Chromosomes and meiosis vocabulary somatic cell gamete homologous chromosome autosome sex chromosome sexual reproduction fertilization diploid haploid meiosis key concept gametes have half the number of chromosomes that body cells have. Describe how alleles from different genes can be inherited together. Each gamete, or sex cell, contains half the number of chromosomes. Meiosis ii is the second major subdivision of meiosis. In order to do this and maintain the proper number of chromosomes, the cells of. Learn vocabulary, terms, and more with flashcards, games, and other study tools. D if sperm, which is a product of meiosis, contains 5 chromosomes, the normal animal cell contains 10 chromosomes. This arrangement allows very long dna molecules to be compacted into a small volume that can more easily be moved during mitosis and meiosis fig 2. Meiosis thus consists of a single phase of dna replication followed by two cell divisions. The main difference is that meiosis involves two successive nuclear divisions that produces four haploid cells. Understand and explain that every organism requires a set of instructions that specifies its traits, that this hereditary information dna contains genes located in the chromosomes of each cell, and that heredity is the passage of these instructions from one generation to another. Notice that the set of chromosomes in the gametes is not a random collection.
Life sciences grade 12 page 4 question 4 the drawing below shows the chromosomes from a cell during meiosis. Mitosis the division of chromosomes is followed by cytokinesis the division of cytoplasm, producing two cells with equal chromosome content. In female meiosis, the two x chromosomes pair and recombine over the entire length of the chromosomes. The microtubules are like a flys tongue, and the kinetochore proteins are like the sticky stuff on the flys tongue that allows it to catch the flycentromere. Chromosomes, mitosis, and meiosis biology libretexts. Meiosis ii separates those doublestranded chromosomes by splitting them at the centromeres. In humans, a womanhastwoxchromosomes,andamanhasan x and a y chromosome.
Homologous pairs matching chromosomes that each came from either the father or the mother. Mitosis, mitotic chromosomes consist of two sister chromatids. Meiosis molecular biology of the cell ncbi bookshelf. Access the answers to hundreds of meiosis questions that are explained in a way thats easy for you to understand. Think think meiosis is the process in which one cell divides into four daughter cells that have half the number of chromosomes as the parent cell. Homologous chromosomes overlap and exchange pieces of the chromosome which caused genetic variability. Think think meiosis is the process in which one cell divides into four daughter cells that have half the number of chromosomes. As a result of meiosis, the chromosome number is halved in the gametes, each of which contains two chromosomes, as shown in the second row in figure 3. Asexual reproduction in eukaryotes uses mitosis, sexual reproduction requires meiosis at some point in life cycle. Name the stage of meiosis 1 where each of the following occurs. Stages of meiosis meiosis i this is a reductive division in which one diploid 2n cell produces two haploid 1n cells.
Vocabulary somatic cell autosome fertilization gamete sex chromosome diploid homologous chromosome sexual reproduction haploid meiosis main idea. Meiosis is necessary in many sexuallyreproducing animals to ensure the same number of chromosomes in the offspring as in the parents. The duplicated chromosomes align on a second spindle, and the sister chromatids separate to produce cells with a haploid dna content. In other words, there are 23 2 46 chromosomes in all body cells. Chromosomes are long, threadlike structures that form part of the chromatin network in the nuclei of cells. Meiosis i separates replicated homologous chromosomes, each still made up of two sister chromatids, into two daughter cells, thus reducing the chromosome number by half.
Meiosis contributes to genetic variation since recombination and crossing over occur as a result of the random separation of homologous chromosomes and the transfer of genes among them. This type of event has occurred in many groups of plants, but it is very rare in animals. Meiosis in order for organisms to continue growing andor replace cells that are dead or beyond repair, cells must replicate, or make identical copies of themselves. Meiosis is a round of two cell divisions that results in four haploid daughter cells that each contain half the number of chromosomes as the parent cell. Chapter 5 the cell cycle, mitosis, and meiosis worksheets. Genes are sections of double stranded deoxyribonucleic acid dna that form discrete units of hereditary information, which means they influence. Compare and contrast mitosis and meiosis pg 275278 think. This means that there are 20 sister chromatids at g2. Halves the chromosome number special type of cell division used only for sexual reproduction halves the chromosome number prior to fertilization parents diploid meiosis produces haploid gametes gametes fuse in fertilization to form diploid zygote becomes the next diploid generation.
Chromosomes replicated during the s phase are divided in such a way as to ensure that each daughter cell receives a copy of every chromosome. Chromosomes and meiosis study guide key concept gametes have half the number of chromosomes that body cells have. Two sister chromatids of one replicated chromosome meiosis. In meiosis, however, the chromosome number in sex cells eggs and sperm. In meiosis, the diploid cell eventually forms four germ cells that have half the chromosomes. If the number of alleles of each gene is not reduced to 1 in the gametes that produce the zygote, there will be 4 copies of each gene in the offspring. Yeast have 16 pairs of chromosomes, or 32 chromosomes per cell.
