Mendelian Ratios and Lethal Genes. Environmental Influences on Gene Expression. Epistasis: Gene Interaction and Phenotype Effects. Genetic Dominance: Genotype-Phenotype Relationships. Phenotype Variability: Penetrance and Expressivity. Citation: Miko, I. Nature Education 1 1 Although mitosis and meiosis both involve cell division, they transmit genetic material in very different ways.
What happens when either of these processes goes awry? Aa Aa Aa. Gene Transmission in Mitosis. Figure 1. Gene Transmission in Meiosis. Figure 2: Examples of polytene chromosomes. Pairing of homologous chromatids results in hundreds to thousands of individual chromatid copies aligned tightly in parallel to produce giant, "polytene" chromosomes.
High-pressure treatment of polytene chromosomes improves structural resolution. Nature Methods 4, All rights reserved. Aberrations That Alter Chromosome Number. Figure 3: Nondisjunction results in daughter cells with unusual chromosome numbers. Nondisjunction, in which chromosomes fail to separate equally, can occur in meiosis I first row , meiosis II second row , and mitosis third row. These unequal separations can produce daughter cells with unexpected chromosome numbers, called aneuploids.
When a haploid gamete does not receive a chromosome during meiosis as a result of nondisjunction, it combines with another gamete to form a monosomic zygote. When a gamete receives a complete homologous chromosome pair as a result of nondisjunction, it combines with another gamete to form a trisomic zygote.
Genetics: A Conceptual Approach , 2nd ed. Figure 4: Jimsonweed seed pod shapes. Trisomy in any of Jimsonweed's 12 chromosomes will cause seed pods to deviate from a wild-type, spherical shape.
References and Recommended Reading Belling, J. Genetics: A Conceptual Approach W. Freeman, New York, Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable.
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How do cells divide? From Genetics Home Reference. Mitosis and meiosis, the two types of cell division. Cells divide and reproduce in two ways, mitosis and meiosis.
Mitosis results in two identical daughter cells, whereas meiosis results in four sex cells. Below we highlight the keys differences and similarities between the two types of cell division. If you have any other comments or suggestions, please let us know at comment yourgenome.
Can you spare minutes to tell us what you think of this website? Open survey. In: Facts In the Cell. During mitosis one cell divides once to form two identical cells. The major purpose of mitosis is for growth and to replace worn out cells. If not corrected in time, mistakes made during mitosis can result in changes in the DNA that can potentially lead to genetic disorders.
Mitosis is divided into five phases: 1. Interphase: The DNA in the cell is copied in preparation for cell division, this results in two identical full sets of chromosomes. Outside of the nucleus are two centrosomes, each containing a pair of centrioles, these structures are critical for the process of cell division.
During interphase, microtubules extend from these centrosomes. Successful cell division depends on three stages: the replication of the DNA and cell organelles in interphase, the division of the nucleus in mitosis and the subsequent division of the cytoplasm and formation of new surface cell membranes and, in plant cells, cellulose cell walls which is described in detail on the next page.
The growth of insect larvae demonstrates the effect of rapid mitosis. Mitosis in plants takes place in the apical meristems Photo credit: Clematis. In cells that are not actively dividing it is not easy to identify the chromosomes that carry the genetic information.
The DNA is a mass of loosely coiled threads. At this stage the DNA can be replicated. Once a cell starts to divide, the DNA becomes packaged more tightly so the chromosomes become shorter and denser.
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