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    during meiosis, homologous chromosomes frequently exchange portions of their dna. this process increases the number of different genotypes that an offspring can inherit. what is the name of this process?


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    get during meiosis, homologous chromosomes frequently exchange portions of their dna. this process increases the number of different genotypes that an offspring can inherit. what is the name of this process? from EN Bilgi.

    7.6: Genetic Variation

    Genetic variation. It is this variation that is the essence of evolution. Without genetic differences among individuals, "survival of the fittest" would not be likely. Either all survive, …

    7.6: Genetic Variation

    Last updated Sep 4, 2021

    7.5: Sexual Reproduction: Meiosis and gametogenesis

    7.7: Mitosis vs. Meiosis and Disorders

    Suzanne Wakim & Mandeep Grewal

    Butte College

    What helps ensure the survival of a species?

    Genetic variation. It is this variation that is the essence of evolution. Without genetic differences among individuals, "survival of the fittest" would not be likely. Either all survive, or all perish.

    Figure 7.6.1 7.6.1 : Profile photos

    Genetic Variation

    Sexual reproduction results in infinite possibilities of genetic variation. In other words, sexual reproduction results in offspring that are genetically unique. They differ from both parents and also from each other. This occurs for a number of reasons.

    When homologous chromosomes form pairs during prophase I of meiosis I, crossing-over can occur. Crossing-over is the exchange of genetic material between homologous chromosomes. It results in new combinations of genes on each chromosome.

    When cells divide during meiosis, homologous chromosomes are randomly distributed to daughter cells, and different chromosomes segregate independently of each other. This called is called independent assortment. It results in gametes that have unique combinations of chromosomes.

    In sexual reproduction, two gametes unite to produce an offspring. But which two of the millions of possible gametes will it be? This is likely to be a matter of chance. It is obviously another source of genetic variation in offspring. This is known as random fertilization.

    All of these mechanisms working together result in an amazing amount of potential variation. Each human couple, for example, has the potential to produce more than 64 trillion genetically unique children. No wonder we are all different!


    Crossing-over occurs during prophase I, and it is the exchange of genetic material between non-sister chromatids of homologous chromosomes. Recall during prophase I, homologous chromosomes line up in pairs, gene-for-gene down their entire length, forming a configuration with four chromatids, known as a tetrad. At this point, the chromatids are very close to each other and some material from two chromatids switch chromosomes, that is, the material breaks off and reattaches at the same position on the homologous chromosome (Figure

    7.6.2 7.6.2

    ). This exchange of genetic material can happen many times within the same pair of homologous chromosomes, creating unique combinations of genes. This process is also known as recombination.

    Figure 7.6.2 7.6.2

    :​​​​​ ​​Crossing-over. A maternal strand of DNA is shown in red. A paternal strand of DNA is shown in blue. Crossing over produces two chromosomes that have not previously existed. The process of recombination involves the breakage and rejoining of parental chromosomes (M, F). This results in the generation of novel chromosomes (C1, C2) that share DNA from both parents.

    During prophase I, chromosomes condense and become visible inside the nucleus. As the nuclear envelope begins to break down, homologous chromosomes move closer together. The synaptonemal complex, a lattice of proteins between the homologous chromosomes, forms at specific locations, spreading to cover the entire length of the chromosomes. The tight pairing of the homologous chromosomes is called synapsis. In synapsis, the genes on the chromatids of the homologous chromosomes are aligned with each other. The synaptonemal complex also supports the exchange of chromosomal segments between non-sister homologous chromatids in a process called crossing over. The crossover events are the first source of genetic variation produced by meiosis. A single crossover event between homologous non-sister chromatids leads to an exchange of DNA between chromosomes. Following crossover, the synaptonemal complex breaks down and the cohesin connection between homologous pairs is also removed. At the end of prophase I, the pairs are held together only at the chiasmata; they are called tetrads because the four sister chromatids of each pair of homologous chromosomes are now visible.

    Figure 7.6.3 7.6.3

    : Crossover between homologous chromosomes Crossover occurs between non-sister chromatids of homologous chromosomes. The result is an exchange of genetic material between homologous chromosomes. This occurs when homologous chromosomes align. Chromatids from each chromosome can cross over and recombine (swap sections). This results in two recombinant chromosomes and two non-recombinant chromosomes.

