The principles of genetics
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The principles of genetics





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The principles of genetics The principles of genetics Presentation Transcript

  • The Principles of Genetics Mendelian Genetics Monohybrid cross Dihybrid cross Polyhybrid cross
  • Definition, Concepts and Topics of Genetics• The word Genetics is derived from the Greek word genetikos,"genitive" combined with genesis, "origin"• Genetics is the most exciting field of biology, it is the science ofgenes, heredity and variation in living organisms. It is concernedwith mechanisms of heredity by which traits “characters” arepassed from generation to generation• Genetics also deals with the molecular structure and function ofgenes, e.g. gene behavior in the context of a cell or organism, patternsof inheritance from parents to offspring, and gene distribution,variation and change in populations• Genes are universal to all living organisms, and are applied tothe study of all living systems, from viruses and bacteria, toplants and animals, Special attention is given to crop plants anddomestic animals and humans
  • Characters studied by MendelSeven Characters in Garden peas
  • Why Garden pea (Pisum sativum) ?• Garden pea has a short life cycle• Garden pea has several observable contrasting characters• Garden pea is a self pollinating plant• The general features for a good genetic experimental organism are:-• short life cycle• easy to grow and breed• produce large number of offspring
  • The monohybrid cross, Law of segregation Inheritance of stem length in Garden pea Phenotype Tall Dwarf Recessive Dominant Parents Tall Genotype DD dd F1 DdPhenotype 3 Tall 1 Dwarf F2 Genotype DD Dd Dd dd DD = Homozygous Dd = Heterozygous dd = Homozygous
  • Explanation of the law of segregationInheritance of stem length in Garden pea D dD DD Dd Tall Talld Dd dd Tall Dwarf 3- Tall 1- Dwarf
  • Law of independent assortmentInheritance of seed shape and color in Garden pea Parents Tall plants, Round seeds Dwarf plants, wrinkled seeds DDWW ddwwP. Gametes DW dw F1 Phenotype: Tall plants Round seeds Genotype: DdWw W DW F1 D w Dw Gametes W dW d w dw
  • Mendel’s Foundations of Genetics• Genes are found in allelic pairs• One allele is dominant and the other is recessive• Law ofsegregation: Each character is controlled by a pair of (factors) genes that segregate at meiosis and reunite in the offspring• Law of independent assortment: Each pair of genes segregate independently of all other pairs during gamete formation
  • About Chromosomes• What is a chromosome?• Eukaryotic DNA: multiple linear diploid chromosomes• Number of chromosomes (types) depends on species• Chromosomes replicateUnwound form ofDNA = Chromatin
  • • Terms: chromosome vs chromatid chromatin vs condensed chromosome centromere vs centriole dulipcated chromosome vs homologous pair• 2 cell types: 1. somatic cell: body diploid = 2 sets 2. gamete: sex cell M & F haploid = 1 set• Human genome has 23 types of chromosome 22 autosomes + 1 sex chromosome (#23) human conception = 23M + 23F = 46 chromosomes NOTE: these are NOT stuck together – NOT identical• How do corresponding M & F chromosomes compare? Same genes in same corresponding positions…but… Are they exactly alike? Alleles: different forms of a gene
  • Eukaryotic cell division• 2 ways that Eukaryotic cells divide: 1. Mitosis: cell division for growth, healing & asexual repro. 1 diploid set  2 identical diploid sets (1 round)   replication  +  somatic cells only somatic cells genetically identical cloning? 2. Meiosis: cell division (2 rounds) for gamete formation 1 diploid set  2 diploid sets  4 haploid sets NOT identical genetic variability strategy of sexual reproduction• What is replication? It precedes cell division 46 X 2 = 92
  • Cell cycle 90%Replication happens here 23 x 2  23 x 2 x 2