Cytogenetics

Question 1

cytogenetics

Answer 1

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

Question 2

chromosomal basis of inheritance

Answer 2

• 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

Question 3

cell cycle

Answer 3

• somatic division-mitosis
• 2N—>4C—>2N
• germ cell division is meiosis
• reduction
• 2N–>4C–>2N–>N

Question 4

mitosis

Answer 4

• interphase
• prophase
• metaphase
• anaphase
• telophase
• copy chromosomes then line up at metaphase plate then divide

Question 5

meiosis

Answer 5

• 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

Question 6

meiotic non-disjunction

Answer 6

• in anaphase I

- fail to separate chromosomes

Question 7

disomy

Answer 7

• presence of 2 chromosomes
• isodisomy-2 chromosomes from the same source- duplication of 1
• heterodisomy- 2 different chromosomes- normal pair

Question 8

nullosomy

Answer 8

• lacking one gene in gamete cells
• nondisjunction leads to no A chromosomes in 2 gametes
• occurs if nondisjunction is in anaphase I

Question 9

nondisjunction II

Answer 9

leads to isodisomy

• nondisjunction happens in meiosis II
• one gamete has 2 copies of same chromosome, another gamete doesn’t have any

Question 10

oogenesis

Answer 10

• 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

Question 11

spermatogenesis

Answer 11

• primary spermatocytes produced throughout reproductive life
• gametes produced continually
• 4 equal gametes per original primary gametocyte

Question 12

oogenesis 2

Answer 12

• primary oocytes all present at birth
• gametes produced once a month
• 1 gamete per original primary gametocyte

Question 13

sex chromosomes

Answer 13

• 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

Question 14

TDF

Answer 14

• testis determining factor

- SRY- sex determining region of the Y

Question 15

female sex determination

Answer 15

• no TDF/ SRY
• ovary development
• proliferation of mullerian ducts
• regression of wolffian ducts

Question 16

male sex determination

Answer 16

• have TDF/SRY
• testis form
• inhibition of mullerian ducts, and then degeneration
• androgen synthesis and wolffian duct proliferation

Question 17

sex determination

Answer 17

• 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

Question 18

lyon hypothesis

Answer 18

• 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

Question 19

mosaics

Answer 19

• 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

Question 20

non-random X inactivation

Answer 20

• occurs when there is a bad X

- same X is always inactivated- abnormal one

Question 21

mechanism of X inactivation

Answer 21

• 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

Question 22

clinical role of cytogenetics

Answer 22

• 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

Question 23

effects of chromosomal abnormalities

Answer 23

• changes in phenotype
• fetal loss
• genetic disease
• malignancy

Question 24

fetal loss

Answer 24

• 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

Question 25

postnatal

Answer 25

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

Question 26

children and adults

Answer 26

- features of a known chromosomal disorder - family history of a chromosomal disorder - mental retardation - infertility - some malignancies

Question 27

what to look for

Answer 27

- numerical or structural abnormalities - metaphase karyotype - size, centromere position, banding pattern

Question 28

specimens

Answer 28

- blood - amniotic fluid - chorionic villi - bone marrow - tissue

Question 29

metacentric

Answer 29

-two arms same length

Question 30

submetacentric

Answer 30

-slightly off center

Question 31

acrocentric

Answer 31

- humans - have short and long arm and stalk and satellite - short arm is p long arm is q

Question 32

telomeres

Answer 32

-composed of repeat sequence DNA at the ends of the chromosome

Question 33

normal variation

Answer 33

-must be distinguished as different from an abnormality

Question 34

chromosomal polymorphism

Answer 34

- 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