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    a variety of a species that exhibits the same trait after several generations of self-fertilization


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    self-fertilization, fusion of male and female gametes (sex cells) produced by the same individual. Self-fertilization occurs in bisexual organisms, including most flowering plants, numerous protozoans, and many invertebrates. Autogamy, the production of gametes by the division of a single parent cell, is frequently found in unicellular organisms such as the protozoan Paramecium. These organisms, however, may also reproduce by means of conjugation, in which cross-fertilization is achieved by the exchange of genetic material across a cytoplasmic bridge between two individuals. Likewise, among higher plants, most of which are monoecious (i.e., bisexual—male and female gametes being produced by the same individual),



    By The Editors of Encyclopaedia Britannica • Edit History

    Related Topics: fertilization cross-pollination outbreeding

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    cross-fertilization, also called Allogamy, the fusion of male and female gametes (sex cells) from different individuals of the same species. Cross-fertilization must occur in dioecious plants (those having male and female organs on separate individuals) and in all animal species in which there are separate male and female individuals. Even among hermaphrodites—i.e., those organisms in which the same individual produces both sperm and eggs—many species possess well-developed mechanisms that ensure cross-fertilization. Moreover, many of the hermaphroditic species that are capable of self-fertilization (q.v.) also have capabilities for cross-fertilization.

    There are a number of ways in which the sex cells of two separate individuals can be brought together. In lower plants, such as mosses and liverworts, motile sperm are released from one individual and swim through a film of moisture to the egg-bearing structure of another individual. In higher plants, cross-fertilization is achieved via cross-pollination, when pollen grains (which give rise to sperm) are transferred from the cones or flowers of one plant to egg-bearing cones or flowers of another. Cross-pollination may occur by wind, as in conifers, or via symbiotic relationships with various animals (e.g., bees and certain birds and bats) that carry pollen from plant to plant while feeding on nectar.

    Methods of cross-fertilization are equally diverse in animals. Among most species that breed in aquatic habitats, the males and females each shed their sex cells into the water and external fertilization takes place. Among terrestrial breeders, however, fertilization is internal, with the sperm being introduced into the body of the female. Internal fertilization also occurs among some fishes and other aquatic breeders.

    By recombining genetic material from two parents, cross-fertilization helps maintain a greater range of variability for natural selection to act upon, thereby increasing a species’s capacity to adapt to environmental change.

    Source : www.britannica.com

    CH. 16 Flashcards

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    CH. 16

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    P generation

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    The true-breeding parents

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    When two individuals of the same species with different characteristics are bred or crossed with each other, this is called:

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    hybridization/ monohybridization

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    1/40 Created by Queen_Angel1

    Terms in this set (40)

    P generation

    The true-breeding parents

    When two individuals of the same species with different characteristics are bred or crossed with each other, this is called:

    hybridization/ monohybridization


    Offspring of crosses between parents with different traits


    Features that appear on an organism.


    A specific characteristic that varies from one individual to another( pretty much the recessive traits)

    Male gametes (sperm cells) are produced within pollen grains, ...

    which are formed in structures called stamens.

    Female gametes (egg cells) are produced in structures called ovules, ....

    which form within an organ called an ovary

    A variety that continues to exhibit the same trait after several generations of self-fertilization is called a:

    true-breeding line Cross fertilization

    The union of a female gamete and a male gamete from different individuals.

    Single-factor cross

    Seeking for only one variant trait from the results of a monohybrid cross

    F1 generation

    The first offspring resulting from a monohybrid cross between the parents

    Why do offspring of the F1 generation exhibit only one variant of each character?

    The gene structure always end up heterozygous, making there be a dominant over a recessive trait.

    Allowing the F1 monohybrids to self-fertilize, producing a generation called the:

    F2 generation

    What are the three important ideas about the properties of traits and their transmission from parents to offspring

    1.Traits exist in two forms: dominant and recessive.

    2.An individual carries two genes for a given character, and genes have variant forms.

    3.The two alleles of a gene separate during the process that gives rise to haploid cells and gametes, so each sperm and egg receives only one allele

    Genes that have variant forms are called:


    Mendel's Law of Segregation:

    The segregation of alleles in the F1 generation gives rise to gametes that carry just one of the two alleles. These gametes combine randomly during fertilization, producing the allele combinations TT, Tt, and tt in the F2 offspring.


    traits passed from one generation to the next

    Who proposed that traits were determined by a discrete unit or particle.

    Gregory Johann Mendel

    There are three possible genotypes, what are those genotypes?

    DD, Dr, rr

    Homozygous recessive Ex:

    rr Heterozygous Ex: Dr

    Homozygous dominant Ex:


    What are the five chromosomal theory of Inheritance?

    1.Chromosomes contain DNA, which is the genetic material.

    2.Chromosomes are replicated and passed from parent to offspring.

    3.The nucleus of a diploid cell contains two sets of chromosomes, which are found in homologous pairs. The maternal and paternal sets of homologous chromosomes are functionally equivalent; each set carries a full complement of genes.

    4.During the formation of haploid cells, the members of different chromosome pairs segregate independently of each other.

    5.Gametes are haploid cells that combine to form a diploid cell during fertilization.


    The actual location of a gene.

    When we say that alleles segregate, what do we mean by allele segragation?

