A1: during sexual reproduction, both parents pass their chromosomes to offspring. if only mitosis occures, there will be double chromosomes of parents' chromosomes which cannot exist.
Q2: what is the different between meiosis and mitosis?
A2: 1. meiosis has two divisions;mitosis has only one division.
2. during mitosis, DNA replication occure in interphrase; in meiosis before meiosis I
3. meiosis has crossing over during prophrase I
4. mitosis has two daughter cells, each diploid; meiosis has four haploid
5. mitosis raise from zygote; meiosis raise from gametes
Q3: what is the main stage of meiosis?
A3: Meiosis I: prophase I, Metaphase I, Anaphase I, Telophase I and cytokinesis
Meiosis II: prophase II, Metaphase II, Anaphase II, Telophase II and cytokinesis
Five Facts:
1. offspring acquire genes from parents by inheriting chromosomes
2. fertilization and meiosis alternate in sexual life cycles
3. meiosis reduces the number of chromosome sets from diploid to haploid
4. genetic variation produced in sexual life cycles contributes to evolution
5. genetics is the study of heredity and hereditary variation
Figure:
the number of chromosomes in a single set is haploid, two sets is diploid. meiosis reduces the number of chromosomes sets from diploid to haploid.
Summary:
The transmission of traits from one generation to the next is called inheritance, or heredity. Coded information in the form of hereditary called genes. Gametes are the vehicles that transmit genes from one generation to the next. DNA packaged into chromosomes which include several hundred genes. A gene's specific location along the length of a chromosome is called the gene's locus. In asexual reproduction, a single individual divide itself by mitosis or clone. Both parent and offspring have same genes. However, in sexual reproduction, two parents give conbinations of genes to offsprings by meiosis and mitosis. A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism, from conception to production of its own offsprong. Somatic cell is any cell except gamete has 46 chromosomes. Homologous chromosomes, or homologs are two chromosomes in a pair have same length, centromere position, and staining pattern. X and Y are sex chromosomes. Female has XX; Male has XY. others are autosomes. 46 chromosomes are two sets of 23 chromosomes-a maternal set and a paternal set. Chromosomes in single set called haploid cell; two sets called diploid cell(2n). Fertilized egg, or zygote, is diploid. The germ cells first do meiosis and half the number of chromosomes.After fertilization, diploid zygote do mitosis.
Meiosis has two divisions: meiosis I and meiosis II. Result in four daughter cells. DNA replication occure in interphase. During prohase I, homologous chromosome pair held together by chiasma and sister chromatid cohesion. Chromosomes line up at metaphase plate. Homologs separate during anaphase I; sister chromatids remain attached at centromere. Sister chromatids separate during anaphase II. Synapsis is the proces that pair up the homologos. Genetic rearrangement between nonsister chromatids known as crossing over. X-shaped region called a chiasma. Independent Assort,emt of chromosomes, crossing over, and random fertilization make variation and evolution.
Key Terms:
- alternation of generations-A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae.
- gametophyte-In organisms (plants and some algae) that have alternation of generations, the multicellular haploid form that produces haploid gametes by mitosis. The haploid gametes unite and develop into sporophytes.
- karyotype-A display of the chromosome pairs of a cell arranged by size and shape.
- recombinant chromosome-A chromosome created when crossing over combines the DNA from two parents into a single chromosome.
- spore-(1) In the life cycle of a plant or alga undergoing alternation of generations, a haploid cell produced in the sporophyte by meiosis. A spore can divide by mitosis to develop into a multicellular haploid individual, the gametophyte, without fusing with another cell. (2) In fungi, a haploid cell, produced either sexually or asexually, that produces a mycelium after germination.
- sporophyte-In organisms (plants and some algae) that have alternation of generations, the multicellular diploid form that results from the union of gametes. The sporophyte produces haploid spores by meiosis that develop into gametophytes.
- autosome- A chromosome that is not directly involved in determining sex; not a sex chromosome.
- haploid cell- A cell containing only one set of chromosomes (n).
- somatic cell-Any cell in a multicellular organism except a sperm or egg.
- synapsis-The pairing and physical connection of replicated homologous chromosomes during prophase I of meiosis.
Video:
No comments:
Post a Comment