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Genetics > Week 7 JP Content > Flashcards

Week 7 JP Content Flashcards

1
Q

How are smears obtained

A
  1. Blood sample taken
  2. Cell induced to initiate mitosis
  3. blocked during metaphase
  4. stained with Giemsa dye
  5. observe under microscope
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2
Q

Def: Genome Structure

A

Includes chromosome number, size of chromosome, gene content, gene order
- Typically species specific

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3
Q

How is genome structure related to speciation?

A

Variations in chromosome number and/or structure are important forces driving speciation

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4
Q

Why do humans have a different chromosome number as chimpanzees?

A

Chromosome 12 and 13 fused to form chromosome 2 in humans

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5
Q

Is the human genome structure optimized through evolution?

A
  • Optimized for current population under current conditions
  • Not overall, will continue to evolve
  • Different selection pressures in todays society
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6
Q

How are chromosomes organized within nucleus?

A

CHROMOSOMAL TERRITORY
- Gene-rich chromosomes: near the center
- Gene-poor chromosomes: near the periphery
INTERCHROMOSOMAL DOMAINS
- REGIONS BETWEEN TERRITORIES

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7
Q

Def: Karyotype

A

Organized visual display of chromosomes
- FISH and Giemsa staining help identification

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8
Q

FISH Karyotype

A

Florescent in situ hybridization
- Chromosomes shown through florescent probes
- Descending order of size and then sex chromosomes

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9
Q

P arm vs q arm

A

Short arm vs long arm

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10
Q

Standardized Human Chromosome Map

A
  • Obtained using Giemsa staining and microscope
  • Regions that contain actively expressed genes and are less condensed are called euchromatin - tend to be GC rich and strain lightly
  • Regions that are tightly condensed and contain fewer expressed genes are called heterochromatin - AT rich and stain more heavily
  • Distances on chromosome measured from centromere
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11
Q

What causes genome structure changes?

A

Nondisjunction

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12
Q

Def: Nondisjunction

A

The failure of chromosomes and sister chromatids to properly separate during cell division

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13
Q

At what stage does nondisjunction occur

A
  • Germline cells: meiosis I / meiosis II
  • Somatic cell: mitosis
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14
Q

What is the result and consequences of nondisjunction

A
  • Abnormalities in chromosome number - aneuploidy and polyploidy
  • Causes dosage imbalance: generally more severe fitness effects in animals than plants
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15
Q

Klinefelter Syndrome

A

XXY
BABIES
- Weak muscles
- slow motor development (taking longer then average to crawl and walk
- Delay in speaking
- testicles not descended into the scrotum
ADULTS
- Low sperm count or no sperm
- low sex drive
- less muscular compared with other men
- increased belly fat
- small testicles and penis
- taller than average height
- decreased facial and body hair
- enlarged breast tissue

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16
Q

Trisomy 13

A

PATAU SYNDROME
Mental retardation and developmental delay, possible deafness, major organ abnormalities and early death

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17
Q

Trisomy 18

A

EDWARD SYNDROME
Mental retardation and developmental delay, skull and facial abnormalities, early death

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18
Q

Trisomy 21

A

DOWN SYNDROME
Mental retardation and developmental delay, characteristic facial abnormalities, short stature, variable life span

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19
Q

XYY

A

JACOB SYNDROME
Tall stature, possible reduction but not loss of fertility, no impact on mental capacity

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20
Q

XXX

A

TRIPLE X SYNDROME
Tall stature, possible reduction of fertility, menstrual irregularity, no impact on mental capacity

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21
Q

XO

A

TURNER SYNDROME
No secondary sexual characteristics, infertility, short stature, webbed neck, no impact on mental capacity

22
Q

Def: Polyploidy

A

> 3 sets of chromosomes in the nucleus of an organism

23
Q

Autopolyploid

A

DUPLICATION OF OWN DNA
1. Meiotic whole-genome nondisjunction: diploid gamete
2. Mitotic whole-genome nondisjunction
3. Mitotic and meiotic non-disjunction combined

24
Q

Alloployploidy

A

Combining the chromosome sets of different species through hybridization

25
Q

What kind of benefits can we obtain from polyplodization?

A
  • Bigger fruits and flowers
  • Fertility is decreases - particularly in 3n, 5n etc.
  • Hybrid vigor in allopolyploids
  • Polyploidization as a mechanism for rapid speciation
26
Q

How do chromosome structures change?

