AP Biology Beyond Mendel’s Laws of Inheritance

AP Biology Journal Assignment  For some of the porphyrias, attacks are precipitated by an environmental trigger. Using OMIM, describe factors that can trigger an attack of two of the following:  acute intermittent porphyria  porphyria cutanea tarda  Coproporphyria  porphyria variegate  erythropoietic protoporphyria Historical reference?

AP Biology Extending Mendelian genetics  Mendel worked with a simple system  peas are genetically simple  most traits are controlled by a single gene  each gene has only 2 alleles, 1 of which is completely dominant to the other  The relationship between genotype & phenotype is rarely that simple

AP Biology Lethal Allele Combinations  Homozygous recessive lethal alleles can eliminate a progeny class  Do they always have to be homozygous recessive?

AP Biology

Multiple Alleles  A gene can have more than two alleles, but a diploid individual only has one or two of them.  Different allele combinations can produce different phenotypes and different severities of symptoms.

AP Biology Incomplete dominance  Heterozygote shows an intermediate, blended phenotype  example:  RR = red flowers  rr = white flowers  Rr = pink flowers  make 50% less color RRRrrr

AP Biology Incomplete dominance true-breeding red flowers true-breeding white flowers X P 100% 100% pink flowers F 1 generation (hybrids) self-pollinate 25% white F 2 generation 25% red 1:2:1 50% pink It’s like flipping 2 pennies!

AP Biology Incomplete dominance in beta fish.

AP Biology Co-dominance  2 alleles affect the phenotype equally & separately  not blended phenotype  example: ABO blood groups  3 alleles  I A, I B, i  I A & I B alleles are co-dominant to each other  both antigens are produced  both I A & I B are dominant to i allele  produces glycoprotein antigen markers on the surface of red blood cells

AP Biology Blood compatibility  Matching compatible blood groups  critical for blood transfusions  A person produces antibodies against antigens in foreign blood  wrong blood type  donor’s blood has A or B antigen that is foreign to recipient  antibodies in recipient’s blood bind to foreign molecules  cause donated blood cells to clump together  can kill the recipient Karl Landsteiner ( ) 1901 | 1930

AP Biology Blood donation clotting

AP Biology The Blood Typing Game nggame/game/index.html

AP Biology Pleiotropy  Most genes are pleiotropic  one gene affects more than one phenotypic character  wide-ranging effects due to a single gene  dwarfism (achondroplasia)  gigantism (acromegaly)

AP Biology

Acromegaly: André the Giant

AP Biology Epistasis  One gene completely masks another gene  coat color in mice = 2 separate genes  C,c: pigment (C) or no pigment (c)  B,b: more pigment (black=B) or less (brown=b)  cc = albino, no matter B allele  9:3:3:1 becomes 9:3:4 How would you know that difference wasn ’ t random chance? Chi-square test!

AP Biology Epistasis in Labrador retrievers  2 genes: (E,e) & (B,b)  pigment (E) or no pigment (e)  pigment concentration: black (B) to brown (b) E–B–E–bbeeB–eebb

AP Biology Epistasis in grain color 9/16 purple 7/16 white F 1 generation All purple (AaBb) X Eggs White (aaBB) White (AAbb) F 2 generation A = enzyme 1 + B = enzyme 2  purple color (anthocyanin) AB AbaBab Ab aB ab AABB AABb AaBB AaBb AABb AAbb AaBb Aabb AaBB AaBb aaBB aaBb AaBb Aabb aaBb aabb Sperm 9:7 9:3:3:1

AP Biology Penetrance and Expressivity  Genotypes vary in penetrance (percent of individuals with an allele who are affected, all or none) and expressivity (severity of symptoms or expression).  Examples: Huntington”s – nearly completely penetrant  Polydactyly – incompletely penetrant  Penetrance and variable expression are not well understood biochemically and are probably due to the complex biochemical environment all genes function in.

AP Biology Polygenic inheritance  Some phenotypes determined by additive effects of 2 or more genes on a single character  phenotypes on a continuum  human traits  skin color  height  weight  eye color  intelligence  behaviors

AP Biology Eye color is polygenic but follows Mendelian patterns of inheritance, how?

AP Biology enzyme Skin color: Albinism Johnny & Edgar Winter albino Africans  However albinism can be inherited as a single gene trait melanin = universal brown color tyrosine melanin albinism

AP Biology OCA1 albinoBianca Knowlton

AP Biology Sex linked traits  Genes are on sex chromosomes  as opposed to autosomal chromosomes  first discovered by T.H. Morgan at Columbia U.  Drosophila breeding  good genetic subject  prolific  2 week generations  4 pairs of chromosomes  XX=female, XY=male 1910 | 1933

AP Biology autosomal chromosomes sex chromosomes Classes of chromosomes

AP Biology Huh! Sex matters?! F 2 generation 100% red-eye female 50% red-eye male 50% white eye male Discovery of sex linkage P X F 1 generation (hybrids) 100% red eye offspring true-breeding white-eye male true-breeding red-eye female

AP Biology RRrr What’s up with Morgan’s flies? x rr R R Rr 100% red eyes Rr x Rr R r RR Rrrr Rr 3 red : 1 white Doesn’t work this way!

