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Flashcards in Chromosome Number Prestudy Deck (41)
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1
Q

What is a nondisjunction?

A

error in cell division whereby improper segregation leads to abnormal chromosome number (monosomy or trisomy).

2
Q

When can nondisjunction occur?

A

in any cell division during Meiosis I, Meiosis II, or mitosis

3
Q

What will nondisjunction during mitosis cause?

A

mosaicism: mixture of normal cells with mutated cells with chromosomal abnormalities

4
Q

What is the main risk factor for meiosis I nondisjunction?

A

age

5
Q

What is euploidy?

A

normal chromosome number (haploids = 23, diploids = 46)

6
Q

What is aneuploidy?

A

any abnormality of chromosome number that is not a multiple of 23.
Example: monosomy (n=45)
trisomy: n = 47

7
Q

What is polypoidy?

A

abnormalities in number of chromosomes with multiples of 23.

Ex: tripoidy n = 69, tetraploidy n=92

8
Q

When is triploidly most common?

A

at fertilization if two sperm fertilize one egg

9
Q

What is the most common mechanism of tetraploidy?

A

after DNA duplicates, but cells fail to divide

10
Q

What is ISCN? Give an example of normal genotype?

A

international system for human cytogenetic nomenclature.

Normal: 46,XX or 46, XY

11
Q

How will a monosomy affect an autosome? Trisomies?

A

all monosomies are lethal in autosomes. Most trisomies are lethal. (potential for live birth- 13, 18, 21)

12
Q

What happens with aneuploidy in sex chromosomes?

A

tolerate aneuploidy better than autosomes do, but at least one X is required for survival

13
Q

Which is usually the least severe disjunction?

A

mosaicism, because the phenotype is less severe due to normal cell lines mixed with abnormal instead of all cells being abnormal

14
Q

How common is aneuploidy in female eggs? Sperm?

A

about 20% in eggs

about 1-2% in sperm

15
Q

What is most likely outcome of aneuploidy in a pregnancy?

A

failure of the pregnancy

16
Q

How common are spontaneous abortions/miscarriages?

A

15% of recognized pregnancies end in miscarriage

17
Q

How often do fertilized eggs fail to come to term?

A

about 50% of fertilized eggs will fail

18
Q

What is the most common cause of miscarriage?

A

chromosome imbalance

19
Q

What is the most common chromosomal abnormality involved in miscarriage? What is the most common class of chromosomal abnormality?

A

45, X is single most common at 20% (turner’s syndrome)

trisomies together make up most common class. (nearly 55%)

20
Q

What are the viable trisomies?

A

21, 18, 13

21
Q

What are the common clinical findings for trisomy 21?

A

down syndrome usually has mental retardation, flat facial profile, prominent epicanthal folds, simian crease, duodenal atresia (intestinal obsturction) and congential heart defects

22
Q

What is the most common cause of trisomy 21?

A

nondisjunction during maternal meiosis I.

Usually only 2-4% mosaic and 5% translocation

23
Q

What is Edwards syndrome?

A

Trisomy 18. Severe mental retardation, prenatal growth deficiency, heart defects, rocker bottom feet, clenched hands, usually die before age 1.
Usually from maternal nondisjunction

24
Q

What is the ISCN nomeclature for trisomy 18 in a female?

A

47,XX,+18

25
Q

What is Patau Syndrome?

A

Trisomy 13. Abnormal midface, eye and forebrain. Polydactyly and midline defects. rapidly fatal

26
Q

What is the Positive Exposure project?

A

project that tries to promote genetic diversity as a good thing, not something to hide away. Photographs children with abnormalities and tries to make them feel good about themselves

27
Q

What will happen to an individual with no X chromosomes?

A

they will die it is lethal. Usually sex chromosome abnormalities are not as serious.

28
Q

What is turner syndrome?

A

Only have single X chromosome. short stature, ovariag dysgenesis, congenital heart defect, lymphatic problems. normal intelligence.

29
Q

What is the karyotype for Turner Syndrome?

A

45,X.

30
Q

What is the only monosomy associated with human live birth?

A

45,X turner syndrome

31
Q

What is the most common cause of turner syndrome?

A
PATERNAL nondisjunction (50% of the time it is meiotic nondisjunct and 80% of that is paternal)
Mosaicism is also pretty common (40%)
32
Q

Will advanced maternal age significantly increase risk for Turner Syndrome?

A

no, turner syndrome is mostly paternal

33
Q

Is turner syndrome often fatal for fetuses?

A

Yes. over 99% of fetuses die before birth. After birth they have high chance of living.

34
Q

What is Klinefelter Syndrome?

A

47, XXY

35
Q

What is the most common cause of Klinefelter syndrome?

A

half of the time it is paternal nondisjunct

half of the time it is maternal and has a maternal age risk effect

36
Q

Does Klinefelter syndrome produce mental retardation?

A

no, but it does typically drop IQ by about 10-15 points

37
Q

When is Klinefelter usually diagnosed?

A

when puberty doesnt occur normally or the man is infertile later in life

38
Q

What is triple X syndrome?

A

47, XXX. Essentially normal phenotype, mild learning problems

39
Q

What usually causes triple X syndrome?

A

maternal nondisjunction.

40
Q

What is 47,XYY syndrome and what are its phenotypes?

A

essentially normal phenotype, but tall and has educational and behavioral problems

41
Q

What is the most common cause of 47,XYY syndrome?

A

always from paternal meiosis II nondisjunction