Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Molecular Basis Of Disease > Numerical Chromosomal Abnormalities > Flashcards

Numerical Chromosomal Abnormalities Flashcards

1
Q

Describe the major phases of the cell cycle

A
  • G1: Cellular contents, excluding the chromosomes are duplicated
  • S phase: Each of the 46 chromosomes is duplicated by the cell
  • G2: The cell double checks the duplicated chromosomes for error, making any needed repairs
  • Mitosis: Forms 2 daughter cells
  • Cytokinesis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Describe what occurs in the S-phase and the type of chromsome formed?

A
  • DNA (single chromatid) is replicated to form sister chromatids
  • These are paired together in homologous chromosomes
  • Homologous chromosomes refer to a pair of chromosomes having the same gene sequences, each derived from one parent (maternal and paternal)
  • In a pair of homologous chromosomes, one is inherited from the male parent, and the other from the female parent
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe the genetic locus location and function in a gene

A
  • A genetic locus is the location of a particular gene on a chromosome
  • At each genetic locus, an individual has two alleles, one on each homologous chromosome
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is mitosis?

A
  • Mitosis = Division of all cells apart from the production of gametes
  • PMAT: Prophase, Metaphase, Anaphase, Telophase
  • 1 diploid = 46 chromosomes (2n) becomes 2 diploid = 46 chromosomes (2n)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe the key stages involved (PART 1)

A
  • Interphase: Chromosomes duplicate and the copies remain attached to each other
  • Prophase: In the nucleus, chromosomes condense and become visible. In the cytoplasm, splindles form
  • Prometaphase: The nuclear membrane breaks apart and the spindle starts to interact with the chromosomes
  • Metaphase: The copied chromosomes align in the middle
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe the key stages involved (PART 2)

A
  • Anaphase: Chromosomes separate into 2 genetically identical groups and move to opposite ends of the spindle
  • Telophase: Nuclear membranes form around each of the 2 sets of chromosomes, the chromosomes begin to spread out, and the spindle begins to break down
  • Cytokinesis: The cell splits into 2 daughter cells, each with the same number of chromosomes as the parent. In humans, such cells have 2 copies of 23 chromosomes (diploid)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Give some key features of mitosis (5)

A
  • Sister chromatids are identical
  • Each daughter cells recieves 1 chromatid of each chromosome and are genetically identical to parent
  • Homologues do not interact
  • Align as 46 separate chromosomes - each behaves independently
  • All somatic cells (from body)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is meiosis?

A
  • Meiosis = Division of cells for production of gametes (sperm/egg)
  • Leads to genetic variation
  • 2 cell divisions of 1 diploid (46 chromosomes) into 4 haploid (23) daughter cells.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe meiosis I

A
  • Align as 23 bivalents (pairs of HCs)
  • Allows for chiasma formation (i.e. recombination)
  • Pulls apart homologues from one another
  • Daughter cells have 23 chromosomes (each with 2 chromatids)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe meiosis II

A
  • Align as independent chromosomes
  • Sister chromatids pulled apart
  • Daughter cells have 23 chromosomes (each of 1 chromatid)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What occurs when homologous chromosomes align?

A
  • HC align which form a bivalent structure (pair of HCs) held together by the synaptonemal complex
  • Once aligned, they undergo crossing over
  • Crossing over = Exchange of genetic material via reciprocal breaking + re-joining between homologous chromosomes
  • Forms a chiasma as the point of contact between the 2 non-sister chromatids of HCs
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the purpose of this?

A
  • Crossing over forms recombinant chromsomes (Opposite strand is of other non-sister chromatids) and non-recombinant chromosomes (same strands as before)
  • Crossing over will then result in recombination - production of different combinations of alleles in offspring
  • Ultimately results in exchange of chromosomal segments and new allele combinations
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe independent assortment?

A
  • Describes How pairs of alleles (maternal + paternal) separate independently from one another during meiosis
  • Occurs randomly - equal chance of pairing or separating with any other chromosome
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

State the 2 mechanisms involved that introduces natural variation in meiosis and what does it result for the daughter cell?

