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Human Heredity Sections 14-1 and 14-2

Human Heredity Sections 14-1 and 14-2. Objectives: 7.2 Interpreting inheritance patterns shown in graphs and charts

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Human Heredity Sections 14-1 and 14-2

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  1. Human HereditySections 14-1 and 14-2 Objectives: 7.2 Interpreting inheritance patterns shown in graphs and charts 8.5 Relating genetic disorders and disease to patterns of genetic inheritanceExamples: hemophilia, sickle cell anemia, Down's syndrome, Tay-Sachs disease, cystic fibrosis, color blindness, phenylketonuria (PKU)

  2. Human Chromosomes • How many chromosomes do we have? Answer: 46 • How many of those are sex chromosomes? Answer: 2 • What are the possible combinations of sex chromosomes? Answer: XX or XY • What are the other chromosomes called? Answer: autosomes

  3. Karyotype: Source: http://www.dnalc.org/view/16243-Gallery-8-Human-female-karyotype.html • Def: a picture of chromosomes, taken in mitosis metaphase, and paired up. • Why would the picture be taken at this point?

  4. Pedigree Charts Source: http://www.citruscollege.edu/lc/archive/biology/Pages/Chapter10-Rabitoy.aspx

  5. Pedigree Charts Activities • Class Activity: Figure 14-3, p.342 • Individual Assignment: Problem Solving, p.343. Add the following questions: • Identify the genotype of each individual. • Is albinism a dominant or recessive trait? • What is the probability of the second-generation couple having another albino child?

  6. Sex-Linked Genes • The X chromosome is much larger than the Y chromosome, carrying many more genes. (See Figure 14-12, p.350) • More than 100 sex-linked genetic disorders have been mapped to the X chromosome.

  7. Sex-Linked Genes • Since males have only one X chromosome, if an allele for a disorder is present on that chromosome, the trait will be expressed. • Common sex-linked disorders: • Colorblindness • Color vision is controlled by three genes on the X chromosome. • 1 in 10 males in the U.S. have some form of colorblindness. • Hemophilia – 2 genes on the X chromosome help control blood clotting (1/10,0000) • Duchenne Muscular Dystrophy – (1/3000)

  8. X-Chromosome Inactivation • Females have two X chromosomes. • One of those chromosomes is switched off, becoming a Barr body --- a dense (but inactive) region in the nucleus. • Males cannot switch off their X chromosome. Source: http://www.123rf.com/photo_2531003_spotted-cat-with-no-tail-stands-attentive-and-alert.html

  9. Chromosomal Disorders • Nondisjunction of homologous chromosomes during _____________, would give gametes abnormal numbers of chromosomes. • When these gametes become diploid again, the number of chromosomes is abnormal. • Some of these zygotes cannot survive; others produce offspring with genetic disorders.

  10. Chromosomal Nondisjunction Source: http://drugline.org/img/term/meiotic-nondisjunction-9351_3.JPG

  11. Some Nondisjunction Disorders • Down syndrome • Autosomal nondisjunction • 3 copies of chromosome 21 (“trisomy 21”) Source: http://www.buzzle.com/articles/teaching-children-with-down-syndrome.html

  12. Some Nondisjunction Disorders • Sex chromosome disorders: • Turner’s syndrome – females with only one X chromosome • Fertile • Sex organs do not develop at puberty • Klinefelter’s syndrome – males with too many X chromosomes • Interferes with meiosis, usually not permitting reproduction • No known cases of babies born without an X chromosome, so it must contain genes important for survival.

  13. Some Nondisjunction Disorders • Sex chromosome disorders: • Y chromosome contains a sex-determining region necessary to produce male sexual development • Can develop even in the presence of multiple X chromosomes • Will not develop if this region of the Y chromosome is absent.

  14. DISORDER DETECTIVES ACTIVITY • http://www.youtube.com/watch?v=th6Njr-qkq0

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