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Mendelian Genetics - Mendel's three laws

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State Higher Vocational School in Krosno
Laboratory of Biochemistry and Medical Biology
38-404 Krosno
Ul. Casimir the Great, 6

Henry Rozanski
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Mendelian Genetics
- M e n d e l i z m

Mendel's three laws
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Johann Gregor Mendel / 1822-1884 /

Greg Johann Mendel was born on 22 June 1822 year, Moravia Silesia (Heisendorf, now Jasienica). He was the son of a peasant.In 1843 he entered the Augustinian monastery in Brno. In the years 1844-1848 he studied theology and agriculture. Two years of studying nature (or rather, physics) and mathematics in Vienna.After graduation he worked as a teacher. In 1856 he began to experience the process of inheritance of traits in plants.

G. J. Mendel is the founder of classical genetics. Investigated the inheritance of traits in peas for 8 years, after which the results of his research were published (1866 year) in the less popular scientific journal of the Society of Naturalists Brno. This was an article titled "Research on plant hybrids." In 1870 he announced another article titled "On some mongrel Hieracium derived from artificial insemination." Mendel tried to interest his research of Carl Wilhelm Negeli'ego, a botanist working for the Swiss in Wroclaw: This, however, ignored these reports. Negeli developed a number of important hypotheses and theories of evolution, which are referred to collectively naegelizmem - see http://www.parazyt.gower.pl/parazytologia2002.htm (in the history department of genetics.)


Carl Wilhelm Nägeli / 1817-1891 /

Mendel's works published in small print run were forgotten for 35 years. The first concerned the work of Mendel's pea varieties crosses, observing the color and shape of seeds, flower color and shape of the pods. The second piece described the inheritance of flower color in Jastrzębca Hieracium.

In 1900, Carl Erich Correns, Erich Tschermak von Seysenegg and Hugo de Vries published a work on the inheritance of plant traits, but it turned out that they were unconscious repetition of the work of Mendel. The work of three scholars were merely confirmation of theses and research results GJMendla. Mendel's first work was published in Poland until 1915.


Erich von Tschermak Seysenegg / 1871-1962 /

Carl Erich Correns / 1864-1933 /

Hugo de Vries / 1848-1935 /

G. Mendel used in their surveys pea Pisum sativum, self-pollinating plants. They were different varieties of peas crisp, opposite characteristics. Were characterized by their uniformity in terms of genetic, that is faithfully inherited their characteristics. They differed in flower color: red and white seed surface (smooth, wrinkled), shoot length (short, long).

Mendel crossed two varieties of peas differing in these traits. The parents marked with a capital P (particeps - providing, giving the hereditary characteristics, Partus - newborn, giving the offspring).Zapylił them artificially, by removing the stamens at the same time.He gathered the seeds and wysiał to the ground.

So the first generation received F1 (Filius - children.) In the first generation all the individuals had red flowers, were high, had a smooth yellow seeds. The direction of the crossing was irrelevant, because they always occurred in the F1 generation individuals of a dominant trait.

The factor responsible for the red color marked with a capital A - a factor that causes the color white - a. distinguished in this way the dominant features, more powerful, dominant, which is covered, wilderness characteristics somewhat inferior, recessive, weaker.This type of inheritance is called Pisum.

If you cross a plant of the genus Snapdragon Antirrhinium with white flowers from plants with red flowers are individuals of the F1 generation will have pink flowers, because the flower color is inherited in an indirect way, ie the lack of total domination of the dominant features of a recessive trait. This type of inheritance is defined as Zea (maize).

In 1909 the Danish geneticist Wilhelm Johannsen factors responsible for the characteristic called genes.


