Understanding Heredity

1. Understanding Heredity Part 1 1

2. The work of gregormendel

3. The Work of Gregor Mendel • ALL living things have a set of characteristics that are contained in genes. • These genes come from our parents and are found in every cell in our body. • Genetics – the scientific study of heredity

4. The Work of GregorMendel, cont. • Gregor Mendel – an Austrian Monk born in 1822 • He laid the foundation for much of our understanding of inheritance patterns • Credited as the “Father of Genetics”

5. The Work of Gregor Mendel, cont. • He was a mathematician/botanist and was in charge of the monastery garden • He noticed that individual plants of the same species were not identical

6. The Work of Gregor Mendel, cont. • He wanted to know why they were not identical, so he experimented on pea plants to help answer the question.

7. The Work of Gregor Mendel, cont. • He selected seven traits found in pea plants to study: • Seed shape • Seed color • Pod shape • Pod color • Plant height • Flower color • Flower position

9. The Work of Gregor Mendel, cont. Why pea plants? • Pea plants are pure breeding – they produce identical offspring when they self-pollinate • They grow fast • They have traits in distinct alternate forms (either/or)

10. The Work of Gregor Mendel, cont. • These characteristics allowed Mendel to control the outcome when he cross-pollinated plants with contrasting traits • The resulting offspring are called a monohybrid cross

11. The Work of Gregor Mendel, cont. How did he make these monohybrid crosses? • Mendel prevented self-pollination in the plants by removing the stamen • He dusted the pollen from one stamen onto another plant’s pistil (cross polination) • The result: cross-breed plants

13. The Work of Gregor Mendel, cont. What happened next? • He called the original plants the Parent (P) generation • The offspring produced by the P generation were the F1 generation; also called hybrids

14. The Work of Gregor Mendel, cont. • All of the hybrids showed the traits of only one of their parents… • The traits from the other parent had disappeared!

15. The Work of Gregor Mendel, cont. Where did those traits go? • To answer that question, Mendel let the F1 plants self-pollinate • This produced the F2 generation: ~ ¾ of the plants showed the traits of their parents (the F1 generation) ~ ¼ of the plants showed the traits of their grandparents (the P generation)

16. The Work of Gregor Mendel, cont. • This lead Mendel to make two conclusions about what he called biological inheritance (we call it genes): • Traits are passed from one generation to the next • Each trait is found in at least 2 contrasting forms

17. The Work of Gregor Mendel, cont. • He further concluded that: • Traits are inherited as distinct units from the parent • Organisms inherit 2 copies of each unit (one per parent) • Organisms donate one of those copies when they make gametes • The 2 copies separate (segregate) during gamete formation • These conclusions became know as the Law of Segregation

18. Modern genetics

19. Modern Genetics • Some traits are dominant over other traits • The unit that seems to disappear is recessive – it can only be expressed when 2 recessive traits combine

20. Modern Genetics, cont. • We refer to traits as genes • Genes are sections of chromosomes • Each form of the gene is called an allele • An organism can be: Homozygous – having 2 identical alleles OR Heterozygous – having 2 different alleles

21. Modern Genetics, cont. • Phenotype – the physical characteristics of the organism (what it looks like) • Genotype – the genetic makeup of the organism (what is actually there) The phenotype of an organism is the result of: • The Genotype • Environmental pressures

22. Probability and Punnett Squares

23. Probabilities • Mendel realized that the Principle of Probability (the likeliness that a particular event will occur) could be used to predict and explain the results of genetic crosses. • If there are 2 possible outcomes, then there is a 1 in 2 or 50% chance of each outcome occurring.

24. Probabilities, cont. • Example: If you flip a coin 3 times in a row, what are the chances it will be heads up every time? ½ x ½ x ½ = 1/8 • Probabilities can predict the average outcome of a large number of events – not the outcome of an individual event. • For that, we need Punnett Squares…

25. Punnett Squares • The gene combination that might result from a genetic cross can be predicted and compared with a Punnett Square • The dominant allele is represented by a capital letter (like T for tall) • The recessive allele is represented by a lower case letter for the same trait (like t for short)

26. PunnettSquares, cont.

27. Punnett Squares, cont. • Monohybrid cross - cross involving a single trait ex. flower color • Dihybrid cross - cross involving two traits ex. flower color & plant height

29. Non-mendelian genetics Beyond Dominant & Recessive Alleles

30. Beyond Dominant & Recessive Alleles • Principle of Independent Assortment: genes for different traits can segregate independently during the formation of gametes • This accounts for the genetic variations among organisms of the same species!

31. Beyond Dominant & Recessive Alleles, cont. • The majority of genes have more than two alleles • Many traits are controlled by more than one gene • Most of the genes that affect the physical appearance of an organism are found on the autosomes

32. Beyond Dominant & Recessive Alleles, cont. 1. Incomplete dominance – case where one allele is not completely dominant over another; produces an intermediate type

33. Beyond Dominant & Recessive Alleles, cont. 2. Codominance – both alleles contribute to the phenotype; it is a blend of the two alleles

34. Beyond Dominant & Recessive Alleles, cont. 3. Multiple Alleles – one individual can only have two alleles but more than two alleles can exist in a population.

35. Beyond Dominant & Recessive Alleles, cont. 4. Polygenic traits – many traits are produced by the interaction of several genes Examples: hair, eye and skin color

36. Beyond Dominant & Recessive Alleles, cont. 5. The characteristics of an organism are also determined by the environment it lives in