    Independent Assortment and Random Fertilization

    During metaphase I, the tetrads move to the metaphase plate with kinetochores facing opposite poles. The homologous pairs orient themselves randomly at the equator. This event is the second mechanism that introduces variation into the gametes or spores. In each cell that undergoes meiosis, the arrangement of the tetrads is different. The number of variations is dependent on the number of chromosomes making up a set. There are two possibilities for orientation at the metaphase plate. The possible number of alignments, therefore, equals 2n, where n is the number of chromosomes per set. Given these two mechanisms, it is highly unlikely that any two haploid cells resulting from meiosis will have the same genetic composition.

    Source : bio.libretexts.org

    Unit 6 Mendelian Genetics and Patterns of Inheritance Flashcards

    Start studying Unit 6 Mendelian Genetics and Patterns of Inheritance. Learn vocabulary, terms, and more with flashcards, games, and other study tools.

    Unit 6 Mendelian Genetics and Patterns of Inheritance

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    Which of the following molecules is the sub unit of DNA that links together to form strands of DNA?

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    A nucleotide

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    What describes an allele whose characteristic phenotype is masked by the presence of a second, different allele?

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    Nelson Science Perspectives 10

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    Terms in this set (41)

    Which of the following molecules is the sub unit of DNA that links together to form strands of DNA?

    A nucleotide

    What describes an allele whose characteristic phenotype is masked by the presence of a second, different allele?


    AB blood type is an example of


    How does this influence the probability of the gamete receiving a dominant allele for pea shape?

    It has no effect on the probability of the gamete receiving a dominant allele for pea shape

    How does DNA help with the transfer of genetic material from parents to offspring?

    Genes in DNA code for the production of proteins, which cause traits to be expressed

    Sarah crosses a homozygous white flower and a homozygous purple flower. The cross results in all purple flowers.

    What is true of the color of pea plants?

    Purple flowers are dominant to white flowers

    What is a gene?

    A set of instructions in the DNA sequence of an organism

    ________ is a source of genetic variation that involves the swapping of sections of chromosomes during meiosis

    Crossing over

    What cellular material is made solely of DNA and proteins?


    One possible form a gene that codes for a particular trait is known as ______

    An allele

    During meiosis, diversity is achieved by the process of...

    I. crossing over

    II. chromosome separation

    III. DNA replication

    I and II only

    Human height is a polygenic trait. This means that the...

    Trait is controlled by more than one pair of genes

    The DNA of a cell is organized into structures called


    Some of the pea plants have purple flowers, whereas others have white flowers. What does this indicate about Rachel's pea plants?

    The pea plants have genetic variation

    During meiosis, the process of crossing over results in new combinations of alleles due to...

    Genetic material is exchanged between chromosomes during this process

    What law does this represent?

    A certain type of flower has two alleles for color (blue, purple), and two alleles for stem height (tall, short). A tall blue flower and a short purple flower are crossed, resulting in tall blue flowers, short blue flowers, tall purple flowers, and short purple flowers.

    Law of Independent Assortment

    Males are more likely to be colorblind than females because

    Males have only one copy of the X chromosome

    Hereditary information is found in ________, which are located in the ________ of the cell

    Genes, chromosomes

    Fifty percent of the offspring produced by a cross between pea plants have seeds with a wrinkled (r) appearance caused by the presence of a homozygous recessive gene. What were the genotypes of the parents?

    Rr x rr

    All cells contain DNA, which provides information for the cells to make

    Different kinds of proteins

    What is the term used to describe the heritable, physical characteristics of a living organism?


    An organisms genotype can best be defined as its

    Inherited combination of alleles

    A(n) ________ is a characteristic arising from genes located on chromosomes that are not gender-determining


    If brown eye color is a dominant trait and blue eye color is a recessive trait, what can be determined about the color of Carla's eyes?

    Carla has brown eyes

    What is a gene with two dominant alleles that are expressed at the same time called?


    Which is the term for one possible form of the gene for a particular trait?


    Since the alleles separate into different gametes, only one allele passes from each parent on to an offspring. This segregation of alleles during meiosis...

    Increases the genetic variability of the offspring

    The fact that each plant gets only one allele from each parent plant is detailed in the Law of _______.


    A student crosses two pea plants. One is homozygous dominant for axial flowers, and the other is heterozygous for axial flowers. If the student examines 200 offspring pea plants, which of the following is a reasonable result?

    200 with axial flowers, 0 with terminal flowers

    Guinea pig coat color is determined by a single gene. The allele for black coat color is dominant to brown. In a cross between two black-haired guinea pigs, 20 offspring are born. If both parents were heterozygous, probability would predict that approximately how many of the 20 offspring would have brown hair?