Wilhelm Johannsen / 1857 - 1927 /

Thomas Morgan then announced the law that genes located on chromosome has its locus, the place of occurrence and are arranged linearly in a certain order. Morgan also showed that for each attribute, there are two genes: one on chromosome 1 in the maternal and paternal chromosome, they are exactly opposite each other and form a pair of allelic. Genes belonging to one pair Aa called Morgan - allelomorfami as produce two forms of the same features. There is interaction between the alleles. If the individual has a characteristic, a hen and a recessive gene trait is dominant heterozygote aA (or Aa). Heterozygous Aa (or AA) is less red dye (antocyjanu) than homozygous AA AA dominant characteristics. A gene encodes enzymes thus providing a synthesis of the dye suitable color of the flower. U wyżlinu can visually see a lower content of red pigment in heterozygotes - pink. AA homozygous individuals have more color, because there are as many as two genes encoding the synthesis of the dye, hence the intense red color. In pea heterozygous or less can be said dye content, but not visually, but through a quantitative analytical methods.


Thomas Hunt Morgan / 1866-1945 /

In the early twentieth century, some geneticists called Mendel's first law of dominance of one characteristic over another. But it was wrong, because the cases are incomplete, incomplete dominance of one characteristic over another. Later, it changed the scene, claiming that the first law of Mendel assumed the presence of homogeneity of the first generation hybrids. The inherited type Pisum generation F1 comprises individuals with red flowers, and a Zea - F1 individuals of pink flowers.

At present, it was assumed that I Mendel is right, the gamete of the same pair of alleles are mutually exclusive and there are always alone. In other words, I Mendel's law is the law of segregation characteristics, ie, a purity of gametes. It should be noted, however, that the concept of the laws of purity of gametes is written by William Bateson'a.

William Bateson / 1861-1926 /

After sowing the seeds I obtained from the F1 generation, Mendel obtained specimens with white flowers and red, with red-flowered plants was three times more than the individuals with white flowers, a ratio of 3:1, and exactly 2,86:1. In the F2 generation was so split features, the color white, as it were freed from the dominion of the red color. Mendel demonstrated that the characteristics of the F1 generation did not merge, but only a temporary fall in the relationship, then split up not yielding any changes.

G.J. Mendel disproved in the nineteenth century the prevailing view that the characteristics of the parent during fertilization to merge with each other and will not split anymore.

And the law is the basis of the corpuscular Mendel, a molecular theory of inheritance of characteristics. Mendel correctly determined that gametes contain one factor responsible for the trait is recessive or dominant factor. Individuals with two different genes responsible for the same trait is called heterozygous, but about two identical genes AA or aa - homozygotes.

Thus, the plants studied by Mendel contained one or two dominant genes and one or two recessive genes. Homozygotes do not undergo fission in the F3 generation, while heterozygotes cleave the F3 generation in a 3:1 ratio.

Let us be clear again. And the law contains the principle of Mendelian segregation of traits, namely: the characteristics of the first generation of hybrids come together in a temporary relationship, and then in the F2 generation are segregated, that is, the divergence of different individuals, not yielding at the same genetic change. It is the law of segregation allelic genes.
W. Bateson called this process the law of purity of gametes, because gametes have only one genome, a team monoploidalny chromosomes, in other words - contain only one gene of the allelic pairs: gene A (dominant) or a gene (recessive).

Inheritance in Pisum called monogenic type (univariate). Gametes purity law only applies to diploid organisms with haploid gametes, and not poliploidów.

The law also includes the separation characteristics of polyploid, which does not make a right Bateson.

Mendel's third law is the law of dominance: a pair of factors determining (defining) characteristic of a hereditary factor is always dominant and one recessive.

Pisum inheritance represents many of the plants. For example, when you cross Datura stramonium fruit without thorns of the prickly fruit of Datura are in F1, all individuals will have a prickly fruit, and F2 will be split in a 3:1 ratio.

U wyżlinu (Zea inheritance) in the F2 generation, followed by cleavage at 1:2:1 ratio (25% of plants with white flowers, 25% of plants with red flowers and 50% of individuals with pink flowers). In type Zea genotype coincides with the phenotype, or genotype is reflected in obvious external features of the eye (visual). The type of inheritance Pisum phenotype does not match the genotype.

