 spherical seeds
• 1, 850 wrinkled seeds

18
(No Transcript)
19
Mendels conclusions from 1st experiment

• disproved belief of blending
• see reappearance of both traits in F2 generation
• concept of dominance and recessiveness
• spherical (S) wrinkled (s)
• spherical seed characteristic was dominant over
  the wrinkled seed characteristic

20
(No Transcript)
21
Mendels conclusions from 1st experiment

• particulate theory units responsible for
  inheritance of specific traits are present as
  discrete particles that occur in pairs and
  segregate during the formation of gametes
• also negates blending concept

22
Mendels conclusions from 1st experiment

• through math, Mendel concluded that each pea
  plant had two units of inheritance one from
  each parent
• only one unit is give to gametes
• when gametes fuse, result has two sets of units

23
Mendels conclusions from 1st experiment

• law of segregation when any individual produces
  gametes, the two units of inheritance separate
  so that each gamete one receives one

24
Mendels 2nd set of experiments

• Do units of inheritance that come from mother
  (or father) stick together when gametes are made?
• Mendel looked at two characteristics
  simultaneously (seed shape seed color)

25
Mendels 2nd set of experiments

• P generation
• spherical, yellow seeds
• (SSYY)
• x
• wrinkled, green seeds
• (ssyy)

26
Mendels 2nd set of experiments

• F1 generation all spherical, yellow seeds
• F2 generation expressed 4 combinations of traits
• spherical, yellow/ spherical, green/ wrinkled,
  yellow / wrinkled, green

27
Mendels 2nd law

• law of independent assortment segregation of
  mothers (or fathers) units of inheritance is
  independent when forming gametes

28
Support for Mendels 2nd law

• if units were linked all F2 offspring would be
  either spherical, yellow seeds or wrinkled, green
  (like the P1 generation) in a 31 ratio
• if units segregated independently, gametes would
  have 4 different combinations (SY, Sy, sY, and
  sy), and would, thus, produce 4 combinations in
  the F2 generation