Heredity

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Heredity Pedigrees

• Chapter 14-1

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Chromosomes

• What is a chromosome?
• A threadlike structure made of tightly
  bound DNA
• Where is it found?
• Chromosomes are found in the nucleus of body
  cells

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Chromosomes

• Every organism has a specific number of
  chromosomes found in the nuclei of all of their
  cells
• Examples humans- 46
• Drosophila- 8

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Chromosomes

• In diploid cells (all body cells), chromosomes
  occur in homologous pairs
• One chromosome in each pair comes from the
  organisms mother
• The other chromosome comes from the organisms
  father

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Chromosomes

• Each homologous pair contains the same type of
  hereditary information in the same order
• This hereditary information is stored in segments
  of DNA we call genes
• Humans only have 46 chromosomes, but have tens of
  thousands of genes!!!
• Genes for certain traits are found in the same
  location on both homologous chromosomes

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Chromosomes

• Genes occur in at least two forms
• These forms are called alleles
• Only one allele is found on each chromosome in
  the homologous pair
• Alleles can be dominant or recessive

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Homologous Chromosomes
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Chromosomes

• Karyotypes- a chart or picture of all of the
  chromosomes in an organisms nucleus
• Scientists use karyotypes to screen for
  chromosomal disorders

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Chromosomes

• In a human karyotype, there are 46 chromosomes
• Autosomes- 44 of the chromosomes (22 pairs of
  homologous chromosomes) contain hereditary
  information for all traits except gender
• Sex Chromosomes- 2 chromosomes (1 homologous
  pair) that contain hereditary information
  specific for gender

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Sex Chromosomes

• Sex Chromosomes are either X or Y
• Females- receive two X chromosomes
• Males- receive one X and one Y

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Pedigrees

• Scientists can create charts called pedigrees to
  help understand how traits are passed down from
  parents to offspring
• Pedigrees are very helpful in understanding
  genetic diseases

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How to Use a Pedigree
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Genetic Disorders
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Disorders Caused by Recessive Alleles
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Disorders Caused by Dominant Alleles
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Disorders Caused by Codominant Alleles

• Sickle Cell Disease
• Chart for Autosomal disorders found on page 345