Exceptions to Mendelian Genetics

1. Exceptions to Mendelian Genetics • Some alleles are neither dominant nor recessive, and some traits are controlled by multiple alleles or multiple genes and may be influenced by the environment

2. Incomplete dominance • the heterozygous phenotype is somewhere between (intermediate to) the two homozygous phenotypes. • We see this often in flowers.

3. incomplete dominance • P generation parents are homozygous red and white • All F1 offspring are pink and heterozygous • When F1 offspring are allowed to self-pollinate, there is a 1:2:1 phenotypic ratio for the F2 offspring

4. Codominance • Both alleles are expressed to some degree in the heterozygous phenotype • Ex. “Erminette” chickens, roan cattle

5. Codominance • In chickens, the allele for black feathers and the allele for white feathers are both being expressed. • In roan cattle, the allele for red coat color and the allele for white coat color are both being expressed.

6. Codominance in Cattle

7. Multiple alleles • More than two alleles may exist for a given trait. An example is coat color in rabbits. • C - full (brown/gray) coat color - dominant to all other alleles • Cch - “Chinchilla” coat color - all gray - dominant to Ch and c alleles • Ch - “Himalayan” coat color - white with black features - dominant to c allele • c - Albino coat color - no pigmentation - recessive to all alleles

8. Multiple Alleles • Human blood types are the result of multiple alleles • Three alleles: IA ,IB , and i • IA andIB are both dominant over i, neither is dominant over the other • When the IA andIB alleles occur together, they are codominant

9. Polygenic traits • Complex traits that are controlled by multiple genes. • It can be difficult to accurately predict the appearance of some polygenic traits in offspring. • Ex. human eye color, coat color in labs

10. Coat color in Labs

11. Qualitative v. Quantitative Traits • Qualitative traits - have a clear quality, simple inheritance, limited environmental influence • Ex. attached earlobes • Quantitative traits - measurable but has many different qualities, complex, large environmental influence • Ex. milking ability

12. Start 10/25

13. Charles Darwin • Introduction to Natural Selection

14. Darwin’s Journey • In 1831, 22-year old Darwin leaves on a 5 year voyage as a naturalist on the HMS Beagle. • The Beagle travels around the world, with numerous stops along the South American continent. • As a naturalist, Darwin must make observations of the natural world, specifically plants, animals, geology, and climate of the various regions.

15. Darwin’s Journey

16. Darwin’s Journey • While on his journey, Darwin makes a number of observations: • Animals living in similar environments exhibit some of the same adaptive features. • Fossil remains of extinct animals resemble some current species.

17. Darwin’s Journey • For example, fossils of the Glyptodon very closely resemble, but are not the same as the armadillo. • This leads Darwin to believe that species must be changing over time.

18. Darwin’s Journey • This notion that species change over time clashes with the beliefs of that time period. • People are firm believers in divine creation - the belief that a divine being was responsible for the creation of all life forms on Earth. • This view is static and does not allow for change.

19. Science in the 1800’s • At the time, a comprehensive fossil record is being established by geologists. • The fossil record contradicts the theory of divine creation. • Many geologists are interested in how the Earth has changed. Several people in the science community begin to discuss species change.

20. Lamarck • In 1809, Lamarck theorizes that: • Physical features change in size based on how much or how little the animal uses them in it’s lifetime. Use and disuse. • These acquired changes are heritable - are passed from parents to offspring.

21. Lamarck One individual giraffe – change in one generation

22. Lamarck • Lamarck theorized that these sorts of traits were heritable. As we will soon see, evolution is something that takes place over generations, not in an individuals lifetime. • Lamarck did lay the foundation for Darwin’s theory by stating that species change with the “physical conditions of life” - the species environment. • These changes are evolutionary adaptations.

23. Darwin’s Journey • Darwin returns from his journey in 1836. • He has overwhelming evidence to show that evolution exists. • He doesn’t publish his theory until 1859. • Why? He sees that species change, but doesn’t yet understand why they are changing

24. Malthus • Darwin finds the answer to his problem in an unlikely place - an essay on economics by Thomas Malthus. • In the paper, Malthus is discussing the growth of human populations and food supply.

25. Malthus • Due to different types of growth, populations could easily exceed resources. • When resources become scarce, war and famine control the population. • What does this have to do with Darwin and evolution?

26. Malthus • To summarize the main point of Malthus’ essay, human populations are limited by their resources. • Humans are limited by their environment. • When humans come to conflict over scarce resources, the stronger, better-equipped will win. • Sound familiar?

27. Natural Selection • That’s because it’s the basis for Darwin’s mechanism of evolution! “Survival of the fittest” • Darwin believes that this applies not simply to humans, but to all living species. • Darwin theorizes that species evolve through the process of natural selection.

28. Natural Selection • Natural selection is defined as the differences in survival and reproduction among individuals in a population as a result of their interaction with the environment. • In other words, some individuals are better able to survive and reproduce because they have traits that make them better at coping with their environment

29. Natural Selection • Two major premises for Darwin’s theory: • Species are not immutable. Immutable means unchangeable. • The driving force behind evolutionary change is natural selection or “survival of the fittest”.

30. Natural Selection • Within a population, genetic diversity exists. • In a particular environment, certain individuals in a population are better suited to survive. • Over time, genes that code for traits that enable individuals to survive and reproduce accumulate (greater allelic frequency). • Evidence indicates modern species evolved from organisms that are now extinct

31. Evolution

32. Natural Selection • Beneficial traits are evolutionary adaptations to the environment, and increase the individuals fitness - the relative ability to survive and leave offspring.

33. Role of mutation • New alleles (different versions of a gene) arise by chance out of random mutations. • Some mutations better equip an organism to survive and reproduce (increase fitness), which will lead to those new traits being passed on. • We consider those traits “beneficial” • If environmental conditions remain the same, over time the beneficial trait will increase in frequency

34. Natural Selection • Darwin presented the following arguments to support evolution: • Populations have a huge reproductive potential • Population sizes remain relatively stable. • Resources are limited. • Individuals compete for limited resources.

35. Natural Selection • There is variation among individuals in a population. • Most of this variation is heritable. • Only the most fit individuals survive. Individuals with traits best adapted for survival in the environment are able to outcompete others. • Over time, traits best adapted for survival in the environment (and the genes behind them) accumulate in the population.

36. Types of Selection • Stabilizing Selection • Directional Selection • Disruptive Selection • Sexual Selection • Artificial Selection Natural Artificial

37. END 10/25/13

38. Directional Selection • Case of the Peppered Moth in England • Pre-Industrialization = light moth is selected for.

39. Directional Selection • After the Industrial Revolution, thick soot covers the trees that the moths live on. • Now, dark moths are selected for.

40. African Swallowtail

41. Sexual Selection Male Competition - Brooklyn Parrots

42. Male Competition

43. Sexual Dimorphism Peafowl

44. Sexual Dimorphism

45. Sexual Selection Female Choice - Blue-Footed Booby

46. Female Choice

47. Stabilizing Selection • Eliminates individuals that have extreme or unusual traits. • Individuals with the most common trait are best adapted. Height variation in humans adheres to stabilizing selection

48. Directional Selection • Favors traits that are at one extreme of a range of traits. • Traits at the opposite extreme are selected against. Example: Industrial Melanism

49. Disruptive Selection • Selection for extreme or unusual traits, while selecting against the common traits. • Example: weeds and disruptive selection for height.

50. Sexual Selection • Differential mating of males (sometimes females) in a population. • Male competition: awards mating opportunities to the strongest males. • Female choice: leads to traits or behaviors that are attractive to females.