DNA Chromosomes Inheritance

DNA Chromosomes and Inheritance DNA and Chromosomes: Chromosomes: thread-like strands of genetic information made of deoxyribonucleic acid (DNA) and protein DNA is a set of instructions for the cell 46 chromosomes in each Diploid cell in the human body Genes: Many genes on each chromosome Each gene codes for one type of protein Part of the chromosome that carries heredity material Nucleic acid: Long molecule found in nucleus of cells DNA – deoxyribonucleic acid RNA – ribonucleic acid The Structure of DNA: Nucleotides are subunits which make up DNA Each nucleotide is made up of 3 chemical groups: A sugar molecule - Deoxyribose A base– four types: A = Adenine T = Thymine G = Guanine C = Cytosine A phosphate - P 80327562865Phosphate molecule Deoxyribose Sugar Base Adenine, Cytosine, Guanine, Thymine Nucleotide: 00Phosphate molecule Deoxyribose Sugar Base Adenine, Cytosine, Guanine, Thymine Nucleotide: Each nucleotide is joined to another by a backbone of sugar-phosphate groups to form a chain of nucleotides. DNA molecule = two chains of nucleotides joined by hydrogen bonds between bases. 5429254127500 355727026797000466090449580A section of a DNA molecule 00A section of a DNA molecule The two nucleotide chains spiral around one another to form the DNA double helix structure. Genetic code: Genetic code is the sequence of bases in the DNA molecule 4138295111760DNA Double Helix 00DNA Double Helix Genetic code determines the order of amino acids in a protein 3 nucleotides (known as a triplet) code for each amino acid in a polypeptide chain e.g. CAG codes for the amino acid valine 3640455698500There are 20 different types of amino acids Bases from one chain pair up with bases from the other chain as follows: G always pairs with C T always pairs with A One strand in double-stranded DNA is complimentary the other. 4138295528955Types of Amino Acids 00Types of Amino Acids Semi-conservative DNA replication DNA replication - the process by which DNA molecules in the nucleus produce an accurate copy of themselves In semi-conservative DNA replication, the two resulting DNA copies each have one strand of parental DNA and one newly constructed strand. -11430022288500DNA replication takes place as follows: 3752850246888000 The nucleotides which attach at (c) are free floating nucleotides found in the nucleus. The enzyme DNA polymerase is involved in the nucleotide attachment process The enzyme ligase is involved in joining the pieces of back-bone in (d) Other Enzymes Involved: Helicase – Separates the two strands SSB – Prevents the strands from joining back together Polymerase – Attaches nucleotides to the strand (extends DNA strand) Primase – Creates RNA primers (a primer is a short chain of nucleotides which serves as a starting point for replication – polymerase can only extend a chain and not initialise one) Sliding Clamp – Holds polymerase on DNA Ligase - Links short DNA chains RNAse H – Removes RNA primers Protein Synthesis: Protein Synthesis – the process by which cells make protein molecules from coded instructions on the chromosome Gene – A section of the DNA that gives instructions for making a polypeptide. Polypeptide molecules are brought together to form longer and more complex protein molecules. 1943100304800Messenger RNA (mRNA) acts as a carrier of triplet codes from the nucleus to the cytoplasm 00 Messenger RNA (mRNA) acts as a carrier of triplet codes from the nucleus to the cytoplasm 0238125Nucleus: DNA stores code needed for the production of proteins Information is stored in the form of triplet code DNA is the reference library of the cell 00Nucleus: DNA stores code needed for the production of proteins Information is stored in the form of triplet code DNA is the reference library of the cell 3876675181610Cytoplasm: Amino acids are assembled to produce polypeptide chains. Polypeptide chains are joined to form proteins 00Cytoplasm: Amino acids are assembled to produce polypeptide chains. Polypeptide chains are joined to form proteins Transcription – the process by which a section of the DNA code is copied into RNA Translation – The process by which the mRNA is used to assemble amino acids in a particular order in the cytoplasm. 