Chapter 13-Meiosis
Terms
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- allele
- homologs appear alike in the microscope but they may have variations in genes called these
- anaphase II
- 1) breakdown of proteins holding sister chromatids together 2) chromatids move to opposite poles as individual chromosomes
- sister chromatids
- two copies of a replicated chromosome held together at the centromere that are seen in prophase, prometaphase, and metaphase of mitosis and meiosis, produced when DNA is synthesized
- n
- the number of chromosomes in a single set is denoted by this letter
- meiosis I
- occurs in 4 phases: prophase I, metaphase I, anaphase I, telophase I, and cytokinesis
- synapsis
- homologous chromosomes loosely pair up and connect along their lengths,aligned gene by gene
- random fertilization
- adds to genetic variability; chromosome combination between gametes
- asexual reproduction
- one parent produces genetically identical offspring by mitosis in which DNA is copied and allocated equally to two daughter cells
- gametes
- reproductive cells (sperm and eggs) that pass genes to the next generation; develop from specialized cells called germ cells; the only type of human cells produced be meiosis
- X
- the sex chromosome that an unfertilized egg cell contains
- tetraploid cell
- 4n, when a pair of homologous chromosomes (4 sister chromatids) join together
- heredity
- transmission of traits from one generation to the next
- reductional division
- meiosis I is called this because it halves the number of chromosome sets per cell (from diploid to haploid)
- chromosome
- in eukaryotic cells, the structure that contains the DNA, is associated with proteins, and carries genetic information; in prokaryotic cells, contains several 100s to 1000s of genes; its the single DNA strand
- prophase II
- 1) spindle apparatus 2) chromosomes still composed of sister chromatids
- cohesions
- protein complex that attaches sister chromatids together
- homologous chromosomes
- two chromosomes in each pair are called this (also called homologs); they are the same length, have the same centromere position, same staining pattern, and carry genes controlling the same inherited characters; each pair has one chromosome from each parent
- 23
- the number of chromosomes inherited from each parent
- 3 unique events of meiosis I
- synapsis/crossing over (with chiasmata), homologous pair one metaphase plate (instead of indiviudal chromosomes), separation of homologs (sister chromatids do not separate in meiosis I)
- kinetochore
- protein structures at the centromeres of the two homologs
- sexual reproduction
- two parents give rise to offspring that have unique combinations of genes inherited from the two parents
- epigentics
- changes in gene function that can be inherited without changing DNA sequence
- karotype
- an ordered display of the pairs of chromosomes from a cell; the chromosomes are analyzed during mitosis as they are condensed enough to be seen in a visible light microscope; the chromosomes are arranged from longest to shortest in length
- crossing over
- nonsister chromatids exchange DNA segments
- centrosome
- organelle that organizes microtubule cytoskeleton
- anaphase I
- 1) breakdown of proteins responsible for sister chromatid cohesion allows homologs to separate 2) homologs move to separate poles 3) sister chromatid cohesion persists at centromere causing chromatids to move towards same pole
- autosomes
- 22 pairs of chromosomes that do not determine sex
- life cycle
- generation to generation sequence of stages in the reproductive history of an organism, from conception to production of its own offspring
- haploid cell
- has a single set of chromosomes; abbr. n; in humans, the number is 23 (n=23); the state of human gametes; each set consists of 22 autosomes and 1 sex chromosome
- 46
- the number of chromosome in a human cell
- telophase II
- 1) nuclei form 2) chromosomes decondense 3) meiotic division produces 4 daughter cells (each with haploid set of unreplicated chromosomes)
- X or Y
- the possible sex chromosome(s) that a sperm cell can contain
- gene
- basic unit of inheritance that are genetic links to parents; program specific traits through protein synthesis; made up of segments of DNA (nucleotides)
- metaphase II
- 1) chromosomes positioned on metaphase plate 2) due to crossing over in meiosis I, two sister chromatids are not identical 3) kinetochores of sister chromatids attach to microtubules
- 4
- number of daughter cells that results at the end of meiosis II that have half as many chromosomes that the parent cell did
- chiasmata
- each chromosome pair forms a tetrad (group of 4 chromatids) in which the tetrad has one or more of these (x-shaped regions where crossing over occurred); even though the synaptonemal complex disassembles (two homologs pull apart slightly), this causes the homologs to remain connectred
- somatic cell
- any cell other than a gamete; has 23 pairs (or 46 total) chromosomes (in a human);
- meiosis
- modified type of cell division that results in one set of chromosomes in each gamete (which is a haploid state); produces cells that undergo no further cell division before fertilization; only diploid cells undergo this
- 92
- number of molecules of DNA (number of chromosomes=number strands of DNA) present in a human somatic cell prior to mitosis
- sex chromosomes
- called X and Y; exception to the general pattern of homologous chromosomes; females (XX) and males (XY); only a small part of these chromosomes are homologous; the X has many genes that do not appear on the tiny Y and the Y has genes lacking on the X
- locus
- specific location of a gene on a certain chromosome
- recombinant chromosomes
- individual chromosomes that carry genes derived from two different parents; a result of crossing over
- clone
- an individual that is genetically identical to its parent; produced by asexual reproduction
- telophase I
- 1) each half of the cell has a complete haploid set of replicated chromosomes 2) cytokinesis occurs 3) cleavage furrow (animals) or cell plate (plants) forms 4) some species, chromosomes decondense and nuclear envelope reforms 5) no replication occurs between meiosis I and II
- meiosis II
- very similar to mitosis; also occurs in 4 phases
- fertilization
- fusion of sperm and egg
- metaphase I
- 1) pair of homologs arrange at the metaphase plate 2) both chromatids of a homolog are attached to kinetochore microtubes
- equational division
- meiosis II is called this because it only involves the division of sister chromatids (haploid) into daughter cells (haploid)
- zygote
- the fertilized egg which is a result of fusion of gametes that has one set of chromosomes from each parent; produces somatic cells by mitosis and develops into an adult; is in a diploid state
- 22
- number of pairs of autosomes in a human cell
- diploid cell
- has two sets of chromosomes; abbr. 2n; in humans, the number is 46 (2n=46); the state of human somatic cells
- prophase I
- 1) chromosomes condense 2) crossing over is completed when homologs are in synapsis 3) homologous pair has one or more chiasmata points where crossing over has occured 4) centrosome movement, spindle formation, and breakdown of nuclear envelope 5) microtubules move to poles attaching to the two kinectochores of two homologs; occupies more than 90% of meiosis
- independent assortment
- Mendel's second law of inheritance; segregation of alleles at one gene occurs independently of the segregation of another
- sister chromatid cohesion
- the close association of these along their lengths is called this
- cytokinesis
- occurs simultaneously with telophase, forming two haploid daugther cells with replicated material