5 Reproduction

Question 1

What are the modes of reproduction?

Answer 1

Asexual reproduction & Sexual reproduction

Question 2

What are the advantages of Asexual reproduction?

Answer 2

Energetically cheaper; good in environments where sexes are not mobile and cannot find a mate, or in environments that are constant

Question 3

What are the three kinds of asexual reproduction in animals?

Answer 3

1) Budding - Smaller offspring grows from larger parent - Bud grows by mitotic cell division 2) Regeneration - replacement of damaged tissues or lost limbs or entire individual - starfish; 3) Parthenogenesis - development of unfertilized egg into new individual - only practiced by females - species often practices sexual reproduction too - fertilized eggs develop into females, unfertilized eggs into males

Question 4

What are advantages of sexual reproduction?

Answer 4

provides genetic diversity - 99.9% of eukaryotes do it

Question 5

What are the three basic features of sexual reproduction?

Answer 5

1) Gametogenesis; spawning of mating; fertilization

Question 6

What is general idea of Gametogenesis?

Answer 6

The making of haploid cells of gametes - involves meiosis and meiotic cell divisions;

Question 7

What specifically happens during Gametogenesis and where does it occur?

Answer 7

1) Produces eggs and sperm - sperm move by beating flagella, eggs non-motile; 2) Occurs in gonads (males testes, females ovaries) 3) Go from diploid (2 set of each chromosome, one from mom, one from dad) to haploid (1 of each chromosome that is a mix of mom/dad

Question 8

What are germ cells?

Answer 8

1) Precursors to gametes 2) Small collection of diploid germ cells in early mammalian embryo that are induced to become primary germ cells from their neighbors - during development germ cells proliferate and migrate to gonads

Question 9

How do germ cells know to develop into sperm or eggs?

Answer 9

Signals comes from gonads - depends on whether gonads have started to develop into testes or ovaries (not based on Y or X chromosome)

Question 10

What is the SRY gene?

Answer 10

The gene responsible for dictating gonad development into testes

Question 11

How do germ cells mature into gametes?

Answer 11

Through Oogenesis (female) and Spermatogenesis (male)

Question 12

What happens during Spermatogenesis?

Answer 12

1) When male reaches puberty germ cells in testes proliferate by mitosis producing diploid spermatogonium 2) Spermatogonia become primary spermatocytes (diploid) and undergo meiosis to form 4 haploid spermatids (cytoplasms connected by cytoplasmic bridges) 3) Will become mature sperm via spermiogenesis

Question 13

Where does spermatogenesis take place?

Answer 13

In seminiferous tubules tightly coiled within each testis

Question 14

How does spermatogonia become mature sperm?

Answer 14

Nucleus compacts, loses cytoplasm, develops flagellum and condenses mitochondria into midpiece between head and tail. Takes ~ 65 days in humans

Question 15

Put these words in order: spermatids, spermatogonium, primary spermatocytes

Answer 15

spermatogonium, primary spermatocytes, spermatids,

Question 16

What happens during Oogenesis?

Answer 16

1) Germs cells take up residence in ovaries and proliferate through mitosis producing Oogonium. 2) Occurs during embryonic development 3) Ooogonium mature into primary Oocytes (diploid) which immediately enters prophase of first meiotic division and arrests at this point until puberty or later. 4) Oocytes will grow larger during this time and acquire raw materials to survive first few cell divisions after fertilization

Question 17

What happens during the Ovarian Cycle?

Answer 17

1) Entry to this cycle triggered by hormonal signals 2) Prophase 1 that was on hold now continues - remainder of Oogenesis continues (maturation of primary Oocyte) 3) Ovulation happens 4) Corpus Leuteums Development

Question 18

What is a follicle?

Answer 18

The thin layer of cells that surround the oocyte

Question 19

How many follicles mature each month between puberty and menopause? What happens to the others? How many are released?

Answer 19

6-12. Other primary oocytes pause at prophase 1. After ~1 week one oocyte will be larger than the others - this oocyte continues to grow, others degenerate.

Question 20

What happens to the primary Oocyte right before ovulation?

Answer 20

Primary Oocyte undergoes meiosis. Just one Oocyte undergoes meiosis per month.

Question 21

What happens during Oogenesis?

Answer 21

1) Chosen Primary Oocyte undergoes meiosis and completes first meiotic division near surface of the cell. 1a) One daughter cell gets almost all of cytoplasm and becomes Secondary Ooocyte 1b) Other daughter cell gets very little cytoplasm and becomes first polar body 2) Secondary Oocyte meiotic division also asymmetrical - larger daughter cell is haploid Ootid which differentiates into mature ovum. 2a) Other daughter cell forms 2nd polar body 2b) 1st polar body also undergoes meiosis II

Question 22

How many cells are formed during Oogenisis and what are they called?

Answer 22

3 polar bodies and 1 ovum (mature haploid egg)

Question 23

When does complete meiotic division occur in Oogenesis?

Answer 23

In most vertebrates (including humans) egg does not complete meiotic division until fertilization occurs. 2) Once expelled from ovary, the ovum is arrested in metaphase of meiosis II

Question 24

What happens during ovulation?