AP Biology _____ What’s up with Morgan’s flies? x ____ 100% red eyes ____ _____ x ____ _____ 100% red females 50% red males; 50% white males

AP Biology

Genes on sex chromosomes  Y chromosome  few genes other than SRY  sex-determining region  master regulator for maleness  turns on genes for production of male hormones  many effects = pleiotropy!  X chromosome  other traits beyond sex determination  mutations:  hemophilia  Duchenne muscular dystrophy  color-blindness

AP Biology  Sex-linked  usually means “X-linked”  more than 60 diseases traced to genes on X chromosome Human X chromosome

AP Biology Map of Human Y chromosome? < 30 genes on Y chromosome Sex-determining Region Y ( SRY ) Channel Flipping ( FLP ) Catching & Throwing ( BLZ-1) Self confidence ( BLZ-2) note: not linked to ability gene Devotion to sports ( BUD-E) Addiction to death & destruction movies ( SAW-2) Scratching ( ITCH-E) Spitting ( P2E) linked Inability to express affection over phone ( ME-2) Selective hearing loss ( HUH) Total lack of recall for dates ( OOPS) Air guitar ( RIF)

AP Biology Sex-linked traits summary  X-linked  follow the X chromosomes  males get their X from their mother  trait is never passed from father to son  Y-linked  very few genes / traits  trait is only passed from father to son  females cannot inherit trait

AP Biology X-inactivation - Epigenetics  Female mammals inherit 2 X chromosomes  one X becomes inactivated during embryonic development  condenses into compact object = Barr body  which X becomes Barr body is random  patchwork trait = “mosaic” XHXhXHXh XHXHXhXh

AP Biology X-inactivation & tortoise shell cat  2 different cell lines in cat

AP Biology What is epigenome?  The epigenome is a set of chemical switches and markers that influence gene expression.  Specifically factors from your environment such as diet, physical activity, and stress influence the epigenome.

AP Biology Mitochondrion  Organelle providing cellular energy  Contains small circular DNA  No crossing over or DNA repair  High exposure to free radicals  Mutation rate is greater than nuclear DNA  37 genes without noncoding sequences  Mitochondrial genes are transmitted from mother to all of her offspring

AP Biology Mitochondrial Inheritance Figure 5.8 Figure 5.7

AP Biology Mitochondrial Disorders  Mitochondrial myopathies – weak muscles  Leber optic atrophy – impairs vision  Ooplasmic transfer technique can enable woman to avoid transmitting a mitochondrial disorder

AP Biology Linkage  Linkage is the transmission of two genes on the same chromosome  Two genes on the same chromosome will not assort randomly in meiosis

AP Biology Expected Results in a Dihybrid Cross Figure 5.10

AP Biology Parents P Genotype PpLl Genes not linked Genotype PpLl Genes linked Self-cross p Ll P L p l

AP Biology Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parents P Genotype PpLl Genes not linked Genotype PpLl Genes linked Self-cross F1F1 p Ll P L p l

AP Biology Parents P Genotype PpLl Genes not linked Genotype PpLl Genes linked Self-cross F1F1 p Ll P L p l Female gametes PLPlpLpl Male gametes PL Pl pL pl Female gametes PLpl Male gametes PL pl

AP Biology Parents P Genotype PpLl Genes not linked Genotype PpLl Genes linked Self-cross F1F1 p Ll P L p l Female gametes PLPlpLpl PPLLPPLlPpLLPpLl PPLlPPllPpLlPpll PpLLPpLlppLLppLl PpLlPpllppLlppll Male gametes PL Pl pL pl Female gametes PLpl PPLLPpLl ppll Male gametes PL pl

AP Biology Parents P Genotype PpLl Genes not linked Genotype PpLl Genes linked Self-cross F1F1 Phenotypic ratio 3: Self-cross p Ll P L p l Female gametes PLPlpLpl PPLLPPLlPpLLPpLl PPLlPPllPpLlPpll PpLLPpLlppLLppLl PpLlPpllppLlppll Male gametes PL Pl pL pl Female gametes PLpl PPLLPpLl ppll Male gametes PL pl Phenotypic ratio 9:3

AP Biology Parents P Genotype PpLl Genes not linked Genotype PpLl Genes linked Self-cross F1F1 Phenotypic ratio 3: Self-cross p Ll P L p l Female gametes PLPlpLpl PPLLPPLlPpLLPpLl PPLlPPllPpLlPpll PpLLPpLlppLLppLl PpLlPpllppLlppll Male gametes PL Pl pL pl Female gametes PLpl PPLLPpLl ppll Male gametes PL pl Phenotypic ratio 9:

AP Biology Parents P Genotype PpLl Genes not linked Genotype PpLl Genes linked Self-cross F1F1 Phenotypic ratio 3: Self-cross p Ll P L p l Female gametes PLPlpLpl PPLLPPLlPpLLPpLl PPLlPPllPpLlPpll PpLLPpLlppLLppLl PpLlPpllppLlppll Male gametes PL Pl pL pl Female gametes PLpl PPLLPpLl ppll Male gametes PL pl Phenotypic ratio 9:3:3

AP Biology Parents P Genotype PpLl Genes not linked Genotype PpLl Genes linked Self-cross F1F1 Phenotypic ratio 3:1 Self-cross p Ll P L p l Female gametes PLPlpLpl PPLLPPLlPpLLPpLl PPLlPPllPpLlPpll PpLLPpLlppLLppLl PpLlPpllppLl ppll Male gametes PL Pl pL pl Female gametes PLpl PPLLPpLl ppll Male gametes PL pl Phenotypic ratio 9:3:3:1

AP Biology Recombination  During crossing over in prophase I chromosomes recombine  New combinations of alleles are created  Parental chromosomes have the original configuration  Recombinant chromosomes have new combinations of alleles

AP Biology Crossing over Disrupts Linkage

AP Biology Recombination  Frequency of recombination is based on percentage of meiotic divisions that result in breakage of linkage between parental alleles  The frequency of recombination between two genes is proportional to the distance between the genes