Chromosomes and Inheritance

1
Chromosomes and Inheritance

• Mitosis and Meiosis
• Transfer of genetic material from one generation
  to the next (parents to offspring)

http//www.genome.gov/glossary.cfm
2
Review

• Whose work have you spent time talking about?
• Can you name some other terms related to
  inheritance and genetics?
• What is the genetic material that chromosomes are
  made of?

Mendel
traits, pedigrees, alleles
DNA
3
DNA Structure putting the pieces together

• Watson and Crick used information from a number
  of sources
• Miescher (nuclein)
• Levene (chemical dataP, N, sugar,
  tetranucleotide theory)
• Chargaff (AT, CG)
• Franklin and Wilkins (X-ray crystallography)
• Griffith and Avery, MacLeod, and McCarty
  (transforming principle DNA)

4
DNA basic structure

• Twisted ladder
• Sides or rails form the backbone
• Rungs contain the genetic code (ACTG)
• What do we call the genetic information?

5
DNA a closer look

• If we cut the DNA molecule in half there would be
  2 strands each strand is ½ (one side) of the
  twisted ladder
• Each strand has a backbone and ½ of the rungs
  (genetic information ACTG)
• The strands are held together (between the rungs)
  by weak bonds called hydrogen bonds
• The strands are complimentary and run in opposite
  directions

6
DNA The Backbone

• The backbone consists of
• Phosphate groups (P) and
• Deoxyribose sugar groups (S)
• The phosphate and sugar groups alternate along
  the entire length of the DNA molecule
• The bonds between P and S are called covalent
  bonds and are stronger than the hydrogen bonds
  found between the genetic information

7
DNA The inside story

• The backbone provides support for the genetic
  information located on the inside of the DNA
  molecule (ladder rungs)
• The genetic information is coded by 4 chemical
  substances called nitrogenous bases
• The nitrogenous bases on one strand bond
  specifically with bases on the other strand to
  form base pairs that run along the entire length
  of the DNA molecule.
• The base pairs are held together by hydrogen bonds

8
The Genetic Alphabet

• Consists of 4 letters, one for each base?

A C G T (nitrogenous bases)
A adenine C cytosine G guanine T thymine
Purines
Pyrimadines
9
Chargaffs ratios

• Chargaff looked at the chemical composition of
  DNA from different types of cells
• He found that, in DNA, the ratio of adenine to
  thymine and the ratio of cytosine to guanine was
  always 11

A T and C G
10
Watson and Crick
Used Chargaffs rules and the chemical structure
of the bases to determine that

• Adenine always bonds with Thymine using 2
  hydrogen bonds
• AT are base pairs
• Cytosine always bonds with Guanine using 3
  hydrogen bonds
• CG are base pairs

11
How does it all fit together?

• In the DNA molecule each nitrogenous base (ACGT)
  is linked to a deoxyribose sugar group
• Remember that the deoxyribose sugar groups are
  linked to phosphate groups
• 1 deoxyribose sugar 1 phosphate group 1
  nitrogenous base (A or C or G or T) a nucleotide

12

• A strand of DNA consists of a string of
  nucleotides held together by covalent bonds
  between the phosphate group of 1 nucleotide and
  the deoxribose sugar of the next nucleotide (the
  backbone)
• The nucleotides are also held together on the
  inside of the molecule by hydrogen bonds between
  the base pairs (the inside story)

13
Time to review

• DNA is a ____ -stranded molecule that looks like
  a _____ _____.
• ACTG are ______ bases and carry _____
  information. They make up the _____ alphabet.
• 1 nucleotide _____ _____ _____
• The backbone of the DNA molecule consists of
  _____ and _____ which alternate and are held
  together by _____ bonds.
• The strands of the DNA molecule are held together
  between the bases by _____ bonds.
• Adenine always pairs with ____ and cytosine
  always pairs with _____.
• A T, and C G are referred to as ____ ____.