Each cell has a nucleus each DNA is located in there DNA is encoded information for all of our physical features Gregor Mendel 1822 1884 Father of the Science of Genetics He discovered how genetic info is passed from generation to generation Ideas about inheritance Mendel had to think out of the box and look at genetics from a fresh perspective 2 ideas Blending Theory of Inheritance the characteristics of the features of the parents are blended in the offspring Problems Children are not always intermediate between their parents Inbreeding and crossbreeding have been used for thousands of years to make new varieties of animals and plants Doctrine of the Fixity of Species each species has a unique and unchanging set of biological characteristics Each species was a perfect creation by God If the species was perfect there was no point for it to change Mendel was in uenced by Franz Unger Botanist did not believe in xity of species Christian Doppler Physicist emphasized measurement and experimentation Mendel s Particulate Theory of Inheritance Inheritance is due to the passage of discrete particulate factors from one generation to the next in an unchanged form He crossbreed different organisms mice then moved to pea plants Reproduction of plants Pollen sperm Egg Offspring seed Advantages of pea plants for genetics Mendel worked with Pure Breeding Varieties of pea plants each had two different forms of the same trait Trait ower color Peas can be cross pollinated or self pollinated Pure bred varieties were available Peas make lots of offspring lots of patterns become available Pure breeding or true breeding always produce progeny of the same type when crossed with themselves or another individual of the same variety He worked with 7 traits For each trait he had two different forms 14 in all Pod shape Pod color Flower position seed shape seed color ower color plant height P1 F1 F2 Generations F1 hybrid red owered plants self fertilized F2 75 Red 25 White Mendel s Law of inheritance Law of Random Segregation To explain his observation each physical trait is coded by 2 factors They come in different forms Each trait is controlled by a pair of factors genes One factor is dominant and the other is the recessive tall is dominant over dwarf red over white etc In sexual reproduction the paired factors separate during gamete formation Pairs reform in fertilizations tall vs dwarf red vs white etc Each trait is controlled by a pair of factors 23 000 genes from mom and dad Mendel s Law 3 during sexual reproduction each parent passes one allele from each gene pair to the offspring Chance determines which allele is passed Here s the Random Segregation for each gene pair we inherit one allele from each parent Homozygous both alleles of a gene pair are the same Heterozygous two different alleles Genotype genetic makeup Phenotype appearance plant will make red owers Pure breeding Red owered parent Homozygous genotype Punnet Square method defect in collagen most common genetic defect in caucasians defect in amino acid metabolism leads to mental retardation unless a special diet is used Cystic Fibrosis recessive and lethal defect in salt movement in and out of cells Phenylketonuria recessive Polydactyly dominant extra toe or nger Achondroplastic dwar sm dominant Marfans Syndrome 1880 s Fertilization Sperm Egg chromosomes discovered 1900 Mendel s work rediscovered 1903 Walter Sutton chromosomes behave like mendel s factors The chromosomes carry the genes the chromosome is found in the nucleus everything starts as a single cell zygote Sperm Egg zygote zygote adult cell division exact duplicates dominant defect in collagen Each cell has two copies of each chromosome 4 chromosomes 2 pairs 2 pairs of HOMOLOGOUS chromosomes homologous chromosomes carry the same genes but may have different alleles different chromosomes nonhomologous carry different genes every chromosomes carry about 1000 genes humans have 46 chromosomes 23 pairs Two types of cell division one cell two identical daughter cell one cell four daughter cells each has half as many chromosomes formation of gametes one cell divides twice to make 4 cells Division 1 homologous chromosomes are separated Division 2 sister chromatids are separated Mitosis Meiosis Meiosis cuts the chromosome number in half by separating the homologous chromosomes into separate cells Diploid cells chromosomes in pairs Haploid cells no pairs of chromosomes Fertilization two haploid cells fuse to make a diploid cell Chromosomes come in pairs Cells have two copies of each gene Members of each pair are homologous they carry the same genes but may have different alleles before cell division each chromosome is copied sister chromatids are exact duplicates that have the same alleles Q2 the name of the type of cell division that results in the formation of gametes eggs and sperm is meiosis Sickle cell anemia recessive due to altered form of Hemoglobin HbA allele for normal hemoglobin HbS sickle cell hemoglobin allele HbAHbA normal Modi cations of Mendell s Law Partial Dominance Codominance Partial Dominance or Codominance Multiple Alleles neither allele is dominant or recessive heterozygous individuals have a distinct phenotype Human Familial Hyperchloresterolemia Genetic defect results in high blood cholesterol levels can block arteries normal 100 mg dL heterozygous 300mg dL fc fc 700mg dL Multiple alleles ABO blood types A allele Ia Ia Ib are codominance B allele Ib O allele i both Ia and Ib are dominant over i
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