Transcript of Mendelism
- 1. MENDELISM ANA 807 PRESENTATION BY ADESEJI WASIU ADEBAYO
Department of Anatomy, University of Ilorin. 08/46KA006 January,
2015
- 2. OUTLINE INTRODUCTION GENETICS BEFORE MENDEL MENDEL
EXPERIMENTS MENDELS PRINCIPLES OF INHERITANCE APPLICATION OF
MENEDLS PRINCIPLES TO HUMAN GENETICS MEDELIAN PRINCIPLES IN HUMAN
GENETICS CONCLUSION REFERENCES 2
- 3. INTRODUCTION Mendelism simply put, refers to the laws of
inheritance postulated by Gregor Mendel. Gregor Mendel was an
Austrian Monk who lived between 1822-84. He experimented on various
plants species and animal He was the first to state the universal
laws governing inheritance of traits. Gregor Mendel is known as
father of modern genetics 3
- 4. GENETICS BEFORE MENDEL Before Mendel Heredity was a mystery
The laws governing inheritance are quite unknown; no one can say
why the same peculiarity is sometimes inherited and sometimes not
so; why the child often reverts in certain characters to its
grandfather or grandmother or other much more remote ancestor -
Charles Darwin, Origin of Species 1872 4
- 5. GENETICS BEFORE MENDEL The concept of inheritance of
physical units (later called genes) was accepted, and scientists
had reported on many hybridization experiments in both animals and
plants. Yet no one had set forth principles of inheritance which
could be used as a universal theory to explain how traits in
offspring can be predicted from traits in the parents. 5
- 6. MENDEL EXPERIMENTS Gregor experimented with pea plants, by
crossing various strains and observing the characteristics of their
offspring. He also experiment on drosophila, but much success was
recorded on pea plants Between 1856 and 1863, Mendel cultivated and
tested some 28,000 pea plants. 6
- 7. MENDEL EXPERIMENTS The choice of Garden pea (Pisum sativum)
was due to the following reasons: Can be grown in a small area
Produce lots of offspring Produce pure plants when allowed to self-
pollinate several generations Can be artificially cross-pollinated
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- 8. MENDEL EXPERIMENTS One peculiarity of pea reproduction is
that the petals of the flower close down tightly, preventing pollen
grains from entering or leaving. This enforces a system of self-
fertilization, in which the male and female gametes from the same
flower unite with each other to produce seeds. As a result,
individual pea strains are highly inbred, displaying little if any
genetic variation from one generation to the next. Because of this
uniformity, we say that such strains are true-breeding 8
- 9. MENDEL EXPERIMENTS The true breed traits of the pea plant
are: Seed shape --- Round (R) or Wrinkled (r) Seed Color ----
Yellow (Y) or Green (y) Pod Shape --- Smooth (S) or wrinkled (s)
Pod Color --- Green (G) or Yellow (g) Seed Coat Color ---Gray (G)
or White (g) Flower position---Axial (A) or Terminal (a) Plant
Height --- Tall (T) or Short (t) Flower color --- Purple (P) or
white (p) 9
- 10. Mendel focused on the study of inheritance of one trait at
a time. In an experiment, Mendel crossed tall and dwarf pea plants
to investigate how height was inherited. This type of crossing
between parents differing in only one trait or in which only one
trait is being considered is termed monohybrid cross. 10
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- 12. MENDEL EXPERIMENTS All the offspring from the cross (First
filialgeneration- F1) were all tall regardless of the way he
performed the cross (tall male with dwarf female or dwarf male with
tall female). Mendel noted that the dwarf characteristic seemed to
have disappeared in the progeny of the cross. 12
- 13. MENDEL EXPERIMENTS Mendel decided to cross the F1
generation with each other to see if the dwarf trait would reappear
in the next generation. When he examined the progeny (F2
generation), he found that they consisted of both tall and dwarf
plants in a ratio of approximately 3:1. Mendel inferred that these
hybrids carried a latent genetic factor for dwarfness, one that was
masked by the expression of another factor for tallness. He said
that the latent factor was recessive and that the expressed factor
was dominant. 13
- 14. MENDEL EXPERIMENTS Mendel repeated the experiment examining
the transmission of other traits such as flower colour, pod colour.
The same pattern and results was observed 14
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- 16. Dihybrid Crosses: The Principle of Independent Assortment
Mendel also performed experiments with plants that differed in two
traits. The purpose of the experiments was to see if the two seed
traits, color and texture, were inherited independently. 16
- 17. He crossed plants that produced yellow, round seeds with
plants that produced green, wrinkled seeds. F1 seeds were all
yellow and round, the alleles for these two characteristics were
dominant. 17
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- 20. MENDELS PRINCIPLES OF INHERITANCE The result of Mendels
experiments led to the principles of inheritance. It was published
in 1865 through a single research paper, Experiments in Plant
Hybridization Unfortunately, this paper languished in obscurity
until 1900, when it was rediscovered by three botanistsHugo de
Vries in Holland, Carl Correns in Germany, and Eric von
Tschermak-Seysenegg in Austria. 20
- 21. Genes In Pairs Genes In Pairs: Genetic characters are
controlled by factors (gene) that exist in pairs of alleles in
individual organisms and are passed from parents to their
offspring. When two organisms produce offspring, each parent gives
the offspring one of the alleles from each pair 21
- 22. Dominance and Recessiveness Dominance and Recessiveness:
When two unlike alleles responsible for a single character are
present in a single individual, one allele can mask the expression
of another allele. That is, one allele is dominant to the other.
The latter is said to be recessive. 22
- 23. The Law of Segregation The Law of Segregation: During the
formation of gametes, the paired alleles separate (segregate)
randomly so that each gamete receives one allele or the other.
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- 24. The Law of Independent Assortment The Law of Independent
Assortment: During gamete formation, segregating pairs of alleles
assort independently of each other. Example: genes on different
chromosomes will segregate independently. Linked genes (close
together on one chromosome) do not follow this law. 24
- 25. MEDELIAN PRINCIPLES IN HUMAN GENETICS Mendels principles
can be applied to study the inheritance of traits in humans. The
genetic analysis of human heredity depends on family records, which
are often incomplete. 25
- 26. Pedigrees diagram the relationships among family members
where squares designate males and circles designate females, a
horizontal line represents mating and vertical lines beneath
reflect offspring. Birth order is left to right, afflicted
individuals are shaded or filled in 26
- 27. Pedigrees : are used to identify dominant and recessive
traits in human families 27
- 28. Mendelian inheritance in humans d) Earlobe attachmenta)
Mid-digital hair b) Tongue rolling c) Widow's peak e) Hitchhiker's
thumb f) Relative finger length All these traits (and more) are
transmitted in Mendelian fashion in humans
- 29. CONCLUSION MENDEL MADE US UNDERSRAND GENETICS 29