chromatin eventually thickens into distinct rods. These form when cell prepares to divide during anaphase of mitosis, made of protein, DNA, and some rRNA- chromatids are called chromosmes after they seperatte in anaphase.
unit of inherited information in DNA, a sequenceof nitrogenous bases containing information to produce a secific RNA molecule- which codes for a specitic protein.
before mitosis can occur the mother cell must double (replicate) her DNA. This so each daughter cell will have the same amount of DNA as the parent cell. After DNA riplication, the chromantin thickens to form paired chromatids joined together by thier shared centromere. The centromere holds the two chromatids together until they are pulled apart in anaphase to become chromosomes.
organisms of different species have a characteristic number of chromsomes in each somatic cell (body cell). Humans have 46 chromosomes or 23 pairs.
a pair of chromosomes governing the same trait. The gene for eye color, for example, is found on the same chromosomee both parents.The gene is therefore homologous.
(n) gametes (sperm or egg) 1/2 the chromosomes number. When two haploid cell join (sperm + egg)- fertilization, diploid number is restored (2n).
formerly called resting stage: lasts several hours to years ( not actually a phase of mitosis.
nucleous disappears, nuclear membrane disappears, centrioleles move toward opposite poles and microtules (spindle fibers) form near the centrioles.
when the nuclear membrane disappears, the chromatids have free access to the cytoplasm and attach to the spindle fibers by their centromere.
chromatids pairs move to center of the cell, the equator
each chromatid pair is attached by its centromere to spindle fibers.
centromeres split in half
spindle fibers pull the chromatids apart to opposite poles-
chromatids are now called chromosomes
each chromatid pair becomes 2 identical chromosomes
cytoplam divison begins (cytokinesis)
opposite of prophase
spindle fiber disappear
chromosomes return to chromatin stage
nuclear membrane reforms around each set of chromosomes
nucleolus reappears in each nucleus.
continued pinching of cell membrane results in 2 duaghter cells. Cells return to interphase and the cycle begins again.
ensures that each daughter cell receives exactly the same number and kind of chromosomes the parent has (somatic cell)
reduces the number of chromosomes so that each daughter cell has one half the number of the parent (in sex cell only)
occurs in somatic cells
only one nuclear and cell division ( cytokinesis)
2 daugter cells has the diploid (sn) number of chromosomes
in male- testes(gonads)-sperm(gamete)
sperm smaller than eggs
sperm mobile (can swim)
sperm are formed in a coiled mass of seminferous tubles that make up the testis.
1.acrosome- produces enzmes that help to penetrate the egg
2. nucleu- contains the genes from the male
3. tail- used when swimming toward the egg. Tails falls off when sperm penetrates the egg.
fetal life oogonia are formed by mitosis.
each surrounded by follicle
third month fetal deevelopment, oogonia develop in oocytes
cells in prophase for 13 years or so (puberty)
an egg that ovulated at age 47 has been in prophase for 47 years.
describes a solution whose solute concentration is higher than the solute concentration inside a cell
first meiotic division
The division that separates the tetrads so that each daughter cell gets two copies of one of the two homologous chromosomes.
second meiotic division
new cells will have a haploid number of chromosomes; in females, only one of the daughter cells becomes a functional gamete; not preceded by chromosomal replication; chromosomes align, separate, and move to opposite poles, and are surrounded by a reformed nuclear membrane
exchange of genetic material between homologous chromosomes during prophase I of meiosis