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Patterns of Inheritance Chromosomes • • • • • Karyotype: Entire set of chromosomes from a single cell Chromosomes. Each double DNA helix is packaged into a chromosome. Every species has a particular number of chromosomes Hereditable information exists in discrete units called genes A gene is the specific portion of chromosome that has the complete information to synthesize … a specific protein Gregor Mendel • Before settling down as a monk in the monastery of St. Thomas in Brünn. • Gregor Mendel tried his hand at several pursuits, including health care and teaching. • He studied botany and mathematics among other subjects. This training proved crucial to his later experiments, which were the foundation for the modern science of genetics. • Although Mendel worked without knowledge of genes or chromosomes, we can more easily follow his experiments. Genetic concepts • A gene´s specific physical location on a chromosome is called locus (plural, loci). • Homologous chromosomes carry the same genes, located at the same loci. • Alternate forms of the gene, is called alleles. • If both homologous chromosomes in an organism have the same allele are a given gene locus, the organism is said to be homozygous at the gene locus • If two homologous chromosomes have different alleles at a given locus, the organism is heterozygous. Pair of homologous chromosomes The M locus contains the M gene, which is involved in determining leaf color. Both chomosomes carry the same allele of the M gene. This tomato plant is homozygous for the M gene. The D locus contains the D gene, which is involved in determining plant height. Both chromosomes carry the same allele of the D gene.This tomato plant is homozygous for the D gene. The Bk locus contains the Bk gene, which is involved in determinig fruit shape. Each chromosome carries a different allele of the Bk gene. This tomato plant is heterozygous for the Bk gene. Mendel´s results, allow us to develop a five-part Model: 1. Each trait is determined by pairs of discrete physical units (alleles), which we now call genes. Each individual has two genes for a given trait. 2. Pairs of genes on homologous chromosomes separate from each other during gamete formation, so each gamete receives only one allele of an organism´s pair of genes. This conclusion is known as Mendel´s law of segregation. Each gamete receives only one of each parent´s pair of genes for each trait. 3. Which member of a pair of genes becomes included in a gamete is determined by chance. 4. When two alternate forms of a gene are present, one (the dominant allele) will mask the expression of the other (the recessive allele). 5. True-breeding (all the offspring produced are identical to the parent plant) organisms have two of the same alleles for a given trait. Mendel´s model • Using letters to represent the different alleles, we will assign the uppercase letter P (dominant allele) to the allele for purple and the lowercase letter p (recessive allele) to the allele for white. • Purple-flowered plant has two alleles for purple (PP), whereas a white-flowered plant has two alleles for white (pp). All the sperm and eggs produced by a PP plant carry the P allele; all the sperm and eggs of a pp plant carry the p allele. F1 P P p P p P p p P p P p Result: 100% P Gametes from F1 plants Sperm eggs | P + F2 offspring P PP P + p Pp p + P Pp p + p pp p P F2 P P P P p p P p p p Results: 75% P, 25% p • Therefore, three types of offspring can be produced: PP, Pp, and pp. The three types occur in the approximate proportions of 1/4 PP, 1/2 Pp, and 1/4 pp. • The actual combination of alleles carried by an organism (for example, PP or Pp) is its genotype. • The organism´s traits, including its outward appearance, behavior, digestive enzymes, blood type, or any other observable feature, make up its phenotype. Punnet Square PPxPp P p P P P P p P P P P p Result: 50 % PP, 50 % Pp (Genotype) Result: 100 % P (Phenotype) Punnet Square Ppxpp p P p P p p p p P p p p Result: Result: Genotype: 50% Pp, 50 % pp Phenotype: 50 % P, 50 % p • Mendel´s Hypothesis can be used to predict the outcome of new types of single-trait crosses. • Mendel hypothesized that genes on different chromosomes are inherited independently. Problem 1 • Your Grandmother (mother side) is diabetic (Recesive) and so is your Grandfather (Father side). • A) What are your chances of being diabetic if both of them got married with a normal homozygous? • (Hint: You must do first your parents.) Problem 1b • Your Grandmother (mother side) is diabetic (Recesive) and so is your Grandfather (Father side). • b) What are your chances of being diabetic if your Grandfather (mother side) is a normal heterozygous and your Grandmother (Father side) is a normal homozygous? Problem 1.c • Your Grandmother (mother side) is diabetic (Recesive) and so is your Grandfather (Father side). • C) What are your chances of being diabetic if both of them got married with a normal heterozygous?