MENDELLIAN PRINCIPLESOF HEREDITY

Christine Joyce Javier ☺II – LOVE

January 18, 2012

Millions of different kinds of organismsabound our Earth and they reproduces only itsown kind. It didn’t ever happen that a cat canproduce puppies as well as dogs can’t producekittens. Cabbage seeds will not ever producepepper. For a long time no one understood howtraits were inherited, until an Austrian monktinkered in his garden and observe his peas.

MENDEL’S GARDEN PEAS EXPERIMENT Gregor Mendel, as a

monk, also spent this time in the garden. He studied the different structural characteristics and growing habits of plants. Finally, he selected the gardenpeas for his experiments. What do you think arethe reasons why he used the peas for his study?

REASONS FOR CHOOSING GARDEN PEAS

1.) Garden peas have presence of observable traits with contrasting forms.

2.) Garden peas reproduce at a fast rate and reproduce several generations in a short time.

3.) They are hardy plants. They do not need much caring.

4.) Garden peas have its own structural adaptation of self-pollination.

PROCEDURE OF THE EXPERIMENT

Mendel used 29, 000 pea plants andobtained 14 varieties of seeds. He chose tostudy the 7 traits. Each trait had two or moreforms, like height in the pea plant is a traitwith two-forms: short and tall. Pea plants donot grow to be middle-sized.

RESULTS OF THE EXPERIMENTTraits – is the general characteristics of the peas(or any other organism). For example, the colorof the seed.

Characters – is the specific characteristics of thepeas (or any other organism). For example,yellow or green seed.

RESULTS OF THE EXPERIMENT

RESULTS OF THE EXPERIMENTAfter the research with plants, the basic

underlying principles of heredity that hediscovered also apply to people and otheranimals because the mechanisms of heredityare essentially the same for all complex lifeforms.

In our book, we have there “3 Principles of

Heredity” but in other references, they just onlyhave 2.

DEFINITION OF TERMS Genes – section of a chromosome; control

what traits any living thing will have and controls what traits a living thing can pass to its young.

Dominant Trait – trait that hides another trait. Recessive Trait – trait that is hidden. Purebreeding or Truebreeding – when the

traits of the offsprings are the same as the parent plant for several generations.

P Generation – parent generation.

DEFINITION OF TERMS Allele - is one of two or more forms of a gene;

groups of genes. F1 Generation – first filial generation, or the

offsprings of P generation. F2 Generation – second filial generation, or the

offsprings of F1 generation. Genotype – genetic makeup of the cell. Phenotype – organism's observable

characteristics or traits; external appearance of an individual.

DEFINITION OF TERMS Homozygous – has 2 of the identical (same)

alleles of a gene. Heterozygous – has 2 different alleles of a

gene. Punnett Square – is a diagram that is used to

predict an outcome of a particular cross or breeding experiment.

Heredity – passing of traits to offspring.

BASIC PRINCIPLES OF HEREDITYSome biologists refer to Mendel‘s

“principles“ as "laws".

1.) The Law of Dominance2.) The Law of Segregation3.) The Law of Independent Assortment

1ST LAW: THE LAW OF DOMINANCE

It states that: “when purbreeding plantshaving contrasting characters are crossed, allthe offsprings will show only one of thecharacters. The character that appears isdominant and the one that does not isrecessive.”

Meaning: When certain genes, come in 2 forms, one trait will be expressed over the other (dominant form over the recessive one).

1ST LAW: THE LAW OF DOMINANCEEx: In the P Generation, there was a purpleflower and a white flower. They werecombined. Don’t expect that the result of theflower color was light violet. For the F1

Generation, all plants have purple flowers. Thepurple form of the trait was visible but thewhite form was hidden. For the F2 Generation,

the ¾ of plants have purple flowers, and ¼ onlyof them have white flowers.

1ST LAW: THE LAW OF DOMINANCE Dominant Form (visible):Purple form

Recessive Form (hidden):White form

2ND LAW: THE LAW OF SEGREGATION

It states that: “two genes of a pair separate

or segregate during gamete formation.Therefore, the traits are distributed.”

Meaning: Members of a pair of genes for hereditary characters separate cleanly from each other so that only one members of the pair of genes goes into a particular gamete.

2ND LAW: THE LAW OF SEGREGATIONEx: During the formation of gametes, mother or

father’s alleles segregate (separate) so that each zygote (fertilized egg) only carries a single complete copy of a gene. In the picture on the next slide, T=Tall and t=short. In the F2 generation, each zygote either has one "T" or one "t" from mother or one "T" or one "t" from father.

2ND LAW: THE LAW OF SEGREGATION They segregated from the dominate factor and expressed in its original state.

3RD LAW: THE LAW OF INDEPENDENT ASSORTMENT

It states that: “the expression of one particular trait does not affect the expression of another trait.”

Meaning: A trait of one gene does not affect the inheritance of another trait. The genes are inherited independently.

3RD LAW: THE LAW OF INDEPENDENT ASSORTMENT Ex: The F2 Generation produced 4 types: round yellow, round green, wrinkled yellow, and wrinkled green. The result was the dominant trait of (round shape) did not affect the recessive trait of anotherkind (green color). Therefore, the green color(recessive) can appear in both round and wrinkled.The seed color trait does not affect the shape of the

seed.

PUNNETT SQUAREIt is a diagram that is used to predict an

outcome of a particular cross or breedingexperiment.

Example: