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Diaz 374

Introduction to Genetics. Diaz 374. What is genetics?. The scientific study of heredity. Gregor Mendel. Born in 1822 in Czechoslovakia. Became a monk at a monastery in 1843. Taught biology and had interests in statistics. Also studied at the University of Vienna. Mendel continued.

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Diaz 374

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  1. Introduction to Genetics Diaz 374

  2. What is genetics? • The scientific study of heredity

  3. Gregor Mendel • Born in 1822 in Czechoslovakia. • Became a monk at a monastery in 1843. • Taught biology and had interests in statistics. • Also studied at the University of Vienna

  4. Mendel continued • After returning to the monastery he continued to teach and worked in the garden. • Between 1856 and 1863 he grew and tested over 28,000 pea plants

  5. Mendel’s Peas • Easy to grow. • Easily identifiable traits • Can work with large numbers of samples

  6. Mendel’s experiments • The first thing Mendel did was create a “pure” generation or true-breeding generation. • He made sure that certain pea plants were only able to self pollinate, eliminating unwanted traits. • He did this by cutting away the stamen, or male part of each flower

  7. Genes and dominance • Trait : a characteristic • Mendel studied seven of these traits • After Mendel ensured that his true-breeding generation was pure, he then crossed plants showing contrasting traits. • He called the offspring the F1 generation or first filial.

  8. What will happen when pure yellow peas are crossed with pure green peas? • Allof the offspring were yellow. • Hybrids = the offspring of crosses between parents with contrasting traits

  9. What did Mendel conclude? • Inheritance is determined by factors passed on from one generation to another. • Mendel knew nothing about chromosomes, genes, or DNA. Why? • These terms hadn’t yet been defined.

  10. What were Mendel’s “factors” • The ‘factors” that Mendel mentioned were the genes. • Each gene has different forms called alleles • Mendel’s second principle stated that some alleles are dominant and some are recessive.

  11. Mendel’s second cross • He allowed the F1 generation to self-pollinate thus producing the F2 generation. • Did the recessive allele completely disappear? • What happened when he crossed two yellow pea hybrid (F1) plants?

  12. Results: • ¾ of the peas were yellow, ¼ of the peas were green. • During the formation of the sex cells or gametes, the alleles separated or segregated to different gametes. (pollen and egg)

  13. Probability • The likelihood of a particular event occurring. Chance • Can be expressed as a fraction or a percent. • Example: coin flip.

  14. Punnett Square • Developed by Reginald Punnett. • A diagram used to show the probability or chances of a certain trait being passed from one generation to another.

  15. Reading Punnett squares • Gametes are placed above and to the left of the square • Offspring are placed in the square. • Capital letters (Y) represent dominant alleles. • Lower case letters (y) represent recessive alleles.

  16. Punnett square example

  17. genotypes • Homozygous = when an organism possesses two identical alleles. ex. • YY or yy • Heterozygous = when an organism possesses different alleles. ex. • Yy

  18. Phenotype vs genotype • Genotype • The genetic makeup • Symbolized with letters • Tt or TT • Phenotype • Physical appearance of the organism • Expression of the trait • Short, tall, yellow, smooth, etc.

  19. Probability and statistics • No one event has a greater chance of occurring than another. • You cannot predict the precise outcome of an individual event. • The more trials performed, the closer the actual results to the expected outcomes.

  20. Punnett square review:

  21. Independent Assortment • The two factor cross. Example: color and shape of peas. • F1 cross to produce the F2 generation Ex RRYY x rryy Round yellow mated with wrinkled green • Offspring would all be hybrid for both traits (RrYy)

  22. What is independent assortment? • Alleles separate independently during the formation of gametes.

  23. The dihybrid cross • Punnett square on board:

  24. Some exceptions to Mendel’s principles: • Some alleles are neither dominant nor recessive. • Many traits are controlled by more than one gene (polygenic traits)

  25. Incomplete dominance • A situation in which neither allele is dominant. • When both alleles are present a “new” phenotype appears that is a blend of each allele. • Alleles will be represented by capital letters only.

  26. Japanese four-o-clock flowers • Red flower plant genotype = RR • White flower plant genotype = WW • Pink flower plant genotype = RW

  27. What happens when a red flower is crossed with a white flower? • According to Mendel either some white and some red or all offspring either red or white. • All are pink

  28. Codominance • When two alleles both appear in the phenotype. • Usually signified using superscripts. • example: color of hair coat in cattle. • crcr= red hairs • cwcw = white hairs • crcw = roan coat (mixture of both colors)

  29. Roan cattle inheritance

  30. Multiple allele inheritance • When two or more alleles contribute to the phenotype. • Human blood types: A,B,O and AB • A and B are codominant to each other. • Both A and B are dominant over O.

  31. Human Blood types: • TYPE A • Allele = IA • Blood cells have small antigens on the surface.

  32. TYPE B • Allele = IB • Cells coated with type B antigens

  33. TYPE AB • genotype = IAIB • Blood cells contain both types of antigens • Known as universal recipient

  34. TYPE O • Allele = i • No antigens on the surface of the blood cells • Known as universal donor

  35. 6 different genotypes • IAIA • IAIB • IBIB • IBi • IAi • i i • Type A • Type AB • Type B • Type B • Type A • Type O

  36. How common are the different blood types? 45 % 40 % 4 % 11 %

  37. Sample Problem: • A man with type AB blood marries a woman with type B blood whose father has type O blood. What are the chances that they have a child with type A blood? Type AB?

  38. Polygenic traits • Traits controlled by two or more genes. • Examples: • Human height, eye and skin color

  39. Assignment / HW • Spongebob genetics worksheet 1

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