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UNIT 7 > MCP 2 > Flashcards

MCP 2 Flashcards

1. discuss the principle of mitosis, meiosis and gametogenesis 2. describe the chromosomal basis of inheritance and the basic structure of chromosomes 3. explain sex determination and to have a working knowledge of X inactivation and reactivation

1
Q

Cytogenetics

A

the science that combines the methods and findings of cytology and genetics
-the study of heredity at the cellular level

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2
Q

Cell cycle

A

somatic division = mitosis (2N)

germ division = meiosis (N)

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3
Q

Mitosis

A

phases: interphase, prophase, metaphase, anaphase and telophase -> followed by cytokinesis and separation of the materials into two new daughter cells (genetically identical to the parent cell)

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4
Q

What is the most important mitotic phase for cytogenetics?

A

metaphase

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5
Q

Meiosis

A

-occurs in the gonads
Meiosis I -> prophase I (recombination) -> metaphase I -> anaphase I (reduction division) -> telophase I –>Meiosis II-> metaphase II -> anaphase II -> telophase II

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6
Q

Recombination

A

-results when two homologs break and exchange places (crossing over) ->an exchange between homologous chromosomes resulting in re assortment of the genes/alleles present on each chromosome

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7
Q

nondisjunction

A

failure of the chromosomes or chromatids to disjoin properly - meiosis nondisjunction can occur at either the first or second division and net result is different

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8
Q

Disomy

A

the presence of 2 chromosomes

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9
Q

Isodisomy

A

2 chromosomes from the same source ==> duplication of 1 chromosome

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10
Q

Heterodisomy

A

2 different chromosomes

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11
Q

Result of meiotic nondisjunction I

A
  • two disomic (heterodisomic)

- two nullsomic

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12
Q

Result of meiotic nondisjunction II

A
  • one disomic (isodisomy)

- one nullsomic

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13
Q

Oogenesis

A
  • oogenesis begins in the developing fetus
  • by the third month of gestation all of the primary oocytes are present
  • these cells reach dictyotene (prophase I) by birth and remain there until ovulation
  • at ovulation the oocyte completes meiosis I and becomes a secondary oocyte
  • meiosis is only completed if fertilization occurs
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14
Q

Sex chromosomes

A
  • the X and Y chromosomes

- of 46 chromosomes (23 pairs) -> 22 autosomal pairs and 1 pair of sex chromosomes

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15
Q

What is the default gender development pattern in humans?

A

Female

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16
Q

Once the sex of an individual has been determined, loss or gain of key genes or sex chromosomes

A

is clinically irrelevant

17
Q

Sex determinations

A

is due to genes on the X, Y and autosomes

occurs very early in development

18
Q

Lyon Hypothesis

A
  • one X is inactivated in somatic cells of females -> called bar bodies appear as dark stain dot
  • total number of bar bodies = total number of chromosomes - 1
  • for normal female there must be two active X chromosomes
  • inactivation occurs early in development, 3-7 days after fertilization
  • inactivation is random, but once established is not reversible in SOMATIC tissues
  • X inactivation results in dosage compensation - so that boys can only have one and are the same as girls
19
Q

Dosage compensation

A

equalization of the amount of active genetic material

20
Q

If a female is a heterozygote

A

she will be a mosaic -> somatic mosaicism -> some cells in her body will express the maternal X and some will express the paternal X

21
Q

Non-random X inactivation

A

results when there is an abnormal X chromosome present that is preferentially inactivated -> skewing the distribution such that the alleles on the other X are always expressed

22
Q

Mechanisms of X inactivation

A
  • epigentic
  • methylation -XIST (x inactivation center)
  • several sites appear to escape inactivation- including the pseudoautosomal region
  • inactive X must be reactivated at meiosis so that active Xs are transmitted to offspring
23
Q

Clinical role of cytogenetics

A
  • identify chromosomal anomalies that may be associated with disease
  • contribute to the diagnosis and treatment of patients
  • individuals of all age groups
  • many different diseases
  • effect of chromosomal abnormalities: change in phenotype, fetal loss, genetic disease, malignancy
24
Q

Fetal Loss

A
  • 1/13 conceptuses with chromosomal abnormality -> 6/10,000 born live
  • 15% of recognized pregnancies end in spontaneous abortion-> 80% first trimester
  • of spontaneous loss -> 60% chromosomal
  • of chromosomal losses 52% are autosomal trisomies
25
Q

Post-natal role of cytogenetics

A
  • about 0.6% of newborns have a chromosome anomaly
  • ambiguous genitalia
  • multiple congenital anomalies
  • features of chromosomal disorder
26
Q

What two categories do most cytogenetically detectable abnormalities fall into?

A

-structural
-numerical
then its important to figure out precisely which gene

27
Q

Potential specimens for cytogenetics

A
  • blood (easiest)
  • amniotic fluid (prenatal)
  • chorionic villi (prenatal)
  • bone marrow (oncology)
  • tissue (skin- when deceased)
28
Q

How do we identify chromosomal abnormalities?

A

karyotype analysis - chromosomes arrested at metaphase (hence why its the most important)

  1. size
  2. centromere position
  3. banding pattern
29
Q

Metacentric

A

when the centromere is located approximately equidistant from each half of the chromosomes

30
Q

Submetacentric

A

when centromere is closer to one end than the other

31
Q

Acrocentric

A

chromosome has modified short arms with stalks containing only multiples copies of rRNA genes that are capped by a modified telomere called a satellite

32
Q

what is the total number of chromosomes defined by?

A

The number of centromeres

33
Q

telomere

A

end of the chromosome- regions are known to be composed of tandem repeated DNA with the sequence (TTAGGG)n -shorten with each replication, have been thought to be implicated in aging process

34
Q

Banding pattern

A

each pair of chromosomes has a unique banding pattern that can be used to identify -> comes from DNA trypsinization weakens prior to staining then stained with either Giemsa or Wrights stains which are positive to attract to negatively charged DNA

35
Q

Chromosomal polymorphism

A

the presence of two or more alternative structural forms for a chromosome within a population

  • inherited as Mendilian traits and can be traced through pedigrees
  • are usually not associated with clinical anomalies or particular diseases

UNIT 7 (10 decks)

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