Genetic inheritance x

Mendelian Genetics Gregor Mendel (late 1800's) Austrian monk Trained in math & chemistry Experimented with plants at monastery Controlled their __________ Studied inheritance of ______ traits E.g., flower color, seed shape Now called ______ inheritance

Traits are inherited characteristics Can have alternative forms E.g., brown versus red hair Some forms can dominate over others Dominant versus ________ traits Mendel had no knowledge of chromosomes or DNA Recognized “_______” that control inheritance Now recognized as genes & alleles Genes are the molecular code for genetic ______ Alleles are _________________ of a gene Occur at ________ on chromosomes Inheritance > genes

Recessive allele = ____ flowers Homologous pair of chromosomes Gene locus (e.g., for flower color) P P p One from mom, one from dad Dominant allele = _____ flowers Recessive allele = ____ flowers Inheritance > genes

Mendel observed inheritance over generations Studied ____________ crosses: Parents have different forms of a single trait E.g., purple versus white flower color Observed _________: outward appearances Inheritance > mono-hybrid cross

E.g., mono-hybrid cross of purple and white peas Parents: x F1 hybrids: ____ offspring are _______ Called first or ___ (hybrid) generation Inheritance > mono-hybrid cross > F1

Produces 3 purple & 1 white offspring Breeding of 2 purple F1s Produces 3 purple & 1 white offspring x F1 generation: F2 generation: Called second or ___ generation Inheritance > mono-hybrid cross > F2

How did white re-appear in the F2 generation? Was present in F1 hyrbids, but dominated by purple Key points: 1. Offspring inherit _______ of a trait One from each parent, which can differ 2. Recessive not expressed if coupled with ______ E.g., dominant produces pigment, recessive doesn’t 3. Traits re-occur through _________ Separation of ___________ chromosomes during gametogenesis (________) Inheritance > mono-hybrid cross > segregation

To understand segregation, track _________ The actual alleles an individual carries In mono-hybrid crosses: 1. Parental genotype is homozygous PP pp X Homozygous _________ Homozygous _________ Inheritance > mono-hybrid cross > segregation

2. Parental alleles segregate during meiosis PP pp female male X meiosis Eggs Sperm P P p p Inheritance > mono-hybrid cross > segregation

3. F1 generation is heterozygous A dominant allele gets paired with recessive allele female male pp PP Parents: x meiosis P P p + p + fertilization Pp Pp Heterozygous condition F1: Only the ________ allele is expressed

? ? ? ? 4. F2 generation will occur in 3:1 ________ ratio female male Pp Pp F1: x Segregation: p ? ? P Pp ? Gametes: ? P ? p ? PP ? pp ______ square F2: Pp ? Genotypic ratio is _____ (1 PP, 2Pp, 1pp) Inheritance > mono-hybrid cross > phenotypic ratio

Complex inheritance patterns 1. Incomplete dominance Heterozygotes are __________ in form (________) E.g., heterozygous snapdragons are _____ Co-dominant allele also influences phenotype Apostrophe indicates co-dominant (subdominant) rather than recessive Inheritance > complex crosses

Gene for blood antigen has __ alleles: A, B, & O 2. One gene with multiple alleles: Human blood types (more in lab) Gene for blood antigen has __ alleles: A, B, & O Blood type Genotype Glycoprotein A AA or AO B BB or BO AB AB O OO Inheritance > complex crosses

3. A single trait influenced by ____ genes Phenotypes usually vary along a _________ Most common kind of inheritance in humans Human skin, eye, & hair color Mendel purposely _________ such traits Human eye color: 2 genes, each with 2 alleles Inheritance > complex crosses

4. Sex-linked inheritance Gene is located on a ___ chromosome, X or Y X and Y are homologous chromosomes (__rd pr.) But are quite different Y is smaller & lacks some ________ X Y Inheritance > complex crosses

Must first discuss Sex determination ___ System of sex determination: Male Female Adults: XY XX Gametes: Gametes: X Y X Offspring: XY XX Only _________ contribution (Y) determines sex ___ gene on Y chromosome codes for ‘_______’ Starts a cascade of fetal ________ changes Inheritance > sex determination

In birds, females have the unusual sex chromosome In bees: Males develop from unfertilized eggs; _____ Females developed from fertilized eggs; ______ In some reptiles, sex is determine by incubation ____. Appears to influence hormones Actual mechanism not well-understood

Back to sex-linked inheritance: E.g., Hemophilia: a recessive ________ disease Causes non-stop bleeding Defective blood-clotting _______ Severe forms can be ______ Mothers can be heterozygous _______ (Hh): H h X Carriers (Hh) ______ suffer from the disease

Males that inherit recessive allele ______ suffer X Y Y chromosome lacks corresponding locus Not possible to be ____________ (carrier)

Females suffer only when homozygous _______ X Rare: father must be ________ (h on X) Why rare? Male sufferers of severe forms ___ young