Genetics the study of the origin of biological variability and its inheritance 4 plants we depend on corn maize rice wheat potato o 70 80 of our calories Genetic info is encoded as the order of nucleotides in DNA The basic functional unit of inheritance gene Gene Genes are arranged linearly on chromosomes DNA RNA protein a linear array of nucleotides capable of making a product o Protein is usually the end product but not always genes at sites Loci Sickle cell anemia molecular disease due to a single base change in the alpha globin gene which changes one amino acid o Change in 6 position DNA is located in the nucleus Genes are carried on chromosomes Chromatin chromosomes before replication consist of a single DNA double helix bound by histone proteins o 50 protein 50 DNA chromatin Interphase G1 S G2 During interphase chromosomes are UNcondensed Mitosis the rest prophase metaphase anaphase telophase Chromosome duplication occurs during S phase of interphase Centromere holding the 2 chromosomes together the center At the start of cell division the chromosomes condense and each has 2 SISTER CHROMATIDS Sister chromatids are exact duplicates Before a cell can divide it has to replicate each chromosome One replicated chromosome 2 sister chromatids G1 one DNA double helix S G2 2 DNA double helices Most organisms are diploid 2n Homologous chromosomes carry the same genes but may have different alleles o Same genes but different forms of the genes slightly different sequences o Similar but not identical DNA sequences o Carry genes for ALL the same traits o May carry different or same traits o NOT exact duplicates of each other are homologous chromosomes but do NOT carry o They re considered homologous because they pair with each other Exceptions o Sex chromosomes same genes during meiosis Some organisms are haploid 1n o Fungi o Some algae o Protozoans Chromosomes are named by their centromere position None of the human chromosomes are totally telocentric but very close to it Human karyotype o 2n 46 o 46 chromosomes 23 pair MITOSIS produces 2 genetically identical daughter cells Each daughter cell gets one chromatid from each chromosome At prometaphase and telophase 2n 4 Mitosis DNA replication mitosis DNA replication etc A new sister chromatid is made from each chromosome Meiosis formation of gametes sex cells 1 diploid cell divides twice and forms 4 haploid cells Each daughter cell gets one chromatid from each pair of homologous chromosomes Meiosis 1 first division o Homologous chromosomes are separated into different daughter cells o Chromosome recombination crossing over occurs Meiosis 2 second division o Sister chromatids are separated into different daughter cells Chiasma site of cross over Tetrads 4 chromosomes 2 homologous chromosomes paired with each other in prophase 1 of meiosis forms when there is at least 1 crossover between 2 homologous chromosome No DNA replication before meiosis 2 Each gamete has one chromatid from each pair of homologues chromosomes Early prophase of meiosis 1 o Homologous chromosomes are aligning o Crossovers o Each chromosomes in meiosis crosses over AT LEAST ONCE o The pair are held together by the crossovers in meiosis held together by centromeres in mitosis Tetrads in late prophase of meiosis 1 Pairing of homologous chromosomes is essential to meiosis Pairing depends on DNA sequence homology The synaptonemal complex is responsible for crossing over At the end of meiosis 1 23 DUPLICATED chromosomes At the end of meiosis 2 23 UNduplicated chromosomes Only haploid or diploid cells can divide by mitosis but only diploid cells can undergo meiosis because haploid cells only have 1 set of chromosome that can t be reduced further Mistakes in meiosis nondisjunction o Trisomy Downs syndrome trisomy 21 XXX Klinefelter s syndrome XXY is NOT trisomy because not 3 X s o Monosomy Mendel and pea plants Elements for Mendel s success o Focused on single pairs of distinct characteristics in pure bred varieties o Peas can be self or cross fertilized o Quantitative approach P1 parental generation F1 1st filial generation o F1 hybrids F1 cross monohybrid cross F2 2nd filial generation Mendel s first 3 postulates o 1 Each trait is controlled by a pair of factors genes o 2 When 2 different factors for a trait are present in an individual 1 is DOMINANT and 1 is RECESSIVE Alleles alternate forms of a gene o 3 During gamete formation the paired factors SEGREGATE RANDOMLY Phenotype the physical expression of a trait Genotype the genetic makeup of an individual Homozygous both alleles for a trait are the same Heterozygous 2 different alleles for a trait are present o 2 heterozygotes being cross 1 2 1 GENOTYPIC ratio 3 1 PHENOTYPIC ratio Test cross cross between an organism of dominant phenotype with one that is recessive Mendel s 4th postulate Mendel s Law of Independent Assortment o Genes for different traits are inherited independently they assort independently into the gametes o Occurs when genes for different traits are located on different chromosomes Know how to do a monohybrid and dihybrid cross The gene that allows us to roll our tongues codes for a muscle that helps tongue contract Most of our genes are used to build out physical bodies Recessive Dominant o Bent fingers o Free lobe o Albinism o Cystic fibrosis o Convex nose o Widows peak o Tongue rolling o Polydactyly o Achondroplastic Cystic fibrosis most common defect in Caucasians o Chronic life threatening lung infections o 1 2 000 o Recessive Phenylketonuria inability to convert phenylalanine into tyrosine o More common in Caucasians o 1 10 000 Achondroplastic dwarfism o 1 50 000 The outcome of genetic crosses depends on chance o Probabilities range from 0 1 Product rule the probability of 2 or more independent outcomes occurring together is equal to the product of their individual probabilities Sum rule the probability that an outcome can occur through 2 or more different combinations of independent events is the sum of the probabilities for each combination Chi square statistical test to determine the probability that a particular outcome occurred by chance o Null hypothesis there is NO difference between the observed and expected Happened by chance o Degrees of freedom n 1 o p 0 05 outcome is due to chance o p 0 05 outcome is NOT due to chance REJECT NULL Genetic crosses are governed by the laws of chance o As sample size increases chance plays LESS of a role Chromosomal theory of inheritance the genes are
View Full Document
Unlocking...