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Pedigree Analysis and Inheritance Patterns in Human Traits

This chapter explores the analysis of pedigrees and the inheritance patterns of human traits, including dominant and recessive traits, sex-linked traits, and autosomal traits. It also discusses the risk of diseases and the importance of genetic counseling and prenatal testing.

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Pedigree Analysis and Inheritance Patterns in Human Traits

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  1. Chapter 6 Matters of Sex

  2. QSR #2 • 1. A trait that is __________________, will be found mostly in males while ___________________ traits will be spread out evenly between males and females. • 2. _________________ are the tips of the chromosomes – only about 5% of the entire chromosome. • 3. The blood-clotting disorder, __________________, is a ____________ trait since its found mostly in males. • 4. The nucleus of a cell in a female, during interphase, has one dark-staining X chromosome called a _____________________________.

  3. MendelianInheritance of Human Traits • Family trees • Pedigree • a graphic representation of genetic inheritance thru a family. • Looks similar to a family tree • Uses symbols • Male • Female • Children • relationships

  4. Pedigrees • Family history of traits recorded over generations • Can tell if the trait is dominant • Recessive • Sex-linked • Autosomal • Circles –females • Squares –males • Marriage horizontal lines • Vertical lines children

  5. Analyzing Pedigrees • Sex-linked vs autosomal • Only seen in males ---sex linked • Both sexes equally---autosomal • Dominant vs recessive • Trait is dominant then every infected individual’s parent will have the disease • Recessive—parents are normal children are infected

  6. Risk of Diseases • Use pedigrees • Genetic counseling • Prenatal testing • Amniocentesis/chorionic villi sampling to determine karyotypes

  7. ON THE FOLLOWING SLIDE, BE SURE TO LABEL: • 1. Dominant or Recessive • 2. Sex-linked or Autosomal

  8. ON THE FOLLOWING SLIDES, BE SURE TO LABEL: • 1. Dominant or Recessive • 2. Sex-linked or Autosomal • 3. Tell the genotype of each person

  9. Practice constructing a pedigree: • Ben and Jan are married with 4 boys. Ben has dimples as does his 2 oldest boys. Jan’s parents do not have dimples. Their youngest son married a female with dimples and together they have 2 daughters and a son – all of who have dimples 

  10. QSR#3Questions for Trait A pedigree(use the letter B/b) 1.  Does a dominant or recessive allele produce the trait?  Explain. 2.  Is it autosomal or sex-linked?  Explain. 3.  What are the genotypes of all the individuals in the pedigree?  (Write them on the pedigree.) 4.  What is the genotype of individual IV-2?  Explain. 5.  What is the genotype of individual IV-6?  Explain. 6.  What is the genotype of individual I-1?  Explain

  11. InhertitanceSymptoms

  12. Recessive Autosomal Heredity • Offspring must have 2 traits before the disorder will show up – must be passed down from both parents • If the parents’ do not show signs of the disorder, they are considered to be CARRIERS • This is why blood relatives should not have children together – no incest!!!! Consanguinity: “shared blood”—family members may share certain traits or disorders

  13. Recessive Autosomal Heredity • 1. males and females are equally affected • 2. Affected males and females can transmit the gene, unless it causes death before reproductive age • 3. The trait can SKIP generations • 4. Parents of an affected child are heterozygous or carriers

  14. CANCER

  15. Recessive Heredity • Ex: Tay-Sachs—problem with chromosome 15 • Recessive disorder of the central nervous system • An enzyme that breaks down lipid produced and stored under tissues is not made and this lipid accumulates in the cells • Survival rate: 4-5 years • Occurs in many Jews

  16. Infants with Tay-Sachs disease appear to develop normally for the first few months of life. Then, as nerve cells become distended with fatty material, a relentless deterioration of mental and physical abilities occurs. The child becomes blind, deaf, and unable to swallow. Muscles begin to atrophy and paralysis sets in. A much rarer form of the disorder which occurs in patients in their twenties and early thirties is characterized by unsteadiness of gait and progressive neurological deterioration. Patients with Tay-Sachs have a "cherry-red" spot in the back of their eyes. The condition is caused by insufficient activity of an enzyme called hexosaminidase A that catalyzes the biodegradation of acidic fatty materials known as gangliosides.

