2What you must know:How the chromosome theory of inheritance connects the physical movement of chromosomes in meiosis to Mendel’s laws of inheritance.The unique pattern of inheritance in sex-linked genes.How alteration of chromosome number or structurally altered chromosomes (deletions, duplications, etc.) can cause genetic disorders.How genetic imprinting and inheritance of mitochondrial DNA are exceptions to standard Mendelian inheritance.
3Chromosome theory of inheritance: Genes have specific locations (loci) on chromosomesChromosomes segregate and assort independentlyChromosomes tagged to reveal a specific gene (yellow).
4Thomas Hunt Morgan Drosophila melanogaster – fruit fly Fast breeding, 4 prs. chromosomes (XX/XY)Sex-linked gene: located on X or Y chromosomeRed-eyes = wild-type; white-eyes = mutantSpecific gene carried on specific chromosome
6Sex-linked genes Sex-linked gene on X or Y Females (XX), male (XY) Eggs = X, sperm = X or YFathers pass X-linked genes to daughters, but not sonsMales express recessive trait on the only X (hemizygous)Females can be affected or carrier
7Transmission of sex-linked recessive traits SpermOva
9Because of this only female cats can be tortoiseshell or calico. X-InactivationBarr body = inactive X chromosome; regulate gene dosage in females during embryonic developmentBecause of this only female cats can be tortoiseshell or calico.
10Human development Y chromosome required for development of testes Embryo gonads indifferent at 2 monthsSRY gene: sex-determining region of YCodes for protein that regulates other genes
11Linked genes: located on same chromosome and tend to be inherited together during cell division
12Genetic Recombination: production of offspring with new combo of genes from parents Unlinked genes: follow law of independent assortment50% frequency of recombination observed for any 2 genes on different chromosomes
13Crossing over: explains why some linked genes get separated during meiosis the further apart 2 genes on same chromosome, the higher the probability of crossing over and the higher the recombination frequency
14Geneticists can use recombination data to map a chromosome's genetic loci
15Linkage Map: genetic map that is based on % of cross-over events 1 map unit = 1% recombination frequencyExpress relative distances along chromosome50% = far apart on same chromosome or on different chromosomes
16Nondisjunction: chromosomes fail to separate properly in Meiosis I or Meiosis II Aneuploidy: incorrect # chromosomesMonosomy (1x) or Trisomy (3x)Polyploidy: 2+ complete sets of chromosomes; 3n or 4nRare in animals, frequent in plantsA tetraploid mammal. Scientists think this species may have arisen when an ancestor doubled its chromosome # by errors in mitosis or meiosis.
18The structure of an individual chromosome can be altered during DNA replication
19Karyotyping can detect nondisjunctions. Down Syndrome = Trisomy 21
20Karyotyping can detect nondisjunctions. Klinefelters Syndrome: 47XYY, 47XXY
21Karyotyping can detect nondisjunctions. Turners Syndrome = 45XO
22Extranuclear Genes Some genes located in organelles Mitochondria, chloroplasts, plastidsContain small circular DNADo not display Mendelian inheritanceMitochondria = maternal inheritance (eggs)Variegated (striped or spotted) leaves result from mutations in pigment genes in plastids, which generally are inherited from the maternal parent.