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Unit 4: Developmental Genetics

Unit 4: Developmental Genetics. 6 days. October 23:. Birth Defects. The medical impact of birth defects is considerable More than 20% of infant deaths are from birth defects An additional 20% may be caused by complications of pre-maturity. Birth Defects.

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Unit 4: Developmental Genetics

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  1. Unit 4: Developmental Genetics 6 days

  2. October 23:

  3. Birth Defects • The medical impact of birth defects is considerable • More than 20% of infant deaths are from birth defects • An additional 20% may be caused by complications of pre-maturity

  4. Birth Defects • In addition to mortality there is a high level of morbidity • Mental retardation and other dysfunctions that limit the productivity of affected individuals

  5. Birth Defects • Developmental anomalies have a major impact on public health • Genetic counseling and prenatal diagnosis, with the option to terminate the pregnancy, are important for helping individuals faced with a risk of serious birth defects in their offspring

  6. Birth Defects • Dysmorphy is the study of congenital birth defects that alter the shape or form of one or more parts of the body of a newborn • A dysmorphologist strives to understand how genes and environmental influences lead to birth defects

  7. Birth Defects • They also suggest diagnostic evaluations • They develop a plan to manage expected complications • They provide the family with an understanding of the causation of the malformation

  8. Birth Defects • Perhaps the most important job is to give recurrence risks to the parents and other relatives

  9. Birth Defects • Three major categories: • Malformations • Deformations • Disruptions

  10. Malformations • Result from intrinsic abnormalities in one or more genetic programs operating during development • Ex. Extra fingers in Greig Cephalopolysyndactyly

  11. Greig Cephalopolysyndactyly

  12. Polydactyly

  13. Syndactyly

  14. Deformations • Caused by extrinsic factors impinging physically on the fetus during development • Especially common during the second trimester when the fetus is constrained within the amniotic sac

  15. Deformations • Ex. Contractions of the joints of the extremities called arthrogryposes • Occasionally accompany constraint of the fetus due to twin or triplet gestation

  16. Congenital Arthrogryposes

  17. Deformations • Most deformations apparent at birth can be treated by external fixation devices or resolve spontaneously

  18. Disruptions • Result from destruction of irreplaceable normal fetal tissue • More difficult to treat than deformations because of the loss of actual tissue

  19. Disruptions • May be caused by vascular insufficiency, trauma, or teratogens • Ex. Amnion disruption which is the partial amputation of a fetal limb, caused by strands of amniotic tissue • Often recognized by the presence of partial irregular digit amputation in conjunction with constriction rings

  20. Amnion Disruption

  21. Malformations • Malformations can have many causes • Chromosome imbalance (25%) • Trisomy 21, 18, 13 are most common • Single gene mutations (20%) • Achondroplasia • Complex inheritance (50%) • Cleft lip and cleft palate • Environmental teratogen (5%) • Fetal alcohol syndrome • Can be drugs, infections, chemicals, radiation, etc.

  22. October 24:

  23. Developmental Biology • A single cell is transformed into an adult human with • 1014 cells • Hundreds of different cell types • Dozens of tissues

  24. Developmental Biology • Has roots in embryology • 19th and early 20th century studies showed that organisms develop from single cells • Used amphibian and avian embryos • Defined many of the fundamental processes

  25. Developmental Biology • Evolution is critically important • Early in development embryos of many species look similar • As development progresses the features shared between species successively transform into more specialized features, that are in turn shared by successively fewer, but more closely related, species

  26. October 31:

  27. Developmental Biology

  28. Homologous Structures • Evolved from a structure present in a common ancestor

  29. Divergent Evolution

  30. Analogous Structures • Appear to be similar, but arose independently

  31. Convergent Evolution

  32. November 4:

  33. Developmental Genetics • Development results from genes interacting with cellular and environmental cues • However, the genome is not an architect’s blueprint, not a literal description of the final form of all structures

  34. Developmental Genetics • Rather it specifies a set of interacting proteins that set in motion different processes like growth, migration, differentiation, and apoptosis • This ultimately results in the correct mature structures, with a high degree of accuracy

  35. Developmental Genetics • For example: • It is not coded for the eye to be spherical • The shape is a consequence of developmental processes

  36. Developmental Genetics • Probability also plays a huge role as well • A mutation being present does not ensure that the organism will have malformations

  37. Developmental Genetics • Environmental factors can be a huge factor in development as well • Many cells use concentration gradients and cell to cell signaling to determine placement and function • Environmental substances can mimic or disrupt this (teratogens)

  38. Developmental Genetics • Sometimes the pathways active in embryonic development are turned off in adulthood • Chemicals that disrupt embryos may cause little to no damage to adults

  39. Developmental Genetics • Isoretinoid • Used to treat acne • Alcohol • Fetal alcohol syndrome • Thalidomide • Sedative used widely in the 1950’s

  40. Fetal Retinoid Syndrome

  41. Fetal Alcohol Syndrome

  42. Thalidomide Syndrome

  43. November 7:

  44. Cellular Processes • Proliferation • Differentiation • Migration • Apoptosis

  45. Human Embryogenesis • After fertilization, the human embryo undergoes a series of cleavages • After 3 days and 4 divisions, the 16 cell morula has been formed

  46. Human Embryogenesis • At day 4 the mass transitions to a blastocyst • Cells that give rise to the placenta form a wall • Cells that will turn in to the embryo itself aggregate to one side (this is called the inner cell mass)

  47. Human Embryogenesis • At this point the embryo acquires its first manifestations of polarity • The inner cell mass is bilaterally symmetrical

  48. Human Embryogenesis • Then the inner cell mass separates again into the epiblast (which will form the embryo proper) and the hypoblast (which will for the amniotic membrane) • The embryo then implants in the endometrial wall between 7 and 12 days after fertilization

  49. Human Embryogenesis

  50. Human Embryogenesis • After implantation, gastrulation occurs • This is where the cells rearrange themselves into the 3 germ layers • Ectoderm • Mesoderm • Endoderm

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