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Concept 4

Concept 4. Review. Types of Dominance. Complete Dominance One allele is dominant over another (recessive) Heterozygote shows dominant phenotype Incomplete Dominance Neither allele is complete dominant (ex. Wavy hair) Heterozygote shows “blended” phenotype Co-dominance

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Concept 4

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  1. Concept 4 Review

  2. Types of Dominance • Complete Dominance • One allele is dominant over another (recessive) • Heterozygote shows dominant phenotype • Incomplete Dominance • Neither allele is complete dominant (ex. Wavy hair) • Heterozygote shows “blended” phenotype • Co-dominance • Neither allele is complete dominant (ex. Blood type) • Heterozygote shows BOTH phenotypes • Multiple Alleles • More than 2 options for phenotype (ex. Blood type) • Polygenic Inheritance • Multiple genes work together to code for the trait (ex. Skin)

  3. What type of inheritance?? • A cross between a purebred animal with red hairs and a purebred animal with white hairs produces an animal that has both red hairs and white hairs. What type of inheritance pattern is involved? Co-dominance!

  4. What type of inheritance?? 2. In a cross between individuals of a species of tropical fish, all of the male offspring have long tail fins, and none of the females possess the trait. Mating two of the F1 fish fails to produce females with the trait. Explain the inheritance pattern of the trait. Sex-linked trait!

  5. What type of inheritance?? 3. Suppose you mate a black rooster with a white hen. The feathers of all the offspring are “blue,” a color that is intermediate between black and white. Explain the inheritance pattern in these chickens. Incomplete Dominance!

  6. What type of inheritance?? 4. In cats, the allele for fur color is sex linked. The allele for black fur is XC, and the allele for orange fur is Xc . From this information, explain why calico (mixed color) cats, XCXc, are always female. Only females have 2 X Chromosomes! Co-Dominance! What type of dominance is this?

  7. What type of inheritance?? 5. Inheritance of the palomino coat color in horses is a result of incomplete dominance. White horse is DD, a chestnut horse is dd, and a palomino horse is Dd. What is the expected ratio of coat colors in the offspring of two palomino horses? Dd x Dd = DD, Dd, Dd, dd 1:2:1

  8. Simpson’s Complex Genetics • Complete the 4 examples based on the different types of inheritance.

  9. Dihybrid Crosses Same as regular (monohybrid) Punnett Square, but now tracks TWO traits Steps to complete any dihybrid cross Write out the full genotype of each parent Sort the alleles independently (meiosis) Write one allele combination (one of each letter) outside each box Complete your cross (end up with 4 letters in each box)

  10. Example Cross two heterozygous tall (Tt), heterozygous red (Rr) individuals Write genotype for each parent T t R r (mother) x T t R r (father) Sort alleles (FOIL)

  11. TR Tr tR tr TR Tr tR tr TTRR TTRr TtRR TtRr TTRr TTrr TtRr Ttrr TtRR TtRr ttRR ttRr TtRr Ttrr ttRr ttrr

  12. TR Tr tR tr TR Tr tR tr TTRR TTRr TtRR TtRr TTRr TTrr TtRr Ttrr TtRR TtRr ttRR ttRr TtRr Ttrr ttRr ttrr 9 : 3 : 3 : 1

  13. Practice • What are the genotypes of SpongeBob, who is heterozygous for his yellow body color and his squarepants, and his wife SpongeSusie, who is blue and has roundpants? • What are the possible gamete combinations for each person? • Complete a Punnett Square and answer the following: • What is the chance of a blue baby? ________ • What is the chance of a squarepants? ________ • What is the chance of a blue squarepants? ________ • What is the chance of a purebred recessive for both traits?

  14. Concept 5 – Mutations and Genetic Engineering

  15. Mutations

  16. What is a mutation? • Any change in the DNA (order of bases/letter) • Gene mutation (change or error in a single gene) • Chromosomal mutation (change or error in an entire chromosome) • To be passed on, the mutation must be in the gametes (sperm/egg) • Mutations in somatic cells (ex. Skin cell damage from sun) are not genetic

  17. Gene Mutations • Ex. Sickle cell, Cystic Fibrosis, Tay Sachs • Cracking the Code http://www.pbs.org/wgbh/nova/body/cracking-the-code-of-life.html

  18. Point Mutation- One nitrogenous base is replaced with another during translation (may code for a different protein)

  19. Frameshift mutation- One nitrogenous base is added or deleted (VERY severe – causes all of the rest of the code to be wrong!)