A
  1. Chromosome Breakage
  2. unequal crossover during meiosis
27
Q

Chromosome breakage

A

Changes chromosome structures leading to
- Missed ligation - loss of chromosome segments (deletion)
- Duplication ligation - gain of chromosomes (duplication)

28
Q

Terminal deletion

A

Chromosome break that detaches part of one arm
- contains telomere and some genetic material

29
Q

Accentric fragment

A

Broken off fragment without centromere that can be lost during cell division

30
Q

Interstitial deletion

A

the loss of an internal segment of a chromosome that results from two chromosome breaks followed by a joining of the ends on either side of the segment

31
Q

Consequence of unequal crossover during meiosis

A
  • Partial deletion heterozygote
  • Partial duplication heterozygote
32
Q

How does unequal crossover during meiosis occur

A
  • Homologs misalign and a copy of gene loops out on each chromosome
  • when recombination occurs both loops on one side and neither on the other
  • leads to deletion on one side and duplication on the other
33
Q

How do we detect duplication and deletion?

A
  • FISH probes to certain genes
  • No fluorescence detected from probe B - deletion (microinterstitial deletion)
  • Two fluorescent spots indicate the target of probe B is duplicated (microduplication)
34
Q

Microdeletions and microduplications

A
  • smaller
  • not easy to detect by chromosome banding analysis
  • Use FISH to detect absence or presence of a particular gene or chromosome sequence
35
Q

Chromosome inversion

A

Wrong orientation of segment in the same chromosome

36
Q

Chromosome Translocation

A

Segment in a different chromosome

37
Q

How are inversion and translocations generated?

A

Caused by chromosome breakage and wrong reattachment
- if no critical gene or regulatory region is broken or in the inverted/translocated regions, there may be no phenotypic consequences
- In germline cells they can affect chromosome segregation and reduce fertility during meiosis

38
Q

Types of chromosome inversion

A
  • Paracentric inversion: centromere outside of inverted region
  • Pericentric inversion: centromere within inverted region
39
Q

Inversion heterozygotes

A

have one normal and one inverted homolog

40
Q

How does paracentric inversion influence crossing over and fertility?

A
  • Forms inversion loop at synapsis
  • Crossing over that occurs outside the inverted region takes place normally
  • Crossing over within the inverted region results in duplications and deletions in the recombinant chromosomes: forms a dicentric chromosome (non-viable) and an acentric fragment (lost in subsequent division)
41
Q

How does pericentric inversion influence crossing over and fertility?

A
  • Crossing over that occurs within a pericentric inversion results in both duplicated and deleted regions in both of the recombinant products
  • Recombination event yields two normal gametes (from the non-crossover chromatids) and 2 abnormal (from crossover)
42
Q

What is chromosomal translocation?

A

Broken ends of nonhomologous chromosomes are reattached, three types
- unbalanced
- reciprocal balanced
- Robertsonian translocation

43
Q

Unbalanced translocation

A

Break off from one chromosome transferred to another causing deletion and addition

44
Q

Reciprocal balanced translocation

A

translocation swap in two non-homologous chromosomes

45
Q

Robertsonian translocations

A

AKA chromosomal fusion
- translocation of whole arm resulting in loss of other centromere due to lack of genes and fusion of the nonhomologous chromosomes

46
Q

Translocation heterozygotes

A

may experience semisterility due to segregation abnormalities

47
Q

What are the consequences of balanced reciprocal translocation?

A
  • Somatic cells: usually no observed effect
  • Germline cells: 1/2 normal, 1/2 inviable
48
Q

How is chromosomal DNA packaged inside the nucleus

A
  • Chromosome: 50% DNA, 50% protein
    Proteins:
  • 50% histone proteins (H1, H2A, H2B, H3, H4)
  • two molecules of histones H2A, H2B, H3 and H4 (octamer) form nucleosome core particles
  • 146 bp wraps around each octamer to form nucleosome
  • remaining 50% of protiens are diverse combination of enzymes, transcription factors etc.
49
Q

Solenoid Structure

A

10-nm fiber coils and forms the solenoid structure (30nm fiber), with 6-8 nucleosomes per turn and histone H1 stabilizing the solenoid

50
Q

Interphase chromosome orgnaization

A

30-nm fibers attached to nonhistone scaffolding proteins at sites called MAR (matrix attachment regions), forming chromatid loops
- chromosome scaffolding gives chromosomes their shape
- the loops on the scaffolds are about 300nm which coil again to form chromosome arm

51
Q

Why are DNA packaged into scaffolds and chromatids?

A
  • Efficient storage and separation of chromosome’s at anaphase
  • Chromatin loops play a role in the regulation of gene expression
  • Active transcription take place in segments of loops distant from MARs
  • Euchromatin (big loops, transcription is high) vs heterochromatin (small loops, low transcription activity
52
Q

What is the total length of DNA in a human

A

7.59 x10^9 km

Genetics (18 decks)

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