Transcript I. Genetics
Integrated Science Ch. 7 Tracking Traits: An Introduction to Genetics CH. 7 Tracking Traits: An Introduction to Genetics Heredity -the passing of traits from parent to offspring I. Genetics: -the study of heredity A. Gregor Mendel: - father of genetics - proposed the Principles of Heredity (1880's) - Austrian monk, taught "high school biology" B.Experimented with peas - several crops per year - don't take up much space - developed "purebreds" - easy to control pollinate Pea Flower Pistil (female) produces eggs Stamens (male) produce pollen - seven distinct, inherited traits Seed shape Seed color Pod shape Pod color Flower color Flower location Plant size P1 F1 F1 F2 II. Principles of Heredity A.Concept of Unit Characters: - traits are controlled by "factors" (genes) which occur in pairs - one from each parent B. Principle of Dominance and Recessiveness: - some alleles dominate, or mask, the effect of other alleles - Allele: one of the "versions" of a gene C. Law of Segregation: - during meiosis (production of gametes), each pair of genes separate Cross Fertilization of Parents Pollen PP pp Cross-Fertilize Pollen P Purebred (Homozygous) Purple-flowered Parent Pp All Purple-flowered (Heterozygous) Offspring p Purebred (Homozygous) White-flowered Parent Self-fertilization of F2 Pp F1 Self-Fertilize PP F2 75% Purple 25% White Pp F2 Pp pp F2 F2 1. Gametes: - specialized, reproductive cells (sperm, egg) - have 1/2 a set of chromosomes Human Egg and Sperm Cells 1.Gametes: - specialized, reproductive cells (sperm, egg) - have 1/2 a set of chromosomes 2. Genotype: - genetic make-up of an organism 3. Phenotype: - physical appearance of an organism 4.Homozygous: - alleles in a gene pair that are identical - TT or tt 5.Heterozygous: - alleles in a gene pair that are different - Tt TT Tt tt D. Principle of Independent Assortment: - alleles separate randomly during meiosis III. Applying Mendel's Principles A.Probability: - the likelihood that an event may happen B. Rules of Probability: 1. Product Rule of Probability: - when events occur in combination, the probability of each event is multiplied by the probability of the other What are the odds of rolling 3 tails in a row? 1/2 x 1/2 x 1/2 = 1/8 2.Probability has No Memory: - Previous events do not influence the probability of future events What are the odds on the next toss being a tail? The odds of rolling 3 tails in a row are 1/8. ? 1/8 1/2 IV. Meiosis A. Homologous Chromosomes: - pairs of chromosomes that are very similar - called homologous pairs - one member of a pair comes from each parent B. Diploid: - a full set of homologous chromosomes (2n) - in humans: 46 (23 pairs) - in pea plants: 14 (7 pairs) C. Haploid: - a half set of chromosomes (n) - occur in Gametes (special reproductive cells: sperm and egg) D. Meiosis: - specialized cell division in which the chromosome number in cells is cut in half - homologous pairs of chromosomes are separated - produces gametes - occurs in 2 stages: 1. Meiosis I: - 2 cells are produced that contain 1 replicated chromosome from each homologous pair 1. Meiosis I: - Crossing-over can occur: - exchange of genes between homologous chromosomes 2. Meiosis II: - similar to mitosis but DNA replication does not occur before division - 4 haploid daughter cells are produced Human Chromosomes (23 homologous pairs) Meiosis I Homologous chromosomes pair and cross over Prophase I Homologous chromosomes exchange DNA & align on equator Homologous chromosomes move to opposite poles Metaphase I Anaphase I Telophase I - Crossing-over can occur: - exchange of genes between homologous chromosomes Flower Color Pollen Shape Purple P Long L Purple P red p Long L round l red p round l P L Sister Chromatids Duplicated Chromosome Sister Chromatids Duplicated Chromosome P PP LL old combination P L new combination P p L pp p LL p P l P PP ll l ppp ll p Homologous Chromosomes Crossing Over p L new combination P l old combination p l Meiosis II Four Anaphase II Prophase II Haploid Metaphase II Telophase II Cells The End