Non-Mendelian Genetics Chapter – Pt Objective: I can explain what causes dominance, and utilize this information to solve genetics problems that do not fit under basic Mendelian principles (laws discovered by Mendel).

Review of Mendelian (Basic) Genetics 1 character encoded for by 1 gene (on 1 type of chromosome) – –Different character = diff. gene on diff. chrms. 1 gene only come in 2 diff. version = alleles (1 character can come as 2 traits) – on homologs – –1 allele is dominant, other is recessive When 2 characters at the same time… – –Must show every possible combination (dihybrid) Chromosome #3Chromosome #19 Hair Color GeneEye Color Gene Black = H Blond = h Brown = E Blue = e

Non-Mendelian Genetics Scientists have observed genetic patterns that do NOT follow Mendel’s rules Scientists have observed genetic patterns that do NOT follow Mendel’s rules This is due to the complex mechanism by which genes are expressed This is due to the complex mechanism by which genes are expressed –How the genotype actually determines the phenotype –How to get from genes to physical trait you see…

Gene Expression How the information in DNA (genotype) becomes the physical trait you see (phenotype) How the information in DNA (genotype) becomes the physical trait you see (phenotype) Will cover more specifically in Ch. 16 Will cover more specifically in Ch. 16

Human Genome Each somatic cell has entire human genome Each somatic cell has entire human genome –All chromosomes ~ 3 billion nucleotides ~ 25,000 genes You have ~100 trillion cells Which cells have half of genome? Gametes! (ovum + sperm) 46

1 Chromosome Out of 46, let’s isolate #11 Out of 46, let’s isolate #11 ~ 2000 different genes Actually have two copies of each gene…why? Homologous pairs! 1 from mom 1 from dad When counting genes, it is considered normal to have 2 copies of each gene (1 from each parent), so we just count the gene ONCE (even though there are really 2 copies)

1 Gene Gene for hemoglobin Gene for hemoglobin –Protein that helps blood transport oxygen Gene could come in different versions called Gene could come in different versions called –Alleles –Symbolize with letters according to dominance Due to homologs, always get 2 alleles! Due to homologs, always get 2 alleles! Gene is made of DNA ~2000 nucleotides long Gene is made of DNA ~2000 nucleotides long Could be H or h This person could be HH – homozygous dominant Hh – heterozygous hh – homozygous recessive

Transcription A transcript (copy) is made of gene (DNA) A transcript (copy) is made of gene (DNA) –Creates a molecule of RNA transcript WHY? WHY? –DNA trapped in nucleus, but have to get information out! RNA transcript is edited RNA transcript is edited –Remove unnecessary info –Makes a messenger RNA

Protein Synthesis mRNA travels to… mRNA travels to…ribosome –Sequence of nucleotides is read to create a sequence of amino acids Due to (primary) sequence of a.a., polypeptide chain will… Due to (primary) sequence of a.a., polypeptide chain will… –Fold to form functioning protein(shape = function)

Protein to Phenotype If protein folded correctly, will perform proper function If protein folded correctly, will perform proper function –Good hemoglobin will allow red blood cells to carry oxygen –See phenotype of ability to exercise without problem Apply to any gene and physical traits Apply to any gene and physical traits

How Mutation alters phenotype If DNA is changed (sequence of nucleotides is different) If DNA is changed (sequence of nucleotides is different) –Gene is mutated (changed) –RNA transcript changed –Amino acid sequence different than “normal” –Protein folded differently –Different phenotype  “Bad” Hemoglobin  Sickle Cell Anemia

Explaining Dominance The dominant allele is “dominant,” because it can make the protein properly The dominant allele is “dominant,” because it can make the protein properly –If the recessive allele makes a defective protein that does NOTHING, then the dominant allele win! But…what if the “recessive” (other) allele does something? But…what if the “recessive” (other) allele does something? H h

Incomplete Dominance Two different alleles are incompletely dominant – –Heterozygote expresses a new phenotype   In-between or intermediate Allele symbols are like variables – you can choose what you want, as long as you know what it means! KEY: C R = Red (R) C W = White (R`) (from the same gene)

Example For snapdragons, red flowers are incompletely dominant over white flowers: heterozygotes are pink. Cross a pink flower with a white flower. What is the probability (%) of having a red offspring? Is there a recessive allele? Is there a dominant allele? 1 genotype = 1 phenotype (heterozygous = pink) Both alleles “lose”  both are incompletely dominant

Codominance Two different alleles are BOTH dominant – –Heterozygote expresses both at same time   Creates a mixed phenotype (patterns) Allele symbols are like variables – you can choose what you want, as long as you know what it means! KEY: C R = Red (R) C W = White (W) (from the same gene)

Example For one species of horse, red coats are codominant with white coats: heterozygotes are roan (a mix of both red AND white). Cross a red horse with a roan horse. What is the probability (%) of having a roan horse offspring? Is there a recessive allele? Is there a dominant allele? 1 genotype = 1 phenotype (heterozygous = roan = red + white) Both alleles “win”  both are co-dominant to each other

Incomplete Dom vs. Co-Dominance

Understanding I.D. & C.D. through Gene Expression (challenging) Depends on protein functionality (complex/varied) Depends on protein functionality (complex/varied) Simple/Complete Dominance: Red vs. White Simple/Complete Dominance: Red vs. WhiteRr Incomplete Dominance: Red vs. White vs. Pink Incomplete Dominance: Red vs. White vs. PinkRR CoDominance: Red vs. White vs. Red&White CoDominance: Red vs. White vs. Red&WhiteRW receptor Red Phenotype R r White Phenotype receptor Red Phenotype ‘ ‘ White PhenotypePink Phenotype receptor Red Phenotype White Phenotype R W &

Multiple Alleles When characters have more than 2 traits because When characters have more than 2 traits because –1 gene has more than 2 alleles (versions) –Example: Pigeons; Character – Feather Color  3 alleles: Ash-red, Blue, Chocolate Brown – With more than 2 alleles, have to specify which is most dominant, 2 nd most dominant, and recessive  Can combine Incomplete Dominance or Co-Dominance

Multiple Alleles Example Trait of pigeon feather color (3 alleles) Trait of pigeon feather color (3 alleles) Most dominantAsh-red 2nd dominantBlue RecessiveChocolate Brown = b = B = B A Key Comparing genotypes and phenotypes Comparing genotypes and phenotypes –(Remember: each individual gets 2 alleles!) Genotype Phenotype bbChocolate brown(1) BBBlue(2) BABABABA Ash-red(3) Bb BABBABBAbBAb

Multiple Alleles Example An ash-red pigeon mates with a blue pigeon An ash-red pigeon mates with a blue pigeon BABABABAb B B A B Bb b B A b bb Ash-red pigeon had an ash-red father and a brown mother Genotype and Phenotype of offspring B A B = Ash Red B A b = Ash Red 50% chance of Ash Red offspring B b = Blue 25% chance of Blue offspring b b = Brown 25% chance of Brown offspring Blue pigeon had an brown father and a blue mother Ash-red pigeon = B A b Blue pigeon = Bb

Multiple Alleles Example 2 Himalayan Bunnies are another example Himalayan Bunnies are another example –1 gene for coat color  4 alleles this time! But 5 phenotypes!!! But 5 phenotypes!!! –C ch allele incompletely dominant with c h allele and c allele  light gray Dark Gray Chinchilla Himalayan= c h = c ch = C White= c Can combine Mult. Alleles with Incom. Dom. or CoDom.