  17. Recessive Heredity • Ex: Phenylketonuria (PKU) • Recessive disorder that results from the absence of an enzyme that converts one amino acid, phenylalanine to a different amino acid tyrosine • Affects the CNS • Common among Nordic or Swedish people

  18. PKU • Normal at first • Then the baby begins to drink milk which has high amounts of phenylalanine • Mental retardation occurs • Special diets until brain is fully developed • Chromosome 12

  19. Dominant Heredity • One gene from either parent and the child is affected • Tongue rolling • Hapsburg lip • Free earlobes • Hitchhiker’s thumb • Almond shaped eyes • Thick lips • Hair in the middle section of your fingers

  20. Dominant Heredity • Ex: Huntington’s Disease • Lethal genetic disorder— AUTOSOMAL DOMINANT • Breakdown of certain areas of the brain • No treatment • Onset is between 30 and 50 • +++++++++++++++++++++++++++++++++++

  21. Sex-LinkeD Recessive • Found on the X chromosome • Females: XX – 2 copies • Males: XY – 1 copy • Ex: colorblindness: Females XcXc • Males XcY • Others: hemophilia and male-pattern baldness

  22. Sex-Linked Dominant • Ex: Rett Syndrome • This type is rarely found in males because many types are fatal or cause them to die before the reproductive age • EX: Fragile X Syndrome

  23. Rett Syndrome Brain disorder – causes the “forgetting” of things previously learned -- very similar symptoms to Autism --only found in female – WHY?

  24. Fragile X syndrome Missing piece of X chromosome Mental retardation, large ears, elongated face ***************************************

  25. QSR #6 • 1. Explain why DOMINANT, x-linked disorders are more commonly found in females. • 2. __________________ is a disorder with chromosome 15 that prevents the body from producing an enzyme needed to break down lipids around nerves of the CNS. • 3.___________________ means “shared blood” and is shown by the symbols:____________________-

  26. Incomplete dominance • Homozygous Red Snap Dragons x Homozygous White Snap Dragons • Pink Snap Dragon • RR x R’R’ • Neither allele is completely dominant over the other one • R—protein to make red pigment • R’—makes no pigment • Pinkish color • Does have segregation of alleles • What happens in the F2 generation?

  27. When Heredity Follows Different Rules • Mendelian Genetics • Simple---dominant or recessive alleles • NOT ALWAYS THIS SIMPLE!!!!!!

  28. Codominance • Both phenotypes appears • Chickens • Black-feathered and white-feathered birds both homozygous • BB x WW • Produces a chicken with black and white feathers—checkered • ++++++++++++++++++++++++++++

  29. Practice problems --

  30. QSR #8 • 1. If both parents carry the recessive allele that causes cystic fibrosis (autosomal recessive trait), whats the % chance that their child will have it? • 2. PKU is a recessive disorder that results from the absence of an enzyme that turns _________________ into tyrosine. • 3. Tay-sachs occurs mainly in ____________.

  31. Sex determination (how bout we review a little :O…) • Autosomes • Chromosomes that are not involved with determining sex • 1-22 pairs • Sex chromosomes • X and y chromosomes that determine the sex of individuals

  32. Sex-linked traits • Traits that are found on the x and y chromsomes • X and y are not homologous • Found by Thomas Hunt Morgan • Used flies and noticed that the male had white eyes; crossed red x white and got red; did not get the 3:1 ratio because only males had white eyes

  33. Sex-linked traits • Color blindness • Male pattern baldness • hemophilia

  34. Multiple Alleles • Traits that are controlled by 2 or more alleles • Pigeon feathers • Ash-red • Wild type blue feathers • Chocolate feather • Blood types – A and B are codominant, O is recessive.

  35. Polygenic Inheritance • Is the inheritance pattern of a trait that is controlled by two or more genes • Genes maybe on the same chromosome or on different chromosomes • When a trait is produced by main gene interactions • Ex: Skin color: • Dominant genes A,B,&C – control dark pigmentation • Recessive genes a,b,&c – has lowest amount of pigmentation • EX: AaBbCc would be what skin color?________________ • ++++++++++++++++++++++++++++++++++++++

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