Genetics 101

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Genetics101
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Chromosome sets

• You have 23 pairs of identical chromosomes, 1
  from each parent
• 22 autosomes
• 1 sex chromosome
• (see karyotype to right)
• Other organisms have different amounts
• Chicken 49 pairs
• Mosquito 3 pairs
• Lettuce 9 pairs

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Chromosomes and sex cells (a.k.a. gametes)

• Your sex cells (sperm and eggs) only contain 1
  set of chromosomes, totaling 23 (as opposed to
  body cells containing 46)
• Non-sex cells are called somatic cells
• All eggs have an X chromosome, whereas ½ sperm
  have an X and ½ have a Y (therefore, dad
  determines gender)

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Traits

• A trait is a physical expression of a gene (hair
  color, height, etc.), also called your phenotype
  
• Genes come in different versions called alleles
• e.g. eyes come in brown, blue, green, hazel
• Some traits are polygenic, meaning their
  expression is controlled by more than one gene
• Your genetic make-up is also called your genotype

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• Punnett squares show probablity of traits being
  passed down to offspring.

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Gene Expression

• You have 2 of each of your many genes, 1 from mom
  and 1 from dad.
• Some genes are dominant and some recessive
• Black hair dominant Blond hair recessive
• alleles can also be codiminate (black and white
  cows) or
• incompletely dominant (gray kittens from black
  and white parents)
• See section 11-2

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You can also look at 2 traits in the same Punnett
square
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Carrying alleles

• Heterozygous 2 different alleles for a given
  trait (Bb)
• Homozygous 2 identical alleles for a given
  trait (can be homozygous dominant or recessive,
  i.e. BB or bb)

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• Each chromosome is composed of a super long
  strand of DNA, and each section of the chromosome
  codes for a specific gene
• you have about 30,000 genes
• 98 of your DNA does not code for DNA, but is
  empty space

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Pedigree charts show how traits are passed within
families

• Is the disease somatic or sex-based or neither?

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Human Genome Project

• The human genome is made up of 3 billion base
  pairs, totaling about 6 feet in each cell. (There
  are about 50 trillion cells in your body, which
  means that all your
• DNA could stretch tothe sun and back
• 500 times)
• To decode the entire genome, scientists split up
  the DNA into fragments and the fragments were
  decoded in different labs, then reassembled

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For more info

• See chapter 11 14 in your text