Meiosis is a specialised type of cell division, the principal function of which is to produce sporesgametes sperm and eggs in mammals that have the haploid number of chromosomes. The y chromosome is very small and carries few genes. Gametes have half the number of chromosomes that body cells have. Meiosis ii segregates the sister chromatids into separate cells. Meiosis germ cells in your reproductive organs undergo the process of meiosis to form gametes. Meiosis is a specialized type of cell division sharing many features with mitosis. Sister chromatids on the other hand are duplicate halves of a chromosome. Function a occurring in somatic cells, the main goal of mitosis is. Meiosis starts with diploid cells cells that have two sets of chromosomes from their parents. Vocabulary homologous chromosomes the same numbered chromosome that pair up from mother and father ex. A kinetic learning approach to mitosis and meiosis brian kreiser,1 rosalina hairston2 1departm ent of b iol og cal sci nces, x 5018, u nv rsity of souther m s ssippi, hattiesburg, ms 39406 email. Chromosomes and meiosis key concept gametes have half the number of chromosomes that body cells have.
During meiosis ii, sister chromatids decouple and the resultant daughter chromosomes are segregated into four daughter cells. With the aid of a simple diagram show how independent assortment leads to genetic. Four haploid cells are therefore produced from each cell that enters meiosis. The process of meiosis i is generally longer than meiosis ii because it takes. Meiosis 1 is a reduction division two cells are formed, each with half the number of chromosomes of the parent cell haploid meiosis 2 is a copying division, involving the two haploid cells formed during meiosis 1.
Lesson summary chromosome number homologous chromosomes are pairs of chromosomes that correspond in body cells. They absorb dye very easily, allowing them to be seen under a microscope, and were discovered in 1888. Haploid cells only have one set of chromosome from their parents. The act of fertilization includes two cells fusing together to become a new zygote. The nuclei of eukaryotic cells contain chromosomes along which genes are arranged. Both mitosis and meiosis are vital for living organisms in terms of growth in size, cell repairment, and production of offsprings, but they differ in some points such as ploidy and division formation. In mitosis, its important that the daughter cells each end up with a full set of chromosomes the diploid number 2n so that they can divide normally and do their jobs like any other body cell they may become. The reduction of chromosome number in meiosis is determined by. All books are in clear copy here, and all files are secure so dont worry about it. Fruit flies have 4 pairs of chromosomes, or 8 chromosomes per cell. What happens to homologous chromosomes and sister chromatids during meiosis l.
In humans, this represents a reduction from 46 23 pairs to 23 chromosomes one complete set in sperm and eggs. Meiosis reduces the original number of chromosomes within a cell by onehalf. They are made up of a strand of dna wound around histones proteins. During this process alleles are swapped and independent assortment shuffles chromosome combinations. Using the nomenclature presented in class, an ovum cell of wheat has n21 chromosomes. Crossing over in which pairs of homologous chromosomes synapse together to form tetrads and exchange genetic information dna. Similar to prophase of mitosis with one important difference.
In meiosis ii, a cell contains a single set of chromosomes. Each species has a characteristic number of chromosomes per cell. Meiosis myohsihs is a form of nuclear division that divides a diploid cell into haploid cells. Since the number of chromosomes in the parent and progeny cells is the same, it is also called as equational division. Meiosis is a form of nuclear division that reduces chromosome number from diploid to haploid. Summarize are homologous chromosomes identical to each other. Haploid one copy of each chromosome designated as n, the number of chromosomes in one set gametes diploid two sets of chromosomes. It reduces the chromosome number in a germ cell by half by first separating the homologous chromosomes in meiosis i and then the sister chromatids in meiosis ii. Pdf meiosis produces haploid cells to maintain the diploid genome after fusion of gametes and is essential for eukaryotic sexual reproduction. Somatic cells ploidy, are diploid 2n, contain two copies of each chromosome type, these two copies are homologous chromosomes, for every chromosome.
These kinetochore proteins also allow attachment of microtubules that pull the chromosomes around the cell during either mitosis or meiosis. Each chromosome, however, still has its duplicated sister chromatid attached. Therefore, each sperm cell and ovum contains only 23 chromosomes rather than 46 the number. Kinetochore attachment to the spindle and chromosome cohesion in mitosis and meiosis. We now know that most chromosomes contain a single molecule of doublestranded dna that form a complex with proteins. Fertilization then causes further random recombination of the genes depending on which sperm fertilized which egg.