a. DNA is a double helix molecule. b. DNA coils around proteins called histones (similar to spools of thread). c. DNA supercoils itself (like a telephone cord). d. DNA is then organized into 2 sister chromatids connected together at the centromere.

From 1990 to 2003, scientists from the National Institutes of Health and the U.S. Department of Energy worked together to…  determine the sequence of the 3 billion chemical base pairs that make up human DNA  identify all of the 20,000 to 25,000 genes in human DNA  store this information in databases  address the ethical, legal and social issues that arise from this project

 to compare human sequences with other species to provide insight into human embryonic development and genetic relationships  to identify genes associated with diseases  to develop of treatments and preventions for genetic disorders

 The human genome contains about 3 billion chemical nucleotide bases (A, C, T, and G).  The average gene consists of 3000 bases, but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million bases.  Chromosome 1 has the most genes (2968), and the Y chromosome has the fewest (231).  The total number of genes is estimated at 20,000 to 25, 000 Almost all (99.9%) nucleotide bases are exactly the same in all people.  The functions are unknown for over 50% of discovered genes. Chromosome Poster

Can you make a relationship between the number of chromosomes and the complexity of an organism? Why or why not?

How do you think this individual inherited an extra chromosome? HINT: Think about meiosis!

 Nondisjunction – a pair of homologous chromosomes or sister chromatids fail to separate during meiosis. i.e. Downs syndrome  Duplication- part of a chromosome is repeated.  Deletion- part of a chromosome is lost  Inversion- part of chromosome is reversed  Translocation- part of chromosome attaches to a non homologous chromosome

 A pedigree is a family tree that records and traces the occurrence of a trait in a family.  It can determine whether a trait is inherited.  It shows how a trait is passed from one generation to the next.  It can determine if an allele is dominant or not.

What is the inheritance pattern for hemophilia? How does a pedigree enable you to determine it?

 An individual with one copy of a recessive allele is called a carrier.  Since most genetic disorders are recessive, they are self limiting.  Males more commonly exhibit sex linked traits because they only need one recessive allele located on the X chromosome.