Chapter 8 Flashcards
parent–offspring relationship in a/sexual reproduction
- asexual reproduction: produces offspring that are identical to the original cell or organism; involves inheritance of all genes from one parent
- sexual reproduction: produces offspring that are similar to the parents, but show variations in traits; involves inheritance of unique sets of genes from two parents
cell division in prok. & euk. cells
- prok. cells reproduce by binary fission (dividing in half)
* euk. cells reproduce by mitosis and cytokinesis
stages of the cell cycle
the cell cycle consists of two stages: • Interphase: duplication of cell contents G1—growth, increase in cytoplasm S—duplication of chromosomes G2—growth, preparation for division • Mitotic phase: division mitosis—division of the nucleus cytokinesis—division of cytoplasm cell contents
phases of mitosis
- prophase
- prometaphase
- metaphase
- anaphase
- telophase
interphase
- the cytoplasmic contents double
- two centrosomes form
- chromosomes duplicate in the nucleus during the S phase
- nucleoli, sites of ribosome assembly, are visible
prophase
- in the cytoplasm, microtubules emerge from centrosomes, forming the spindle
- in the nucleus, chromosomes coil & become compact & nucleoli disappear.
prometaphase
- spindle microtubules reach chromosomes, where they attach at kinetochore
- centrosomes move to opposite poles
- nuclear envelope disappears.
metaphase
- mitotic spindle is fully formed.
* sister chromatids align at the cell equator.
anaphase
- sister chromatids separate at the centromeres.
- daughter chromosomes are moved to opposite poles
- cell elongate
telophase
- cell continues to elongate
- nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei
- chromatin uncoils & nucleoli reappear
- spindle disappears
cytokinesis in animal vs. plant cells
• animal cells:
cytokinesis occurs as a cleavage furrow forms from a contracting ring of microfilaments
• plant cells:
a cell plate forms in the middle, from vesicles containing cell wall material
cancerous cells
• cancer cells escape controls of cell cycle:
- start out as normal body cells
- undergo genetic mutations
- lose ability to control tempo of their own division and divide rapidly, often in absence of growth factors
- spread to other tissues through circulatory system
- grow w/out being inhibited by other cells
- creating chaos causing disease
functions of mitosis
- cell repair and replacement
- growth
- sperm and egg production
somatic cells
- 23 pairs of homologous chromosomes
* one from each parent
gametes
diploid cells vs. haploid cells
- sperm and egg cells (occurs in meiosis)
- diploid cells: have 2 homologous chromosomes
- haploid cells: have 1 set of chromosomes
meiosis
- a process that converts diploid nuclei to haploid nuclei
* 2 haploid gametes combine in fertilization to restore diploid state in zygote
why sexual reproduction requires meiosis
- offspring would have twice as many chromosomes as parents
* no genetic variation
meiosis I
• prophase I:
- homologous chromosomes come together in pairs
- site of crossing over between homologous (non sister) chromatids
• metaphase I:
- tetrads (pairs of homologous chromosomes) line up at metaphase plate
• anaphase I/telophase I:
- homologous chromosomes separate during ana I
- sister chromatids remain attached
meiosis II
• sister chromatids separate during anaphase II
similarities & differences btwn mitosis and meiosis
• similarities:
- begin with diploid parent cell
- have chromosomes duplicated during the previous interphase
• differences:
- mitosis: produces 2 genetically identical diploid somatic daughter cells
- meiosis: produces 4 genetically unique haploid gametes
genetic variation (produced in sexual reproduction)
- independent orientation at metaphase I
- random fertilization
- crossing over
karyotyping
• an ordered display of magnified images of an individual's chromosomes arranged in pairs • allows for observation of... - homologous chromosome pair - chromosome # - chromosome structure
nondisjunction
• the failure of chromosomes or chromatids to separate normally during meiosis.
• can happen during:
- meiosis I: if both members of a homologous pair go to 1 pole
- meiosis II: if both sister chromatids go to one pole
• fertilization after nondisjunction creates zygotes with altered #s of chromosomes
