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MBG 2040 > Chapter 8 - Chromosome Variation > Flashcards

Chapter 8 - Chromosome Variation Flashcards

1
Q

What is monoploidy?

A
  • One set of chromosomes
  • Males are usually infertile
  • No pairing in Meiosis I so cannot make gametes
  • Ex. ants, bees, wasps
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2
Q

What is polyploidy?

A
  • More than normal # of chromosomes
  • Ex. triploid/tetraploid
  • Bigger and can out-compete
  • So evolution favours these plants
  • 30-35% of flowering plants
  • Rare in animals
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3
Q

What are autopolyploids?

A
  • Sets are identical
  • Chromosomes derived from same species
  • More vegetative growth and less seed production
  • Larger cells
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4
Q

How/when does autopolyploidy occur through mitosis?

A
  • Cytokinesis stops
  • No cell division
  • 2x genetic info in autotetraploid
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5
Q

How/when does autopolyploidy occur through meiosis?

A
  • Non-disjunction occurs in Meiosis I (no segregation)
  • Produces a 2n gamete
  • Produces an autotriploid zygote
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6
Q

What are some examples of polyploid plants?

A
  • Seedless varieties of citrus are triploids or pentaploids
  • Odd # makes plants sterile
  • Not as much genetic diversity
  • Ex. watermelon, bananas, grapes
  • Strawberries = 8N
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7
Q

What is a problem with polyploidy?

A
  • Many are sterile due to problems with pairing/separation of homologous chromosomes in meiosis
  • Ex. Bananas 3N = 33
  • > 11 univalents and 11 bivalents
  • > Number of chromosomes can vary
  • > need stoichiometrically equal # of genes to be viable
  • > could produce gametes with 2 copies of one chromosome and 1 copy of another
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8
Q

What are the 3 ways that triploid cells can segregate/pair in meiosis?

A
  • 2 homologous chromosomes pair, whereas the other segregates randomly
  • All 3 chromosomes pair and segregate randomly
  • None of the chromosomes pair and all 3 move to the same cell
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9
Q

What are allopolyploids?

A
  • Some polyploids are the result of crosses b/n 2 or more species (usually related)
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10
Q

What is the process of creating allopolyploids?

A
  • Gametes from 2 diploid plants form hybrid
  • The hybrid is sterile b/c meiosis is irregular
  • The chromosomes are doubled, creating a tetraploid
  • Meiosis in the tetraploid is regular
  • Euploid gametes produced by the tetraploid can combine to propagate the organism sexually
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11
Q

What is an example of a allohexaploid?

A
  • Bread wheat
2N=14 x 2N=14
Sterile 2N=14
- Meiosis will not work bc there are no homologous chromosomes
Doubled to 4N=28
- Can now undergo meiosis I and II
Crossed with 2N=14
Sterile 3N=21
Doubled to 6N=42 (allohexaploid) or can be called 3N=42 (amphidiploid)
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12
Q

What is an example of an allotetraploid?

A
  • Upland cotton
  • 2N = 52
    Cross b/n American and Old World cotton (both 2N=26)
    2N=26 Sterile
    Doubled to 4N=52 Fertile
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13
Q

What was crossed in the development of triticale?

A

Rye and wheat
4N=28 x 2N=14
Sterile 3N=21
Doubled to 6N=42 Triticale (A functional diploid or amphidiploid)

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14
Q

What is special about triticale?

A
  • High protein of wheat
  • High lysine of rye
  • Hardy even in poor soil conditions
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15
Q

What occurs in animal polyploidy? What is an example?

A
  • Interspecies crosses can result in sterile animal
  • Chromosome doubling is not well tolerated
    Ex. Sterile Mule
    (Hardy and strong)
  • Liger is fertile bc it has homologous chromosomes
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16
Q

When can polyploids be fertile?

A

Polyploids produced by chromosome doubling in interspecific hybrids may be fertile if their constituent genomes segregate independently

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17
Q

What is aneuploidy? What can cause it?

A
  • Diploid genome which lacks a chromosome or has an extra chromosome
  • Ex. 2N+1 trisomies
  • Ex. 2N-1 monosomies
  • Meiotic nondisjunction
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18
Q

What is the karyotype of Down syndrome?

A

47, +21

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19
Q

What is the karyotype of Patau syndrome?

A

47, +13

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20
Q

What is the karyotype of Edward syndrome?

A

47, +18

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21
Q

What is the karyotype of Turner syndrome?

A

45, X

22
Q

What is the karyotype of Klinefelter syndrome?

A

47, XXY

23
Q

What is the karyotype of Triplo-X syndrome?

A

47, XXX

24
Q

A diploid organism has 2n = 36 chromosomes. How many chromosomes will be found in a trisomic member of this species?

A

2n + 1 = 36 + 1 = 37 chromosomes

25
Q

How does frequency of trisomies compare with age?

A

Frequency of trisomies increases with age

  • Eggs are stalled in Prophase I
  • Recombination between the homologous pair
26
Q

How does formation of eggs in humans work?

