Cytogenetics Flashcards
1
Q
cytogenetics
A
- science that combines the methods and findings of cytology and genetics
- study of heredity at the cellular level
2
Q
chromosomal basis of inheritance
A
- humans have 46 chromosomes in a somatic cell, 23 pairs
- 22 pairs of autosomes, 2 pair of sex chromosomes
- members of a pair are homologous chromosomes
- one homolog from each parent
3
Q
cell cycle
A
- somatic division-mitosis
- 2N—>4C—>2N
- germ cell division is meiosis
- reduction
- 2N–>4C–>2N–>N
4
Q
mitosis
A
- interphase
- prophase
- metaphase
- anaphase
- telophase
- copy chromosomes then line up at metaphase plate then divide
5
Q
meiosis
A
- I and II
- prophase I has recombination
- anaphase I is the reduction division 2N to N, 4C to 2C, becomes haploid
- then meiosis II goes to N and C
6
Q
meiotic non-disjunction
A
- in anaphase I
- fail to separate chromosomes
7
Q
disomy
A
- presence of 2 chromosomes
- isodisomy-2 chromosomes from the same source- duplication of 1
- heterodisomy- 2 different chromosomes- normal pair
8
Q
nullosomy
A
- lacking one gene in gamete cells
- nondisjunction leads to no A chromosomes in 2 gametes
- occurs if nondisjunction is in anaphase I
9
Q
nondisjunction II
A
leads to isodisomy
- nondisjunction happens in meiosis II
- one gamete has 2 copies of same chromosome, another gamete doesn’t have any
10
Q
oogenesis
A
- begins in the developing fetus
- by 3rd month of gestation, primary oocytes are present
- these cells reach dictyotene (prophase I) by birth and remain there until ovulation
- at ovulation, the oocyte completes meiosis I, becomes secondary oocyte
- secondary oocyte can become fertilized and complete meiosis II
11
Q
spermatogenesis
A
- primary spermatocytes produced throughout reproductive life
- gametes produced continually
- 4 equal gametes per original primary gametocyte
12
Q
oogenesis 2
A
- primary oocytes all present at birth
- gametes produced once a month
- 1 gamete per original primary gametocyte
13
Q
sex chromosomes
A
- 1 pair- X and Y
- females XX, males XY
- normal recombinant area above SRY and TDF in the pseudoautosomal region
- then rare region for crossing over
- the sex linked regions
14
Q
TDF
A
- testis determining factor
- SRY- sex determining region of the Y
15
Q
female sex determination
A
- no TDF/ SRY
- ovary development
- proliferation of mullerian ducts
- regression of wolffian ducts
16
Q
male sex determination
A
- have TDF/SRY
- testis form
- inhibition of mullerian ducts, and then degeneration
- androgen synthesis and wolffian duct proliferation
17
Q
sex determination
A
- due to genes on the X, Y and autosomes
- occurs very early in development
- loss of one sex chromosome later in life is clinically irrelevant
18
Q
lyon hypothesis
A
- 1 X inactivated in somatic cells of females
- barr bodies
- for determination of normal female there must be 2 active X chromosomes
- inactivation occurs early in development, 3-7 days after fertilization
- inactivation is random, but once established is not reversible in somatic tissue
- results in dosage compensation- right amt of proteins
19
Q
mosaics
A
- females are mosaic for heterozygous traits
- if gene is on X chromosome, different ones will be inactivated and cause different proteins
- yellow fur vs black fur in kitties
20
Q
non-random X inactivation
A
- occurs when there is a bad X
- same X is always inactivated- abnormal one
21
Q
mechanism of X inactivation
A
- epigenetic mechanism
- methylation initiated at XIST
- several sites appear to escape inactivation, including pseudoautosomal region
- inactive X must be reactivated at meiosis o that active Xs are transmitted to offspring
22
Q
clinical role of cytogenetics
A
- id chromosomal anomalies that may be associated with disease
- contribute to the diagnosis and treatment of patients
- individuals of all age groups
- many different diseases
23
Q
effects of chromosomal abnormalities
A
- changes in phenotype
- fetal loss
- genetic disease
- malignancy
24
Q
fetal loss
A
- 1 in 13 conceptuses with chromosomal abnormality, 6 in 1000 are live born
- 15% of recognized pregnancies end in spontaneous abortion
- 80% of those in the 1st trimester
- of the SAbs, 60% have a chromosomal defect
- of the chromosomal losses, 52% are autosomal trisomies
25
Q
postnatal
A
- about 0.6% of newborns have a chromosome anomoly
- features of a known disorder
- ambiguous genitalia
- multiple congenital anomalies
26
Q
children and adults
A
- features of a known chromosomal disorder
- family history of a chromosomal disorder
- mental retardation
- infertility
- some malignancies
27
Q
what to look for
A
- numerical or structural abnormalities
- metaphase karyotype
- size, centromere position, banding pattern
28
Q
specimens
A
- blood
- amniotic fluid
- chorionic villi
- bone marrow
- tissue
29
Q
metacentric
A
-two arms same length
30
Q
submetacentric
A
-slightly off center
31
Q
acrocentric
A
- humans
- have short and long arm and stalk and satellite
- short arm is p long arm is q
32
Q
telomeres
A
-composed of repeat sequence DNA at the ends of the chromosome
33
Q
normal variation
A
-must be distinguished as different from an abnormality
34
Q
chromosomal polymorphism
A
- presence of two or more alternative structural forms for a chromosome that occurs in a frequency of at least 1 % within a population
- inherited as mendelian characters and can be traced through pedigrees
- the variation is usually not associated with specific clinical anomalies or a particular disease
