Patterns of Inheritance aka Genetics Parents pass heritable traits to offspring (genes) Gregor Mendel –1860’s, Austrian monk experimented with garden peas –tracked traits from parents to subsequent generations

Cross fertilization –Pollen from one plant to fertilize another plant P = Parents F 1 = 1 st generation of offspring Hybrid (cross) = offspring of two different varieties –e.g. purple vs. white flowers How?

Mendel tracked 7 characteristics –Each had two distinct forms –Controlled Started with pure varieties

Monohybrid cross –Differs by one characteristic No blending (pink) –What happened to the white? Showed up in F 2

Mendel’s 4 hypotheses 1.Alternate versions of each gene = alleles (Purple or White) 2.Offspring inherit 2 alleles, 1 from each parent for each characteristic (color) Homozygous = each allele is the same (PP or pp) Heterozygous = different alleles (Pp) 3.Dominant = determines appearance, and Recessive = not apparent 4.Gametes (sperm or egg) carry only one allele as a result of pair separation during meiosis = Law of segregation

Pure parent plants –All purple (PP) –All white (pp) Gametes will be either P or p F 1 are all purple because of dominance (Pp) F 2 results in a mathematically predictable 3:1 ratio Phenotype = expressed traits Genotype = genetic makeup Punnett square –Hybrid posibilities

Alleles of a gene reside at the same locus on homologous chromosomes –Separated by independent assortment in meiosis…ultimately within separate gametes

What happens if there are 2 characteristics? Are they packaged together? Or, independently from one another? Seed characteristics (alleles) –Round (R) or wrinkled (r) –Yellow (Y) or green (y) Hypothesis: They are packaged together.

Hypothesis: Each pair of alleles are independent of one another F 1 produces equal amounts of 4 possible genotypes F 2 reveals even more genotypic possibilities (9:3:3:1) Dihybrid cross is equivalent to two monohybrid crosses (12:4 or 3:1) Law of independent assortment

Black coat is dominant (B) Chocolate coat is recessive (b) Normal vision (N) vs. blind (n) What are the results of a dihybrid cross of heterozygous parents (black, normal vision) ? *progressive retinal atrophy (PRA) causes blindness Phenotype of heterozygous parents? Genotype of heterozygous parents? Gamete possibilities –Sperm? –Eggs?

Black coat is dominant (B) Chocolate coat is recessive (b) Normal vision (N) vs. blind (n) What are the results of a dihybrid cross of heterozygous parents (black, normal vision) ? Phenotype of heterozygous parents? black, normal vision Genotype of heterozygous parents? BbNn x BbNn Gamete possibilities –Sperm: BN, bN, Bn, bn –Eggs: BN, bN, Bn, bn

Sperm: BN, bN, Bn, bn Eggs: BN, bN, Bn, bn What is the genotypic ratio of the offspring? What is the phenotypic ratio of the offspring? BN bn Bn bN BN bNBnbn

Sperm: BN, bN, Bn, bn Eggs: BN, bN, Bn, bn BN bn Bn bN BN bNBnbn BNBNBNbNBNBnBNbn bNBNbNbNbNBnbNbn BnBNBnbNBnBnBnbn bnBNbnbNbnBnbnbn

Can you know the genotype by looking at the phenotype? What are their genotype possibilities?

Can you know the genotype by looking at the phenotype? What are their genotype possibilities? bb BB or Bb

Testcross Perform a testcross to determine an unknown genotype Mate an unknown genotype (black lab) X homozygous recessive (chocolate lab)

Some examples of dominant and recessive traits in humans (at one gene locus)

Class total Bent pinky – dominant (BB or Bb) Blue eyes – recessive (ee) No mid-digital hair – recessive (mm) Tongue rolling – dominant (RR or Rr) Widow’s Peak – dominant (WW or Ww) Right over left Thumb – recessive (cc) Attached ear lobes – recessive (aa) Hitchhiker’s thumb – recessive (hh)

How do we determine inheritance of human traits? Can’t Testcross Pedigree – family tree of genetic history E.g. tracking deafness (dd) in an isolated family –Since deafness appeared in F1 of grandparents…carriers Abigail? John? Hepzibah?

Other single gene disorders Recessive –Albinism –Cystic fibrosis Thick mucous excretion of lungs and other organs; requires life long treatment –Sickle cell anemia Probability increases with less variability (inbreeding) Dominant –Extra fingers, toes –Webbed fingers, toes –Dwarfism Normal body; short arms and legs DD die, Dd survive, non- dwarfs (99.99% pop.) are dd Dominant lethal disorders less common; usually kill embryo David Rappaport

Identifying disorders: –Amniocentesis is sampling of amniotic fluid –Chorionic villus sampling (CVS) of placental tissue –Ultrasound

Traits that don’t conform to Mendel’s laws Incomplete dominance –E.g. snapdragons –Heterozygotes differ from homozygotes –Predictable 1:2:1 ratio Different than “blending” hypothesis –No testcross necessary

More than two alleles per gene 3 alleles in blood type – OAB –4 possible phenotypes = O, A, B, AB –6 possible genotypes; co-dominance

Rh factor = “+” and “-” along with O, B, A –Rhesus incompatibility disease –30 combinations; much more complicated “O-” was considered universal donor; but new research shows not always the case

Pleiotropy Gene influences multiple characteristics

Polygenic Inheritance Additive effects of multiple genes on a single phenotypic characteristic

Sex-linked genes X-linked recessive alleles More common in males than females –Males only needs to inherit one sex-linked recessive allele from mom to be expressed –Females has to inherit two sex-linked recessive alleles for expression Examples –Red-green color blindness –Hemophilia