[Chapter 9] Reproduction

Question 1

What do the offspring of asexual reproduction receive?

Answer 1

All offspring inherit the same number and kinds of genes of its parents.

Question 2

What are Genes?

Answer 2

Sequences of DNA that encode heritable information about traits.

Question 3

What is a Clone?

Answer 3

A genetically identical copy of the parent, barring mutations all offspring of asexual reproduction are clones.

Question 4

What is an Allele?

Answer 4

Each unique molecular form of the same gene.

Question 5

What are Gametes?

Answer 5

The mature reproductive cells formed by the meiosis of germ cells.

Question 6

What is a Zygote?

Answer 6

The first cell of a new individual.

Question 7

What does it mean if a cell has a diploid number?

Answer 7

It means that it has a pair of each type of chromosome.

Question 8

What are Homologous Chromosomes?

Answer 8

A pair of chromosomes that have the same length, shape, and assortment of genes. They appear zipped together during meiosis.

Question 9

True or False: In Meiosis, the cells go through two cell cycles.

Answer 9

True, though it only goes through interphase.

Question 10

What happens in Prophase 1?

Answer 10

Chromosomes were duplicated earlier, in interphase. Now they start to condense. Each pairs with its homologue and swapssegments with it. New microtubules are forming a bipolar spindle. One of the two centrosomes moves to the opposite side of the nuclear envelope, which begins to break up.

Question 11

What happens in Metaphase 1?

Answer 11

Prior to metaphase I, one set of microtubules had tethered one chromosome of each type to one spindle pole and another set tethered its homologue to the other spindle pole. A tug-of war between the two sets has now aligned the chromosomes midway between the two spindle poles.

Question 12

What happens in Anaphase 1?

Answer 12

One of each duplicated chromosome, maternal or paternal, moves to a spindle pole; its homologue moves to the opposite pole. Motor proteins that interact with microtubules bring about the movement.

Question 13

What happens in Telophase 1?

Answer 13

One of each type of chromosome has arrived at a spindle pole. In most species, the cytoplasm divides at this time. All of the chromosomes are still duplicated.

Question 14

What happens in Prophase 2?

Answer 14

In each cell, one of two centrioles moves to the opposite side of the cell, and a new bipolar spindle forms. Some spindle microtubules harness one chromatid of each chromosome to a spindle pole; other microtubules harness its sister chromatid to the other pole.

Question 15

What happens in Metaphase 2?

Answer 15

By now, microtubules from both spindle poles have finished a tug-of-war. They have aligned all of the still-duplicated chromosomes midwaybetween the poles.

Question 16

What happens in Anaphase 2?

Answer 16

The sister chromatids of each chromosome move apart and are now individual, unduplicated chromosomes. Microtubules pull them toward opposite spindle poles as other microtubules push the poles apart. A parcel of one of each type of chromosome will end up near each pole.

Question 17

What happens in Telophase 2?

Answer 17

A new nuclear envelope encloses each parcel of chromosomes, so there are now four nuclei. The cytoplasm divides. Each of the daughter cells now has a haploid number (n) of unduplicated chromosomes.

Question 18

What does ‘Crossing Over’ mean?

Answer 18

A process by which a chromosome and its homologous partner exchange corresponding segments.

Question 19

True or False: Crossing over between a pair of homologous chromosomesputs novel combinations of alleles in both, which results innovel variations in forms of traits among offspring.

Answer 19

True. Gene swapping would be pointless if each type of gene never varied.

Question 20

How many possibilities of combinations are there between human sperm and eggs for maternal and paternal chromosomes?

Answer 20

8,388,608 (2^23) combinations.

Question 21

What is a Sporophyte?

Answer 21

A diploid multicelled body found in most plant life cycles. Spores form in part of it.

Question 22

What is Gametophyte?

Answer 22

A multicelled haploid body inside which one or more gametes form.

Question 23

True or False: In animals, haploid germ cells give rise to gametes.

Answer 23

False, in animals diploid cells give rise to gametes.

Question 24

What is Fertilization (in relation to sexual reproduction)?

Answer 24

The fusion of the haploid nuclei of two gametes.

Question 25

Why does meiosis precede fertilization?

Answer 25

Because if it did not then the chromosome number would double every generation, which would change the individual’s hereditary information.

Question 26

Sexual or Asexual Reproduction: Meiosis, gamete formation, and fertilization.

Answer 26

Sexual reproduction.

Question 27

Why do meiosis and fertilization shuffle parental alleles?

Answer 27

So offspring inherit new combinations of alleles.

Question 28

Does meiosis half the parental chromosome number?

Answer 28

Yes, then the fusion of two gamete nuclei during fertilization restore the parental chromosome number in the zygote.

Question 29

What three events give rise to novel combinations of alleles?

Answer 29

1. Crossing over to prophase 12. The random alignment of maternal and paternal chromosomes at metaphase 13. The chance meeting of gametes at fertilization