Biology: Reproduction Flashcards
(33 cards)
Karokinesis
Nuclear division.
Centromere
Central region that holds together sister chromatids.
Chromatin
Uncoiled DNA during interphase.
Prophase
The chromosomes condense, and the centriole pairs (in animals) separate and move toward the opposite poles of the cell. The spindle apparatus forms between them, and the nuclear membrane dissolves, allowing the spindle fibers to interact with the chromosomes.
Metaphase
The centriole pairs are now at opposite poles of the cell. The fibers of the spindle apparatus attach to each chromatid at the centromere to align the chromosomes at the equator of the cell, forming the metaphase plate.
Anaphase
The centromeres split so that each chromatid has its own distinct centromere, thus allowing sister chromatids to separate. The sister chromatids are pulled toward the opposite poles of the cells by the shortening of the spindle fibers. Spindle fibers are composed of microtubules.
Telophase
The spindle apparatus disappears. A nuclear membrane forms around each set of newly formed chromosomes. Thus, each nucleus contains the same number of chromosomes (the diploid number 2N) as the original or parent nucleus. The chromosomes uncoil, resuming their interphase form.
Cytokinesis
Near the end of telophase, the cytoplasm divides into two daughter cells, each with a complete nucleus and its own set of organelles. In animal cells, a cleveage furrow forms, and the cell membrane indents along the equator of the cell and finally pinches through the cell, separating the two nuclei.
Prophase I
The chromatin condenses into chromosomes, the spindle apparatus forms, and the nucleoli and nuclear membrane disappear. Homologous chromosomes (chromosomes that code for the same traits, one inherited from each parent) come together and intertwine in a process called synapsis. Since each chromosome has 2 sister chromatids, each synaptic pair of homologous chromosomes contains four chromatids and is therefore often called a tetrad. Sometimes chromatids of homologous chromosomes break at corresponding points and exchange equivalent pieces of DNA; this process is called crossing over. Note that crossing over occurs between homologous chromosomes and not sister chomatids of same chromosomes. The chromatids involved are left with an altered but complete set of genes. Recombination among chromosomes results in diversity.
Metaphase I
Homologous pairs (tetrads) align at the equatorial plane, and each pair attaches to a separate spindle fiber by its kinectochore.
Anaphase I
The homologous pairs separate and are pulled to opposite poles of the cell. This process is called disjunction, and it accounts for a fundamental Mendelian law. During disjunction, each chromosome of paternal origin separates from its homologue of maternal origin, and either chromosome can end up in either daughter cell. Thus, the distribution of homologous chromosomes to the 2 intermediate daughter cells is random with respect to parental origin. Each daughter cell gets a unique pool of genes.
Telophase I
A nuclear membrane forms around each new nucleus. At this point, each chromosome still consists of sister chromatids joined at the centromere.
Second Meiotic Division
Very similar to mitosis, except Meiosis II not preceded by chromosomal replication. The new cells have the haploid number of chromosomes.
Gonads
Organs that produce gametes. Male ones called testes, which produce sperm in tightly coined seminiferous tubules. Female ones called ovaries produce oocytes (eggs).
Internal Fertilization
Practiced by terrestrial vertebrates and provides a direct route for sperm to each the egg cell. This increases the chance for fertilization success, and females produce fewer eggs. The number of eggs produced is affected by other factors as well. If the early development of the offspring is outside the mother’s body, more eggs will be laid to increase chances of offspring survival. The amount of parental care after is also related to the amount of eggs produced. Species that care for their young produce fewer eggs.
Male Reproductive Physiology
The testes are in an external pouch called the scrotum that maintains the testes’ temperature at 2-4 degrees Celsius lower than the body temperature, a condition essential for sperm survival. Sperm pass from the testes through the vas deferens to the ejaculatory duct and then to the urethra. The urethra passes through the penis and opens to the outside at its tip. In males, urethra’s a common passageway for both reproductive and excretory systems.
Spermatogenesis
Sperm production. Occurs in the seminiferous tubules.
Diploid cells called spermatogonia differentiate into diploid cells called primary spermatocytes, which undergo the first meiotic division to yield 2 haploid secondary spermatocytes of equal size; the 2nd meiotic division yields 4 haploid spermatids of equal size. After meiosis, the spermatids undergo a series of changes leading to the production of mature sperm, or spermatozoa, which are specialized for transporting the sperm nucleus to the egg, or ovum.
After a male has reached sexual maturity, approximately 3 million primary spermatocytes begin spermatogeneis a day, maturation process taking 65-75 days.
Female Reproductive Anatomy
Ovaries found in abdominal cavity, below digestive system. They consist of thousands of follicles, which is a multilayed sac of cells that has, nourishes, and protects an immature ovum. The follicle cells produce estrogen.
Once a month, an immature ovum is released from ovary into the abdominal cavity drawn into the nearby oviduct, also known as the fallopian tube. Each tube opens into the upper end of a muscular chamber called the uterus, which is the site of fetal development. The lower, narrow end of the uterus is called the cervix. It connects with the vaginal canal, the site of sperm deposition during intercourse and also the path through which a baby is expelled during child birth.
At birth, all the eggs that a female will ovulate during her lifetime are already present in the ovaries.
Oogenesis
Production of female gametes in the ovarian follicles. At birth, all of the immature ova (primary oocytes) that a female makes during her lifetime are already in her ovaries. Primary oocytes are diploid cells that form by mitosis in ovary. After menarche (the first time a female gets her period), one primary oocyte per month completes meiosis I, yielding 2 daughter cells of unequal size–a secondary oocyte and a small cell known as a polar body. The secondary oocyte is expelled from follicle during ovulation. Meiosis II doesn’t occur until fertilization.
The oocyte cell membrane is surrounded by 2 layers of cells; the inner layer is the zona pellucida, and the outer layer is the corona radiata. Meiosis II occurs when these layers are penetrated by sperm, yielding 2 haploid cells–a mature ovum and another polar body. (1st polar body may also undergo Meiosis II, but eventually both polar bodies will die). The mature ovum is a large cell with alot of cytoplasm, RNA, organelles, and nutrients needed by a developing embryo.
Estrogens
Steroid hormones necessary for normal female maturation. They stimulate the development of the female reproductive tract and contribute to the development of secondary sexual characteristics and sex drive. They’re also responsible for the thickening of the endometrium (uterine wall). Estrogens are secreted by the ovarian follicles and the corpus luteum.
Progesterone
A steroid hormone secreted by the corpus luteum during the luteal phase of the menstrual cycle. It stimulates development and maintenance of the endometrial walls in preparation for implantation.
The Menstrual Cycle
The hormonal secretions of the ovaries, hypothalmus, and anterior pituitary play important roles in female reproductive cycle. From puberty through menopause, interactions between these hormones result in the monthly menstrual cycle. It can be divided into the follicular phase, ovulation, the luteal phase, and menstruation.
Follicular Phase
Beings with the cessation of the menstrual flow from the previous cycle. During the phase, FSH (follicle stimulating hormone) from the anterior pituitary promotes the development of the follicle, which grows and begins secreting estrogen.
Ovulation
Midway through the cycle, ovulation occurs. A mature ovarian follicle bursts and releases an ovum. Ovulation is caused by a surge in LH (Lutenizing hormone) that’s preceded, and in part caused, by a peak in estrogen levels.
