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Gene 340 > Module 1: Chromosomes and Gene Dosage > Flashcards

Module 1: Chromosomes and Gene Dosage Flashcards

1
Q

What is a mutation?

A

Any permanent heritable change in the sequence of genomic DNA.

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2
Q

What is a polymorphism?

A

The occurrence together in a population of two or more alternative genotypes, each at a frequency greater than that which could be maintained by recurrent mutation alone.

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3
Q

What is a variant?

A

An allele that differs from wild-type.

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4
Q

What percent of missense mutations cause diseases?

A

50%

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5
Q

What percent of Nonsense mutations, RNA processing mutations (splice site), and Splice site mutations leading to frameshift missense mutation (stop codon)?

A

10%

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6
Q

What is a missense mutation?

A

A mutation that changes a codon specific for one amino acid to a different amino acid.

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7
Q

What is a nonsense mutation?

A

A mutation that changes an amino acid to a stop codon.

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8
Q

Non-polar means?

A

hydrophobic

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9
Q

Polar means?

A

Hydrophilic

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10
Q

Polar side chains can form hydrogen bonds to what?

A

Water

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11
Q

Non polar side chains are packed into what?

A

Hydrophobic core region

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12
Q

A folded conformation is in what type of environment?

A

Aqueous

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13
Q

What types of mutation is Sickle-Cell Disease?

A

A Missense Mutation. At Amino acid position 6 the Glutamic acid (GAA) is mutated to a Valine (GTA) due to an A->T mutation

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14
Q

What percent of deletion or insertions of number of bases make up disease causing mutations?

A

25%

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15
Q

What percent of larger gene deletions, inversions, fusions, and duplications make up disease causing mutations?

A

5%

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16
Q

Describe what a deletion is.

A

The loss of a sequence of DNA from a chromosome

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17
Q

Describe what a duplication is.

A

The addition of a repeated sequence of DNA from a chromosome.

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18
Q

Describe what an insertion is.

A

A chromosome abnormality in which a DNA segment from one chromosome or an outside source , is inserted into another chromosome.

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19
Q

What is a frameshift mutation?

A

A mutation involving a deletion or insertion that is not an exact multiple of three base pairs and changes the reading frame of the gene downstream of the mutation

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20
Q

What is a promoter?

A

A DNA sequence located in the 5′ end of a gene at which transcription is
initiated.

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21
Q

What is an intron?

A

A segment of a gene that is initially transcribed but then removed from within
the primary RNA transcript by splicing together the sequences (exons) on either side
of it

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22
Q

What is an exon?

A

A transcribed region of a gene that is present in mature messenger RNA.

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23
Q

What is a termination codon?

A

One of the three codons (UAG, UAA, and UGA) that terminate

synthesis of a polypeptide. Also called a stop codon or chain-termination codon.

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24
Q

What is a splice site?

A

A genetic alteration in the DNA sequence that occurs at the boundary of an exon and an intron

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25
Q

What is a Gain of function mutation?

A

A mutation associated with an increase in one or more of the

normal functions of a protein. To be distinguished from novel property mutation.

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26
Q

What is a loss of function mutation?

A

A mutation associated with a reduction or a complete loss of

one or more of the normal functions of a protein.

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27
Q

What is a silent mutation?

A

A change in the sequence of nucleotide bases without a subsequent change in the amino acid or function of the overall protein

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28
Q

What is oogonia?

A

Diploid germ cells in ovaries of female embryos

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29
Q

How do Oogonia divide?

A

Divide by mitosis and enter meiosis 1 to become primary oocytes

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30
Q

Describe the process of Gametogenesis

A

Oogonia divide by mitosis and enter meiosis 1 to become primary oocytes
Primary oocytes arrest in diplotene stage of meiosis 1 until after birth
At puberty, one primary oocyte per month resumes meiosis at ovulation
Completion of meiosis 1 produces a secondary oocyte and first polar body
Secondary oocyte arrests in metaphase of meiosis 1
At fertilization, meiosis 2 is completed and produces a mature ovum and second polar body

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31
Q

What contributes to chromosome segregation errors? (e.g. trisomies)

A

meotic arrest

32
Q

What is Spermatogonia?

A

Diploid germ cells found only in testis

33
Q

Describe gametogenesis for spermatogonia?

A

Spermatogonia divides by mitosis to form primary spermatocytes
After puberty, maturation begins to form sperm
Primary spermatocytes undergo symmetrical division at meiosis 1 to produce two secondary spermatocytes
Secondary spermatocytes undergo symmetrical division at meiosis 2 to produce two spermatids
Spermatids mature to become sperm
Equal numbers of X and Y sperm are produced

34
Q

How many sperm cells are produced in meiosis of each spermatocyte?

A

4 haploid sperm cells

35
Q

How many rounds are there in cell divison?

A

2

36
Q

True or false: Chromosomes duplicate twice and nuclei divide once

A

False: Chromosomes duplicate once and nuclei divide twice

37
Q

Meiosis 1 reduces the chromosomes from what to what?

