2 What 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.
3 Chromosome theory of inheritance: Genes have specific locations (loci) on chromosomesChromosomes segregate and assort independentlyChromosomes tagged to reveal a specific gene (yellow).
4 Thomas 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
6 Sex-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
7 Transmission of sex-linked recessive traits SpermOva
9 Because 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.
10 Human 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
11 Linked genes: located on same chromosome and tend to be inherited together during cell division
12 Genetic 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
13 Crossing 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
14 Geneticists can use recombination data to map a chromosome's genetic loci
15 Linkage 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
16 Nondisjunction: 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.
18 The structure of an individual chromosome can be altered during DNA replication
19 Karyotyping can detect nondisjunctions. Down Syndrome = Trisomy 21
20 Karyotyping can detect nondisjunctions. Klinefelters Syndrome: 47XYY, 47XXY
21 Karyotyping can detect nondisjunctions. Turners Syndrome = 45XO
22 Extranuclear 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.