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CELS191 > lecture 15 - meiosis errors > Flashcards

lecture 15 - meiosis errors Flashcards

1
Q

What is the proportion of live births that down syndrome occurs in?

A

1/750

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2
Q

What is aneuploidy?

A

An abnormal number of chromsomes (too many or too few).

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3
Q

Is down syndrome a case of aneuploidy?

A

Yes (extra chromosome)

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4
Q

What chromosome is affected, and how, in down syndrome?

A

Three copies of chromosome 21.

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5
Q

What does the term ‘trisomy 21’ mean?

A

There is an extra chromsome 21 (which causes down syndrome)

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6
Q

What is trisomy?

A

A condition when there is an extra copy of a particular chromosome present in the cell nuclei.

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7
Q

Does the frequency of down syndrome increase or decrease with the age of the mother?

A

Increases - 40% of cases from mothers over 45 years old.

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8
Q

What is trisomy 21 (in down syndrome) caused by?

A

Non-disjunction in either meiosis I or meiosis II.

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9
Q

What is non disjunction of chromosomes?

A

The failure of chromosomes to desperate during meiosis, resulting in daughter cells with either too many or too few chromosomes.

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10
Q

What does non disjunction in meiosis I result in?

A

Failure of specific homologues to seperate at first divisions, so upon second division, 2 gametes have two copies of a certain chromsome (1 maternal, 1 paternal), while the other 2 daughter cells have none of that chromosome.

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11
Q

What does non disjunction in Meiosis II result in?

A

Non disjunction at the second division results in a daughter cell with two identical copies of a chromosome, and a daughter cell with no copies of the particular chromosome. The other two daughter cells will be normal.

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12
Q

In Down Syndrome, is it more likely to have an extra copy of the mother or father’s chromomse 21?

A

Mothers (in 95% of individuals)

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13
Q

What is Klinefelter syndrome?

A

A condition where male (XY) individuals have an extra X sex chromosome.

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14
Q

What causes the extra sex chromosome found in individuals with Klinefelter syndrome?

A

Non disjunction

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15
Q

What condition describes having sex chromosomes XXY?

A

Klinefelter syndrome

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16
Q

Are individuals with Klinefelter syndrome male or female?

A

Male, but they have some feminine features/physique as a result of extra X chromosome.

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17
Q

What are the traits associated with Klinefelter syndrome?

A

Feminine features (breast development, pubic hair pattern, wide hips, etc.), intellectual and IQ impairment

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18
Q

What is Turner syndrome?

A

A condition where females are missing an X sex chromosome (XO).

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19
Q

What are physcial characteristics of individuals with Turner Syndrome?

A

Folds in skin around neck, short stature, intellectual impairment

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20
Q

Are individuals with Turner Syndrome male or female?

A

Female (they only have an X chromosome)

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21
Q

What is polyploidy?

A

The heritable condition of possessing more than two complete sets of chromosomes (at least three times the haploid chromosome number, n)

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22
Q

What causes polyploidy?

A

When cells are not reduced during meiosis, so the resultant gamete has at least 1 extra pair of homologous chromosomes. I.e. zygote has 4n chromosomes rather than 2n.

23
Q

How does polyploidy confer fertility?

A

When plants are hybridised, the first offspring are generally sterile as they do not have the require homologous pairs required for gamete production (as homologues from different species will not line up together). Therefore, if polyploidy occurs and the plant duplicates its chromosomes, each will have a pair and the resultant gametes will be fertile.

24
Q

What are triploids?

A

Individuals with 3 of each chromosome (rather than homologous pairs). Due to the odd number, meiosis cannot produce gametes with all 3 chromosomes, so sexual reproduction leads to offspring with incomplete genetic information.

25
Q

How do triploids generally reproduce?

A

Asexually

26
Q

Why can’t triploids produce sexually?

