Genetics Lecture

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GeneticsLecture
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Part IDNA
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DNA
DNA is a rather large molecule containing
nitrogen and phosphate
DNA is a polymer made from many thousands of
nucleotides strung together
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Nucleotide

• It is made of a
• Deoxyribose (5 carbon Sugar)
• Phosphate group (PO4)
• Base (A,C,G,T)

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• Nitrogenous base
• A single or double ring molecule containing
  nitrogen
• There are 4 different kinds
• Adenine (A)
• Thymine (T)
• Cytosine (C)
• Guanine (G)

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Erwin Chargoff

• His research showed that in all the DNA he
  studied the amount of Guanine (G) equaled the
  amount of Cytosine (C) and the amount of A
  amount of T

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Rosalind Franklin

• Her X-ray Diffraction data showed that DNA was
  organized as a helix

Photo 51
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DNA structure
2 strands
2 or 3 strands?
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James Watson Francis Crick
They guessed where to put the phosphates (on
the outside) and bases (on the inside)
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Phosphates are on the outside,Bases are on the
inside
DNA Structure
Nucleotides are strung together Like beads on a
string
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DNA Structure
The strands are held together by
Hydrogen bonds
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DNA Structure
Pairs of bases form the rungs
Like a ladder The sugar phosphate backbone are
the rails
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The sugar phosphate backbone looks like this
Phosphate Sugar phosphate Sugar phosphate sugar
Phosphate Sugar phosphate Sugar
-BASE -BASE -BASE -BASE -BASE
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DNA Structure
Bases are hydrogen bonded to each other which
joins the two strands
Adenine can only H-bond to Thymine and Cytosine
can only H- bond to Guanine
Complementary Base Pairing
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DNA Structure
Anti-parallel
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Anti-parallel
-BASE -BASE -BASE -BASE -BASE
-BASE -BASE -BASE -BASE -BASE
Phosphate Sugar phosphate Sugar phosphate sugar
Phosphate Sugar phosphate Sugar
Phosphate Sugar phosphate Sugar phosphate sugar
Phosphate Sugar phosphate Sugar
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Part II Chromosomes
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Chromosomes

• Linear units of DNA
• Come in pairs (homologous pairs)
• Each species has characteristic number
• Number of chromosomes doesnt matter how
  evolved a species is.
• Bacteria do not have chromosomes
• they have circular pieces of DNA

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Chromosome Anatomy

• Chromosomes come in two forms
• duplicated
• unduplicated
• Duplicated chromosomes are made up of two
  chromatids
• Referred to as sister chromatids
• Chromatids are joined at a region called the
  centromere
• Chromatids are identical
• Each chromatid is a double helix of DNA

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Genes

• Functional units of DNA
• Code for proteins
• Humans have 20-25K genes
• Only 3 of genome contains genes

http//www.ornl.gov/sci/techresources/Human_Genom
e/faq/genenumber.shtml
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Human Genome

• Refers to all the DNA in human cells
• Contains 3 Billion base pairs
• Sequencing (HGP) completed April 25th 2003

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What is the Human Genome Project?

• The Human Genome Project (HGP) was an
  international 13-year effort formally begun in
  October 1990.
• The project was planned to last 15 years, but
  rapid technological advances accelerated the
  completion to 2003.
• Project goals were to determine the complete
  sequence of the 3 billion DNA subunits (bases),
  identify all human genes, and make them
  accessible for further biological study.

http//www.ornl.gov/sci/techresources/Human_Genome
/faq/faqs1.shtmlgenetics
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Karyotype

• Picture of a species chromosomes

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Making a Karyotype

• First the chromosomes are stained

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Making a Karyotype

• Then they are organized by height and centromere
  location

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Autosomes vs sex chromosomes

• Chromosome pairs 1- 22 are called Autosomes
• Chromosome pairs 23 are called the X and Y
  chromosomes
• Referred to as the Sex Chromosomes because they
  contain genes which determine gender
• Two Xs means you are genetically female
• One X and a Y means you are genetically male
• Presence of a Y chromosome means the person is
  male

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Male or Female?
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Homologous Pairs

• You have two copies of every chromosome
• You received one from your mother
• Your received one from your father
• Homologous pairs have the same genes but not
  always the same form of the gene
• 23 pairs
• 23 x 2 46

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Abnormal Karyotypes

• Too many or too few chromosomes is bad
• Trisomy means you have 3 copies of one chromosome
• Only viable for 13, 18, 21, X
• Monosomy means one chromosome is missing its pair
• Only viable for X or Y
• Both are caused by errors during Meiosis

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Karyotype Nomenclature

• Total number of chromosomes
• The makeup of the sex chromosomes
• Any extra chromosomes
• Examples
• 46, XX
• 46, XY
• 47, XY, 21

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Haploid Gametes

• In order to get one set of chromosomes from each
  parent, their gametes had to contain only half
  the normal number of cells
• This is known as the haploid number
• The haploid number is
• half the total number of chromosomes
• the number of pairs

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Haploid Vs Diploid

• The haploid number is half the total number of
  chromosomes or the number of pairs
• All non-sex cells contain the diploid number of
  cells
• The diploid number is the total number of
  chromosomes

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Gametes Zygotes

• Gametes are sex cells
• Egg cells
• Sperm cells
• All gametes are haploid
• When gametes join they form a zygote
• All zygotes are diploid