Genetics & InheritanceGenetics & Inheritance

The Chromosome Theory of The Chromosome Theory of InheritanceInheritance

Chromosome Theory of Chromosome Theory of Inheritance:Inheritance:

• Genes that code for various traits are Genes that code for various traits are found on chromosomes which are made of found on chromosomes which are made of DNA and found in the nucleus of each cellDNA and found in the nucleus of each cell

Thomas Hunt Morgan (1910): Studies Thomas Hunt Morgan (1910): Studies DrosophiliaDrosophilia melanogastermelanogaster ;common fruit ;common fruit flyfly

Discovered the gene for eye color and wing Discovered the gene for eye color and wing size were both located on the same size were both located on the same chromosome (X) = Linkagechromosome (X) = Linkage

LinkageLinkage = genes located on the same = genes located on the same chromosomechromosome

The closer the genes are on the The closer the genes are on the chromosome, the greater the likelihood of chromosome, the greater the likelihood of crossing overcrossing over

The Law of Independent Assortment does not The Law of Independent Assortment does not apply to linked genes!apply to linked genes!

Gene LinkageGene Linkage

Barbara McClintock & Harriet Creighton Barbara McClintock & Harriet Creighton (1950): Studied (1950): Studied Zea maysZea mays ; corn ; corn

Looked at chromosome #9Looked at chromosome #9They noticed that 2 copies of it were different They noticed that 2 copies of it were different

sizessizesConclusion = Conclusion = Crossing OverCrossing Over had occurred, an had occurred, an

abnormal event caused a piece of another abnormal event caused a piece of another chromosome to attach itself to one of the chromosome to attach itself to one of the copies of chromosome #9copies of chromosome #9

Crossing Over disrupts normal Linkage Groups!Crossing Over disrupts normal Linkage Groups!

Human ChromosomesHuman ChromosomesChromosomes: Humans have 46 individual chromosomes inevery cell of the body except the sex cells

22 pairs = Autosomes (regular, information carryingchromosomes)

1 pair = Sex Chromosomes, determines gender (XX =female, XY = male)

Which Parent determines Which Parent determines the sex of the child?the sex of the child?

MODES OF INHERITANCEMODES OF INHERITANCE

Different ways of inheriting genetic traitsDifferent ways of inheriting genetic traits 1. 1. Complete DominanceComplete Dominance: dominant allele : dominant allele

completely masks out the recessive trait (AA, Aa)completely masks out the recessive trait (AA, Aa) Autosomal Dominant = trait carried on an Autosomal Dominant = trait carried on an

autosome by a dominant gene (A)autosome by a dominant gene (A) Autosomal recessive = trait carried by a Autosomal recessive = trait carried by a

recessive allele (aa)recessive allele (aa) Example: flower color in pea plantsExample: flower color in pea plants P = Purple, p = whiteP = Purple, p = white

MODES OF INHERITANCEMODES OF INHERITANCE2. Incomplete Dominance: One allele of a gene pair is not

fully dominant over the other; being heterozygousproduces an intermediate form, no masking occurs (AA,Aa, aa)

Example: Flower color in snapdragonsRR = red, rr = white, Rr = pink

MODES OF INHERITANCEMODES OF INHERITANCE 3. 3. CodominanceCodominance: both alleles express themselves when : both alleles express themselves when

heterozygous (Blood types A, AB, B, O). There is no true heterozygous (Blood types A, AB, B, O). There is no true recessive trait.recessive trait.

AB Blood type is an example of AB Blood type is an example of CodominanceCodominance = Both = Both alleles in the heterozygous form (alleles in the heterozygous form (IIAAIIBB ) end up ) end up expressing themselves equally. Both traits show up in expressing themselves equally. Both traits show up in the phenotype.the phenotype.

Example: coat color in horsesExample: coat color in horses RR = red , WW = White , RW = roanRR = red , WW = White , RW = roan (RR = red , R(RR = red , R’’RR’’ = White , R R = White , R R’ ’ = roan)= roan)

RR x WWRR x WW RW x RWRW x RW

MODES OF MODES OF INHERITANCEINHERITANCE

4. Polygenic Traits: trait is controlled by morethan one pair of genes (Eye color, Skin color,Human Height). This usually results incontinuous variation. Polygenic inheritance isconsidered the opposite of Pleiotropy.

