MENDELISMThe Religion of Genetics

By.P.B.TIRUPATHI PICHIAH [TIRU]

Dept of Human Nutrition.Chonbuk National University, S.Korea.

http://iamtiru.yolasite.com

Gregor Johann Mendel : The Master Mind behind the birth of GENETICS

Born on : 22 July 1822, Died : 6th January 1884 [62y].1843 : Entered 'Koniginklosser', an Augustinian foundation in Altbrunn.1847: Became priest .1851-1853 : Went to Vienna, studied physics, statistics & natural science.1856 : At Brunn, he started investigation.1865 : published his work.

Mendel’s Paper.

You can Download from:

http://www.esp.org/foundations/genetics/classical/gm-65.pdf

Questions in Mendel’s Mind:

Some characteristics present in one generation (parents) suddenly disappears in the next Generation (Offspring) and again reappears in the subsequent generation (Offspring's offspring). WHY?????????

Why Mendel Choose Pea Plant as a model for his study?

1. Clearly visible Traits (Characters)2. Easy to manipulate (artificial pollination) 3. Life span short4. Next generation can be obtained in short duration.

What were those characters or traits in the pea plant ?

1. Color and smoothness of the seeds

2. Color of the cotyledons (part of the embryo within the seed)

3. Color of the flowers

4. Shape of the pods

5. Color of unripe pods.

6. Position of flowers and pods on the stems.

7.Height of the plants

Terminology

Allele: Loci or Location for a gene.

Locus : is the spot each genes has on a chromosome.

Diploid cells have two genes (a gene pair) for each trait, each on a homologous chromosome.

Homologous chromosome : Homologous chromosomes are chromosome pairs, one from each parent, that are similar in length, gene position and centromere location.

What is Dominant and Receive Trait?

A genetic trait in which one copy of the gene is sufficient to yield an outward display of the trait; dominant genes mask the presence of recessive genes; dominant traits can be inherited from a single parent.

Dominant Trait:

Recessive Trait

An inherited trait that is outwardly obvious only when two copies of the gene for that trait are present—as opposed to a dominant trait where one copy of the gene for the dominant trait is sufficient to display the trait. The recessive condition is said to be masked by the presence of the dominant gene when both are present; i.e., the recessivecondition is seen only in the absence of the dominant gene.

Phenotype ?

the complete observable characteristics of an organism or group, including anatomic, physiologic, biochemical, and behavioral traits, as determined by the interaction of genetic makeup and environmental factors.

Genotype ?

The entire genetic makeup of an organism, the type species of a genus, defined by the complement of allelic forms of each gene or genetic markers present in an organism's genome.

A B C

PP Pp pp

A B C

Laws given by Mendel?

Mendel's First Law : The law of segregation of characteristics.

The Law of Segregation states that when any individual produces gametes, the copies of a gene separate so that each gamete receives only one copy.

Mendel's Second Law : The law of independent Assortment.

The Law of Independent Assortment, also known as "Inheritance Law", states that alleles of different genes assort independently of one another during gamete formation.

Independent assortment occurs during meiosis I in eukaryotic organisms, specifically metaphase I of meiosis, to produce a gamete with a mixture of the organism's maternal and paternal chromosomes. Along with chromosomal crossover, this process aids in increasing genetic diversity by producing novel genetic combinations.

INHERITANCE OF ONE GENE (Tall vs. Dwarf) : monohybrid cross

T T t t

T t

T T T t T t t t

INHERITANCE OF ONE GENE (Purple color flower vs. White ) : monohybrid cross

Conclusion for Mono Hybrid Cross:

1. Unless mutations occur, Mendelian traits are inherited in a predictable Fashion.

2. The F 1 generation shows 100% same phenotype that of the dominant parent, as they exhibit the dominant phenotype. The recessive traits is masked by the dominant gene.

3. The F 2 generation shows 75% dominant phenotype and 25% recessive (phenotypic ratio= 3:1 and Genotype 1:2:1). The recessive phenotype appears in the F 2

Test Cross:

The crossing of an organism, with an unknown genotype, to a homozygous recessive organism (tester). A cross between an individual of unknown genotype or a heterozygote (or a multiple heterozygote) to a homozygous recessive individual.

Law of Dominance

1. Character are controlled by discrete units called FACTORS.2. FACTORS occurs in pairs.3. In a dissimilar pair of factors one member of the pair dominates (dominant) the other (recessive).

Incomplete Dominance

Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele. This results in a combined Phenotype.

Eg.In cross-pollination experiments between red and white snapdragon plants, the resulting offspring are pink. The dominant allele that produces the red color is not completely expressed over the recessive allele that produces the white color.

Incomplete Dominance

Allele R Allele R

mRNA

Enzymes

Substrates

Color giving pigments

Allele R Allele r

mRNA

Enzymes

Substrates

Color giving pigments

Allele r Allele r

mRNA

Enzymes

Substrates

Color giving pigmentsNo Pigments

Q. Can you have a heterozygous red or hybrid Red flower? A. No.

RR =Red, Rr = Pink and rr = White.

There for hetrozygous is a hybrid, that resembles the intermediate between the two parents instead of one.

What is Co-dominance ?

Both the allele contribute to the phenotype of the organism by showing up simultaneously (at the same time) in heterozygous individuals.

Cattle or horses actually have both red and white hairs intermixed, or are spotted. Roan is a third phenotype.

WWW

W

R W

RW

RW WW

roan

roan

white

white

INHERITANCE OF TWO GENES : Dihybrid Cross

Use of Mendelism in Medical Science

1.Monogenic genetic disorders:

Inheritance of a single copy of a defective gene found on a non-sex chromosome.Eg. Polycystic kidney disease and Huntington's Disease.

Autosomal Recessive InheritanceEven one correct copy of the gene can Keep the individual alive.

Both copy corrupted – GAME OVER .

Huntington's disease and Marfan syndrome.Mutations to BRCA1 and BRCA2 genes which have been associated with breast cancer also are transmitted in this pattern.

X-linked recessive inheritance pattern with carrier mother

Duchenne muscular dystrophy, color blindness and hemophilia A .

X-linked recessive inheritance pattern with affected father

No Child Affected.

Pedigree Analysis:

A pedigree chart is a diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next.

Healthy Male

Healthy Female

Carrier Male

Carrier Female

Affected Male

Affected Female

Thank You

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