gregor mendel’s laws
TRANSCRIPT
-
7/28/2019 Gregor Mendels Laws
1/17
Gregor Mendels Laws
Mendelian inheritance (orMendelian
genetics orMendelism) is a set of
primary tenets relating to the transmission
of hereditary characteristics from parent
organisms to their children.
The laws of inheritance were derived by
Gregor Mendel, an Austrian monk.
-
7/28/2019 Gregor Mendels Laws
2/17
History
Between 1856 and 1863, he cultivated andtested some 28,000 pea plants.
His experiments brought forth two
generalizations which later became knownas Mendel's Laws of HeredityorMendelian inheritance.
Although his results were published in1865, it went largely un noticed, but it wasrediscovered by three scientists in 1900.
-
7/28/2019 Gregor Mendels Laws
3/17
Mendels experiments.
Mendel discovered that by crossing white flower
and purple flower plants, the offspring was
purple flowered, rather than being a mix of the
two. He then conceived the idea of heredity units,
which he called "factors", one which is a
recessive characteristic and the other dominant.
Mendel said that factors, later called genes,normally occur in pairs in ordinary body cells, yet
segregate during the formation of sex cells.
-
7/28/2019 Gregor Mendels Laws
4/17
Terminology
Allele: One of two or more forms a gene may take.
Dominant: An allele whose expression overpowers theeffect of a second form of the same gene.
Gamete: A reproductive cell.
Heterozygous: A condition in which two alleles for agiven gene are different from each other.
Homozygous: A condition in which two alleles for agiven gene are the same.
Recessive: An allele whose effects are concealed inoffspring by the dominant allele in the pair.
-
7/28/2019 Gregor Mendels Laws
5/17
-
7/28/2019 Gregor Mendels Laws
6/17
-
7/28/2019 Gregor Mendels Laws
7/17
Mendel's Law of Segregation
Mendel's law of segregation, also known
as Mendel's First Law, essentially has
four parts.
1. Alleles exist- They are alternate forms
of the same gene- for eg. Gene which
codes for colour of the pea pod or flower-
gene is same but can be either green oryellow.
-
7/28/2019 Gregor Mendels Laws
8/17
Mendel's Law of Segregation
2. For each characteristic feature, an organisminherits two alleles, one from each parent, i.e.one from the father and one from the mother. Intrue breeding organisms- both alleles will be
same-TT/tt and in hybrid, it will be Tt. 3. If the two alleles differ, then one, the
dominant allele, is fully expressed in theorganism's appearance; the other, therecessive allele, has no noticeable effect onthe organism's appearance. In other words,the dominant allele is expressed in thephenotype of the organism;
-
7/28/2019 Gregor Mendels Laws
9/17
Mendel's Law of Segregation
However this does not always hold true,today.
There are several examples we know that
disprove this "law", e.g. Mirabilis jalapa,the "Japanese wonder flower.This iscalled incomplete dominance.
There is also codominance e.g. Humanblood types where A and B arecodominant and O is recessive.
-
7/28/2019 Gregor Mendels Laws
10/17
Mendel's Law of Segregation
4. The two alleles for each
characteristic segregate during gamete
production.
The two alleles of the organism are
separated into different gametes, ensuring
variation.
-
7/28/2019 Gregor Mendels Laws
11/17
Mendel's Law of Segregation
The Law of Segregation states that the
members of each pair of alleles separate
when gametes are formed.
A gamete will receive one allele or the
other.
A
-
7/28/2019 Gregor Mendels Laws
12/17
Genetic diagram
A genetic diagram is done in order to find out thepossibilities of a cross between two knownparents.
Mendels always started the crosses with pure
bred parents for one character, calledmonohybrid.
The diagram is also known as the Punnettsquare.
In the following diagram, parents are one puregreen (GG) and the other pure yellow (gg). Theresulting offspring are Gg the F1 generation.
-
7/28/2019 Gregor Mendels Laws
13/17
-
7/28/2019 Gregor Mendels Laws
14/17
Second law of inheritance
An individual's physical appearance or phenotype isdetermined by its alleles. An individual possesses twoalleles for each trait; one allele is given by the femaleparent and the other by the male parent. They are
passed on when an individual matures and producesgametes, egg and sperm. When gametes form thepaired alleles separate randomly so that each gametereceives a copy of one of the two alleles. The presenceof an allele doesn't promise that the trait will be
expressed in the individual that possesses it. Inheterozygous individuals the only allele that in expressedis the dominant. The recessive allele is present but itsexpression is hidden.
-
7/28/2019 Gregor Mendels Laws
15/17
Mendels Second law
The Law of Independent assortment states
that two or more pairs of alleles segregate
independently of one another during
gamete formation.
-
7/28/2019 Gregor Mendels Laws
16/17
Mendels Second law
The genetic diagram again begins with two
pure bred parents, this time with two
characters or dihybrid.
They are pure green and round seeds
(GGYY) and pure yellow and wrinkled
seeds ( ggyy). The F1 generation is a
hybrid of GgYy, which is crossed again togive the following results.
-
7/28/2019 Gregor Mendels Laws
17/17