Ch. 13

Question 1

Cytogenetics

Answer 1

classical area of genetics that links chromosome variations to specific traits (like illnesses)

Question 2

Heterochromatin

Answer 2

Darkly staining; consists of mostly repetitive DNA

Question 3

Euchromatin

Answer 3

Lighter staining; contains most protein-encoding genes

Question 4

telomeres

Answer 4

chromosome tips composed of many repeats of TTAGGG; shorten w/ each cell division

Question 5

What is a karyotype?

Answer 5

chromosome chart that is used in clinics to display chromosomes arranged by size and structure
- humans have 24 chromosome types
- autosomes are numbered 1-22 by size

Question 6

When are karyotypes performed?

Answer 6

during mitotic metaphase when DNA coils tightly to enable visualization

Question 7

What are karyotypes used for?

Answer 7

confirm clinical diagnosis, reveal effects of environmental toxins, clarify evolutionary relationships

Question 8

What centromere position is telocentric?

Answer 8

At the tip

Question 9

What centromere position is acrocentric?

Answer 9

Close to the center

Question 10

What centromere position is submetacentric

Answer 10

Off-center

Question 11

What centromere position is metacentric?

Answer 11

at the center

Question 12

How can chromosomes be imaged?

Answer 12

From any type of human cell that has a nucleus (no RBC)

Question 13

What is the most common application of human chromosome testing?

Answer 13

Prenatal Diagnosis- check relatives for atypical chromosomes, explain infertility, diagnose or track cancers

Question 14

What techniques are used to detect chromosomes?

Answer 14

amniocentesis and chorionic villus sampling (CVS) - older OR cell-free fetal DNA testing (newer)

Question 15

Amniocentesis

Answer 15

needle is used to remove small sample of amniotic fluid from uterus of a pregnant woman (15-16 wks) w an ultrasound to follow needle’s movement

Question 16

Chorionic Villus Sampling

Answer 16

provides earlier results than amniocentesis, does not detect metabolic problems but has greater risk of spontaneous abortion (10-12 wks of pregnancy)

Question 17

What is the maternal age effect?

Answer 17

risk of the procedure (amniocentesis) = risk of miscarriage as maternal age increases (over 35)

Question 18

Cell-Free Fetal DNA Testing

Answer 18

20% DNA pieces found in blood from placenta so genomes can be reconstructed from DNA pieces & analysis based on proportions
- test done 10 wks+ (noninvasive prenatal diagnosis/testing)

Question 19

What is chromosomal shorthand?

Answer 19

a way to describe structure, #, and abnormalities of chromosomes in karyotype or genetic analysis
- symbols & shorthand describe the type of aberration
- #’s correspond to bands and subbands (identify specific genes)
- normal male: 46,XY and normal female: 46,XX

Question 20

What happens in atypical chromosomes?

Answer 20

abnormal chromosome # or structure; most embryos and fetuses with atypical chromosomes stop developing before birth

Question 21

Polyploidy

Answer 21

extra chromosome sets; increase in # of chromosome sets
- account for 17% spontaneous abortions
- 1 in 10k live births, usually fatal within a month

Question 22

Triploid (3N)

Answer 22

cells that have 3 sets of chromosomes
produced by fertilization of one egg by 2 sperm (69, XYY, most common) or fusion of haploid and diploid gametes

Question 23

Aneuploidy

Answer 23

an extra or missing single chromosome due to nondisjunction during meiosis; change in chromosome # involving less than duplication of a whole chromosome set (abnormal)

Question 24

Autosomal monosomy

Answer 24

rarely observed in miscarriages or live births or most likely lethal before pregnancy is recognized

Question 25

Autosomal trisomy

Answer 25

50% chromosomal abnormalities in miscarriages, only a few autosomal trisomies result in live births (trisomy 13, trisomy 18, trisomy 21- only one survived until adulthood)

Question 26

Autosomal Aneuploids

Answer 26

cease development before birth; frequency trisomies in newborns are those of chromosomes 21, 18, 13 (carry fewer genes than other autosomes)

Question 27

Nondisjunction

Answer 27

a type of chromosomal error that occurs when chromosomes fail to separate properly during cell division - produces gamete with an extra chromosome and another with one missing chromosome - during meiosis I: copies of both homologs in 1 secondary oocyte/spermatocyte (and none in the other) - during meiosis II: both sister chromatids in one gamete (and none in the other)

Question 28

Monosomy

Answer 28

One chromosome absent; 2n-1

Question 29

Trisomy

Answer 29

one extra chromosome set; 2n-1

Question 30

Deletion

Answer 30

part of a chromosome missing

Question 31

Duplication

Answer 31

part of a chromosome present twice

Question 32

Translocation

Answer 32

two chromosomes join long arms or exchange parts

Question 33

Euploidy

Answer 33

1+ more than one complete set of chromosomes (can be normal or abnormal)

Question 34

Trisomy 21: Down syndrome

Answer 34

most common trisomy in newborns; distinctive facial and physical problems

Question 35

Trisomy 18: edwards syndrome

Answer 35

nondisjunction in meiosis II in oocyte; generally doesn't survive - serious mental and physical disabilities - oddly-clenched fists

Question 36

Trisomy 13: Patau Syndrome

Answer 36

rare & generally does not survive 6 months, intellectual & physical disability, fusion on developing eyes into one large eyelike structure in center of face (or small/absent eye), extra fingers & toes

Question 37

Sex Chromosome Aneuploids

Answer 37

more common than autosomal aneuploidy; at least one copy of an X chromosome is needed for human survival - involves both X and Y chromosomes

Question 38

Turner (XO) Syndrome (45, X)

Answer 38

short stature, webbing @ back of neck, incomplete sexual development (infertile)-individuals who are mosaics may have children, impaired hearing 1 in 2,5000 female births- 99% affected fetuses die in utero

Question 39

Klinefelter (XXY) Syndrome (47,XXY)

Answer 39

incomplete sexual development, rudimentary testes and prostate, long limbs, large hands and feet, some breast tissue development most common genetic or chromosomal cause of male infertility 1 in 500 male births

Question 40

47, XYY syndrome

Answer 40

nondisjunction in male, producing a sperm with 2 Y chromosomes that fertilizes a normal oocyte 96% phenotypically normal- 1 in 1,000 male births, modest features w/ subtle speech & reading disabilities

Question 41

How can a chromosome be structurally atypical?

Answer 41

too much/too little genetic material or stretch of DNA that is inverted or moved and inserted into a different type of chromosome

Question 42

Balanced atypical chromosome

Answer 42

normal amount of genetic material

Question 43

Unbalanced atypical chromosome

Answer 43

extra or missing DNA sequences

Question 44

Deletions and Duplications

Answer 44

remove/double DNA sequences, are types of CNV variants often not inherited (arise de novo- from beginning) more genes = more severe

Question 45

Cri-du-chat (cat cry) syndrome

Answer 45

deletion of 5p-

Question 46

Translocation

Answer 46

reciprocal translocation robertsonian translocation reciprocal- breaks ends and then rearranges

Question 47

Robertsonian Translocation

Answer 47

most common structural chromosome abnormality in human, involves two acrocentric chromosomes (14 & 21), tips are lost monosomy 21 lethal, trisomy 14q lethal, monosomy 14 lethal