Mendelian Genetics inheritance of traits Why Peas Many

Mendelian Genetics – inheritance of traits

Why Peas? ? ü Many varieties (character, traits) ü Easy to control pollination ü Could choose distinct characters

First Experiments: True-breeding parent generation Why aren’t all the floweres light purple?

Mendel’s Law of Segregation White “heritable factor” did not disappear in F 1 generation but only purple “heritable factor” was acting. Ø Alternative version of genes (heritable factors) account for variations in inherited characters. ØFor each character, an organism inherits two alleles (versions of the gene) one from each parent. ØIf the two alleles differ, one is fully expressed – DOMINANT; the other does not affect the organism’s appearance - RECESSIVE trait. ØThe two alleles segregate during gamete production

Mendelian Genetics Terms • • Homozygous Heterozygous Phenotype Genotype Punnett square Monohybrid cross Testcross

Testcross

What happens if looking at two traits simultaneously? • Dihybrid cross True-breeding Parent (P) F 1 F 2: 9: 3: 3: 1 x

Mendel’s Law of Independent Assortment • Each character is independently inherited – segregate independently during gamete formation • Practice dihybrid crosses • Use rules of probability to predict outcomes of genetic crosses

http: //www. biology. arizona. edu/me ndelian_genetics/problem_sets/mo nohybrid_cross/monohybrid_cross. html

More Complicated Situations… 1. Incomplete dominance

Multiple Alleles IAIA = A; IAi = A IAIB= AB ii = O IBIB=B; IBi = B A, B – codominant i - recessive

Other situations: • Pleiotropy – one gene affects several phenotypes • Epistasis – one gene affects the phenotypic expression of another gene • Polygenetic inheritance – additive effect of two or more genes on a single phenotypic character

Human Disorders that follow Mendelian Patterns of Inhertitance • Recessively inherited disorders: albinism, cystic fibrosis, Tay-Sachs disease, sickle-cell anemia • Dominantly inherited disorders: Achondroplasia, Huntington’s disease

Cystic Fibrosis

Tay-Sachs Disease

Achondroplasia

Huntington Disease Late Acting – middle age Western Europeans

Screening for inherited disorders

Pedigrees

Pedigree – Huntington disease

Pedigree – Sickle cell anemia

Chromosomal Theory of Inheritance Thomas Morgan Fruitflies 4 pairs of chromosomes Wild type phenotype Mutant phenotype White-eyed males only

Sex-linked traits Located on Sex chromosomes: X or Y Females XX; Males XY X-linked recessive Hemophilia, color blindness