Polyploidy

1
Polyploidy

• more than two haploid sets of chromosomes are
  present,
• 2n diploid,
• 3n triploid,
• 4n tetraploid,
• etc.

2
Amphidiploid

• double diploid,
• 2n1 2n2
• have balanced gametes of the type n1 n2,
• these gametes fuse to make fertile 2n1 2n2.

3
Allopolyploidy Applications
B. oleracea (cabbage, cauliflower, Brocolli,
kale, etc.)
2n 18
n1 n2 19
B. campestris (turnip, turnip rape)
2n 20
4
4n x 2n 3n?

• The creation of triploids can be accomplished by
  crossing a tetraploid with a diploid,
• Most triploid individuals are sterile.

5
Generation of a Triploid Cells
6
Meiosis in a Triploid Organism
7
Why Wouldnt this work?
8
Environmental Applications?
grass carp (Ctenopharyngodon idella)

• Triploid grass carp prefer pondweeds,
• do not prefer plants such as cattail, water
  lily, etc.

9
Polyploidy Summary

• More than 2 whole sets of chromosomes,
• Autopolyploidy,
• from the same genome,
• naturally occurring, or induced,
• often results in larger varieties,
• Allopolyploidy,
• from different genomes,
• naturally occurring, or induced,
• often results in larger varieties,
• Autotriploids,
• most often sterile
• can produce beneficial traits.

10
Monoploidy

• a haploid of a diploid is monoploid,
• has one chromosome set.

11
Monoploid

• male wasps, bees and ants have only 1 haploid
  genome,
• males develop from unfertilized eggs,
• gametes are formed by mitosis.

12
Monoploid Applications

• monoploid plants can be created by culturing
  pollen grains (n 1),
• the population of haploid organisms is then
  screened for favorable traits,
• the plants are then treated with colchicine which
  generates a 2n plant homozygous for the favorable
  traits.

13
Chromosomal Mutations

• chromosome number,
• structure,

14
Chromosome Structure

• Changes in chromosome structure can come about
  due to,
• deletions
• duplications
• rearrangements

15
Chromosomal Deletions

• a deletion results in a lost portion of a
  chromosome,

16
Deletion Causative Agents

• heat,
• radiation,
• viruses,
• chemicals,
• errors in recombination.

17
Terminal Deletions
Off the End
18
Intercalary Deletions
From the Middle
19
Intercalary Deletions
From the Middle
20
Recognizing Deletions
21
Homologous Pairs?
Hemizygous
Hemizygous gene is present in a single dose.
Psuedodominance hemizygous genes are expressed.
22
Deletions

• result in partial monosomy,
• remember monosomy 2n, -1,
• the organism is monosomic for the portion of the
  chromosome that is deleted,
• as in monosomy, most segmental deletions are
  deleterious.

23
Cri-du-chat Syndrome(46, -5p)
24
46, -5p

• ...terminal deletion of the small arm (petite
  arm) of chromosome 5,
• Cri-du-chat Syndrome,
• 0.002 live births,
• anatomic mutations,
• often mental retardation,
• abnormal formation of vocal mechanisms.

25
Chromosomal Duplication

• ...an event that results in the increase in the
  number of copies of a particular chromosomal
  region,

26
Duplication Cause and Effect

• Causes
• duplications often result from unequal crossing
  over,
• can occur via errors in replication during
  S-Phase.
• Effects
• results in gene redundancy,
• produces phenotypic variation,
• may provide an important source for genetic
  variability during evolution.

27
Unequal Crossing Over
Produces both duplications and deletions!
28
Duplication Phenotypes
29
Duplication in Evolution

• essential genes do not tolerate mutation,
• duplications of essential genes, then subsequent
  mutations, confers adaptive potential to the
  organism,
• new gene family members are recruited to
  perform new functions.

30
algae
nutrients
need uptake
31
Arabidopsis
32
Chromosome Structure

• Changes in chromosome structure can come about
  due to,
• deletions
• duplications
• rearrangements

33
Chromosomal Inversions

• inversion aberration in which a portion of the
  chromosome is turned around 180o.

