Chapter 11 and 51

Question 1

sexual life cycle

Answer 1

• made up of meiosis and fertilization
• diploid cells
• somatic cells of adults have 2 sets of chromosomes
• haploid cells
• gametes have only 1 set of chromosomes

Question 2

features of meiosis

Answer 2

meiosis includes 2 rounds of division
1. meiosis I and meiosis II
2. each has prophase, metaphase, anaphase, and telophase

Question 3

synapsis

Answer 3

• during early prophase I
• homologous chromosomes become closely associated
• includes formation of synaptonemal complexes

Question 4

crossing over

Answer 4

• genetic recombination between nonsister chromatids
• Chiasmata: site of crossing over
• contact maintained until anaphase I
• humans typically have 2 or 3 crossing over per chromosome

Question 5

unique features of meiosis

Answer 5

• 1st meiotic divsion is termed the “reduction division”
• NO DNA replication between meiotic divisions
• 2nd meiotic division does not further reduce the number of chromosomes

Question 6

the process of meiosis

Answer 6

• meiotic cells have an interphase period that is similar to mitosis with G₁, S, and G₂ phases
• after interphase, germ-line cells enter meiosis I

Question 7

meiosis prophase I

Answer 7

• chromosomes coil tighter and become visible, nuclear envelope breaks down, spindle forms
• each chromosome composed of 2 sister chromatids
• Synapsis:
• homologues become closely associated
• crossing over occurs between nonsister chromatids
• remain attached at chiasmata (chiasmata move to the end of the chromosome arm before metaphase I)

Question 8

meiosis metaphase I

Answer 8

• terminal chiasmata hold homologues together after crossing over
• microtubules attach to each homologue
• homologues are aligned at the metaphase plate side-by-side
• orientation of each pair of homologues on the spindle is random-independent assortment

Question 9

meiosis anaphase I

Answer 9

• microtubules of the spindle shorten (chiasmata break)
• homologues are separated from each other and move to opposite poles
• each pole has a complete haploid set of chromosomes consisting of one memeber of each homologous pair

Question 10

meiosis telophase I

Answer 10

• nuclear envelope re-forms around daugther nucleus
• sister chromatids are no longer identical because crossing over (prophase I)
• cytokinesis may/may not occur after telophase I

Question 11

meiosis II

Answer 11

**Resembles a mitotic division
**
* Prophase II: nuclear envelopes dissolve and new spindle apparatus forms
* Metaphase II: chromosomes align on metaphase plate
* Anaphase II: sister chromatids are separated from each other
* Telophase II: nuclear envelope re-forms around 4 sets of daughter chromosomes; cytokinesis follows

Question 12

final results of meiosis

Answer 12

• 4 cells containing haploid sets of chromosomes
• in animals, develop directly inot gametes
• in plants, fungi, and protists, divide mitotically
  (produce greater # of gametes, adults with varying # of gametes)

Question 13

errors in meiosis

Answer 13

nondisjunction: failure of chromosomes to move to opposite poles during either meiotic division
aneuploid gametes: gametes with missing/extra chromosomes
(^^ the most common cause of spontaneous abortion) (75% of embryos have abnormal # of chromosomes = miscarriage)

Question 14

meiosis vs mitosis

Answer 14

meiosis is characterized by 4 features:
1. synapis and crossing over
2. sister chromatids remain joined at their centromeres throughtout meiosis I
3. kinetochores of sister chromatids attach to the same pole in meiosis I
4. DNA replication is suppressed between meiosis I and II

Question 15

asexual reproduction

Answer 15

• genetically identical cells are produced from a single parent cell through mitosis
• single-celled organisms utilize fission
• cnidarians reproduce by budding

Question 16

parthenogenesis

Answer 16

• females produce offspring from unfertilized eggs
• common in arthropods
• known in lizards

Question 17

Hermaphroditism

Answer 17

• one individual has both testes and ovaries
• may be sequential: change sex
• protogyny: female to male change
• protandry: make to female change

Question 18

amphibian reproduction

Answer 18

• in most species fertilization is external
• eggs of most species to develop in water

Question 19

Internal fertilization has led to three strategies for development

Answer 19

1. Oviparity
Fertilized eggs are deposited outside mother’s body to complete their development
2. Ovoviviparity
Fertilized eggs are kept within mother to complete development, young obtain food from egg yolk
3. Viviparity
Young develop within mother and obtain nourishment from her blood

Question 20

bird reproduction

Answer 20

(oviparity)
- Internal fertilization but males lack a penis
- Amniotic egg
Extraembryonic membranes
Adaptation for life on land
**- All birds practice internal fertilization
**
- Hard calcareous shell on egg
- Birds are endotherms
- Must incubate eggs to keep them warm

Question 21

reproduction in mammals

Answer 21

monotremes
* lay eggs and incubate eggs in nest
* lack nipples, milk seeps for skin when licked
marsupials
* give birth to incomplete developed fetuses, which mature in the mothers pouch
placentals
* retain young in uterus for long period of development
* nourished by placenta from mother’s blood

Question 22

male reproductive system

Answer 22

• seminiferous tubules: sites of sperm production
• Leydig cells produce testosterone
  converts indifferent external genitalia into penis & scrotum
  begins being secreted 9-10 weeks after conception
  Gamete production
  
  • spermatogonium (germ cells) divides by mitosis to produce two diploid cells
  • total of 4 haploid spermatids produced

Question 23

female reproduction system

Answer 23

at puberty, granulosa cells secrete estrogen
- triggers menarche, 1st menstrual cycle
- stimulates secondary sexual characteristics

at birth, ovaries contain 1 millon follicles
during each menstrual cycle, a group of follicles are used to reinitiate developement