Basic GeneticsBasic Genetics

Gregor Mendel

The Father

of Genetics

Gregor Mendel

Objectives:Objectives: To distinguish between To distinguish between

heredity and inheritanceheredity and inheritance

To define pollinationTo define pollination

To identify the major parts To identify the major parts of a flowering plantof a flowering plant

To describe Mendel’s To describe Mendel’s experiments in heredityexperiments in heredity

HeredityHeredity – – transmission of transmission of traits traits from parents tofrom parents to their their

offspringoffspring

Inheritance passing of traits byheredity

Mendel’s experimentsMendel’s experiments used pea plantsused pea plants

PollinationPollination – transfer of pollen from – transfer of pollen from anthers to stigma in flowersanthers to stigma in flowers

1)1) self pollination self pollination occurs within the occurs within the same flowersame flower or or same plantsame plant

2) 2) cross pollinationcross pollination occurs between occurs between different plantsdifferent plants

Receptical

Mendel’s Crosses with Pea PlantsMendel’s Crosses with Pea Plants

Pure tallplants

X Pure shortplantsP1

parentalgeneration

Cross Pollination

All Tall plantsF1

first filialgeneration

Self Pollination

787 tall plants, 277 short plants F2

second filialgeneration

3 to 1 ratio

Objective:Objective:

To describe Mendel’s 3 To describe Mendel’s 3 principles of inheritanceprinciples of inheritance

1) 1) Principle of Dominance and Principle of Dominance and RecessivenessRecessiveness

Each trait is Each trait is controlled by 2 controlled by 2 factorsfactors, , one one factor factor ((dominant dominant ) ) may may mask the othermask the other factor factor ((recessiverecessive ) ) preventing it from having an effect.preventing it from having an effect.

P1 F1 F2

2) 2) Principle of SegregationPrinciple of Segregation

The two The two factors for a factors for a characteristicharacteristic c separate separate during the during the formation of formation of eggs and eggs and sperm.sperm.

3) 3) Principle of Independent Principle of Independent AssortmentAssortment

Factors for Factors for different different characteristics characteristics are are distributed distributed to reproductive to reproductive cells cells independently.independently.

Objectives:Objectives:

To define geneTo define gene

To define alleleTo define allele

GeneGene – segment of DNA on a – segment of DNA on a chromosome that chromosome that codes for a codes for a

particular proteinparticular protein

genes genes occur in occur in pairspairs

AlleleAllele – alternative form of a gene – alternative form of a gene

g = yellow pods

G = green pods

t = short

T = tall

Dominant capital letter

Recessive Lowercase letter

Objectives:Objectives:

To define genotype and To define genotype and phenotypephenotype

To distinguish between To distinguish between homozygous and homozygous and heterozygousheterozygous

To define multiple allelesTo define multiple alleles

GenotypeGenotype – – genetic makeup genetic makeup of an organism ( of an organism (genesgenes))

(internal information)

(external appearance)

Phenotype –physical characteristics of an organism

What does Phenotypes come form

Example of Genotype and Example of Genotype and PhenotypePhenotype

TT

genotype

Tall

phenotype

HomozygousHomozygous – – when when both both allelesalleles of a pair are the of a pair are the samesame

homozygous dominant

homozygous recessive

TT

tt

HeterozygousHeterozygous – – when when bothboth allelesalleles of a pair are of a pair are notnot the samethe same

heterozygous (tall)

Tt

Multiple allelesMultiple alleles – – 3 or more3 or more alleles alleles that control a trait that control a trait

ExampleExample – blood type (I – blood type (IAA,I,IBB,i,ioo))

GENOTYPESGENOTYPES IIAAIIAA IIAAiioo

RESULTING PHENOTYPESRESULTING PHENOTYPES Type AType A Type AType A

IIBBIIBB IIBBiioo

Type BType B Type BType B

IIAAIIBB Type ABType AB

iiooiioo Type OType O

Objectives:Objectives:

To define probabilityTo define probability

To predict the results To predict the results of monohybrid of monohybrid crosses by using a crosses by using a Punnett squarePunnett square

Probability =number of times a particular event occursnumber of opportunities for the event to occur

ProbabilityProbability – likelihood that a – likelihood that a particular event will occurparticular event will occur

Example 1: Example 1: Flipping a CoinFlipping a Coin

Chances of coming up heads = ½

Example 2: Example 2: Rolling DiceRolling Dice

16 x

16

=136

probabilityof rolling a

six on 1 dice

probabilityof rolling a

six on 1 dice

probabilityof rolling a

six on 2 dice

monohybrid crossmonohybrid cross – –

Objectives:Objectives:

To define test crossTo define test cross

To define incomplete To define incomplete dominancedominance

To define codominanceTo define codominance

Test crossTest cross – an individual – an individual with with unknown genotypeunknown genotype is is crossed crossed withwith a a homozygous homozygous

recessiverecessive individual individual used to used to

determine the determine the genotype genotype of any of any individual whose individual whose phenotype is phenotype is dominantdominant

In rabbits, In rabbits, blackblack fur color is fur color is dominant over browndominant over brown fur color fur color

B = black furb = brown fur

bb

BB or Bb

Incomplete DominanceIncomplete Dominance

when 2 when 2 or more allelesor more alleles influence the phenotypeinfluence the phenotype

resultsresults in a trait in a trait intermediate intermediate between between the the dominantdominant and and recessive traitsrecessive traits

Incomplete Incomplete DominanceDominance

CodominanceCodominance – condition in – condition in which which both allelesboth alleles of a gene are of a gene are

expressedexpressed

exampleexample – roan coat in horses – roan coat in horses

white hair (Hwhite hair (HWW)) is codominant with is codominant with redred hair (hair (HHRR))

horses with genotype (horses with genotype (HHRRHHWW) ) have have coats with a mixture of coats with a mixture of redred andand whitewhite hairshairs (roan) (roan)

Roan CoatRoan Coat

Objectives:Objectives:

To predict the results of To predict the results of dihybrid crosses by using dihybrid crosses by using a Punnett squarea Punnett square

dihybrid crossdihybrid cross – cross – cross between individuals that involves between individuals that involves two pair of contrasting traitstwo pair of contrasting traits