5. Pleiotropy = when a single gene has morethan one phenotypic expression. Example:Sickle Cell Anemia = misshapen red bloodcells ultimately causes other problems suchas anemia, pneumonia, heart & kidney failure,bone abnormalities, and impaired mentalfunctioning.

MODES OF INHERITANCEMODES OF INHERITANCE

6. 6. EpistasisEpistasis = one gene affects the = one gene affects the phenotypic expression of a second phenotypic expression of a second gene. (Skin pigmentation) One gene gene. (Skin pigmentation) One gene codes for color, the other codes for the codes for color, the other codes for the amount of pigment.amount of pigment.

MODES OF INHERITANCEMODES OF INHERITANCE

7. 7. Multiple AllelesMultiple Alleles: a gene having : a gene having more than two alleles (Blood types)more than two alleles (Blood types)

PHENOTYPESPHENOTYPES % of Population% of Population GENOTYPESGENOTYPES AA 39% 39% IIAAIIAA , I , IAAIIii

BB 12%12% IIBBIIBB , I , IBBIIii

** ABAB 4%4% I IAAIIBB

OO 45%45% IIiiIIii

Blood TypesBlood TypesDiscovered in 1900 by Dr. Karl LandsteinerDiscovered in 1900 by Dr. Karl LandsteinerBased on the presence or absence of Based on the presence or absence of

specific specific agglutinogensagglutinogens (clotting factors) on (clotting factors) on the surface of red blood cells (RBC’s = the surface of red blood cells (RBC’s = Erythrocytes)Erythrocytes)

For example: a person with blood type A For example: a person with blood type A posseses posseses A-antigensA-antigens and and Anti-B Anti-B antibodiesantibodies

The blood will clot if a foreign Antigen is The blood will clot if a foreign Antigen is presentpresent

Donor vs. RecipientDonor vs. Recipient

• Universal DonorUniversal Donor = = Blood type O ; contains Blood type O ; contains no A or B antigens no A or B antigens No Clotting reaction No Clotting reaction

Universal RecipientUniversal Recipient = Blood type = Blood type ABAB ; ; contains both A & B antigens contains both A & B antigens Will Will recognize antigens from any blood typerecognize antigens from any blood type

Rh FactorRh Factor

Rh Factor = Rh Factor = ((RhRhesus monkey) You esus monkey) You either have it (+) or you don’t (-) either have it (+) or you don’t (-)

Sensitization can occur by:Sensitization can occur by:– .).)Rh+ blood transfused into Rh- personRh+ blood transfused into Rh- person– .).)Rh- mother carries a fetus who is Rh+Rh- mother carries a fetus who is Rh+

IIAAIIA x A x IIBBIIBB IIAAIIiix Ix IBBIIii

MODES OF INHERITANCEMODES OF INHERITANCE 8. 8. Sex-Linked InheritanceSex-Linked Inheritance: trait carried on the : trait carried on the

sex chromosomes; usually the X (XX = female; sex chromosomes; usually the X (XX = female; XY = male)XY = male)

X-Linked Recessive = XX-Linked Recessive = Xaa (Colorblindness, Hemophilia) (Colorblindness, Hemophilia) X-Linked Dominant = XX-Linked Dominant = XAA; Y-Linked (Rare); Y-Linked (Rare)

CarrierCarrier = person not affected by the trait but can = person not affected by the trait but can pass it on to offspring = Xpass it on to offspring = XAA X Xa a Only females Only females can be carriers for sex-linked traits because if a can be carriers for sex-linked traits because if a male has the gene, he will also exhibit the trait!male has the gene, he will also exhibit the trait!

MODES OF INHERITANCEMODES OF INHERITANCE

9. 9. X – inactivationX – inactivation: one of the two X : one of the two X chromosomes in a female does not uncoil chromosomes in a female does not uncoil during embryonic development. The during embryonic development. The chromosome that remains coiled is called chromosome that remains coiled is called a a Barr Body Barr Body and contains genes that will and contains genes that will not get expressed. This could cause a not get expressed. This could cause a sex-linked trait to affect a female that sex-linked trait to affect a female that would normally be only a carrier.would normally be only a carrier.

