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Genetics (MDSC 341) > Chromosomes, Mitosis, Meiosis, Sex Chromosomes, and Aneuploidy > Flashcards

Chromosomes, Mitosis, Meiosis, Sex Chromosomes, and Aneuploidy Flashcards

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1
Q

Where are telomeres located on chromosomes?

A

Telomeres are located on the ends of chromosomes to provide protection and prevent chromosome from shortening.

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2
Q

What is the role of the cohesin complex?

A

To hold sister chromatids together in mitosis and meiosis II until segregation

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3
Q

What is the role of the synaptonemal complex?

A

To hold homologs together during meiosis I, allowing for crossing over

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4
Q

What is chromatin?

A

Chromatin is defined as DNA and protein in chromosomes.

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5
Q

What are nucleosomes made up of?

A

Nucleosomes contain 8 histone proteins each.

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6
Q

What is the key function of nucleosomes?

A

Nucleosomes help DNA condense to form a “beads on a string” appearance.

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7
Q

What are sister chromatids?

A

Identical DNA molecules, all alleles are the same.

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8
Q

What are homologous chromosomes?

A

Chromosomes that code for the same genes but may have different alleles for such genes.

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9
Q

What are nonhomologous chromosomes?

A

Chromosomes which code for completely different genes.

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10
Q

What is the name for a chromosome that has its centromere in the middle?

A

A metacentric chromosome.

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11
Q

What is the name for a chromosome that has its centromere offset from the middle?

A

An acrocentric chromosome.

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12
Q

What does it mean if an organism is diploid?

A

It carries two sets of its chromosomes.

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13
Q

What does it mean if an organism is haploid?

A

It carries one set of its chromosomes

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14
Q

What is mitosis?

A

Division resulting in two daughters that have the same number of chromosomes as the mother cell.

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15
Q

What is meiosis?

A

Cell division in gamete forming reproductive cells that result in four cells with half the number of chromosomes

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16
Q

During what phase of the cell cycle does mitosis occur?

A

The M phase.

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17
Q

During what phase of the cell cycle does replication occur?

A

The S phase (synthesis).

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18
Q

What is the order of phases in the cell cycle?

A

G1, S, G2, M.

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19
Q

During what round of replication does reductional division occur in meiosis, when daughter cells receive half the number of chromosomes as the parent cell?

A

Meiosis I.

20
Q

What occurs during Prophase I of meiosis?

A

Chromosomes condense, pair, and cross-over with the help of the synaptonemal complex.

21
Q

What occurs during Metaphase I of meiosis?

A

Tetrads of homologous chromosomes align on the quatorial plane.

22
Q

What occurs during Anaphase I of meiosis?

A

Homologous chromosomes pull apart, eventually resulting in reductional division.

23
Q

What occurs during Telophase I of meiosis?

A

Chromosomes arrive at the pole and the nucleus forms.

24
Q

What occurs during Prophase II of meiosis?

A

Chromosomes condense.

25
Q

What occurs during Metaphase II of meiosis?

A

Chromosomes align on the equatorial plane.

26
Q

What occurs during Anaphase II of meiosis?

A

Sister chromatids are pulled apart.

27
Q

What occurs during Telophase I of meiosis?

A

Nuclei re-form, each chromatid is now considered a chromosome.

28
Q

How does meiosis facilitate Mendel’s 1st Law of Segregation?

A

Separation of homologous chromosomes during Anaphase I ensures that the two alleles of the parent cell are separated and go to different daughter cells.

29
Q

How does meiosis facilitate Mendel’s 2nd Law of Independent Assortment?

A

Crossing over contributes to independent assortment so genes do not remained paired together when they go to daughter cells. The alternate orientations of non-homologous chromosome pairs in metaphase I also results in independent assortment (maternal and paternal copies of chromosome pairs separate without regard to the assortment of other homologous chromosome pairs).

30
Q

Who proposed the chromosome theory of inheritance, that chromosomes carry Mendel’s hereditary units?

A

Walter Sutton

31
Q

What are homogametic organisms?

A

Organisms with a matching pair of sex chromosomes (XX in females, ZZ in males)

32
Q

What are heterogametic organisms?

A

Organisms with a non-matching pair of sex chromosomes (XY in males, ZW in females)

33
Q

What does it mean if an organism is hemizygous for a gene?

A

The organism has only one allele, usually this would occur for x-linked traits in males

34
Q

What are the five common characteristics of X-linked traits?

A
  1. Trait appears in more males than females
  2. Mutation and trait never pass from father to son
  3. Affected male passes X-linked mutation to all daughters
  4. Trait often skips a generation if recessive
  5. Recessive trait only appears in successive generations if sister of an affected male is a carrier.
35
Q

What is non-disjunction?

A

When two homologous chromosomes do not separate correctly in anaphase I of meiosis.

36
Q

What is a monozomy?

A

When an organism receives one less copy of a chromosome than expected.

37
Q

What is a trisomy?

A

When an organism receives one extra copy of a chromosome.

38
Q

What are the three trisomies that are non-lethal in humans?

A

Trisomy 21, 13, and 18.

39
Q

Why are some aneuploidies tolerated while others are nod?

A

Aneuplodies are generally only tolerated in chromosomes that code for a small number of genes.

40
Q

What is an aneuploidy?

A

When an organism receives incomplete sets of chromosomes.

41
Q

What is meiotic non-disjunction?

A

When chromosome separation fails during either meiosis I or meiosis II, leading to gametes that have incomplete sets of chromosomes.

42
Q

What is one of the main causes of meiotic non-disjunction which results in aneuploidy?

A

Failure to synapse and cross-over can result in unpaired homologs in metaphase I that may both segregate to the same pole during anaphase I.

43
Q

What is euploidy?

A

When an organism has complete sets of chromosomes.

44
Q

If a geneticist were to closely examine the make-up of a single autosomal chromosome from one of your cells, that chromosome would be found to be:

A

A mosaic of genes derived from all four of your grandparents

45
Q

Do triploid organisms usually result from the fusion of three gametes simultaneously?

A

No, they usually result from the union of haploid and diploid gametes, especially in fruits such as bananas or watermelons. In humans three gametes sometimes fuse, however these triploids do not survive.

Genetics (MDSC 341) (7 decks)

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