In order to check whether your peas individuals are heterozygous or homozygous - perform a test to be a crossword puzzle. Plants of hybrid crosses with the parental form of recessive genes / aa /. If the peas with red flowers intersect with peas with white flowers (genotype aa!) And get a split in a 1:1 ratio, it means that it is heterozygous (50% of plants with red flowers and 50% of plants with white flowers.)

It is worthwhile to recall some information about the inheritance of germ cells and sex. Males (diploid) have two sex chromosomes: X and Y, while females (diploid) - the two chromosomes, X and X but the female bovine are therefore homozygous sex chromosomes - allosomów. Heterozygous males śa allosomów terms. Y chromosomes are smaller than X and can be distinguished microscopically. Chromosome X and Y form a pair, however, during the formation and maturation of sperm (male gametes) split up the chromosomes into two daughter cells. Thus, during spermatogenesis (sperm formation) occurs 50% of the sperm containing the Y chromosome and 50% of individuals with X chromosome sperm are so monoploidalne, which is haploid, in contrast to somatic cells - autosomes (body cells), which are diploid. Females (the process of formation of ova is ovocytów oogenesis, ie ovogeneza) produce in the gonads of only one kind of sex cells - gametes - the X chromosome

If the X sperm cell connects to the egg (always X) is a diploid zygote is homozygous and will be a girl with XX genotype. However, if a Y sperm fertilizes an egg cell is heterozygous diploid zygote will be XY and give birth to a boy.

The processes of segregation and purity characteristics of gametes can be written with symbols:

Q: (parents diploidalni) AA aa

Monoploidalne gametes (haploid): AA aa
insemination, crossroads, the formation of a diploid zygote
F1: Aa aA (heterozygotes)
Heterozygotes respectively form gametes:
Heterozygote Aa - A gametes and gametes and
Heterozygote aA - and gametes and gametes A
F2 homozygous arise and heterozygous genotypes:

AA (homozygous), Aa (heterozygous), aA (heterozygote), aa (homozygous)


Both in the types of inheritance Zea and Pisum ratio of heterozygotes to homozygotes is the same: 2:2. The type of inherited long Zea maize, flowers color in Mirabilis ialapa eccentric and feathers in chickens. In type Pisum inherited hair color in mice.

Pisum Inheritance can be presented in the form of a checkerboard Punetta:

A a
A AA Aa
a aA aa


Mentioned earlier, geneticist W. Bateson in 1901, said a fission in the ratio of 1:3 in animals. He observed that in poultry in the inheritance of comb (pea and single), with a crest of a pea was the dominant feature.

If you cross two varieties of Drosophila: gray and black, in F1 we get all the individuals of gray, and F2, gray and black flies in a 3:1 ratio.

If you cross a variety of fruit fly on the wings of the normal variation of vestigial wings in F1 we obtain flies with normal wings, and F2, 3 times more flies with normal wings than flies with vestigial wings.

According to Mendel's law, resistance is inherited as tomatoes, mushrooms Altenaria solani. If you do not intersect, a variety resistant to the disease-resistant variety, in the F1 generation to get tomatoes that are sensitive to the disc, and F2 three times more than non-resistant tomatoes resistant to the mushroom. Resistance is a recessive trait 9recesywną)



Inheritance type Pisum:
3: 1

Inheritance type Zea
1: 2: 1


Mendel's Second Law states: qualities belonging to one pair of alleles are inherited independently from those of another pair. In other words, it is the law of succession of independent features.

Interbreeding took Mendel pea varieties differing in two pairs of traits. Interbreeding of pea seeds smooth and yellow with the form of a wrinkled and green seeds. The color yellow and smooth seeds are dominant traits. The genotype of the characteristics of parental plants is shown as a parent letter AABB, and individuals with recessive traits AABB. For gametes undergoing single chromosome band, therefore sex cells are formed with genotype AB and ab. Once connected to the gametes may be formed diploid zygote with genotype AABB.

