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Genetics. The Study of Heredity. Heredity The passing of traits from parents to their offspring Causes children to resemble their parents. Genetics - The study of heredity. The Study of Heredity. Gregor Mendel - the father of modern genetics
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The Study of Heredity Heredity • The passing of traits from parents to their offspring Causes children to resemble their parents. • Genetics- The study of heredity
The Study of Heredity Gregor Mendel - the father of modern genetics • Austrian monk - trained in mathematics and natural sciences. • Work conducted over period of 8 years with common garden peas -1856 to 1865. Kept careful records. Applied mathematical studies to his work. Worked with different kinds of plants. Selected peas
The Study of Heredity Selected peas because they: • Grew rapidly. • Produced many seed (offspring). • Flower structure made it easy to control Pollination Transfer of pollen from stamen to pistil of a flower. Pistil- female reproductive structure - egg at base. Stamen- male reproductive structure - produces pollen contains sperm. Self –pollination- process where pollen from stamen falls on pistil of the same flower. Cross-pollination- process where pollen from stamen of 1 flower falls on pistil of another flower on another plant.
The Study of Heredity Identified 7 different characteristics in pea plants Each had two contrasting forms. • Seed Shape - Round Vs. Wrinkled • Seed Color - Yellow Vs. Green • Flower Color - Purple Vs. White • Pod Shape - Inflated Vs. Constricted • Pod Color - Green Vs. Yellow • Flower Position - Axial Vs. Terminal • Plant Height - Tall Vs. Short
The Study of Heredity His experiments were different from earlier workers • Studied only 1 trait at a time, rather than everything about the offspring at once. • Studied results of many matings and pooled the results - earlier workers had looked at only a few offspring from a single mating Counted 7324 peas for seed shape (F2 generation) Counted 8023 peas for seed color (F2 generation) • Used the large number of offspring to discover definite ratios of characteristics among the offspring. 5474 Round Seed: 1850 Wrinkled Seed 2.96:1 6022 Yellow Seed: 2001 Green Seed 3.01:1
The Study of Heredity Mendel's Experiments and Observations • When the plants were allowed to self-pollinate, the trait always stayed the same - called them "Truebreeding" or "Pure"plants; Tall plants x Tall plants produced Tall plants. • Removed stamens from the pure plants that produced wrinkled seeds. Dusted pistil with pollen from plants that produced only round seeds Called these the Parental or P1 generation • All of the offspring of this cross resulted in plants that had round seed Called this the First Filial or F1 generation; Also called Hybrids Hybrid- offspring from a cross between parents differing in 1 or more traits. Found that 1 trait of the parents always disappeared in the F1 generation. • The F1 generation plants were allowed to self-pollinate Called the next generation the Second Filial or F2 generation. Found that some F2 plants had round seed; some had wrinkled seeds. Similar results were obtained with the other traits always 75% of 1 trait; 25% of other trait - a 3:1 ratio.
The Study of Heredity Mendel’s Cross P1 Round Seed x Wrinkled Seed F1 All Hybrid Round Seed Hybrid Round Seed x Hybrid Round Seed F2 ¾ Round Seed; ¼ Wrinkled Seed
The Study of Heredity Mendel's Conclusions • Did not know anything about cell reproduction Work based on hypothesis that Factorsor units carried the traits he was studying - called Genestoday. • Observed that offspring of true breeding plants with contrasting traits showed the trait of only 1 parent plant Called trait Dominant– disappearing trait called Recessive • Observation lead to his Law of Dominance - one form of a hereditary trait, the dominant trait, Dominatesor prevents the expression of the recessive trait. • Mendel hypothesized that factors exist in pairs since the plants which had 1 trait could produce seeds with the opposite trait.
The Study of Heredity Mendel’s Conclusions • Mendel hypothesized that paired factors separate or segregate during gamete formation - lead to Law of Segregation - During gamete formation the pairs of genes responsible for each trait separate so that each gamete contains only 1 gene for each trait. • During fertilization the zygote gets 1 gene for the trait from mom and 1 from dad. • The different forms of a gene for a trait are known as Alleles • Combination of alleles or genetic makeup is the organism’s Genotype • The appearance of the organism regardless of its genetic makeup is its - physical appearance - Round, yellow, etc.
The Study of Heredity • Dominance is expressed by a capital letter - usually the first letter of the dominant trait; Recessive trait is expressed by a small letter (same as the dominant trait) For round Vs. wrinkled seed - R - dominant; r - recessive Hybrid would be Rr • During gamete formation the pairs of genes responsible for each trait separate so that each gamete contains only 1 gene for each trait. Rr / \ R r
The Study of Heredity Mendel’s Cross P1 Round Seed x Wrinkled Seed RR x rr F1 All Hybrid Round Seed (Rr) Hybrid Round Seed x Hybrid Round Seed Rr x Rr F2 ¾ Round Seed; ¼ Wrinkled Seed RR, Rr rr
The Study of Heredity Genetic Terminology • Dominant - trait which stays visible • Recessive - trait which disappeared • Alleles - alternate forms of a gene for a trait • Genotype - genetic makeup of a trait • Phenotype - physical appearance of a trait • Homozygous - both alleles are the same • Heterozygous - two alleles are different • Homozygous Dominant - pure dominant • Homozygous Recessive - pure recessive • Heterozygous Dominant - Hybrid with 1 dominant -
The Study of Heredity Mendel’s Laws • LAW OF DOMINANCE - one form of a hereditary trait, the dominant trait, dominatesor prevents the expression of the recessive trait. • LAW OF SEGREGATION - During gamete formation the pairs of genes responsible for each trait separate so that each gamete contains only 1 gene for each trait. • LAW OF INDEPENDENT ASSORTMENT - Alleles segregate independently of each other during gamete formation.
