Cell Division

Question 1

What is Down syndrome?

Answer 1

The first human genetic disorder attributable not to a gene mutation but to an abnormal number of chromosomes, resulting from a failure of chromosome segregation during meiosis.

Question 2

What is the chromosome count in Down syndrome?

Answer 2

Individuals with Down syndrome have 47 chromosomes, with three copies of chromosome 21.

Question 3

What is Trisomy 21?

Answer 3

An aberrant genotype that gives rise to an abnormal phenotype, including morphological differences of the head and tongue, learning disabilities, and health issues.

Question 4

From where does the extra chromosome 21 typically come in Down syndrome cases?

Answer 4

In 80% of cases, the third chromosome 21 comes from the egg; in 20%, from the sperm.

Question 5

What are chromosomes?

Answer 5

Long, brightly staining, threadlike bodies within the nucleus that carry genes.

Question 6

What is mitosis?

Answer 6

A kind of nuclear division followed by cell division that results in two daughter cells containing the same number and type of chromosomes as the original parent cell.

Question 7

What is meiosis?

Answer 7

A kind of nuclear division that generates egg or sperm cells containing half the number of chromosomes found in other cells within the same organism.

Question 8

What is fertilization?

Answer 8

The union of haploid gametes to produce diploid zygotes.

Question 9

What is a diploid?

Answer 9

Zygotes and other cells carrying two matching sets of chromosomes.

Question 10

What is a karyotype?

Answer 10

An arrangement of stained chromosomes in homologous pairs of decreasing size, used by geneticists to study the chromosomes of a single organism.

Question 11

What is chromatin?

Answer 11

Composed mainly of DNA and protein, it carries genetic information and serves as a scaffold for packaging and managing that information.

Question 12

What occurs during interphase?

Answer 12

Cells grow and replicate their chromosomes.

Question 13

What are the three parts of interphase?

Answer 13

G1 (gap 1), S (synthesis), and G2 (gap 2).

Question 14

What happens during prophase of mitosis?

Answer 14

Chromosomes condense, centrosomes move apart, and nucleoli begin to disappear.

Question 15

What is the metaphase plate?

Answer 15

An imaginary equator halfway between the two poles where the chromosomes align during metaphase.

Question 16

What happens during anaphase?

Answer 16

Sister chromatids move to opposite spindle poles as centromeric connections break.

Question 17

What is cytokinesis?

Answer 17

The division of the cytoplasm, resulting in two smaller independent daughter cells with identical nuclei.

Question 18

What are regulatory checkpoints in the cell cycle?

Answer 18

Moments at which the cell evaluates the results of previous steps, ensuring proper chromosome separation.

Question 19

What are somatic cells?

Answer 19

Cells that divide via mitosis or enter G0 and make up the majority of an organism’s tissues.

Question 20

What are germ cells?

Answer 20

Cells set aside for producing gametes in reproductive organs.

Question 21

What is the significance of meiosis?

Answer 21

It produces gametes containing half the number of chromosomes other body cells have.

Question 22

What is reductional division?

Answer 22

The term used for meiosis I, where the chromosome number is reduced by half.

Question 23

What occurs during prophase I of meiosis?

Answer 23

Homologs condense and pair, and crossing-over occurs.

Question 24

What is crossing-over?

Answer 24

The exchange of parts between nonsister chromatids during prophase I.

Question 25

What is independent assortment?

Answer 25

The process where each bivalent aligns independently of the others, leading to a random mix of maternal and paternal chromosomes.

Question 26

What can errors in recombination cause during meiosis?

Answer 26

Nondisjunction, where homologs fail to separate properly.

Question 27

What occurs during Telophase I?

Answer 27

Nuclear envelopes re-form, homologous chromosomes reach opposite poles, and reductional division occurs.

Question 28

What is reductional division?

Answer 28

Meiosis I is called a reductional division because the chromosome number is reduced by half.

Question 29

What follows Telophase I?

Answer 29

Cytokinesis, which usually forms two daughter cells.

Question 30

What is Interkinesis?

Answer 30

A relatively brief interphase between meiosis I and II where chromosomes do not replicate.

Question 31

What happens during Meiosis II?

Answer 31

Sister chromatids separate to produce haploid gametes.

Question 32

How many haploid gametes are produced from Meiosis I?

Answer 32

Four haploid gametes are produced after the second division.

Question 33

What occurs during Prophase II?

Answer 33

Chromosomes condense, nuclear envelope breakdown occurs, and the spindle apparatus re-forms.

Question 34

What happens during Metaphase II?

Answer 34

Chromosomes align at the metaphase plate, and sister chromatids attach to microtubules.

Question 35

What is the difference between Metaphase II and mitotic metaphase?

Answer 35

In Metaphase II, the chromosome number is half compared to mitotic metaphase, and genetic variation is present due to crossing-over.

Question 36

What occurs during Anaphase II?

Answer 36

Sister centromeres split, allowing sister chromatids to migrate to opposite poles.

Question 37

What happens during Telophase II?

Answer 37

Nuclear membranes re-form, cytokinesis follows, and four distinct haploid cells are formed.

Question 38

What is equational division?

Answer 38

Meiosis II is an equational division because the chromosome number remains constant from start to finish.

Question 39

What are segregational errors?

Answer 39

Mistakes in chromosome segregation that cause abnormalities in offspring.

Question 40

What is nondisjunction?

Answer 40

A failure of homologous chromosomes or sister chromatids to separate, leading to aneuploidy.

Question 41

What is aneuploidy?

Answer 41

A condition in which an individual has extra or missing chromosomes. ## Footnote Example: Down syndrome (trisomy 21) results from an extra copy of chromosome 21.

Question 42

How does meiosis contribute to genetic diversity?

Answer 42

Through independent assortment and crossing-over.

Question 43

What is independent assortment?

Answer 43

Random alignment of homologous chromosomes during metaphase I, producing unique gametes.

Question 44

What is crossing-over?

Answer 44

Exchange of genetic material between nonsister chromatids in prophase I, creating recombinant chromosomes.

Question 45

How does sexual reproduction enhance genetic diversity?

Answer 45

Through random fertilization, where each sperm and egg is genetically unique.

Question 46

What is the main difference between mitosis and meiosis?

Answer 46

Mitosis occurs in all eukaryotic cells for growth, while meiosis occurs only in sexually reproducing organisms to produce haploid gametes.

Question 47

What is the role of mitosis in organisms?

Answer 47

It promotes growth and the continual replacement of cells.