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Karyotypes

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  1. Karyotypes

  2. Human Chromosomes • Karyotype – a picture of arranged chromosomes. The picture is created by photographing the cell during mitosis and then “cutting and pasting” the chromosomes from the photograph. • Humans have a total of 46 chromosomes. 44autosomes and 2 sex chromosomes • If you are female, biologists will write it as 46XX, male 46XY.

  3. Karyotype

  4. Remember Back… • Disorders can be caused by mutations, which are changes to the normal order of DNA bases (A,T,C,G) • However, not all disorders are caused by point and frameshift mutations.

  5. Chromosomal Disorders • Humans should have 23 pairs of homologous chromosomes (one from mom and one from dad) • Some disorders occur based on an improper number of chromosomes. These errors occur during meiosis and are known as nondisjunction.

  6. Non Disjunction candy animation • Nondisjunction is the improper separation of chromosomes during meiosis.

  7. EXAMPLES

  8. Down’s Syndrome • Trisomy 21 • Most often, Do21wn syndrome results in three copies of chromosome due to nondisjunction during meiosis. • Chances of a woman having Down syndrome child increase with age. • Down syndrome children have a tendency for leukemia, cataracts, faster aging, and mental retardation.

  9. Patau Syndrome • Trisomy 13 • Eye, brain, circulatory defects and cleft palate • Rarely live past 1 year old (More than 80% die in first year.) • Caused by a nondisjunction

  10. Edward’s Syndrome • Trisomy 18 • 80% of affected are female. • Defects in every organ • Rarely live past one year, most die within the first month • Caused by nondisjunction

  11. Klinefelter’sSyndrome • Males have one Y chromosome and two or more X chromosomes. • Many do NOT have obvious symptoms. Usually not diagnosed until puberty • Other affected individuals are sterile males; testes and prostate are underdeveloped. Can have language and learning problems. • Individuals have large hands and feet and long arms and legs.

  12. Jacob Syndrome • XYY males with Jacob syndrome have two Y chromosomes instead of one. • Results from nondisjunction during meiosis II. • Usually taller than average; suffer from persistent acne; tend to have lower intelligence.

  13. Other Chromosomal Disorders • Another type of chromosomal disorder is chromosome translocation. • This is when the chromosome abnormality is caused by the rearrangement of large sections between nonhomologous chromosomes. • This often results in different cancers.

  14. Pedigree Charts • Intro to Pedigree Link

  15. Using Pedigrees to studyHuman Traits A pedigree is a chart that can be used to study how a trait is passed from one generation to the next. A pedigree is like a family tree, with genetic information added to it. A pedigreechart shows the relationship within a family of a single trait. A pedigree shows you each family member’s PHENOTYPE and then you can infer the genotypes of family members based on when and how a trait is passed from one generation to the next.

  16. Pedigree Chart Generation symbols Marriage line unshaded box = unaffected does not have the condition Children line Shaded box = affected (has the condition) Square = Boy Circle = Girl

  17. Carriers Child 2 from the 3rd generation has the recessive condition. His parents are not shaded, so where did the condition come from??? aa

  18. Carriers We know that the parents of the child must be carriers (heterozygotes) of the condition. Since they are un-shaded they do not have the trait. However, since they produced an offspring with the trait, that tells us they have the recessive allele and passed it on. Aa Aa aa

  19. Carriers Sometimes, but not often you might see carriers as half shaded on a pedigree.

  20. Colorblindness – A Case Study of Mrs. Lee (Anatomy teacher)

  21. Colorblindness • Sex-linked recessive (occurs more often in males) • Affected people cannot distinguish between certain colors • Normally, red and green appear as browns Rhett, Mrs Lee’s son, is colorblind. (She gave him a genetic disease)

  22. Colorblind Test Plates

  23. Grandmama Smith Granddaddy Smith Paw-Paw Maw-Maw Uncle David Daddy Mama Uncle Carmack Uncle Larry Tommy Kevin ME! Steven Rhett Abby

  24. Who has the full-blown colorblindness?

  25. Grandmama Smith Granddaddy Smith Paw-Paw Maw-Maw Uncle David Daddy Mama Uncle Carmack Uncle Larry Tommy Kevin Mrs Lee! Steven Rhett Abby

  26. Who carries the gene for colorblindness, but is not colorblind themselves?

  27. Grandmama Smith Granddaddy Smith Paw-Paw Maw-Maw Uncle David Daddy Mama Uncle Carmack Uncle Larry Tommy Kevin ME! Steven Rhett Abby

  28. seX-linked traits • The colorblind gene is on the X chromosome. Here are to 2 options for males: • XY = not colorblind (X is healthy) • X’Y = colorblind (X is affected) • Since there is no other X chromosome to counteract the defective X, the boy is colorblind.

  29. seX-linked traits • The colorblind gene is on the X chromosome. Here are to 3 options for females: • XX = not colorblind (both Xs are healthy) • XX’ = “carrier” but not colorblind (one X is affected, the other is healthy) • X’X’ = colorblind (both Xs are affected)

  30. Now lets fill in the genotypes for the family pedigree.

  31. X’Y XX XY XX’ XY XX’ XY X’Y XY XY XX’ XY X?Y XX? X’Y

  32. Follow up questions… • Why is Kevin’s (IV-2) genotype X?Y? (Note: He died when he was 12 days old.) • Why is Abby’s (V-2) genotype XX?? • Without genetic testing, what is one way that (in the future) we might know Abby’s genotype? • If a female is colorblind, what 2 things must be true of her parent’s genotypes for this gene?