PowerLecture: Chapter 12 Chromosomes and Human Inheritance

Philadelphia Chromosome 1st abnormal chromosome associated with a cancer Causes chronic myelogenous leukemia (CML)

Sex Chromosomes Discovered in late 1800s Mammals, fruit flies XX is female, XY is male In some other groups XX is male, XY female Human X and Y act homologues

Karyotype Preparation Fig. 12-3a-e, p.189

Karyotype Diagram Fig. 12-3f, p.189

Karyotype Preparation Fig. 12-4, p.189

Autosomal Dominant Inheritance Trait typically appears in every generation Fig. 12-10a, p. 190

Autosomal Dominant Inheritance example… Achondro-plasia Fig. 12-5, p.190

Achondroplasia Autosomal dominant allele Homozygous usually leads to stillbirth Heterozygotes display a type of dwarfism (short arms and legs relative to other body parts)

Huntington Disorder Autosomal dominant allele Causes involuntary movements, nervous system deterioration, death Symptoms appear after age 30 People often pass allele on before they know they have it

Autosomal Recessive Inheritance Patterns If parents are both heterozygous, child will have a 25% chance of being affected Fig. 12-10b, p. 191

Galactosemia Caused by autosomal recessive allele Gene specifies a mutant enzyme in the pathway that breaks down lactose lactose galactose enzyme 1 + glucose galactose-1- phosphate enzyme 2 galactose-1- phosphate enzyme 3 intermediate in glycolysis

Hutchinson-Gilford Progeria Mutation causes accelerated aging No evidence of it running in families Appears to be dominant Seems to arise as spontaneous mutation Usually causes death in early teens

The Y Chromosome Fewer than two dozen genes identified SRY gene (sex-determining region of Y) is the master gene for male sex determination

The X Chromosome Carries more than 2,300 genes Most for nonsexual traits Genes on X chromosome can be expressed in both sexes

Sex Determination diploid germ cells in female diploid germ cells in male meiosis, gamete formation in both female and male: eggs sperm X x Y X X Fertilization: X X X XX XX sex chromosome combinations possible in new individual XY XY X Fig. 12-8a, p.192

Thomas Morgan Worked with fruit flies Reciprocal crosses - 2 crosses where the trait of each sex is reversed Example - 1- White eyed male X Red eyed female 2- White eyed Female X Red eyed male

White-eyed males show up in F2 Thomas Morgan X X 1/2 Y Y recessive male all red- eyed F1 offspring 1/2 1/4 X X 1/4 1/4 X X 1/2 1/4 X X homozygous dominant female 1/2 gametes White-eyed males show up in F2 generation Fig. 12-9, p.193

Examples of X-Linked Traits Red-Green Color blindness Hemophilia A Duchenne Muscular Dystrophy

Hemophilia Fig. 12-11, p.194

Duplication Gene sequence repeated several to hundreds of times Can occur through unequal crossing over Can be found in normal chromosomes May have adaptive advantage Useful mutations may occur in copy

Duplication normal chromosome one segment repeated three repeats

Deletion Loss of some segment of a chromosome Most are lethal or cause serious disorder

Deletion Cri-du-chat Fig. 12-13, p.196

Inversion Section of DNA is reversed Usually not a problem for carrier May cause problems in meiosis segments G, H, I become inverted In-text figure Page 196

Translocation A piece of one chromosome becomes attached to a nonhomologous chromosome Most are reciprocal Example - Philadelphia chromosome

Translocation one chromosome In-text figure Page 206 a nonhomologous nonreciprocal translocation In-text figure Page 196

Duplications & Translocations Karyotype comparing gibbon chromosomes to human chromosome regions. Fig. 12-14, p.197

Chromosome Structure Alterations to chromosome structure are usually bad Duplications are adaptive: one gene functions normally - the other is free to mutate Chromosome structure evolves

Chromosome Structure Human n=23 Chimpanzees, gorilla, or orangutan n=24 During human evolution, two chromosomes fused to form chromosome #2

Chromosome Structure human chimpanzee gorilla orangutan Fig. 12-15, p.197

Aneuploidy Individuals have one extra or less chromosome (2n + 1 or 2n - 1) Major cause of human reproductive failure

Polyploidy Individuals have three or more of each type of chromosome (3n, 4n) Common in flowering plants Lethal for humans

Nondisjunction n + 1 n + 1 n - 1 n - 1 chromosome alignments at metaphase I NONDISJUNCTION AT ANAPHASE I alignments at metaphase II anaphase II CHROMOSOME NUMBER IN GAMETES Fig. 12-16b, p.198

Nondisjunction Fig. 12-16a, p.198

Nondisjunction Down Syndrome - Trisomy 21 Risk of Down syndrome increases dramatically in mothers over age 35

Down Syndrome Fig. 12-17, p.199

Nondisjunction Turner Syndrome- Monosomy X (XO) Klinefelter Syndrome- XXY XYY

Fig. 12-19b,p.200

Phenotypic Treatments Symptoms of many genetic disorders can be minimized or suppressed by Dietary controls Adjustments to environmental conditions Surgery or hormonal treatments

Genetic Screening Large-scale screening programs detect affected persons Newborns in United States routinely tested for PKU Early detection allows dietary intervention and prevents brain impairment

Preimplantation Diagnosis in-vitro fertilization At the 8 cell stage 1 cell is removed and its genes analyzed If cell has no defects, the embryo is implanted