Mendelian GeneticsMendelian Genetics

How Genes Work

Who Are You?Who Are You?

Phenotype–How you

look; PHysical appearance

Genotype–Your genetic

makeup; GENEs

Modern genetics began with Gregor Mendel’s quantitative experiments with pea plants

Father of GeneticsFather of Genetics

Figure 9.2A, B

Stamen

Carpel

Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation

Figure 9.2C

This illustration shows his technique for cross-fertilization

1 Removed stamensfrom purple flower

White

Stamens

Carpel

PurplePARENTS(P)

OFF-SPRING

(F1)

2 Transferred pollen from stamens of white flower to carpel of purple flower

3 Pollinated carpel matured into pod

4 Planted seeds from pod

Genetics BasicsGenetics BasicsChromosomes occur in pairs, one from

MOM, one from DAD (homologues)Genes are carried on chromosomes Genes code for a trait or characteristic

(I.e. hair color)Alternate forms of that trait are called

ALLELES (ie. Blond, brown, redhead, etc)

Alleles…Alleles…

Alleles can be dominant or recessive

Heterozygous vs. homozygousOnly way to “see” a recessive

trait?

Mendel ‘s Mendel ‘s basic lawsbasic laws

Law of Segregation

Law of Independent Assortment

The chromosomal basis of Mendel’s principles

Figure 9.17

Walter Sutton’s Theory of Walter Sutton’s Theory of Chromosomal InheritanceChromosomal Inheritance

(Mendel’s proof)(Mendel’s proof)Gametes contribute to heredity via

nuclear material (chromosomes)Homologues segregate during

meiosisHomologues separate

independently of other homologous pairs

ProbabilityProbability

Mathmatical model of how often specific events will happen

# of occurances/# of attempts

Punnett SquarePunnett Square

Visual representation or model of – what alleles can be present in

gametes – how those alleles can recombine in

offspringUsed to determine the probability of

offspring’s genetic makeup

Monohybrid CrossMonohybrid Cross

One gene–2 alleles considered (one from

mom, one from dad

Dihybrid CrossDihybrid Cross

2 genes–4 alleles considered

How can we determine Homo- How can we determine Homo- vs. heterozygous individuals?vs. heterozygous individuals?

Test Cross–Must use homo recessive to

conduct cross in order to “see” the questionable allele

What Mendel Didn’t SeeWhat Mendel Didn’t SeeMultiple allelesCodominanceEpistasisPolygenic traits or Continuous VariationPleiotropyIncomplete Dominance or “blended

inheritance”Environmental EffectsSex linked and sex influenced traits

CoDominanceCoDominance–Both alleles expressed at the

same time; both dominant

Incomplete dominance: neither allele is fully dominant (blended inheritance)

Figure 9.12Ax

EpistasisEpistasis Sequential action of genes

– Product of one gene influences another (one gene gives “permission” for another allele to work

– Gene action acts as a biochemical pathway & feedback inhibition

Ex: Indian corn coloration

PleiotropyPleiotropy

Where one allele may have multiple effects on phenotype–

Normal and sickle red blood cells

Figure 9.14x1

Individual homozygousfor sickle-cell allele

Sickle-cell (abnormal) hemoglobin

Abnormal hemoglobin crystallizes,causing red blood cells to become sickle-shaped

Sickle cells

Breakdown of red blood cells

Clumping of cells and clogging of

small blood vessels

Accumulation ofsickled cells in spleen

AnemiaHeart failure

Pain and fever Brain

damageDamage to

other organs

Spleen damage

Kidney failure

RheumatismPneumonia and other infections

Paralysis

Impaired mental

function

Physical weakness

Continuous VariationContinuous Variationor Polygenic Traitsor Polygenic Traits

Multiple genes acting to influence a characteristic–Produces gradual changes, not

distinct “borders”Ie. Height, weight, nose length, skin pigment

Figure 9.16

P GENERATION

F1 GENERATION

F2 GENERATION

aabbcc(very light)

AABBCC(very dark)

AaBbCc AaBbCc

Sperm

Fra

cti

on

of

po

pu

lati

on

Skin pigmentation

Environmental InfluenceEnvironmental Influence

Example = color change of fur in arctic animals

Same eyes, different lighting Same eyes, different lighting

Multiple AllelesMultiple Alleles

More than one allele per gene

3 alleles (ABO)– 4 phenotypes (A, B, AB, O)

Uses concept of glycoproteins (sugar name tags or antigens) to mark cells

Non-recognition of the correct “name tag” for blood type can cause agglutination

Landsteiner Blood GroupsLandsteiner Blood GroupsType A – galactosamine – AA

(homo) or AO (hetero)Type B – galactose – BB or BOType AB – galactosamine +

galactose (codominant)Type O – no sugar marker - OO

Blood Donor FactsBlood Donor Facts

Universal Donor Universal Recipient

Rh factorRh factorRh factor can be + or –+ is like a “seen” name tag or antigen - is “invisible”Rh- moms that have Rh+ babies are subject

to spontaneous abortions – Erythroblastosis fetalis

– Controlled with an injectionof RhoGam to “hide” babies cells

Sex LinkedSex Linked “Sex on the X” Specific

trait/disorder is found on sex chromosome, usually the X

Usually recessive traits

Seen more often in males than females

Ex: color blindness, hemophilia

Barr Body inactivationBarr Body inactivation

In females, both X chromosomes are not metabolically active

Random inactivation of one X chromosome may influence traits expressed