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

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

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

4. Mendel’s Experiments X Used purebred plants Chose plants with traits that would be carried to next generation each time seeds produced. X 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 X Some produced red flowers, and some only white X He then crossed all red with all white X Yielded some plants with all red flowers Reasoned that some factor must cause the red to be dominant over white

6. Mendel’s Experiment X Law of Dominance – overriding or dominant factors make certain recessive traits disappear. X Allele – matched pair of genes that control a trait X 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 X Mendel let some plants self-pollinate Offspring called an F1 generation Some all red and some all white X Let F1 reproduce X Plants from all red produced some white flowers Called the F2 generation

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

9. Inheritance X 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 X Developed by mathematician R.C. Punnett X Illustrates the possible combinations of a particular trait

11. Punnett Square Rr RRR Red Homozygous Rr Red Heterozygous rRr Red Heterozygous rr White Homozygous X 75% Red X 25% White X 3:1 Red to White

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

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

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

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

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

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

18. Sex Determination X Female has XX Female XX Male XY XX YX XXXY X Male has XY

19. Gene Transfer X DNA shaped in spiral a coil Also known as a double-helix If flattened out it would resemble a ladder X 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 X During mitosis and meiosis, the chromosome separates X Prior to cell division, DNA copies itself by replication X 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 X Systematic process of matching genetic factors from parent plants to produce offspring that are superior to parents X Early man used a primitive form of plant breeding

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

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

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

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

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

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

28. Animal Breeding X Some new breeds have been developed by crossbreeding X 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. n Developed on the King Ranch in Texas n All Santa Gertrudis are descendants of the bull “Monkey” Santa Gertrudis

30. Animal Breeding X 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 X Other breeds developed by crossing Bos indicus – Brangus, Simbrah, Braford, and Charbray

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