MENDELIAN GENETICS




        Gregor Mendel
 Studied inheritance in peas
Mendel’s Garden




He artificially crossed plants




He became known as the
  “Father of Genetics”
Genetics : the study of the
            inheritance of traits

  1. Traits are controlled by
     genes on chromosomes.
  ...
Mendel’s Principle of Dominance:

If an allele from one parent is
expressed while the matching allele
from the other paren...
Homozygous : allele from each
             parent is the same
                 ( pure )
  TT = tall       tt = short

Hete...
Mendel’s Law of Segregation :

The alleles from each parent are
separated during the formation of
gametes ( sex cells ).

...
The number of chromosomes per cell
has been reduced and the
chromosomes, ( and therefore the
alleles ), from each parent h...
For particular traits, the results of
a cross between two parents can be
predicted using the laws of
probability.



A mon...
Reginald Punnett developed the
Punnett Square to predict outcomes
of crosses




For each possibility, determine the
chanc...
Cross: Tt x Tt
              Possible eggs: T or t
              Possible sperm: T or t
Prediction : chances for offspring...
Mendel’s Law of Independent
           Assortment

  Different traits are inherited
  independently of each other

A dihyb...
Prediction from Punnett square:




    Phenotypic ratio = 9:3:3:1
Genotypic ration=1:2:1:2:4:2:1:2:1
Test Cross:
   A cross to determine if an
individual is heterozygous or
homozygous for a given trait.

Example: NN and Nn ...
Non-Mendelian Inheritance

1. Incomplete dominance
    Neither allele is dominant and
    the hybrid is a blend
2. Codominance

    Both alleles are expressed
    equally
3. Multiple alleles
    More than two alleles for a
    trait exist in the population

  Human blood type is controlled
  ...
4. Polygenic Inheritance

     Several alleles control a
     trait at the same time.
Polygenic phenotypes have a
continuous range of expressions and
show a typical bell-shaped curve of
values in a population
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  1. 1. MENDELIAN GENETICS Gregor Mendel Studied inheritance in peas
  2. 2. Mendel’s Garden He artificially crossed plants He became known as the “Father of Genetics”
  3. 3. Genetics : the study of the inheritance of traits 1. Traits are controlled by genes on chromosomes. 2. Genes exist in different forms called alleles. 3. There can be many alleles for a particular trait. 4. All the alleles an organism has is its genotype. 5. The physical expression of alleles is a phenotype. 6. Each parent provides one or more alleles for a trait.
  4. 4. Mendel’s Principle of Dominance: If an allele from one parent is expressed while the matching allele from the other parent is not expressed, that allele is said to be dominant and the allele not expressed is said to be recessive. Capital letters stand for dominant Lower case letters mean recessive In peas, tall ( T ) is dominant to short ( t )
  5. 5. Homozygous : allele from each parent is the same ( pure ) TT = tall tt = short Heterozygous : different allele from each parent ( hybrid ) Tt = tall ( tall dominates )
  6. 6. Mendel’s Law of Segregation : The alleles from each parent are separated during the formation of gametes ( sex cells ). The formation of sex cells ( sperm or egg ) is called meiosis. Meiosis is also known as reduction division During division of cells to form gametes, chromosomes inherited from each parent are separated ( segregated )
  7. 7. The number of chromosomes per cell has been reduced and the chromosomes, ( and therefore the alleles ), from each parent have been segregated.
  8. 8. For particular traits, the results of a cross between two parents can be predicted using the laws of probability. A monohybrid ( one factor ) cross: Female = Tt, so ½ of eggs = T and ½ of eggs = t Male = Tt, so ½ sperm = T and ½ sperm = t
  9. 9. Reginald Punnett developed the Punnett Square to predict outcomes of crosses For each possibility, determine the chance for occurring and then multiply the chances.
  10. 10. Cross: Tt x Tt Possible eggs: T or t Possible sperm: T or t Prediction : chances for offspring TT = ¼ Tt = ½ tt = ¼ From Punnett square: Genotypic ratio = 1:2:1 Phenotypic ratio = 3:1
  11. 11. Mendel’s Law of Independent Assortment Different traits are inherited independently of each other A dihybrid ( two-factor ) cross : Cross: TtBb x TtBb Possible eggs: TB,Tb,tB,tb Possible sperm : TB,Tb,tB,tb
  12. 12. Prediction from Punnett square: Phenotypic ratio = 9:3:3:1 Genotypic ration=1:2:1:2:4:2:1:2:1
  13. 13. Test Cross: A cross to determine if an individual is heterozygous or homozygous for a given trait. Example: NN and Nn look the same due to dominance crossing each with the recessive trait will show the difference: NN x nn = all Nn Nn x nn = ½ Nn and ½ nn The test determines which is pure and which is hybrid.
  14. 14. Non-Mendelian Inheritance 1. Incomplete dominance Neither allele is dominant and the hybrid is a blend
  15. 15. 2. Codominance Both alleles are expressed equally
  16. 16. 3. Multiple alleles More than two alleles for a trait exist in the population Human blood type is controlled by three alleles I (type A) A IB (type B) i (type O) I I and I i = type A A A A IBIB and IBi = type B IA IB = type AB ii = type O
  17. 17. 4. Polygenic Inheritance Several alleles control a trait at the same time.
  18. 18. Polygenic phenotypes have a continuous range of expressions and show a typical bell-shaped curve of values in a population

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