A

Cannot produce viable gametes - During Meiosis I, the 3 homologues are split into 2 cells with 1 in one and 2 in the other. Meiosis further splits them resulting in two daughter cells with 2 homologous chromosomes and two with 1 chromosome.

27
Q

What are the types of chromosomal aberrations? (4)

A

Deletion, Duplication, Inversion, Translocation

28
Q

What are chromosomal aberrations?

A

Alteration of chromosomes during meiosis, when parts of chromosomes are lost, gained or rearranged between different chromosomes.

29
Q

What is the difference between chromosomal aberrations and crossing over?

A

Chromosomal aberrations are alterations to a single chromosome, or the exchange of parts between non-homologues, while crossing over exchanges genes between homologous pairs.

30
Q

What is chromosomal deletion (aberration)?

A

A segment of DNA is removed/deleted.

31
Q

What is chromosomal duplication (aberration)?

A

The repeating of a segment of DNA in the adjacent section of DNA

32
Q

What is chromosome inversion?

A

The reversal of a segment within a chromsome.

33
Q

What is translocation in a Chromosome?

A

The movement of a segment from one chromsome to a non-homologous chromosome.

34
Q

What is le Jeune syndrome?

A

deletion of the tip of the short arm of chromosome 5. Leads to abnormalities such as a cat like cry.

35
Q

What is the other name for le Jeune syndrome?

A

Cri Du Chat syndrome

36
Q

What is familial down syndrome?

A

Down syndrome passed down to offspring from a phenotypically normal mother with a fused chromosome 14 and 21

37
Q

What is centric fusion of chromosomes?

A

When parts of two different chromosomes are fused together in the centromere - the short arm from one chromosome and long arm of another.

38
Q

Centric fusion is also known as?

A

Robertsonian translocation

39
Q

What is the consequence of centric fusion/Roberstonian translocation on the chromosome number in the gametes after meiosis.

A

Some gametes will not have a complete set of chromomosomes, and some will have an extra arm of one chromosome and half an arm of another chromosome.

40
Q

What is the effect on the zygotes produced from a normal individual and an individual with robertsonian translocation of their 14 and 21 chromosomes.

A

Some will not have enough copies of certain chromosomes (which is lethal), some will have fused 14 or 21 chromosomes like the parent, some will be normal.

41
Q

What are the 4 outcomes of zygotes produced from a phenotypically normal translocation carrier mother with centric fusion of her 21 and 14 chromosomes?

A

Lethal, Down’s syndrome, translocation carrier (same as mother), normal

42
Q

What is X chromosome inactivation?

A

The deactivation of 1 X chromosome out of 2 within a female.

43
Q

What are Barr bodies?

A

A phenomenon observed via microscope, appearing as dark areas in the nucleus that represents an inactive, condensed X chromosome.

44
Q

Do male or females have Barr bodies visible with a microscope?

A

Females - they have an inactive, condensed X chromosome as they initially have 2.

45
Q

How many Barr bodies are visible in male individuals?

A

0

46
Q

How many Barr bodies are visible in female individuals?

A

1

47
Q

How many Barr bodies are visible in individuals with Klinefelter syndrome?

A

1

48
Q

How many Barr bodies are visible in individuals with Turner syndrome?

A

0

49
Q

How many Barr bodies are visible in individuals with XXX chromosomes?

A

2

50
Q

What is mosaic patterning?

A

A phenomenon in females in which different parts of the body, e.g. the skin, exhibit different phenotypes due to the expression of genetically different X chromosomes.

51
Q

What is the developmental cause of mosaic patterning?

A

During development of XX cells, different X chromosomes are activated in different cells. At 100 cells, activation becomes fixed. Subsequent division leads to different cells having genetically different X chromosomes expressed.

52
Q

Why are most traits not mosaic in females, despite different cells expressing different copies of the X chromosome?

A

Because many gene products and proteins move around the body, and many are controlled by autosomes, not sex chromosomes.

53
Q

What sex has the potential for mosaic patterning.

A

Female

CELS191 (35 decks)

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