  20. Mutation • Mrs West is the coolest Point Mutation: • Mqs West is the coolest Deletion (frameshift): • Msw Esti st hec oolest

  21. Chromosome Mutations • Chromosome number or structure changes http://staff.tuhsd.k12.az.us/gfoster/standard/bmut.htm • Nondisjunction = chromosomes do not separate properly during meiosis • Gametes that are missing an entire chromosome usually result in miscarriage • Examples • 3 copies of chromosome 21 (Down Syndrome) • 3 copies of chromosome 18 (Trisomy 18 – Eliot) • XXY (Kleinfelter’s Syndrome) • XO (missing second sex chromosome – Turner’s Syndrome)

  22. Causes and Results of Mutations • Can be random errors during meiosis, transcription or translation • Environmental factors (carcinogens) can cause changes to chromosome structure or gene sequence • Most mutations have negative effects, but some could be positive and lead to a new advantageous trait in a population

  23. Pedigrees • Diagram of family relationships • Square = male Circle = female • Blank = no disease Shaded = disease (sometimes half shaded = heterozygous/carrier)

  24. Pedigree analysis • In humans, pedigree analysis is an important tool for studying inherited diseases • Pedigree analysis uses family trees and information about affected individuals to: • figure out the genetic basis of a disease or trait from its inheritance pattern • predict the risk of disease in future offspring in a family (genetic counseling)

  25. Pedigree analysis • Basic patterns of inheritance • autosomal, recessive • autosomal, dominant • X-linked, recessive • X-linked, dominant (very rare)

  26. female male affected individuals Sample pedigree - cystic fibrosis

  27. Autosomal recessive traits • Trait is rare in pedigree • Trait often skips generations (hidden in heterozygous carriers) • Trait affects males and females equally • Autosomal recessive traits are the most common in populations.

  28. Autosomal recessive diseases in humans • Most common ones: • Cystic fibrosis • Sickle cell anemia • Phenylketonuria (PKU) • Tay-Sachs disease • For each of these, overdominance (heterozygote superiority) has been suggested as a factor in maintaining the disease alleles at high frequency in some populations • With sickle cell anemia, Heterozygotes have superior resistance to malaria than either homozygote. • This benefit is thought to be the reason that the gene mutation has not been eliminated from the population.

  29. Autosomal dominant pedigrees • Trait is common in the pedigree (found in every generation) • Affected individuals transmit the trait to ~1/2 of their children (regardless of sex) • Non-affected individuals do NOT pass on the trait • These are rare in the overall population

  30. Autosomal dominant traits • There are few autosomal dominant human diseases (why?), but some rare traits have this inheritance pattern ex. achondroplasia (a sketelal disorder causing dwarfism)

  31. X-linked recessive pedigrees • Trait is rare in pedigree • Trait skips generations • Affected fathers DO NOT pass to their sons • Males are more often affected than females

  32. X-linked recessive traits ex. Hemophilia in European royalty

  33. X-linked dominant pedigrees • Trait is common in pedigree • Affected fathers pass to ALL of their daughters • Males and females are equally likely to be affected • VERY rare in population

  34. X-linked dominant diseases • X-linked dominant diseases are extremely unusual • Often, they are lethal (before birth) in males and only seen in females ex. incontinentia pigmenti (skin lesions) ex. X-linked rickets (bone lesions)

  35. Pedigree Analysis in real life: complications Incomplete Penetrance of autosomal dominant traits => not everyone with genotype expresses trait at all Ex. Breast cancer genes BRCA-1 and BRCA-2 & many “genetic tendencies” for human diseases

  36. Pedigree Analysis in real life: complications Sex-limited expression => trait only found in males OR females

  37. III-1 has 12 kids with an unaffected wife 8 sons - 1 affected 4 daughters - 2 affected Does he have reason to be concerned about paternity?

  38. Pedigree Practice • For each pedigree (A-D) • Write type of inheritance pattern (autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive) • Identify the genotypes of the numbered individuals

  39. Inbreeding • Mating between two genetically-related individuals • Often seen in royalty and isolated populations (islands, etc.) • Recessive disorders appear at higher rates • Decrease in genetic variation (an allele may disappear altogether)

  40. What is the pattern of inheritance? What are IV-2’s odds of being a carrier?

  41. Selective Breeding • Choosing to mate individuals with preferred traits • Used frequently in domesticated animals and commercial crops to get favorable traits

  42. Breeding the perfect Black Lab How do we get a true-breeding line for both traits?? black individuals = fetch well grey individuals = don’t drool

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