Chromosomes

Chromosomes

Bacterial chromosomes
1. Prokaryotes
2. single circular DNA molecule
3. one chromosome
  1. all genes needed for life
4. not associated with proteins - naked DNA
5. single copy of gene except cell division
Plasmids
1. in some prokaryotes
2. Eukaryotes don't have
3. small extra DNA molecules
4. circular; naked
5. contains few genes not necessary for life
6. not replicated at the same time or rate
7. copies can be transferred
8. can cross species barrier
  1. released at death and absorbed by new cell
  2. natural
  3. artificially possible
Differences between chromosomes
1. diff. chromosomes carry diff. genes
2. length
3. position of centromere
4. at least two different types
5. different gene sequnece
Eukaryote chromosomes
1. linear DNA molecules
2. histone proteins
  1. globular in shape
  2. wider than DNA
  3. many with DNA wound around
  4. adjacent separated by short DNA stretches
3. made of DNA and proteins
Homologous chromosomes
1. same gene sequence but not alleles
2. allows species to interbreed
Haploid nuclei
1. one chromosome of each pair
2. one full set of chromosomes
3. gametes have it
Diploid nuclei
1. pairs of homologous chromosomes
2. two full sets of chromosomes
3. zygote has it
4. all cells except gametes are diploid
5. two copies of each gene
6. dominant allele prevents effects of recessive mutation
7. more vigorous organisms
Chromosome numbers
1. characteristic feature of species members
2. only same numbers can interbreed
3. can change due to evolution
  1. rare and unlikely
Sex determination
1. by sex chromosomes
  1. X chromosome
    1. large
    2. centromere near middle
    3. all humans have at least one
    4. females have 2
    5. one passed on in egg cell
  2. Y chromosome
    1. smaller
    2. centromere near end
    3. one in males
      1. SRY or TDF
2. autosomes
  1. chromosomes that don't determine sex
3. half sperm have X; half have Y
4. sex determined at fertilization
Karyograms
1. shows chromosomes of organisms
  1. homologous pairs
  2. decreasing lengths
2. visible in cell in mitosis
  1. clearest: metaphase
3. some stains - distinctive banding on diff. chromosomes
4. arranged in pairs by length
  1. done manually before
  2. now digital
5. micrograph taken of dividing cells
6. types distinguished by:
  1. position of centromere
  2. banding pattern
  3. size/length

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