A
  • Meiosis begins in fetus then arrests
  • Germ cells remain arrested in prophase I until ovulation
  • This is a prophase arrest (DNA exchange can occur at this point in time)
27
Q

Why is there a correlation b/n the incidence of trisomies and maternal age?

A
  • Bivalents with crossovers near ends are fragile and increasingly unstable over time
  • If bivalent dissociates, nondisjunction of homologues occurs
28
Q

Why might association b/n sister chromatids (cohesion) breakdown in older women?

A 
- Unknown
Possibilities:
- Length of prophase arrest
- Hormonal changes
- Environmental factors
29
Q

What chemicals can cause nondisjunction?

A
  • Colchicine (used to treat plants to promote chromosome doubling)
  • Bisphenol A (BPA; used in plastic bottles)
30
Q

How does Down syndrome occur?

A
  • 96% due to meiotic nondisjunction events

- About 80% in oogenesis and 20% in spermatogenesis

31
Q

What are some treatments for Turner syndrome (XO)?

A
  • Growth hormone therapy to increase stature

- Estrogen for breast development

32
Q

What are some treatments for Klinefelter syndrome (XXY)?

A
  • Testosterone therapy coupled with breast tissue removal

- More typical male phenotype

33
Q

Why do Triple X females have a milder phenotype than XO?

A
  • X-inactivation
34
Q

What is a deletion/deficiency?

A
  • Missing chromosome segment
35
Q

What is a duplication?

A
  • Extra chromosome segment
36
Q

What is hypoploidy? What is an example?

A
  • Occurs as a result of deletion
  • Less genetic material
  • Ex. Cri-du-chat syndrome
    46, XX (5p-)
37
Q

What is hyperploidy?

A
  • More genetic material

- Occurs as a result of duplication of a chromosome segment or gain of entire chromosomes

38
Q

How can a chromosome be rearranged?

A
  • A chromosome may become rearranged internally
    OR
  • It may become joined to another chromosome
39
Q

What is pericentric inversion?

A
  • Portion of 2 chromosomes is swapped
40
Q

What is paracentric inversion?

A
  • Heterozygote has one normal chromosome and one with inverted segment
  • In Prophase I, chromosomes form inversion loop (allows homologous sequences to align)
41
Q

What is a translocation?

A
  • Segment from one chromosome is detached and reattached to a different (nonhomologous) chromosome
42
Q

What is reciprocal translocation?

A
  • Pieces of 2 nonhomologous chromosomes are exchanged without net loss of genetic material
43
Q

What configuration forms between chromosomes of a heterozygous individual with translocation?

A
  • Crosslike configuration forms during prophase I of meiosis

- Because each chromosome has sections that are homologous to 2 other chromosomes

44
Q

What are the 3 ways chromosomes can separate in anaphase I after translocation?

A
  • Alternate
  • Adjacent-1
  • Adjacent-2
45
Q

What does alternate segregation look like and what is the result?

A
  • 2 translocated chromosomes together and 2 normal together
  • Joined diagonally
  • Viable gametes are formed
  • 2 gametes have both normal chromosomes, and other 2 have both translocated chromosomes
46
Q

What does adjacent-1 segregation look like and what is the result?

A
  • Split horizontally (N1 with T2 and T1 with N2)
  • Nonviable gametes are formed
  • Each gamete has 1 normal and one translocated chromosome
  • Some genes are present in 2 copies and others are missing
47
Q

What does adjacent-2 segregation look like and what is the result?

A
  • Rare
  • Split vertically (N1 with T1 and N2 with T2)
  • Nonviable gametes are formed
  • Each gamete has 1 normal and one translocated chromosome
  • Some genes are present in 2 copies and others are missing in each gamete
48
Q

What are compound chromosomes and how are they formed?

A
  • Formed by fusion of homologous chromosomes, sister chromatids or homologous chromosome segments
49
Q

What are robertsonian translocations and how are they formed?

A
  • Fusion of 2 nonhomologous chromosomes at their centromeres
  • Short arm of acrocentric chromosome is exchanged with long arm of another
  • Creates a large metacentric chromosome
  • A fragment that often fails to segregate is lost
50
Q

What is special about human chromosome 2?

A
  • It is metacentric

- Has arms that correspond to 2 different acrocentric chromosomes in the genomes of great apes

51
Q

What are some examples of translocation leading to disease?

A
  • 5% of Down syndrome cases are caused by Robertsonian translocation of chromosome 21 long arm onto long arm of #14.
  • Translocations can cause cancer by moving a gene to a chromosome where it will be misregulated
52
Q

How is translocation seen when a parent who is a translocation carrier is crossed with a normal parent?

A
  • Carrier parent has normal phenotype
  • Gametogenesis produces gametes (each have one translocated chromosome)
  • 2/3 of offspring will have normal phenotype and 1/3 will show disease (ex. Down syndrome)
  • Other chromosomal combinations result in spontaneously aborted embryos

MBG 2040 (7 decks)

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