This is true of most other organisms as well. Sexual reproduction involves two parents. As you can see from Figure below , in sexual reproduction, parents produce reproductive cells—called gametes —that unite to form an offspring. Gametes are haploid cells. This means they contain only half the number ofchromosomes found in other cells of the organism. Gametes are produced by a type of cell division called meiosis , which is described in detail in a subsequent concept.
The process in which two gametes unite is called fertilization. The fertilized cell that results is referred to as a zygote. A zygote is diploid cell, which means that it has twice the number of chromosomesas a gamete. Cycle of Sexual Reproduction. Sexual reproduction involves the production of haploid gametes by meiosis.
This is followed by fertilization and the formation of a diploid zygote. The number of chromosomes in a gamete is represented by the letter n. Why does the zygote have 2n, or twice as many, chromosomes? Reproduction: Asexual vs. Sexual Cell division is how organisms grow and repair themselves. Asexual Reproduction Asexual reproduction involves a single parent.
Binary fission occurs when a parent cell splits into two identical daughter cells of the same size. Fragmentation occurs when a parent organism breaks into fragments, or pieces, and each fragment develops into a new organism. Starfish, like the one in Figure below , reproduce this way. A new starfish can develop from a single ray, or arm. Starfish, however, are also capable of sexual reproduction. Budding occurs when a parent cell forms a bubble-like bud. The bud stays attached to the parent cell while it grows and develops.
When the bud is fully developed, it breaks away from the parent cell and forms a new organism. Budding in yeast is shown in Figure below. If the organisms of a species all fail to reproduce then the species may become extinct.
Asexual reproduction does not involve sex cells or fertilisation. Only one parent is required, unlike sexual reproduction which needs two parents. Since there is only one parent, there is no fusion of gametes and no mixing of genetic information. As a result, the offspring are genetically identical to the parent and to each other.
They are clones. This means that, in any plant or animal, there are actually two templates for every enzyme. In some cases, the two templates are the same homozygous , but in many cases the two templates are different heterozygous. Here is a well-known example from pea plants that helps understand how pairs of genes can interact.
Peas can be tall or short. One thing to notice in Deppe's quote is that a mutation in a single gene may have no effect on an organism, or its offspring, or its offspring's offspring. For example, imagine an animal that has two identical copies of a gene in one allele. A mutation changes one of the two genes in a harmful way.
Assume that a child receives this mutant gene from the father. The mother contributes a normal gene, so it may have no effect on the child as in the case of the "short" pea gene. The mutant gene might persist through many generations and never be noticed until, at some point, both parents of a child contribute a copy of the mutant gene.
At that point, taking the example from Deppe's quote, you might get a short pea plant because the plant does not form the normal amount of gibberellin. Another thing to notice is that many different forms of a gene can be floating around in a species.
The combination of all of the versions of all of the genes in a species is called the gene pool of the species.
The gene pool increases when a mutation changes a gene and the mutation survives. The gene pool decreases when a gene dies out. One of the simplest examples of evolution can be witnessed in an E. To get a better grip on the process, we'll take a look at what happens in this cell. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar.
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