Probability The likelihood of an event occurring as expressed as a ratio or a percentage. • Flipping a coin – ½ heads; ½ tails • Cards - Chance of drawing an ace –4/52 or 1/13 Chance of drawing a spade - 13/52 or 1/4 Chance of drawing the Ace of Spades 1/13 x 1/4 = 1/52
Probability Product Rule • To find the probability of 2 events occurring you multiply the individual probabilities. Chance of a head – ½ ; Chance of another head – ½ Chance of 2 heads in a row – ½ x ½ = ¼ Chance of 4 heads in a row – ½ x ½ x ½ x ½ = 1/16 • Each gamete has ½ chance of getting a particular allele Homozygous Dominant - RR: Alleles - R or R = 1/1 Homozygous Recessive - rr: Alleles - r or r = 1/1 Heterozygous Dominant - Rr: Alleles - R or r; ½ R; ½ r
Probability PUNNETT SQUARE • Special chart used to show possible combinations resulting from a cross of 2 organisms. • Put female gametes along top; male gametes along left side • Squares show possible genotypes of offspring -used to determine phenotype and ratio of offspring. • Used to predict; it doesn’t mean it will happen
Types of Crosses MONOHYBRID CROSS - involves only one set of contrasting factors for a trait • Cross a homozygous yellow with a homozygous green Yellow – dominant (Y); green - recessive (y) Y Y P1 YY x yy y F1 all Yy heterozygous yellow y • Cross two of the F1 generation Y y Yy x Yy Y F2 – ¼ YY; ½ Yy; ¼ yy ¾ Yellow; ¼ green y Yy Yy Yy Yy YY Yy Yy yy
Types of Crosses DIHYBRID CROSS - involves two sets of contrasting traits at one time; genes are on separate chromosomes • Each gamete contains 1 allele for each trait • LAW OF INDEPENDENT ASSORTMENT - Alleles segregate independently of each other during gamete formation.
Types of Crosses Het Round, Het Yellow RrYy x Het Round, Het Yellow RrYy Gametes: RY Ry rY ry
Types of Crosses INCOMPLETE DOMINANCE/NONDOMINANCE • Phenotype between dominant and recessive trait • Heterozygous condition • Example - Four-O-Clocks RR - red flowers rr - white flowers Rr - Pink flowers • Cross of 2 pink flower plants - Rr x Rr Results – ¼ red (RR); 2/4 (½) Pink (Rr); ¼ white
Types of Crosses Determination of Sex • By the Sex Chromosomes- x or y Other chromosomes are called Autosomes • Male - xy; Female - xx • Get ½ males and ½ females on Punnett square x x x y xx xx xy xy
Types of Crosses SEX LINKED CHARACTERISTICS • Recessive trait linked with a certain sex - usually males • Carried on the x-chromosome; Male has only 1 x, the trait is visible Females with 2 x's - not visible if 1 of the x has a dominant gene for the trait. • Female only shows trait in homozygous recessive. • Woman is called a "Carrier" in heterozygous condition. • Examples: Red-Green color blindness Hemophilia
Types of Crosses Male Female
Types of Crosses MULTIPLE ALLELES • More than 2 alleles exist for a particular trait • In humans - blood types is an example of multiple alleles 3 different alleles - A, B, O Alleles A and B are codominant O is recessive
Types of Crosses Blood Type • Due to presence of antigens on the red blood cells - produces antibodies in blood Type A - Antigen A on cells Plasma contains anti B Type B - Antigen B on cells Plasma contains anti A Type O - No Antigens on cells Plasma has anti A and anti B Type AB - Antigens A and B on cells Plasma lacks anti A and anti B
Types of Crosses Phenotypes and genotype combinations • Type A - AA or AO • Type B - BB or BO • Type AB - AB • Type O - OO
Types of Crosses Blood Donor Receives Group to from O O, A, B, AB O Universal Donor A A, AB O, A B B, AB O, B AB AB O, A, B, AB Universal Recipient
Other Related Topics GENE LINKAGE • Concerned with the presence of 2 different genes on the same chromosome • Does not follow usual dihybrid results - follows monohybrid. • Variation can occur due to crossing over - pieces of chromatids exchange places during synapsis of tetrads in meiosis.
Other Related Topics LETHAL GENES • Genes which can cause death or harm in the homozygous condition. • Examples: Sickle-cell anemia PKU Tay Sachs - Jews of middle eastern European origin. Diabetes mellitus
Other Related Topics NONDISJUNCTION • Failure of chromosomes to segregate properly during gamete formation. • Can involve sex chromosomes as well as the autosomes - zygote gets an improper number of chromosomes • Examples: Down's Syndrome - three #21 chromosomes - autosomal Turner's Syndrome - has only 1 x, no y chromosome - female Klinefelter's Syndrome - xxy - male Jacob’s Syndrome- xyy - male –thought to show criminal behavior at one time; not any higher.
Other Related Topics Normal Male Male – Down’s
Other Related Topics Klinefelter’s Syndrome Turner’s Syndrome Jacob’s Syndrome
Other Related Topics MUTATIONS • Change in the genetic code or genes of an organism. • Can occur naturally or by exposure to agents that produce mutations. Breaks during crossing over which do not reattach. Increased chance of breakage by exposures to mutagens Mutagens- agents that cause mutations. Radiation - x-rays, UV, gamma Chemicals