Heredity: Patterns of Inheritance

Genetics: The science of heredity.

It all started with an idea..

In 1866 Gregor Mendel, an Austrian monk, presented the results of some difficult experiments on inheritance of the garden pea. Currently, Mendels work seems elementary compared to modern day genetics, but it is still just as important.

Garden peas are like hermaphrodites, they have both male and female parts and are able to self-fertilize. Because they had both reproductive parts it made it easy for Mendel to conduct experiments with complete control over what gender the parent plants would be...and thus being able to control the offsprings gender. For his experiments, Mendel chose a parent plant that was true breeding, meaning that all the self-fertilizing offspring displayed the same forms of traits as their parents.

After getting the same results over and over, Mendel decided to change things up. He then decided to test the question of what would happen when he crossed his different true-breeding varieties with each other.

The offspring of two different varieties are called hybrids, and the cross-fertilization itself is known as a hybridization, or more simply a cross. The true breeding parental plants are called the P generation (P for parental), and their hybrid offspring are the F1 generation (F for filial, from the latin word for "son"). Then when the F1 plants self fertilize or fertilize each other, their offspring are the F2 generation.

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I.

monohybrid cross

The example shown above of an offspring

hybrid is also an example of a monohybrid

cross. Mono, meaning one, and standing for

the fact that the parent plants only differ

in one character.

II.

dihybrid cross

Breaking down the word to Di - hybrid

you will see that di, meaning two, implies

that this kind of hybrid has parent plants

that differ in two characters.

What is a character??

A heritable feature that varies among individuals, such as flower color, is called a character. And for each variant of a character, such as blue or white flowers, is called a trait.

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Testcross

1)Mating between an individual of an unknown genotype and a homozygous recessive individual.

2)This will show whether the unknown genotype includes the recessive allele.

3)The Testcross was used by Mendel to confirm true breeding genotypes (It was his proof that the parent plants in his experiments were actually "true").

How to find the connection in your family.

A Pedigree.

This shows the inheritance of a trait in a family through multiple generations, demonstrates dominant or recessive inheritance, and can also be used to deduce genotypes of family members.

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The difference between

Genotype & a Phenotype.

Genotype:

1)A representation of an organisms genetic constitution.

2)A Genotype plays the part of the genetic structure of an organism.

3)Total number of genes transmitted from a parent to it's offspring.

Phenotype:

1)The meaning behind a genotype.

2)An outward expression of the genotype.

3)What an organism looks like because of its specific genotype, as well as its physiological traits and behavior.

Example: In a garden some flowers bloom. And in this garden blue flowers are dominant over white flowers. Let F stand for the Blue trait in the allele for the flowers, and then let f stand for the White trait in the allele for the flowers. The genotypes could vary..

FF , Ff , ff

Well the genotypes above have more meaning then just a representation of a trait by use of letters from the alphabet. A capitol letter signifies dominance because it is larger. A lowercase letter signifies recessive because it is smaller. And if you can distinguish the difference between dominant and recessive traits than you will be able to distinguish the Phenotypes.

FF=Homozygous Blue Flowers

Ff=Heterozygous Blue Flowers

ff=Homozygous White Flowers

Dominant traits are common and recessive traits are more rare.

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What is an allele?

An allele is the alternative versions of a gene.

And Multiple Alleles are where there are more than two possible alleles, any one of which can occupy a locus. Multiple Alleles determine major blood groups in humans.

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More to come soon....going to take a break.