Genetics basics

Mendelian activity

Parent Generation

Parent Generation

Cross pollination

Parent Generation

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• result

Parent Generation

F1 Generation

Parent Generation

F1 Generation

Parent Generation

F1 GenerationSelf pollination

Parent Generation

F1 Generation

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• result

Parent Generation

F1 Generation

F2 Generation, 3:1 ratio

Parent Generation

F1 Generation

F2 Generation, 3:1 ratio

Parent Generation

F1 Generation

F2 Generation, 3:1 ratio

What Do the Peas Look Like?What Do the Peas Look Like?

Mendelian vocabulary

Hereditary factorsHybridPure or purebreed

Dihybrid CrossDihybrid Cross• Traits: : Seed shape & Seed color• Alleles::

R round / r wrinkled

Y yellow / y green

RrYy x RrYy

RrYy x RrYy

RY Ry rY ryRY Ry rY ry RY Ry rY ryRY Ry rY ry

All possible gamete combinationsAll possible gamete combinations

Genetic TerminologyGenetic Terminology

TraitTrait - any characteristic that can be - any characteristic that can be passed from parent to offspring passed from parent to offspring

HeredityHeredity - passing of traits from - passing of traits from parent to offspring parent to offspring

GeneticsGenetics - study of heredity - study of heredity

Types of Genetic Types of Genetic CrossesCrosses

Monohybrid cross Monohybrid cross - - cross involving a cross involving a single traitsingle traite.g. flower color e.g. flower color

Dihybrid crossDihybrid cross - - cross involving two traits cross involving two traits e.g. flower color & plant heighte.g. flower color & plant height

AllelesAlleles - - two forms of a two forms of a gene gene (dominant & (dominant & recessive)recessive)

DominantDominant - - stronger of two genes expressed stronger of two genes expressed in the hybrid; represented byin the hybrid; represented by aa capital letter capital letter (R)(R)

RecessiveRecessive - - gene that shows up less often in gene that shows up less often in a cross; represented by aa cross; represented by a lowercase letter (r)lowercase letter (r)

TerminologyTerminology

GenotypeGenotype - - gene combination for a traitgene combination for a trait (e.g. RR, Rr, rr) (e.g. RR, Rr, rr)

PhenotypePhenotype - - the physical feature the physical feature resulting from a genotyperesulting from a genotype (e.g. red, (e.g. red, white)white)

TerminologyTerminology

GenotypesGenotypes

HomozygousHomozygous genotype – When the two genotype – When the two alleles are same (dominant or 2 recessive alleles are same (dominant or 2 recessive genesgenes) ) e.g. TT or tt;e.g. TT or tt; also called also called pure pure 

HeterozygousHeterozygous genotype – When the 2 genotype – When the 2 alleles are different- one dominant & one alleles are different- one dominant & one recessive allele    (recessive allele    (e.g. Tt);e.g. Tt); also called also called hybridhybrid

Mendel’s LawsMendel’s Laws

1. Law of Dominance2. Law of Segregation

3. Law of Independent assortment

Law of DominanceStates that on crossing homozygous organisms for single pair of contrasting characters, only one characters make its appearance in F1 generation and is name as Dominant character.

Law of SegregationLaw of Segregation

• During the During the formation of gametesformation of gametes (eggs or (eggs or sperm), the two sperm), the two allelesalleles responsible for a responsible for a trait trait separate from each other.separate from each other.

• Alleles for a trait are then "recombined" at Alleles for a trait are then "recombined" at fertilization, producing the genotype for fertilization, producing the genotype for the traits of the offspringthe traits of the offspring.

Law of Independent Law of Independent AssortmentAssortment

• AllelesAlleles for for differentdifferent traits traits are are distributeddistributed to sex cells (& offspring) to sex cells (& offspring) independentlyindependently of one another. of one another.

• This law can be illustrated using This law can be illustrated using dihybrid crossesdihybrid crosses..

Mendel´s pollination method

Mendel’s Experimental Mendel’s Experimental MethodsMethods

•Mendel Mendel hand-pollinatedhand-pollinated flowers using a flowers using a paintbrushpaintbrush

–He could He could snip (cut) the snip (cut) the stamensstamens to prevent self- to prevent self-pollinationpollination

•He traced traits through the He traced traits through the several generationsseveral generations

•

Why peas?Why peas?

Why peas,Why peas, Pisum Pisum sativumsativum??

Can be grown in a Can be grown in a small areasmall area Produce Produce lots of offspring lots of offspring Produce Produce purepure plants when plants when allowed to allowed to self-pollinateself-pollinate several generations several generations Can be Can be artificially cross-artificially cross-pollinatedpollinatedBisexual.Many traits known.Above all, easy to growAbove all, easy to grow

• Some slides were taken from a previous work Some slides were taken from a previous work by Dr. R. Siva (VIT University, INDIA)by Dr. R. Siva (VIT University, INDIA)