A

Reduces chromosomes from 2n to n

38
Q

What phase in meiosis 1 does genetic exchange between nonsister chromatids of a homologous pair occur?

A

Prophase 1

39
Q

What does crossing over do?

A

Exchanges genetic information

40
Q

What type of Division is Meiosis 1

A

A reductional division

Ex: a cell had four chromosomes (2 pairs of homologs) Now it has two (one copy of each nonhomolog).

41
Q

Does chromatid separation occur in Meiosis 1 or Meiosis 2?

A

Chromatid separation occurs in meiosis 2 during anaphase 2.

42
Q

What is a centromere?

A

The primary constriction on the chromosome, a region at which the sister
chromatids are held together and at which the kinetochore is formed. Required for
normal segregation in mitosis and meiosis

43
Q

What are kinetechores?

A

A structure at the centromere to which the spindle fibers are attached.

44
Q

What is cohesin?

A

A protein complex that mediates sister chromatid cohesion, homologous recombination & DNA looping (Holds sister chromatids together)

45
Q

What protects centromeric cohesin from degradation?

A

Shugoshin

46
Q

When is cohesin degraded?

A

During Metaphase 2

47
Q

What is nondisjunction?

A

The failure of two members of chromosome pair to separate during meiosis 1 or 2

48
Q

What usually is the cause of inviable gametes or abnormal chromosome numbers?

A

Nondisjunction

49
Q

What are sister chromatids?

A

Identical copies of a replicated chromosome

50
Q

What are homologous chromosomes?

A

Same size, shape, and banding

51
Q

What are autosomes?

A

All chromosomes except for X & Y

52
Q

What are sex chromosomes?

A

they are unpaired, they are the X & Y chromosomes, , they determine the sex of a baby.

53
Q

What is Aneuploidy?

A

The presence of an abnormal number of chromosomes in a cell

54
Q

Which disorders result from aneuploidy that come from maternal chromosomes?

A

Down syndrome (most common)
Trisomy 18
Trisomy 13

55
Q

Which disorders result in aneuploidy from the Paternal chromosome?

A 
Triploidy (double fertilization)
Supermale syndrome (XYY)
56
Q

Which disorders results in aneuploidy from either the mother or father?

A 
Turner Syndrome (More often paternal)
Klinefelter Syndrome (nearly 50-50)(XXY
57
Q

What is triploidy?

A

A cell with three copies of each chromosome (3n), or an individual made up of
such cells.

58
Q

What is a trisomy?

A

The state of having three representatives of a given chromosome instead of the
usual pair, as in trisomy 21 (Down syndrome).

59
Q

What is a karyotype?

A

The chromosome constitution of an individual. The term is also used for a
photomicrograph of the chromosomes of an individual systematically arranged as
well as to describe the process of preparing such a photomicrograph.

60
Q

Explain why it is important for cells to reduce from 2n to n

A

You want to end up with a haploid cell because if they were diploid, they would become not compatible with life

61
Q

What is homolog pairing and Recombination?

A

It is a way to swap genetic information between the mom & dad alleles in order to make new combinations.

62
Q

What acts as scaffolds for many kinetochore proteins?

A

CENP

63
Q

What attaches to microtubules of the mitotic spindle at the kinetochore?

A

Chromosomes

64
Q

What does shugoshin do?

A

Holds chromosomes together

65
Q

During what phase of meiosis 2 is Shugoshin removed and centromeric cohesin is degraded?

A

Metaphase 2

66
Q

What are homologs?

A

They contain same set if genes but can have different alleles for some genes

67
Q

What do nonhomologs say?

A

Carry a completely unrelated set of genes

68
Q

Explain gene dosage.

A

When you have longer chromosomes or receive an additional chromosome you have more genes, Having more genes means there is a higher dosage of proteins which leads to an unbalance dosage of proteins.

69
Q

Why do individuals show symptoms in Turner Syndrome?

A

This is because not all of the genes are inactivated

70
Q

Which sex chromosome is essential for life?

A

The X chromosome

71
Q

Which parent of origin are the Aneuploidies of Down Syndrome (most), Trisomy 18, & Trisomy 13?

A

These come from the Maternal chromosome

72
Q

Which parent of origin are the Aneuploidies of Turner Syndrome, & Klinefelter syndrome?

A

These can come from either the maternal or paternal chromosomes.

73
Q 
Which parent of origin are the Aneuploidies 
of Triploidy (double fertilization), & Supermale syndrome (XYY)?
A

These come from the paternal side

74
Q

What is the risk for recurrence in future pregnancies with sporadic autosomal trisomy?

A

About 1% above the maternal age related risk

75
Q

What is the risk for recurrence in future pregnancies with a Robertsonian translocation?

A

The risk is significantly increased if one of the parents is a balanced carrier

76
Q

What is the risk for recurrence in future pregnancies with sex chromosome-aneuploidIy?

A

There is no increased risk for recurrence.

77
Q

What is mosaicism due to?

A

Nondisjunction occurring during fertilization

Gene 340 (3 decks)

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