34
Paracentric Inversion

• ...an inversion in which the centomere is not
  included,

B
A
C
...a paracentric inversion does not change arm
length ratio.
35
Inversion Heterozygotes

• an organism with one wild-type and one
  chromosome containing an inversion,

not heterozygous for the genes, heterozygous for
the chromosomes.
36
Inversion Loopno crossing over
37
Paracentric
Produces haploid gamete.
38
Paracentric
Produces gamete with inversion.
39
Paracentric
Produces a chromosome with two centromeres. Nonvia
ble gametes.
40
Dicentric

• ...a chromosome having two centromeres

41
Non-Viable (gametes) Segregate
42
Dicentric/Ascentric
results only when the crossing over occurs
within the region of the paracentric inversion,
43
Paracentric
No centromeres. Deletions. Nonviable gametes.
44
Acentric

• a chromosome having no centromeres,
• segregates to daughter cells randomly, or is
  lost during cell division,
• deletions impart partial monosomy.

45
Paracentric Outcomes
1 Normal Gamete, 1 Inversion Gamete, No Crossover
Classes
Recombination is not inhibited, but recombinant
gametes are selected against.
46
Pericentric Inversion

• ...an inversion in which the centromere is
  included,

...a pericentric inversion results in a change in
chromosome arm length.
47
Pericentric
48
Recombination and Inversions

• Paracentric and Pericentric
• 1 Normal Gamete,
• 1 Inverted Gamete,
• No Crossover Classes No Recombination,

Inversions select against recombinant gametes,
thus preserves co-segregation of specific alleles.
49
Inversions and Evolution

• Inversions lock specific alleles together,
• all offspring get their alleles from either a
  wild-type, or inverted chromosome,
• If the set of alleles is advantageous, the set
  can be maintained in the population.

50
Assignment

• Understand the differences between
  Interference, and the suppression of
  recombination resulting from inversions,
• Be able to recognize data, and predict results
  given either case.

51
Chapter 5

• Do all of the practice questions.

52
Translocations

• translocation aberration associated with the
  transfer of a chromosomal segment to a new
  location in the genome.

53
Terminal Translocation
54
Reciprocal Translocation
55
Translocation and Semi-Sterility

• semi-sterility a condition in which a
  proportion of all gametophytes (in plants) or
  zygotes (in animals) are inviable.
• Up to 50 are inviable as a result of
  translocations.

56
Robertsonian Translocations

• the fusion of long arms of acrocentric
  chromosomes,

57
Down Syndrome

• 95 of Down Syndrome individuals are a result of
  Trisomy 21,
• the probability of having a second Down Syndrome
  child is usually similar to the population at
  large,
• However, there is second cause of Down Syndrome
  caused by a Robertsonian translocations that is
  heritable.

58
Familial Down Syndrome
59
Assignment

• Do a Punnett Square or a Split Fork Diagram of,
• Parent 1 wild-type for Chromosomes 14, 21
• x
• Parent 2 heterozygous for 14q21q translocation.

60
Hint
gametes
61
Assignment(think about these...)

• Truncated Genes
• genes that are no longer full length, due to a
  mutation,
• Gene Fusions
• genes that contain coding sequence from two
  different genes, resulting from a chromosomal
  mutation.

62
Syntenic

• Relationship of two or more loci found to be
  linked in one species literally on the same
  thread.
• Conserved Synteny state in which the same two
  loci are found to be linked in several species.

63
Cereals
64
Conserved Synteny
Description of DNA segments in which gene order
is identical between species.
65
Trinucleotide Repeat Expansions
FMR1
Fragile X Mental Retardation 1
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
cgg
gt 200
...
66
(No Transcript)
67
Fragile Site Mutations
68
(No Transcript)
69
Dosage Compensation

• X chromosomes in females provide twice the genes,
  as in males,
• Drosophila female genes are expressed at 50 of
  the male levels,
• Mammals one X chromosome in females is silenced.

70
Canadian Cat Scientists Sees it First
Barr Body
71
Lyon Hypothesis
Mary Lyon in humans, X chromosomes from father
and mother are randomly inactivated.
72
X Inactivation
Barr Body

• The structure of the chromosome is altered.

73
X-Linked Mosaicism

• Different cell lineages contribute to
  different body locations on the body.

74
Epigenesis

• A change in gene regulation brought about without
  a change in DNA sequence,
• often to the structure of the chromosome,
• or through modification of the nucleotide bases,
• or through post transcriptional regulation.

75
Chapter 5 Review

• know genotypes and phenotypes,
• trisomy,
• monosomy,
• inversions,
• duplications,
• deletions,
• polyploidy,
• dosage compensation.
• be able to predict heritability, and recognize
  data-sets and infer the condition.

76
Monday

• Reciprocal Translocations,
• Mapping deletions,
• Review
• Work some problems.