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General Biology Unit Three Genetics Genetics – the study of heredity Heredity – the passing of traits from one generation to the next Trait – a physical or physiological characteristic coded for by a gene Gene – a portion of a chromosome that codes for a particular protein Allele – a form of a gene Genetics Gregor Mendel – “Father of Modern Genetics” Established three laws working with peas – two are still used in genetics 1st Law – the Law of Segregation 2nd Law – the Law of Independent Assortment Mom (female) Dad (male) Recessive allele Dominant allele Homologous chromosomes Genetics Genotype – the set of genes an organism has Homozygous – alleles are the same type Heterozygous – alleles are different Genetics Phenotype – the expression of the genotype Purebred – having a homozygous genotype Hybrid – having a heterozygous genotype D D d D d d D D d Dd Dd d Dd Dd Punnett Square D D d D D d D d d D d d Complete Dominance D d D DD Dd d Dd dd Monohybrid Cross Genotypic Ratio – 1:2:1 Phenotypic Ratio – 3:1 Complete Dominance d D d Dd dd Complete Dominance d Dd Monohybrid Cross Genotypic Ratio – 2:2 Phenotypic Ratio – 2:2 dd Dihybrid Cross B B’ B BB BB’ B’ BB’ B’B’ Incomplete Dominance Cross Genotypic Ratio – 1:2:1 Phenotypic Ratio – 1:2:1 A O B AB BO O AO OO Codominance Genotypic Ratio – 1:1:1:1 Phenotypic Ratio – 1:1:1:1 Genetics Autosomes – all chromosomes except for the ones that determine sex Sex chromosomes – chromosomes that determine sex Sex linked traits – traits controlled by genes on the sex chromosomes Human Sex Chromosomes ♀ ♂ X X X Y Human Sex Chromosomes ♀ ♂ XB Xb Xb XBXb XbXb Y XBY XbY Sex Linked Cross Genetics Sex limited traits – traits that are found only in one sex Sex influenced traits – traits that are expressed differently in both sexes Mutations A mutation is any change in the DNA of an organism Mutations occur due to: - pathogen infection - exposure to radiation - introduction of chemicals - nondisjunction Mutations Mutations involve: - base pair substitutions - base pair insertions or deletions - DNA segments Mutations Nondisjunction Nondisjunction is the failure of chromosomes to separate during anaphase I of meiosis The normal separation, disjunction, produces daughter cells with 23 chromosomes each Nondisjunction Nondisjunction results in one daughter cell with 24 chromosomes and the other with 22 chromosomes Nondisjunction Monosomy is the result of the fertilization of a normal gamete and one that has only 22 chromosomes Trisomy is the product of the fertilization of a normal gamete and one that has 24 chromosomes Disjunction Nondisjunction Genetic Disorders Remember: Nondisjunction in gametes causes a change in chromosome numbers that affects the development of an embryo Approximately 90% of nondisjunction events are maternal in origin Genetic Disorders The presence of an extra chromosome (trisomy) or lack of one (monosomy) accounts for approximately 50% of all spontaneous abortions Genetic Disorders Only three autosomal trisomies are survivable: * trisomy 13 – Patau syndrome * trisomy 18 – Edward syndrome * trisomy 21 – Down syndrome Genetic Disorders Most fetuses with Patau or Edward syndrome will die before birth The few that are born are severely deformed and usually die within their first year Genetic Disorders Karyotype of Down syndrome (trisomy 21) Genetic Disorders Down syndrome is the most survivable of the trisomies, but approximately 75% die before birth and 20% of those born will die before the age of ten Genetic Disorders Down syndrome effects: * short stature * a flat face with almond shaped eyes * enlarged protruding tongue * broad hands with short fingers * varying degrees of mental retardation Genetic Disorders Of those that survive past the age of ten, life expectancy has been extended to sixty years However, after the age of forty many develop early onset Alzheimer disease Genetic Disorders Nondisjunction also occurs with the sex chromosomes: * trisomy 23 – Klinefelter syndrome (XXY) * trisomy 23 – Triplo-X syndrome (XXX) * monosomy 23 – Turner syndrome (XO) Genetic Disorders Triplo-X syndrome (XXX) results in a female phenotype that is usually infertile and may exhibit some intellectual impairment Genetic Disorders Klinefelter syndrome (XXY) results in a sterile male phenotype that is of normal intelligence and upon the onset of puberty exhibits unusually long arms, sparse body hair, undeveloped testes and enlarged breasts Genetic Disorders Turner syndrome (XO) results in a sterile female phenotype that fails to develop secondary sex characteristics at puberty and is usually short in stature Approximately 97% of all (XO) fetuses die before birth DNA & RNA Structure The monomers are nucleotides Nitrogen base Functions: Heredity Protein synthesis aaaaaaaaaaa Phosphate group Pentose sugar DNA & RNA Structure Examples: •DNA •RNA Double Single stranded stranded, with three double helix forms – molecule tRNA, rRNA, and mRNA DNA & RNA Structure DNA & RNA Functions DNA & RNA Base Pairing DNA & RNA Base Pairing DNA replication | | | | | | | | | | | | | | | | | | A T G C A T T G A AG C T G G T A G TACGTAACTTCGACCAT C | | | | | | | | | | | | | | | | | | RNA transcription | | | | | | | | | | | | | | | | | | AU G C A U U G A AG C U G G U A G TACGTAACTTCGACCATC | | | | | | | | | | | | | | | | | | DNA Replication Protein Synthesis Protein synthesis goes on all the time in most cells This very important process is directed by the genetic code on DNA Protein Synthesis Protein synthesis occurs in two processes: ~ transcription (production of RNA from DNA) ~ translation (production of proteins from RNA) Both processes are fueled by ATP Protein Synthesis: Transcriptio Protein Synthesis: Transcription RNA polymerase attaches to specific areas of the DNA (genes) and “unzips” the hydrogen bonds The RNA polymerase also begins the building of the RNA by adding RNA nucleotides in accordance with the DNA base sequence Protein Synthesis: Transcriptio n Protein Synthesis: Transcriptio Protein Synthesis: Transcription Once transcribed, mRNA and tRNA are sent out of the nucleus and to the ribosomes in the cytoplasm rRNA is transferred to the nucleolus to become a part of newly formed ribosomes Protein Synthesis: Translation mRNA carries a series of codons that code for specific amino acids A codon is a sequence of three nucleotide bases on mRNA Since there are only four RNA bases and there are three in each codon, there are 64 condon possibilities Protein Synthesis: Translation The genetic code is the use of these 64 codons coding for 20 amino acids Remember - the synthesis of a specific protein requires a specific sequence of amino acids Protein Synthesis: Translation Therefore the sequence of codons on mRNA must be sequentially specific The genetic code is commaless and non-overlapping, meaning it is read in frames of three without gaps or overlaps Protein Synthesis: Translation There is one initiation codon - AUG There are three stop codons - UAA, UAG & UGA Protein Synthesis - Translation Translation is the process by which RNA produces proteins in ribosomes - mRNA carries the code from DNA - tRNA carries amino acids to the ribosome - rRNA is a component of the ribosome Protein Synthesis: Translation By way of the genetic code, RNA “translates” from the language of nucleic acids to that of proteins Protein Synthesis: Translation Protein Synthesis: Review Protein Synthesis: Review