Answer 24

After 2 weeks of follicle growth, follicle ruptures and egg is released - the follicle cells that remain in the ovary continue to proliferate and form a mass of tissue ~size of a marble called the Corpus Luteum

Question 25

What is the Corpus Luteum?

Answer 25

The marble sized mass of follicle tissue that remains in the ovary after the egg is released. Functions are an endocrine gland and produces estrogen and progesterone for 2 weeks then degenerates unless pregnancy occurs

Question 26

What hormones does the Corpus Luteum produce?

Answer 26

Estrogen and progesterone

Question 27

Where does fertilization take place?

Answer 27

In the oviduct (fallopian tube)

Question 28

What happens during implantation?

Answer 28

1) Egg is released into body cavity close to opening of oviduct and is drawn into oviduct 2) Egg is then fertilized in oviduct where first few cell divisions take place 3) egg moves down oviduct to uterus where eggs attaches itself to lining of uterus. Implantation occurs in the Endrometrium of the Uterus

Question 29

Which hormones control the Ovarians and Uterine Cycles?

Answer 29

Gonadotropin Releasing Hormone (GnRH); Follicle Stimulating Hormone (FSH); Leutenizing Hormone (LH), Estrogen

Question 30

How are the ovarian and uterine cycles controlled by hormones leading up to ovulation?

Answer 30

1) When puberty occurs: hypothalamus increases the release of GnRH and the anterior pituitary secretes 2 tropic hormones: FSH and LH 2) FSH and LH trigger small set of primary oocytes to mature in ovaries - follicles of oocytes steadily increase production of estrogen 3) Estrogen is initially a negative feedback on FSH and LH release, but by day 12 estrogen switches to positive feedback 4) Surge of LH (and FH to a lesser extent) occur and triggers ovulation

Question 31

How are the ovarian and uterine cycles controlled by hormones after ovulation?

Answer 31

Spike of LH triggers ovulation and LH, FSH and Estrogen levels are high. After ovulation Corpus Leuteum secretes progesterone (and also some estrogen) which controls growth and maintains endometrium. Corpus Leuteum inhibits GnRH, LH and FSH release and prevents new follicles from beginning to mature. If egg is not fertilized - Corpus Leuteum degenerates and GnRH, FSH and LH all increase - releases hypothalamus and pituitary from negative feedback and cycle begins again.

Question 32

What happens during fertilization?

Answer 32

Union of haploid sperm and haploid egg into a single diploid Zygote through the following steps: 1) sperm & egg recognize each other, 2) sperm is activated, enabling it to gain access to egg’s plasma membrane, 3) plasma membrane of egg fuses with plasma membrane of single sperm, 4) egg blocks entry of all additional sperm, 5) egg is metabolically activated and stimulated to start development, 6) egg and sperm nuclei fuse to create diploid nucleus of zygote

Question 33

How do the egg and sperm recognize each other?

Answer 33

Through specific molecule mediated interactions which direct the sperm towards the egg. This also prevents fertilization of eggs by sperm of other species. Egg releases chemical attractant that increase motility of sperm and cause them to swim towards egg

Question 34

How does the sperm successfully penetrate the protective layers of the egg?

Answer 34

Egg is surrounded by thick jelly coat and protein envelope (Zona Pellucida in humans). Acrosome helps sperm get through these barriers.

Question 35

What is the Arcosome?

Answer 35

The membrane-enclosed cap at the front of the sperm head which contains enzymes for digesting protective layers of eggs as well as actin and other proteins to help spem contact egg plasma membrane

Question 36

What happens during sperm activation via the acrosome?

Answer 36

1) Sperm first penetrates the jelly coat of egg 2) Acrosome binds to specific receptors in Zona Pellucida which triggers the acrosomal reaction 3) acrosomal enzymes are released which digests a hole through the Zona Pellucida and creates a pathway for the sperm to get to the plasma membrane of the ovum

Question 37

What happens when the sperm’s plasma membrane comes in contact with the egg’s plasma membrane?

Answer 37

The eggs and sperm membranes fuse and the sperm nucleus is brought into the egg cytoplasm

Question 38

How does the egg block polyspermy?

Answer 38

Fast Primary block to polyspermy: Influx of Na+ ions changes charge different across membrane (rapid depolarization) and prevents other sperm from binding to plasma membrane. 2)The Cortical Reaction is the secondary block to polyspermy

Question 39

What happens during the Cortical Reaction?

Answer 39

Protein envelope is converted to a physical barrier that sperm cannot penetrate: Sperm entry into egg stimulates local release of Ca++ ions from stores in the ER into the cytoplasm - this increase in cytosollic Ca++ spread through cell in a wave and causes cortical granules that are stored underneath the plasma membrane to fuse with plasma membrane and release contents - this causes the Zona pellucida to harden and degrade sperm binding molecules on surface of envelope - protein envelope rises to form fertilization envelope (not in mammals)

Question 40

How do the sperm and the egg nuclei fuse?

Answer 40

In mammals the nuclear membranes do not fuse directly together - Approach each other but remain distinct until membrane of each nucleus has broken down in preparation for zygote’s first mitotic division