254571547942500A molecule of RNA produced from the DNA contains the code for the manufacture of one polypeptide chain 684530142875Transcription: 00Transcription: 1905015113000 723904254500 134620521970Thymine in DNA is replaced by Uracil in RNA 00Thymine in DNA is replaced by Uracil in RNA Inheritance: 3018155186055Chromosomes from the body cell of a man 00Chromosomes from the body cell of a man 270637035750500Homologous Chromosomes: There are 23 pairs of homologous chromosomes in the human cell 69469059626500Homologous chromosomes are identical in length shape and appearance 28651201165225Homologous chromosomes: Chromosomes that are paired during meiosis. Such chromosomes are alike with regard to size and also position of the centromere. They also have the same genes, but not necessarily the same alleles, at the same locus or location. 00Homologous chromosomes: Chromosomes that are paired during meiosis. Such chromosomes are alike with regard to size and also position of the centromere. They also have the same genes, but not necessarily the same alleles, at the same locus or location. Chromosomes, DNA and Genes Overview: A pair of homologous chromosomes consist of two chromosomes each of which is a molecule of DNA Each DNA molecule is a series of codes that carry instructions to make polypeptide molecules Each code occupies a specific place on the chromosome called a locus Each locus on a chromosome is a gene A gene is the functional unit of the chromosome – codes for specific polypeptide molecule Genetic Inheritance: Haploid Cells : Gamete cells 23 chromosomes One copy of each gene Represented as n Diploid Cells: Normal cells 46 chromosomes 2 copies of each gene Represented by 2n One Diploid cell forms 2 haploid cells by meiosis: 8902701333500 7689853479800023 chromosomes are inherited from the father and 23 from the mother: Alleles: Different forms of the same gene Same locus, different chromosomes Haploid cells – one allele for each gene Diploid cells – two alleles for each gene Genotype: Refers to the particular forms in which chromosomes exist at the loci on the chromosomes Genotype determines the characteristics of an organism Genotype is determined by the sequence of base pairs in the DNA strand. Homozygous Genotype – Both alleles the same Heterozygous Genotype – alleles are different Dominant alleles show their characteristics whether genotype is homozygous or heterozygous – written as capital letter (e.g. Hh and HH) Recessive alleles only show their characteristics when the genotype is homozygous – written as small letter (e.g. hh) Phenotype: The name given to the actual appearance of the genotype in an organism Physical/ physiological characteristics Monohybrid Crossing: Looks at the way specific characteristics are passed from the parent generation to the offspring generation Example: Parental Phenotypes: Brown Eyes x Blue Eyes Parental Genotypes: BB x bb b b B Bb Bb B Bb Bb Gametes: Offspring genotypes: Bb, Bb, Bb, Bb, Offspring phenotypes: All brown-eyed Test Cross: 144208538862000Used to determine an unknown genotype: Co-dominance: Both alleles equally dominant Both alleles are expressed in the phenotype E.g. Genotype Phenotype CRCR Red Flowers CWCW White Flowers CWCR Pink Flowers Examples: human blood, hair colour 372427529019500More complex ratios e.g. 1:2:1 Sickle-cell anaemia Painful and fatal disease Causes red blood cells to distort when blood is deoxygenated A certain allele causes sickle cell anaemia when in homozygous form Normal Allele = HBA Sickle-cell Allele = HBS Phenotypes: HBAHBA = Normal Blood HBSHBS = Sickle-cell anaemia HBA HBS = Co-dominance + Resistant to Malaria Multiple Alleles: In some cases a single characteristic is controlled genetically by one gene which has 3 alleles For the characteristic to appear in the phenotype only two of these alleles must be present. Inheritance in blood groups: 4 human blood groups: Group A. Group B, Group AB, Group O Controlled by single gene with three alleles: 305625510541000A B O A and B are dominant to O 48006026606500A and B are co-dominant 345376511938000 Sex Inheritance: Sex is determined by sex chromosomes X and Y X is much longer than Y Female Genotype = XX Male Genotype = XY Sex-Linkage: Examples of medical conditions caused by sex linked genes: Haemophilia- blood clotting is defective and sufferer may bleed uncontrollably from the slightest cut Sex-linked colour blindness – inability to distinguish red from green Both examples caused by defective gene on X chromosome Male (XY) suffers from the condition Female (XX) usually does not, but carries a defective gene Y chromosome is small and does not contain many genes Appearance of recessive allele on a region of the X chromosome which does not have a corresponding region on the Y chromosome will result in the expression of the recessive trait in the phenotype. 272224532829500Therefore sex-linked conditions only occur in men 1612905461000