Genetics and Genetics and InheritanceInheritance

Genetics: the scientific study of Genetics: the scientific study of heredityheredity

People in the 1770’s believed that People in the 1770’s believed that traits blendedtraits blended

Most of the leading scientists in the Most of the leading scientists in the 19th century accepted this "blending 19th century accepted this "blending theory." theory." 

Lemark’s IdeaLemark’s Idea The inheritance of acquired The inheritance of acquired

characteristics. Until the late characteristics. Until the late nineteenth century, people nineteenth century, people believed that acquired traits were believed that acquired traits were passed down.passed down.

Tattoos, body building, accidents.Tattoos, body building, accidents. The giraffe’s long neck is NOT an The giraffe’s long neck is NOT an

acquired trait.acquired trait.

Gregor MendelGregor Mendel Studied to be a monk in Austria in Studied to be a monk in Austria in

mid 19mid 19thth century. century. Influenced by society to become a Influenced by society to become a

noble person – a person of God.noble person – a person of God. Mendel loved science, and to pass Mendel loved science, and to pass

time – he took care of the garden. time – he took care of the garden. Fell in love with it. Fell in love with it.

Began to notice certain similar Began to notice certain similar characteristics.characteristics.

More Mendel…More Mendel… He observed multiple He observed multiple

generations of pea plants, and generations of pea plants, and noticed subtle changes – and noticed subtle changes – and wondered why they occurred.wondered why they occurred.

He collected data for years and He collected data for years and began to formulate hypotheses.began to formulate hypotheses.

Mendel picked common garden Mendel picked common garden pea plants for the focus of his pea plants for the focus of his research because they:research because they:– can be grown easily in large can be grown easily in large

numbers numbers – reproduction can be reproduction can be

manipulated.  manipulated.  – Pea plants have both male and Pea plants have both male and

female reproductive organs.  As female reproductive organs.  As a result, they can either self-a result, they can either self-pollinate themselves or cross-pollinate themselves or cross-pollinate with another plant.  pollinate with another plant. 

Mendel observed seven traits that Mendel observed seven traits that are easily recognized and apparently are easily recognized and apparently only occur in one of two forms:only occur in one of two forms:

1.   1.   flower colorflower color is purple or white is purple or white 2.   2.   seed colorseed color is yellow or green is yellow or green 3.3.flower positionflower position is axil or terminal    is axil or terminal   

       4.4.pod shapepod shape is inflated or constricted is inflated or constricted 5.5.stem lengthstem length is long or short is long or short 6.6.pod colorpod color is yellow or green is yellow or green 7.7.seed shapeseed shape is round or wrinkled is round or wrinkled

Mendel’s ExperimentMendel’s Experiment The key to his experiment was that The key to his experiment was that

he started with pure breed plants.he started with pure breed plants.

Pure breed means that they contain Pure breed means that they contain only one type of gene – YYonly one type of gene – YY

Allele – different versions of the Allele – different versions of the same gene.same gene.

Mendel’s Experiment Mendel’s Experiment Continued….Continued….

In cross-pollinating – he crossed In cross-pollinating – he crossed yellow and green seedsyellow and green seeds

Mendel found that the first offspring Mendel found that the first offspring

generation (F1) produced ALL yellow generation (F1) produced ALL yellow peas. peas.

Results of F2Results of F2

After he obtained the F1 After he obtained the F1 offspring, he self – pollinated a offspring, he self – pollinated a yellow seeded plant with itself.yellow seeded plant with itself.

The results (F2 generation) The results (F2 generation) had a 3:1 ratio – 3 yellow and had a 3:1 ratio – 3 yellow and 1 green.1 green.

Mendel continued this Mendel continued this practice 28,000 times over practice 28,000 times over about 20-30 years with about 20-30 years with different traits.different traits.

Mendel came up with 2 Mendel came up with 2 fundamental laws.fundamental laws.

Mendel’s LawsMendel’s Laws Law of Independent Law of Independent

Assortment – each trait is Assortment – each trait is found on separate genes and found on separate genes and each gene comes in pairs that each gene comes in pairs that will separate on their own.will separate on their own.

Law of Segregation - TBTAALDLaw of Segregation - TBTAALD

Mendel's TheoryMendel's Theory Mendel's TheoryMendel's Theory

– Each individual has two factors (we now call Each individual has two factors (we now call these genes) for each trait.these genes) for each trait.

– When both genes are the same, the individual When both genes are the same, the individual is said to be homozygous for that trait. If the is said to be homozygous for that trait. If the two genes are different, the individual is two genes are different, the individual is heterozygous for that trait.heterozygous for that trait.

– Alternate types of genes for each trait are Alternate types of genes for each trait are alleles.alleles.

– The actual genetic makeup of an individual is The actual genetic makeup of an individual is the genotype.the genotype.

Phenotype refers to the outward expression of Phenotype refers to the outward expression of the genes. the genes.

What Did Mendell gather from his What Did Mendell gather from his Data Data

2 big Laws2 big Laws Mendel's First Law: Law of Mendel's First Law: Law of

SegregationSegregation, says that only one , says that only one allele is passed to a gamete, and allele is passed to a gamete, and gametes join randomly when gametes join randomly when uniting to form offspring.uniting to form offspring.

Mendel's Second Law: Law of Mendel's Second Law: Law of Independent AssortmentIndependent Assortment

Analyzing Mendel's Analyzing Mendel's ResultsResults

Punnett Squares Punnett Squares - an easy way - an easy way to express the probabilies of to express the probabilies of genotypes genotypes

A dihybrid cross involves a study of A dihybrid cross involves a study of inheritance patterns for organisms inheritance patterns for organisms differing in two traits. differing in two traits.

Mendel invented the dihybrid cross to Mendel invented the dihybrid cross to determine if different traits of pea plants, determine if different traits of pea plants, such as flower color and seed shape, such as flower color and seed shape, were inherited independently. were inherited independently.

in a dihybrid cross that led Mendel to in a dihybrid cross that led Mendel to propose that alleles of different genes propose that alleles of different genes are assorted independently of one are assorted independently of one another during the formation of gametes. another during the formation of gametes.

Punnet Square for Dihybrid Punnet Square for Dihybrid CrossCross

S=smooth seedS=smooth seed s=dented seeds=dented seed Y=yellowY=yellow Y=greenY=green

Heterozygous smooth seed plant Heterozygous smooth seed plant that is also heterozygous yellow that is also heterozygous yellow seeded plant seeded plant

Heterozygous smooth seed plant Heterozygous smooth seed plant that is also heterozygous yellow that is also heterozygous yellow seeded plant is mated withseeded plant is mated with

Smooth, yellow phenotype Smooth, yellow phenotype

Smooth, green phenotype Smooth, green phenotype

Dented, yellow phenotype Dented, yellow phenotype

Dented, green Dented, green phenotype phenotype