MCP 2

Question 1

Cytogenetics

Answer 1

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

Question 2

Cell cycle

Answer 2

somatic division = mitosis (2N)

germ division = meiosis (N)

Question 3

Mitosis

Answer 3

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)

Question 4

What is the most important mitotic phase for cytogenetics?

Answer 4

metaphase

Question 5

Meiosis

Answer 5

-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

Question 6

Recombination

Answer 6

-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

Question 7

nondisjunction

Answer 7

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

Question 8

Disomy

Answer 8

the presence of 2 chromosomes

Question 9

Isodisomy

Answer 9

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

Question 10

Heterodisomy

Answer 10

2 different chromosomes

Question 11

Result of meiotic nondisjunction I

Answer 11

• two disomic (heterodisomic)

- two nullsomic

Question 12

Result of meiotic nondisjunction II

Answer 12

• one disomic (isodisomy)

- one nullsomic

Question 13

Oogenesis

Answer 13

• 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

Question 14

Sex chromosomes

Answer 14

• the X and Y chromosomes

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

Question 15

What is the default gender development pattern in humans?

Answer 15

Female

Question 16

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

Answer 16

is clinically irrelevant

Question 17

Sex determinations

Answer 17

is due to genes on the X, Y and autosomes

occurs very early in development

Question 18

Lyon Hypothesis

Answer 18

• 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

Question 19

Dosage compensation

Answer 19

equalization of the amount of active genetic material

Question 20

If a female is a heterozygote

Answer 20

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

Question 21

Non-random X inactivation

Answer 21

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

Question 22

Mechanisms of X inactivation

Answer 22

• 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

Question 23

Clinical role of cytogenetics

Answer 23

• 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

Question 24

Fetal Loss

Answer 24

• 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

Question 25

Post-natal role of cytogenetics

Answer 25

- about 0.6% of newborns have a chromosome anomaly - ambiguous genitalia - multiple congenital anomalies - features of chromosomal disorder

Question 26

What two categories do most cytogenetically detectable abnormalities fall into?

Answer 26

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

Question 27

Potential specimens for cytogenetics

Answer 27

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

Question 28

How do we identify chromosomal abnormalities?

Answer 28

karyotype analysis - chromosomes arrested at metaphase (hence why its the most important) 1. size 2. centromere position 3. banding pattern

Question 29

Metacentric

Answer 29

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

Question 30

Submetacentric

Answer 30

when centromere is closer to one end than the other

Question 31

Acrocentric

Answer 31

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

Question 32

what is the total number of chromosomes defined by?

Answer 32

The number of centromeres

Question 33

telomere

Answer 33

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

Question 34

Banding pattern

Answer 34

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

Question 35

Chromosomal polymorphism

Answer 35

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