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The Science of Genetics

The Science of Genetics. Original Power Point Created by Andy Harrison. Modified by the GA Agriculture Education Curriculum Office July 2002. Introduction. Genetics began as people noticed the similarity of offspring to parents

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The Science of Genetics

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  1. The Science of Genetics Original Power Point Created by Andy Harrison Modified by the GA Agriculture Education Curriculum Office July 2002

  2. Introduction • Genetics began as people noticed the similarity of offspring to parents • Animals or plants were selected based on certain desirable traits • Later became known as selective breeding

  3. Gregor Mendel • Austrian monk: 1822 –1884 • Noticed the texture of seeds differed • For example, some were smooth and round, others were not smooth and not round • Also noticed the difference in colors of flowers, length of stems, etc.

  4. Mendel’s Experiments • Used purebred plants • Chose plants with traits that would be carried to next generation each time seeds produced. • Crossed purebred plants with other purebred plants. • Removed petals • Removed pollen from stamens and placed on stigma of pistil of different type of plant

  5. Mendel’s Experiment • Some produced red flowers, and some only white • He then crossed all red with all white • Yielded some plants with all red flowers • Reasoned that some factor must cause the red to be dominant over white

  6. Mendel’s Experiment • Law of Dominance – overriding or dominant factors make certain recessive traits disappear. • Allele – matched pair of genes that control a trait • Law of Segregation – alleles responsible for trait separate and then combine with other parent at fertilization – each parent provides one of two genes for the trait

  7. Inheritance • Mendel let some plants self-pollinate • Offspring called an F1 generation • Some all red and some all white • Let F1 reproduce • Plants from all red produced some white flowers • Called the F2 generation

  8. Inheritance • Mendel concluded that traits or factors associated with red or white flowers separated before pollen merged with egg • Law of segregation - alleles responsible for traits from each parent are separated and then combined with factors from other parents at fertilization.

  9. Inheritance • Law of Independent Assortment – factors or genes for certain characteristics are passed on to the next generation separate from the factors or genes that transmit other traits.

  10. Punnett Square • Developed by mathematician R.C. Punnett • Illustrates the possible combinations of a particular trait

  11. Punnett Square • 75% Red • 25% White • 3:1 Red to White

  12. Genetics • The study of how traits are passed on to future generations • Genotype – the genetic composition of an individual • Phenotype – how the allele expresses itself

  13. Genetics • Homozygous – Genes that contain 2 dominant alleles (RR) or 2 recessive alleles (rr) • Heterozygous – Genes containing 1 dominant allele and 1 recessive allele (Rr)

  14. Gene Transfer • Traits are located on chromosomes • Chromosomes are made of strands of DNA • Contains proteins and amino acids • Each segment of the chromosome that controls a trait is a GENE • Some traits are controlled by one gene, others under multi-genetic control • In Mendel's law of dominance, one allele is expressed and one is hidden

  15. Meiosis • Similar to mitosis • Has an additional step • Chromosomes are divided so each sperm or egg contains a chromosome • Results in one egg or 4 sperm

  16. Gene Transfer • At fertilization the egg and sperm unite • Newly formed cell contain two chromosomes • There is a pair of alleles for each trait • Haploid • For example, sex cells have only one chromosome • Diploid • Chromosomes are in pairs • Some cells have more than two pair • Also known as polyploid

  17. Sex Determination • Each parent contributes one chromosome which pairs with a chromosome from the other parent • Sex Chromosomes • X: comes from the female • Y: comes from the male

  18. Female XX Male XY X Y X X XX XY Sex Determination • Female has XX • Male has XY

  19. Gene Transfer • DNA shaped in spiral a coil • Also known as a double-helix • If flattened out it would resemble a ladder • The two “sides” of the ladder are connected by nitrogen containing bases • Adenine - A • Thymine - T • Cytosine - C • Guanine - G • Adenine can only pair with Thymine • Cytosine can only pair with Guanine

  20. Gene Transfer • During mitosis and meiosis, the chromosome separates • Prior to cell division, DNA copies itself by replication • Messages in DNA are transferred by RNA (a messenger substance) • This “message” determines how the molecules of new DNA are to be arranged

  21. Plant Breeding • Systematic process of matching genetic factors from parent plants to produce offspring that are superior to parents • Early man used a primitive form of plant breeding

  22. Plant Breeding • All plants came from wild plants that were domesticated • The domesticated species are called cultivars

  23. What Plant Breeders Look For • Increased yield • Disease resistance • More efficient water use • Temperature tolerance • Ease of harvest • Uniform maturity • Quality of fruit or usable portion

  24. Plant Breeding • Breeders have increased adaptation of plants by a systematic system of plant breeding • Hybrid – crossing two purebred lines to result in a superior plant • Corn most common hybrid • Many vegetables and flowers now hybrids • Heterosis – the result of the crossing of unrelated parents • Results in increased performance

  25. Hybrid Corn • First developed in 1909 • Information on use taught to growers by Extension Service and Vocational Ag Classes in schools • Breeder develops parent lines by inbreeding selections from populations • Then crosses parent lines to create hybrids

  26. A B AB Hybrid Corn • Crosses are made by collecting pollen from one plant and depositing on silk of recipient plant.

  27. Animal Breeding • Less animals than in 1950, but production has increased • Most slaughter animals are crossbred due to hybrid vigor (heterosis benefit) • Selected for weight gain, size, conformation, litter size, etc.

  28. Animal Breeding • Some new breeds have been developed by crossbreeding • Santa Gertrudis - cross of two different species: Bos taurus X Bos indicus • Most cattle in America or Europe – Bos taurus • Cattle from India - Bos indicus (Brahman)

  29. Santa Gertrudis • Developed on the King Ranch in Texas • All Santa Gertrudis are descendants of the bull “Monkey”

  30. Animal Breeding • Texas cattlemen wanted to combine gentle nature and carcass quality of the Shorthorn breed with vigor, heat resistance, and insect resistance of the Brahman cattle • Other breeds developed by crossing Bos indicus – Brangus, Simbrah, Braford, and Charbray

  31. Animal Breeding • Computers have aided in sorting data • Results in expected progeny differences (EPD’s) • Use data of offspring to make selections of which animals to breed to others or to keep • Animals selected with leaner carcasses and better quality muscle result in increased flavor

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