* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chromosomal Basis of Inheritance
Survey
Document related concepts
Causes of transsexuality wikipedia , lookup
Gene expression programming wikipedia , lookup
Designer baby wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Sexual dimorphism wikipedia , lookup
Microevolution wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Genomic imprinting wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Genome (book) wikipedia , lookup
Y chromosome wikipedia , lookup
Neocentromere wikipedia , lookup
Transcript
Chapter 15 Chromosome Theory of Inheritance • Chromosomes actually segregate (homologs) and assort (nonhomologous) in meiosis • Compare with dihybrid cross from chapter 14 • Influenced by Mendel’s laws Determining Sex • Anatomical and physiological differences are numerous • Chromosomal basis for determining sex is presence of the Y chromosome – Significantly smaller • Only short regions on either end of Y are homologous with X Gametic Sex • Males produce sperm either X or Y • Females produce eggs all X • Offspring’s sex determined the moment of conception – X sperm fertilizes egg = female – Y sperm fertilizes egg = male • Gonads, reproductive organs, are generic until 2 months – Development depends on SRY gene, located on Y chromosomes – Actually codes for proteins that regulate other genes – Without, gonads become ovaries; default sex is female Alternate Chromosomal Systems • X-Y system – Mammals – Determined by sperm, X or Y • X-0 system – Insects, only one sex chromosome, X – Females XX, males X0 • Z-W system – Birds and fishes – Determined by egg, Z – Female ZW, male ZZ • Haploid-diploid system – Bees and ants – Fertilization determines – Fertilized = female = diploid = 2 parents – Unfertilized = male = haploid = no father Sex (X)-linked Genes Genes located on either sex chromosome, especially the X (in humans) Fathers pass X to all daughters but no sons Mothers pass X to all offspring Recessive alleles Female express phenotype only if homozygous Males express only if egg bore the recessive allele Males are hemizygous because other terms can’t apply More males have sex-linked recessive disorders Color Blindness F: normal; M: affected F: carrier; M: normal F: carrier; M: carrier • N represents color-blind gene • Loci carried on sex (X) chromosomes • Muscular dystrophy and hemophilia are similar examples X Inactivation • Females have 2 X chromosomes, but don’t make double the proteins – Barr body is the inactivated and condensed X chromosome • Reactivated in ovaries so both X’s are transferable – Males and females each with same dose (1 copy) of genes • Decision is random and independent, can be mom or dad’s allele, in each embryonic cell – Inactivity is conserved in all mitotic descendents – Females are mosaics • Heterozygous for a sex-linked = ½ cells express 1 allele and ½ express other • E.g coat color in cats Tortiseshell/Calico Cats • X-linked gene (O) determines orange fur • Males have one X so if O is orange, o is black • Females have 2 X’s – Heterozygotes (Oo) have 1 X inactivated – Some cells express O others o = patches of orange and black • Rare, but possible to have male’s this color Phenotype Alterations • Small-scale – Random mutations create all new alleles = new phenotypic traits • Large-scale – Physical and chemical disturbances can damage chromosomes – Errors in meiosis can alter chromosomal number – Often lead to miscarriages or genetic disorders • Plants often tolerate better than animals Nondisjunction • Separation during anaphase doesn’t occur properly • Fertilization of gamates from nondisjunction results in aneuploidy – Abnormal chromosome number • extra = trisomy, fewer = monosomy • Polyploidy 2+ sets of chromosomes • Common in plants Human Disorders Fetal testing can diagnose most, often times affected individuals are miscarried Down Syndrome Trisomy 21; 47 chromosomes; risk increases with age Sex chromosome relationships Less disruptive Y chromosome carries few genes X chromosome extra copies are inactivated Sex Chromosome Disorders Sex Chromosome Abnormalities Genotype Gender Syndrome Physical Traits XXY, XXYY, XXXY Male Klinefelter syndrome Sterile, small testicles, breast enlargement XYY Male Jacob’s syndrome Normal male traits, previously thought ‘supermales’, karyotype ID XO Female Turner syndrome sex organs don't mature, sterile, short stature XXX female Trisomy X tall stature, learning disabilities, limited fertility, karyotype ID Altering Chromosomal Structure • Deletion: a chromosomal fragment is lost • Duplication: segments repeat – Pieces from deletions can attach to another chromosome • Inversion: a segment breaks and flips 180° • Translocation: chromosome segment moves from 1 to another non-homolog Altered Chromosome Disorders Cri du chat (cry of the cat) Deletion in chromsome 5 Small head, unusual facial features, cry of a cat Huntington’s disease Duplication of CAG sequence in DNA on chromosome 4 Effected has 42-120 copies, normal is 11-34 copies Codes for glutamine, produces a polyglutamine <36 glutamines produces huntingtin protein, more is mutant