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Introduction to Genetics Learning Targets I can define and provide an example of the following: genotype, phenotype, dominant allele, codominant alleles, incompletely dominant alleles, homozygous, heterozygous, and carrier. Genetics Terms Heredity is the passing of traits from parents to offspring Traits are inherited characteristics such as eye color, height, hair color Fertilization is the uniting of male and female gametes Pollination is plant fertilization More Terms Gametes-specialized cells involved in sexual reproduction; sperm or egg; pollen or ovum Gene-sequence of DNA that codes for a protein and thus determines a trait Probability-likelihood that a particular event will occur More terms Alleles are the various genes for the same trait Dominant traits are those that are always expressed when present (brown eyes) Recessive traits are only expressed if the dominant trait is absent (blue eyes) More terms Homozygous means possessing a pair of identical alleles for a trait; can be dominant or recessive. Shown by AA or aa Heterozygous means possessing a pair of unlike alleles; dominant trait is expressed; recessive trait is carried; Aa More Terms Phenotype is the physical appearance of a trait Genotype is the actual genetic makeup; XX for females; XY for males Even more terms True breeders -organisms that produce offspring identical to themselves if allowed to self-pollinate Hybrids – offspring of crosses between parents with different traits Learning Targets I can define and provide an example of the following: genotype, phenotype, dominant allele, codominant alleles, incompletely dominant alleles, homozygous, heterozygous, and carrier. Gregor Mendel http://science.discovery.com/tvshows/greatestdiscoveries/videos/100-greatestdiscoveries-shorts-genetics.htm Gregor Mendel Father of genetics Born 1822 on farm in Austria (now Czech Republic) Entered monastery in 1843 Mendel Sent to University of Vienna; studied botany and other subjects Became chief gardener at the monastery Monks helped feed not only themselves but their community Mendel Mendel sought to increase production and yield of their crops Mendel started breeding peas in 1857 to study inheritance His study took 10 years to complete His methods are still used today because he kept meticulous records Why Peas? • Many varieties have two clearly different traits Flower color Seed color Seed shape • Plants are easy to control Male and female parts on same flower (dioecious) Pollen is male ; ovule is female Learning Targets I can describe the basic mechanisms of plant processes, especially movement of materials and plant reproduction. I can explain the functions of unique plant structures. Flowers http://www.youtube.com/watch?v=O pzvKdmAoI0 Parts of a Flower Sepals-outermost circle of floral parts; usually green and look like leaves Petals-often brightly colored; found just inside the sepals Leaf-photosynthetic organ that contains on or more Bundles of vascular tissue Parts of a Flower Terms Stamen-male part of the flower; made of filament and anther Filament-a long thin structure that supports the anther Anther-flower structure in which haploid male gametes are produced Parts of a Flower Terms Pistils (Carpels)-innermost part of a flower that produces the female gametes Stigma- sticky portion at the top of the style where pollen grains land Style-narrow stalk of the carpel in a flower Ovary-a flower structure that contains one or more ovules from which the female gametes are made Ovule-female gamete Vascular Tissue in Plants Xylem-vascular tissue that carries water from the roots to the rest of the plant Phloem-vascular tissue that transports nutrients and carbohydrates made by photosynthesis Vascular Bundles-a plant stem structure that contains xylem and phloem tissue Plant Life Cycle Plant Fertilization http://www.youtube.com/watch?v=L dlxUJhoyx4 Plant Fertilization Learning Targets I can describe the basic mechanisms of plant processes, especially movement of materials and plant reproduction. I can explain the functions of unique plant structures. Learning Targets I can identify and explain Mendel’s laws of segregation and independent assortment I can construct and interpret Punnett squares (calculating and predicting phenotypic and genotypic ratios of offspring) Mendel’s Procedure 1. Remove immature stamen from plant 2. Took brush and removed pollen from one plant 3. Then brushed pollen onto ova of another plant 4. Allowed plant to seed and then planted the seeds Mendel’s Peas Studied over 30,000 plants in 10 years Usually followed his plants for 3 generations Studied flower color, seed color, seed shape, height Always started with true breeders Covered plants to keep pollinators away Mendel’s Peas Began by crossing tall & short plants Expected an intermediate height plant Instead all plants were tall Let these plants self pollinate and got 3:1 ratio Three tall plants to every short plant He decided that each trait had at least two factors for each trait; called these alleles Probability and Punnett Squares The principles of probability can be used to predict the outcomes of genetic crosses. Flipping a coin 50/50 chance of getting a head every time Punnett Squares A diagram used to predict genetic probabilities Can compare genetic variations that will result from a specific cross Monohybrid Crosses A monohybrid cross occurs between two parents that breed true for different versions of a single trait Allows tracking of one trait only Monohybrid Cross P Generation T t t T Tt Tt Tt Tt All were tall Monohybrid Cross F1 Cross T T t TT Tt Phenotype: 3:1 Genotype: 1:2:1 t Tt tt Rule of Dominance To be dominant, an organism must possess either two dominant alleles or at least one dominant allele To be recessive, the organism must receive two recessive alleles; one from each parent Principle of Segregation Pairs of alleles separate during gamete formation in meiosis. The fusion of gametes pairs the alleles again at fertilization Principle of Independent Assortment Each pair of alleles separates independently of each other during gamete formation Incomplete Dominance R Snap Dragons r Red crossed with White Expected 3:1 ratio Red to White r R Rr Rr Rr Rr Got all PINK! Codominance The expression of two different alleles in a heterozygote Many genes have different alleles; but usually only two or less are expressed in the individual Blood is expressed in different alleles: A, B, AB or O A and B are dominant; O recessive AB is codominant Dihybrid Crosses A cross where two traits are examined Predicts two different traits Parents will have four possible gametes displaying the various combinations of the two traits Mendel used seed shape and seed color for one of his dihybrid crosses Dihybrid Cross RRYY R = round Y = Yellow r = wrinkled y=green x rryy Dihybrid Parent Cross RY RY RY RY ry RrYy RrYy RrYy RrYy ry RrYy RrYy RrYy RrYy ry RrYy RrYy RrYy RrYy ry RrYy RrYy RrYy RrYy Dihybrid Cross Crossing pure breeding homozygous dominant with pure breeding homozygous recessive RRYY X rryy All offspring are heterozygous for the trait RrYy Dihybrid F1 Cross RY rY Ry ry RY RRYY RrYY RRYy RrYy rY RrYY rrYY RrYy rrYy Ry RRYy RrYy Rryy Rryy ry RrYy rrYy Rryy rryy F1 Generation Dihybrid Cross Allowing F1 to cross pollinate results in a 9:3:3:1 ratio 9 will be round, yellow 3 will be round, green 3 will be wrinkled, yellow 1 will be wrinkled, green Learning Targets I can identify and explain Mendel’s laws of segregation and independent assortment I can construct and interpret Punnett squares (calculating and predicting phenotypic and genotypic ratios of offspring)