    Source : quizlet.com

    Genetic Recombination

    Genetic Recombination

    Genetic recombination is an important research direction for allergic reactions today and in the future and it will open up a new way for the development of hypoallergenic peanuts.

    From: Peanuts: Processing Technology and Product Development, 2016

    Related terms:

    MeiosisGenetic DivergenceGenotypeEnzymesChromosomesMutationProteinsDNAAlleles

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    Genetic Recombination

    D. Carroll, in Brenner's Encyclopedia of Genetics (Second Edition), 2013


    Genetic recombination refers to the rearrangement of DNA sequences by the breakage and rejoining of chromosomes or chromosome segments. It also describes the consequences of such rearrangements, that is, the inheritance of novel combinations of alleles in the offspring that carry recombinant chromosomes. Genetic recombination is a programmed feature of meiosis in most sexual organisms, where it ensures the proper segregation of chromosomes. Because the frequency of recombination is approximately proportional to the physical distance between markers, it provides the basis for genetic mapping. Recombination also serves as a mechanism to repair some types of potentially lethal damage to chromosomes.

    Genetic recombination is often used as a general term that includes many types of DNA rearrangements and underlying molecular processes. Meiotic recombination is an example of a reaction that involves DNA sequences that are paired and homologous over very extended lengths. This type of process, which is illustrated in Figure 1, is termed general, legitimate, or homologous recombination. Recombination of this type is reciprocal, because each participating chromosome receives information comparable to what it donates to the other partner. The event shown in Figure 1 is also designated as a crossover, since all the information on both sides of the effective break has been exchanged.

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    Figure 1. Simplified diagram of a meiotic recombination event. Vertical bars indicate individual chromatids (i.e., DNA molecules); ovals are centromeres. We imagine two pairs of sister chromatids after premeiotic DNA synthesis that are distinguished by color and by genetic markers at locations A/a and B/b. If meiosis were to proceed without recombination, the markers would segregate 2:2 in linked pairs in the resulting gametes or spores, as indicated below the left diagram. If one reciprocal recombination event takes place between the two markers, the linkage relationships are changed, yielding two new chromatids as shown and ultimately four distinct haploid products.

    Gene conversion is a form of homologous recombination that is nonreciprocal. This is recognized by the recovery of unequal numbers of the parental markers at a particular locus, and a simple example is shown in Figure 2. Conversion events can be accompanied by a crossover, or not (as shown in Figure 2). In the latter case, conversion looks like a very localized double crossover, but it is nonreciprocal and is likely the result of a single event.

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    Figure 2. Illustration of a gene conversion event. Unlike the reciprocal recombination shown in Figure 1, information has been transferred only from one parent to the other, and the extent of the information exchanged is smaller.

    Homologous recombination can occur between homologous chromosomes or sister chromatids in mitotic cells as well. In addition, essentially analogous events may take place between homologous sequences that are present at different locations on nonhomologous chromosomes; this is often called ‘ectopic recombination’. Recombination that involves very limited or no homology between the interacting DNA sequences is termed illegitimate or nonhomologous recombination. Sometimes, a few matched base pairs (bp) are seen precisely at illegitimate recombination junctions, and these are called microhomologies. An event supported by homologies of 100 bp or more would typically be classified as homologous; a match of 10 bp or fewer would be nonhomologous; and there is evidently a gray area in between.

    In conservative recombination events, the number of copies of the interacting chromosomes or DNA sequences is maintained through the process, while in nonconservative events, two original copies are reduced to one in the product. This distinction can be made for both homologous and nonhomologous recombination.

    Site-specific recombination events are mediated by sequence-specific recombination enzymes often encoded by viruses or transposable elements. The molecular processes they catalyze may rely on very short stretches of homology between the interacting DNAs, or they may be entirely nonhomologous.

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    Double-Strand Break-Induced Recombination in Eukaryotes

    Fekret Osman, Suresh subramani, in Progress in Nucleic Acid Research and Molecular Biology, 1997

    Genetic recombination is of fundamental importance for a wide variety of biological processes in eukaryotic cells. One of the major questions in recombination relates to the mechanism by which the exchange of genetic information is initiated. In recent years, DNA double strand breaks (DSBs) have emerged as an important lesion that can initiate and stimulate meiotic and mitotic homologous recombination. In this review, we examine the models by which DBSs induce recombination, describe the types of recombination events that DBSs stimulate, and compare the genetic control of DBS-induced mitotic recombination in budding and fission yeasts. © 1998 Academic Press

    Source : www.sciencedirect.com

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