MODES OF INHERITANCEMODES OF INHERITANCE

10. 10. Sex-Influenced TraitsSex-Influenced Traits: expressed : expressed in both sexes, but they are expressed in both sexes, but they are expressed differently (Pattern Baldness)differently (Pattern Baldness)

B= Normal; b= BaldB= Normal; b= Bald female (bb) = bald; male (bb female (bb) = bald; male (bb oror Bb) Bb)

=bald=bald

BB x BbBB x Bb Bb x BbBb x Bb

MODES OF INHERITANCEMODES OF INHERITANCE

11. 11. Sex-Limited TraitsSex-Limited Traits: autosomal : autosomal traits expressed in only one sex (Lion’s traits expressed in only one sex (Lion’s mane)mane)

MODES OF INHERITANCEMODES OF INHERITANCE• 12. 12. Dihybrid CrossesDihybrid Crosses: : follow 2 follow 2

traits at a time (AaBb)traits at a time (AaBb) Example: A = purple flowers, a = white B Example: A = purple flowers, a = white B

= Tall, b = short= Tall, b = short If you cross two parents, where the father If you cross two parents, where the father

is AABB and the mother is aabb: the is AABB and the mother is aabb: the possible gametes are AB x ab. This can possible gametes are AB x ab. This can be determined using the be determined using the F.O.I.L methodF.O.I.L method..

Dihybrid CrossesDihybrid Crosses

F = firstF = first O = outsideO = outside I = insideI = inside L = lastL = last AABB x aabb --> AABB x aabb --> RrYy x RrYyRrYy x RrYy

Results = 100% AaBb

GENETIC DISORDERSGENETIC DISORDERS

Disorders or diseases related to a Disorders or diseases related to a persons genes or chromosomes; persons genes or chromosomes; inherited in the same ways as other inherited in the same ways as other traits.traits.

2 Mechanisms exist:2 Mechanisms exist:

Genetic DisordersGenetic Disorders

1. Inherited on Genes1. Inherited on Genes: inherited as a : inherited as a trait (Autosomal, sex-linked, sex trait (Autosomal, sex-linked, sex influenced, etc...)influenced, etc...)

colorblindnesscolorblindness hemophilia “bleeder’s disease”hemophilia “bleeder’s disease” muscular dystrophymuscular dystrophy albinismalbinism ProgeriaProgeria

Genetic DisordersGenetic Disorders 2. Chromosome Abnormalities2. Chromosome Abnormalities: not : not

caused by a genecaused by a gene A.) Extra or Missing Chromosomes. A.) Extra or Missing Chromosomes.

AneuploidyAneuploidy = abnormal chromosome = abnormal chromosome numbernumber

– Non-DisjunctionNon-Disjunction = failure of chromosome pairs to = failure of chromosome pairs to separate properly during meiosis, end up with separate properly during meiosis, end up with daughter cells having either too many or not enough daughter cells having either too many or not enough chromosomes in them.chromosomes in them.

Ex. Down Syndrome “Trisomy 21”Ex. Down Syndrome “Trisomy 21”

Genetic DisordersGenetic Disorders

B.) Mutated Chromosome = damaged DNA, B.) Mutated Chromosome = damaged DNA, genes located in that section are damagedgenes located in that section are damaged

Deletion: missing gene or piece of Deletion: missing gene or piece of chromosomechromosome

Duplication: extra piece, genes duplicatedDuplication: extra piece, genes duplicated Translocation: gene switches chromosomesTranslocation: gene switches chromosomes Inversion: fragment of gene gets turned Inversion: fragment of gene gets turned

aroundaround

1. 1. KaryotypingKaryotyping = genetic map of all = genetic map of all the chromosomes that an organism the chromosomes that an organism

possessespossesses 2. 2. AmniocentesisAmniocentesis = test done before = test done before

birth, take sample of amniotic fluid birth, take sample of amniotic fluid (C.V.S.)(C.V.S.)

3. 3. Genetic CounselingGenetic Counseling = determine = determine family medical historyfamily medical history

SCREENING FOR SCREENING FOR DISORDERSDISORDERS

THE END!!THE END!!