Heredity Ch. 13, 14

Traits Physical attributes (hair color)

Genes Sections of DNA that code for a specific trait AGCGTTTACT = red hair (phenotype)

Chromosomes DNA wrapped around histones

Alleles Different forms of a gene R: red allele r: gray allele

Genetics Review Genotype: Rr Phenotype: red hair

Charles Darwin Natural Selection Favorable traits are passed on to offspring Unfavorable traits mean death & no offspring! But he couldn’t figure out how…

A few years later: 1860’s Gregor Mendel: Inheritance How traits are passed on (parent  offspring)

Why study peas? Many varieties: Control reproduction: Short lifespan: white flowering plant or purple flowering plant Control reproduction: cross-pollinate/hybrid or self-pollinate/purebred Short lifespan: Three generations in only three years P-generation, F1-generation, F2-generation

Pea Traits Collected thousands of pieces of data

Let’s do some science!

Mendel’s Experiment 1 Self pollinated pea plants to many generations Purebred P-generation

Mendel’s Experiment 1 P gametes Resulting F1-generation Hybrid Law of Dominance Genotype: Heterozygous alleles Pp

Mendel’s Experiment 1 F1 gametes Resulting F2-generation Phenotype: 3 purple: 1 white Genotype: 1PP:2Pp:1pp

Law of Segregation Discrete units of a trait segregate into separate gametes during gamete formation

Ex: Complete Dominance In rabbits long ears are dominant to floppy ears. If a purebred long eared rabbit mates with a hybrid rabbit, what is the probability a bunny will be a hybrid?

Monohybrids are cool, but… Observing two traits in one cross

Experiment 2 P-generation gametes: Resulting F1-generation? Purebred: round RR yellow YY green rr wrinkled yy Resulting F1-generation?

Experiment 2 P-generation gametes: Resulting F1-generation Purebred: round RR yellow YY green rr wrinkled yy Resulting F1-generation Hybrid Round Rr and Yellow Yy Resulting F2-generation?

Experiment 2 F1-generation gametes Resulting F2-generation (RrYy X RrYy) Resulting F2-generation All pea styles

Law of Independent Assortment The inheritance of one gene does not influence inheritance of another

Ex: Dihybrid Cross In cats Brown hair (B) is dominant to white hair (b) AND short tail (S) is dominant to long tail (s) cross a purebred short tailed, white cat with a purebred brown, long tailed cat

Ex: Dihybrid Cross In cats Brown hair (B) is dominant to white hair (b) AND short tail (S) is dominant to long tail (s) Parents: SSbb X ssBB FOIL:

Ex: Dihybrid Cross In cats Brown hair (B) is dominant to white hair (b) AND short tail (S) is dominant to long tail (s) F1: Hybrid for both traits SsBb F2 generation??????

Ex: Dihybrid Cross In cats Brown hair (B) is dominant to white hair (b) AND short tail (S) is dominant to long tail (s) F2 Generation 9 brown and short tail 3 white and short tail 3 brown and long tail 1 white and long tail

Complicated Genetics Life is complex

Ex: Incomplete Dominance F1 hybrids have an intermediate appearance Ex: Snapdragons red x white 

Ex: Incomplete Dominance F1 hybrids have an intermediate appearance Ex: Snapdragons red x white  pink Key RR - red RW - pink WW - white

Ex: Codominance Both alleles are expressed dominantly Ex: Roan horses Neither allele is recessive Ex: Roan horses red x white 

Ex: Codominance Both alleles are expressed dominantly Ex: Roan horses Neither allele is recessive Ex: Roan horses red x white  Red and White Key RR - red RW - roan WW - white

Ex: Multiple Alleles More than two alleles are present for one trait Ex: Blood Groups A is dominant over O B is dominant over O A & B are codominant

Ex: Multiple Alleles More than two alleles are present for one trait Ex: Blood Groups A is dominant over O B is dominant over O A & B are codominant Key AA & AO: type A BB & BO: type B AB: type AB OO: type O

Ex: Sex-linked Traits Traits that are associated with the X chromosome Ex: Red-green colorblindness

Ex: Sex-linked Traits Traits that are associated with the X chromosome Ex: Red-green colorblindness Key: XCXC: female normal XCXc: female carrier XcXc: female colorblind XCY: male normal XcY: male colorblind

Epistasis* Multiple genes affect one trait Gene 1 codes for brown or black mice Gene 2 codes for pigment in general

Pleiotropy* One gene affects multiple traits Ex: Cats with blue eyes are deaf

Polygenic Inheritance* A continuum of one trait is affected by multiple genes Ex: human skin color Three separate genes code for 7 shades of skin color

Visualizing Genetics

Pedigrees Show relationships within a family Track traits or disease in a family

Example of Pedigree Charts Dominant or Recessive? Is this pedigree dominant or recessive?

Example of Pedigree Charts Dominant or Recessive? Is this pedigree dominant or recessive?

Trisomy 21 Occurs when an individual receives an extra 21st chromosome Causes Down’s Syndrome

Trisomy 13 Occurs when an individual receives an extra 13th chromosome Causes Patau Syndrome

Klinefelter’s Syndrome Occurs when males receive an extra X chromosome Causes men to be sterile

Jacob’s Syndrome Occurs when males receive an extra Y chromosome. Causes men to become overly aggressive

Monosomy X Syndrome Occurs when females only receive one X chromosome Causes Turners Syndrome