BIOL 1441 1st Edition Lecture 23 Outline of Last Lecture I Meiosis II Stages of Meiosis I III Stages of Meiosis II IV Meiosis and diversity V Heredity VI Chromosomes somatic cells gametes VII Twins VIII Asexual sexual reproduction IX Genetic variation Outline of Current Lecture I Gregor Mendel II Theories of inheritance III Genes IV Mendel s laws of inheritance V Law of segregation VI Punnett square VII Test Crosses VIII Law of independent assortment These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Current Lecture I II III IV V Gregor Mendel a Father of Genetics b Austrian monk scientist c Studied heredity of physical traits in pea plants Theories of Inheritance a Blending hypothesis idea that genetic material from the two parents blends together i Blue and yellow paint blend to make green b Particulate hypothesis idea that parents pass on discrete heritable units genes i Mendel documented a particulate mechanism through his experiments with garden peas Genes What are they a Nucleotides i Phosphate Deoxyribose DNA sugar nitrogen base A T C G ii Adenine thymine 2 H bonds iii Guanine cytosine 3 H bonds b DNA mRNA Protein c Codon 3 DNA bases encode for 1 amino acid d Amino acids string together to form proteins e Genes segments of DNA that code for a specific proteins i Allele variants of the gene ii Gene for eye color 1 Alleles blue green brown hazel etc f Each gene resides at a specific locus location on a chromosome g One allele is dominant over the other and affects its expression what you see h Gene Expression i Alleles are dominant or recessive ii Dominant allele masks the expression of the recessive allele 1 Dominant 1 allele for expression 2 Recessive 2 alleles for expression iii Gene for hair color 1 Alleles brown and blond 2 Dominant allele brown color 3 Recessive allele blond color i Genotypes i Homozygous organism with two identical alleles for a gene ii Heterozygous organism that has two different alleles for a gene Mendel s Laws of Inheritance a Law of segregation two alleles in a pair segregate separate into different gametes during gamete formation VI i Only one allele is put on one gamete b Law of independent assortment each pair of alleles sort independently of each other during gamete formation i metaphase I meiosis homologous chromosomes align and randomly divide c Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments d Picked traits only had 2 possible outcomes i White flower or purple flower ii Wrinkled seed or a smooth seed e Observable feature character characteristic f Variants of character traits g Mendel s Experimental Approach i True breed plants that produce offspring of the same variety when they self pollinate pollinate flowers on same plant ii Homozygous for trait 1 Both alleles same 2 Flower color purple purple iii Typical experiment Mendel mated two contrasting true breeding varieties hybridization 1 Heterozygote hybrid 2 True breeding parents parental generation 3 Hybrid offspring F1 generation 4 Self pollinate F1 individuals produce F2 generation h Mendel s Observation i Mendel discovered a ratio of about three to one purple to white flowers in the F2 generation ii White flower trait did not disappear it was masked or hidden in F1 generation i Mendel s Model i Mendel developed a hypothesis to explain the 3 1 inheritance pattern he observed in F2 offspring ii 2 alleles for every gene one from each parent 1 Purple purple 2 Purple white 3 White white j Dominant vs Recessive Traits i Dominant trait hides or masks the recessive trait in F1 generation ii Recessive trait reappears in F2 generation need two recessive genes to be expressed Law of Segregation a Two alleles in a pair segregate into different gametes VII VIII b Two alleles for a gene separate segregate during gamete formation and end up in different gametes c Egg or a sperm receives only one of the two alleles that are present in the somatic cells of an organism d Segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis Punnett Square a Possible combinations of sperm and egg can be shown using a Punnett square b Diagram for predicting the results of a genetic cross between individuals of known genetic makeup c Capital letter dominant allele i P purple d Lowercase letter recessive allele i p white e Genotypes i Homozygous organism with two identical alleles for a gene 1 PP purple purple 2 pp white white ii Heterozygous organism that has two different alleles for a gene 1 Pp purple white f Genotype or Phenotype i Organism s traits do not always reveal its genetic composition genotype 1 PP purple 2 Pp purple ii Distinguish between an organism s physical appearance and it s genetic makeup iii Genotype genetic makeup PP or Pp or pp iv Phenotype physical appearance purple or white Testcross a How can we tell the genotype of an individual with the dominant phenotype i Homozygous dominant PP ii Heterozygous Pp b Testcross breeding the mystery individual with a homozygous recessive pp individual c If any offspring display the recessive phenotype the mystery parent must be heterozygous d Types of Crosses i Test cross tell you the genotype of a dominant trait 1 PP x pp or Pp x pp ii Monohybrid cross cross 2 heterozygous individuals for one trait 1 Pp x Pp iii Dihybrid cross cross 2 heterozygous individuals for two traits 1 PpYy x PpYy IX e Monohybrid Cross i Monohybrid individuals that are heterozygous for one character ii A cross between heterozygotes is called a monohybrid cross 1 crossing F1 generation f Dihybrids i Crossing two true breeding parents differing in two characters produces dihybrids in the F1 generation ii Heterozygous for both characters g Dihybrid Cross examining 2 traits i Cross between F1 dihybrids determines whether two genes are transmitted to offspring as a package linked or independently ii Linked on same chromosome h Predictions i Dependent linked inherited together F1 will only produce YR and yr 1 Phenotypic ratio of 3 1 ii Independent inherited separately F1 will produce YR Yr yR yr 1 Phenotypic ratio of 9 3 3 1 2 Genes are packaged into gametes in all possible combinations as long as each gamete has one allele for each gene Law of Independent Assortment a Each pair of alleles segregates independently of other pairs of alleles during gamete formation b Because