    The two sister chromatid

    After several generations of self fertilization of a true breeding line, all of the offspring would have the same trait of the original parent, True/False

    True: In a true breeding line the offspring have the same traits from generation to generation

    When two true breeding plants that differ in characters cross their mono-hybrids display...

    dominant traits and the recessive traits which are masked.


    A diagram that shows the occurrence of a genetic trait in several generations of a family.

    Recessive X linked alleles affects which gender the most?

    Males more than females

    Genes found on one sex chromosome but not the other are called....

    X-linked Co-dominant:

    the state in which two genetic traits are fully expressed and neither dominates

    What are the functions of these antibodies found in a blood type?

    To spot out other blood types that aren't similar as it's own.

    I'm so darn tired.

    I just wanna go back home, watch my Korean drama, finish my chores and probably lay in bed texting forever!!!

    This is serious


    Two factor cross:

    When an experimenter follows the inheritance of two different characters.

    BIO Character

    A general feature of an organism.

    BIO Trait:

    A specific variant of a feature of an organism.

    Source : quizlet.com

    8.2 Laws of Inheritance – Concepts of Biology – 1st Canadian Edition


    Learning Objectives

    By the end of this section, you will be able to:

    Explain the relationship between genotypes and phenotypes in dominant and recessive gene systems

    Use a Punnett square to calculate the expected proportions of genotypes and phenotypes in a monohybrid cross

    Explain Mendel’s law of segregation and independent assortment in terms of genetics and the events of meiosis

    Explain the purpose and methods of a test cross

    The seven characteristics that Mendel evaluated in his pea plants were each expressed as one of two versions, or traits. Mendel deduced from his results that each individual had two discrete copies of the characteristic that are passed individually to offspring. We now call those two copies genes, which are carried on chromosomes. The reason we have two copies of each gene is that we inherit one from each parent. In fact, it is the chromosomes we inherit and the two copies of each gene are located on paired chromosomes. Recall that in meiosis these chromosomes are separated out into haploid gametes. This separation, or segregation, of the homologous chromosomes means also that only one of the copies of the gene gets moved into a gamete. The offspring are formed when that gamete unites with one from another parent and the two copies of each gene (and chromosome) are restored.

    For cases in which a single gene controls a single characteristic, a diploid organism has two genetic copies that may or may not encode the same version of that characteristic. For example, one individual may carry a gene that determines white flower color and a gene that determines violet flower color. Gene variants that arise by mutation and exist at the same relative locations on homologous chromosomes are called alleles. Mendel examined the inheritance of genes with just two allele forms, but it is common to encounter more than two alleles for any given gene in a natural population.


    Two alleles for a given gene in a diploid organism are expressed and interact to produce physical characteristics. The observable traits expressed by an organism are referred to as its phenotype. An organism’s underlying genetic makeup, consisting of both the physically visible and the non-expressed alleles, is called its genotype. Mendel’s hybridization experiments demonstrate the difference between phenotype and genotype. For example, the phenotypes that Mendel observed in his crosses between pea plants with differing traits are connected to the diploid genotypes of the plants in the P, F1, and F2 generations. We will use a second trait that Mendel investigated, seed color, as an example. Seed color is governed by a single gene with two alleles. The yellow-seed allele is dominant and the green-seed allele is recessive. When true-breeding plants were cross-fertilized, in which one parent had yellow seeds and one had green seeds, all of the F1 hybrid offspring had yellow seeds. That is, the hybrid offspring were phenotypically identical to the true-breeding parent with yellow seeds. However, we know that the allele donated by the parent with green seeds was not simply lost because it reappeared in some of the F2 offspring (Figure 8.5). Therefore, the F1 plants must have been genotypically different from the parent with yellow seeds.

    The P plants that Mendel used in his experiments were each homozygous for the trait he was studying. Diploid organisms that are homozygous for a gene have two identical alleles, one on each of their homologous chromosomes. The genotype is often written as YY or yy, for which each letter represents one of the two alleles in the genotype. The dominant allele is capitalized and the recessive allele is lower case. The letter used for the gene (seed color in this case) is usually related to the dominant trait (yellow allele, in this case, or “Y”). Mendel’s parental pea plants always bred true because both produced gametes carried the same allele. When P plants with contrasting traits were cross-fertilized, all of the offspring were heterozygous for the contrasting trait, meaning their genotype had different alleles for the gene being examined. For example, the F1 yellow plants that received a Y allele from their yellow parent and a y allele from their green parent had the genotype Yy.

    Figure 8.5 Phenotypes are physical expressions of traits that are transmitted by alleles. Capital letters represent dominant alleles and lowercase letters represent recessive alleles. The phenotypic ratios are the ratios of visible characteristics. The genotypic ratios are the ratios of gene combinations in the offspring, and these are not always distinguishable in the phenotypes.


    Our discussion of homozygous and heterozygous organisms brings us to why the F1 heterozygous offspring were identical to one of the parents, rather than expressing both alleles. In all seven pea-plant characteristics, one of the two contrasting alleles was dominant, and the other was recessive. Mendel called the dominant allele the expressed unit factor; the recessive allele was referred to as the latent unit factor. We now know that these so-called unit factors are actually genes on homologous chromosomes. For a gene that is expressed in a dominant and recessive pattern, homozygous dominant and heterozygous organisms will look identical (that is, they will have different genotypes but the same phenotype), and the recessive allele will only be observed in homozygous recessive individuals.

    Source : opentextbc.ca

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