If you intersect with each plant with two pairs of genes that will not split the two but on four types of gametes with genotypes: AB, ab, aB, Ab, the ratio 1:1:1:1. These four different gametes can give 16 zygotes with different combinations:

12 subjects with yellow seeds, 4 specimens seeded green - so here is the ratio of 3:1

12 individuals with seeds smooth, four individuals from wrinkled seeds - so here it is a ratio of 3:1

These features are inherited so whatever.

On the chessboard Punetta can observe two main features, including:

9 smooth and yellow seeds

3 seeds are yellow, but wrinkled

3 seeds are green and smooth

A seed is wrinkled and green


Thus, the ratio of splitting the two independently inherited genes is 9:3:3:1.

In the F2 generation animals were created with different characteristics than are parents. Recessive traits were combined with those of the parent. Recombination occurred, the resulting new varieties, which is important in evolution because it leads to new forms of plants. Similarly, in the animal world.

Interbreeding of plants can be used for more important different characteristics. With 3 pairs of genes (features) created 8 different gametes, and 64 genotypic combinations in the zygotes. The formula for the calculation of the 2n gametes, where n is the number of pairs of genes.

Mendel's Second Law relates to genes nieallelicznych. It is the segregation of traits as in the law, however applies to genes belonging to different allelic pairs.

Hybrids differ in two pairs of genes is dihybrydy, and many - polihybrydy.

9:3:3:1 ratio calculations showed the owl said W. Bateson.


Inheriting the characteristics of two different


P: AABB (smooth, yellow), AABB (wrinkled, green)

G: (gametes) AB, ab

F1: plain yellow

F2:

AB

Ab

aB

ab

AB

ABAB

AbAB

aBAB

ABab

Ab

ABAb

AbAb

AbaB

Abab

aB

ABaB

AbaB

aBaB

aBab

ab

abAB

Abab

aBab

abab



Wild varieties of butterfly Zygaena ephialtes (Krasnik variable) cross freely. In the F2 generation is observed cleavage of 9:3:3:1, eg when crossing ephialtes peucedani Z. and Z. ephialtes coronillae two pairs of different characteristics. Features peucedani are prevailing (dominant) and thus manifested in heterozygotes in the F1 generation. The F2 is split and the next are similar to the parental forms new forms: Z. ephialtes icterica and Z. ephialtes ephialtes. The ratio of individuals are: 9 peucedani: 3 icterica: 3 ephialtes: 1 coronillae.

Zygaena ephialtes peucedani genotype AABB is a Zygaena ephialtes coronillae has genotype AABB.

A - The red dye is present in all leaf spots and large dot and the large wings of a small rear (dominant trait, the dominant)

and - the red pigment spots in two front wings, the other spots of the wings and back are colorless (recessive trait, recessive)

B - the dominant red color

b - the color yellow recessive

P: AABB x AABB coronillae peucedani

Gametes: AB ab

F1: ABAB peucedani

F2:

 

AB

Ab

aB

ab

AB

ABAB

AbAB

aBAB

ABab

Ab

ABAb

AbAb

AbaB

Abab

aB

ABaB

AbaB

aBaB

aBab

ab

abAB

Abab

aBab

abab

Mendelizm summary: 

And the law is Mendel; gamete alleles of the same pair of mutually exclusive and there are always alone. And right other words, a right segregation Mendel characteristics or purity law gamete. It should be noted, however, that the concept of the laws of purity of gametes is written by William Bateson'a.

Mendel's Second Law states: qualities belonging to one pair of alleles are inherited independently from those of another pair. In other words, it is the law of succession of independent features.

Mendel's third law is the law of dominance: a pair of factors determining (defining) characteristic of a hereditary factor is always dominant and one recessive.

Mendelizm is generally theory, hypotheses and laws based on the results of GJ Mendel and the chromosome theory of inheritance, T. Morgan. Mendelizm influences on development trends in all areas of biology and philosophy of biology.

Henry Rozanski
Document copyrighted
Krosno 2002-2003

Mendelian Genetics - Mendel's three laws
 

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