A
  • Natural variation arises by:
  • Independent assortment of chromosomes
  • Recombination (via crossing over)
  • Means daughter cells are genetically unique
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Describe the normal human karyotype

A
  • Karyotype = Number + visual apperance of chromosomes in an organism
  • Humans have 23 pairs of chromosomes
  • 22 pairs autosomes and 1 pair sex chromosomes (XX or XY)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

State the 3 types of chromosomes found and what chromosomes they are found in?

A
  • Based on the location of the centromere
  • Metacentric: p & q arms even length, 1-3, 16-18
  • Submetacentric: p arm shorter than q, 4-12, 19-20, X
  • Acrocentric: Long q, small p, p contains no unique DNA, 13-15, 21-22, Y
17
Q

State what haploid and diploid mean?

A
  • HAPLOID: One set of chromosomes (n=23) as in a normal gamete.
    DIPLOID: Cell contains two sets of chromosomes (2n=46; normal in human)
18
Q

State what polyploid and aneuploid mean?

A
  • POLYPLOID: Multiple of the haploid number (e.g. 4n=92)
  • ANEUPLOID (non-disjunction): Chromosome number which is not an exact multiple of haploid number - due to extra or missing chromosome(s) (e.g. 2n+1=47)
19
Q

Difference between trisomy and monosomy aneuploid?

A
  • Trisomy = extra chromosome
  • Monsomy = missing chromosome
20
Q

What leads to chromosomal abnormalities?

A
  • Meiosis leads to genetic variation
  • If the process goes wrong through meiotic non-disjunction, it can lead to disease - chromosomal abnormalities
21
Q

What is meiotic non-disjunction and how does it arise?

A
  • Meiotic non-disjunction is the failure of homologous chromosomes (MI) or sister chromatids (MII)
  • To segregate properly at opposite poles during meiosis, results in the production of gametes that have an improper chromosome complement.
  • When a normal gamete combines with a gamete that has an extra chromosome, the resulting zygote is trisomic
  • Occurs at either Meiosis I or Meiosis II
22
Q

State 3 examples of autosomal aneuploidies?

A
  • Trisomy 13 (Patau’s, 2 in 10,000 births)
  • Trisomy 18 (Edward’s, 3 in 10,000)
  • Trisomy 21 (Down’s, 15 in 10,000)
  • Others happen but do not carry to term (won’t survive)
23
Q

State 3 examples of sex chromosome aneuploidies?

A
  • Turner’s (45,X) (1 in 5000 female births)
  • Triple X syndrome (47,XXX) (1 in 1000 female births)
  • Klinefelter’s (47,XXY) (1 in 1000 male births)
24
Q

What is mitotic non-disjunction?

A
  • Failure of sister chromatids to segregate properly to opposite poles during mitosis
  • Only a portion of cells will be affected - Meiotic ND occurs in zygote so every cell will be affected (carrying extra or missing chromosome)
  • Majority of cells will be 2n, some 2n+1 (mosaic/trisomic) and 2n-1 (monosomic- these will die out)
25
Q

What is mosacism?

A
  • The presence of two or more genetically different cell lines (cells with different number of chromosomes) derived from a single zygote
  • As a result of mitotic ND
26
Q

What mechanism occurs in maternal non-disjunction?

A
  • Zygote (trisomic) cell will recognise that there are wrong number of chromosomes and throw out one of the copies (randomly) to bring back cell to disomic
  • Occurs via trisomy rescue anaphase lag - scenarios:
  • normal biparental contribution (each from one parent)
  • If both of the retained chromosomes come from the same parent, then uniparental disomy results
27
Q

How does this result in mosacism?

A
  • This will result in mosacisim as it goes from 100% of cells being trisomic to a portion of the cells
  • Below shows possible scenarios
  • VD
28
Q

What is the clinical relevance of having a mosaic phenotype compared to a complete trisomic phenotype?

A
  • Mosaic phenotype thought to be less severe
  • Difficult to assess as only proportion of cells are affected: Dependent on
  • What are the proportions of different cell types?
  • Which tissue/organs are affected?
29
Q

How can partial trisomy/monosomy arise?

A
  • Full monosomy arises by non disjunction
  • Partial monosomy/trisomy (microdeletion/duplication syndromes) far more common
  • Mechanism different
  • Partial in the sense it is lacking parts of gained additional parts of the chromosome

Molecular Basis Of Disease (30 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions