Genetics is the scientific study of genes and heredity—of how certain qualities or traits are passed from parents to offspring as a result of changes in DNA sequence. The traits of organisms are controlled by genes on chromosomes. A gene is the part of a chromosome that contains the genetic code for a particular protein. The position of a gene on a chromosome is called its locus. Each gene may have different versions, called alleles. In sexually reproducing species, chromosomes are present in cells in pairs. Chromosomes in the same pair are called homologous chromosomes. They have the... Show more Genetics is the scientific study of genes and heredity—of how certain qualities or traits are passed from parents to offspring as a result of changes in DNA sequence. The traits of organisms are controlled by genes on chromosomes. A gene is the part of a chromosome that contains the genetic code for a particular protein. The position of a gene on a chromosome is called its locus. Each gene may have different versions, called alleles. In sexually reproducing species, chromosomes are present in cells in pairs. Chromosomes in the same pair are called homologous chromosomes. They have the same genes at the same loci. The genes may be present as the same or different alleles. During meiosis, when gametes are produced, homologous chromosomes separate and go to different gametes. Thus, the two alleles for each gene also go to different gametes. When gametes unite during fertilization, the resulting zygote inherits two alleles for each gene. One allele comes from each parent. The two alleles that an individual inherits make up the individual's genotype. The two alleles may be the same or different. An individual with two alleles of the same type is called a homozygote. An individual with two alleles of different types is called a heterozygote. The expression of an individual's genotype is called its phenotype. The phenotype refers to the individual's traits. Different genotypes may produce the same phenotype. This will be the case if one allele is dominant to the other. For example, if B is dominant to b, only the B allele will be expressed in a Bb heterozygote. The recessive b allele will be expressed only in a bb genotype. Show less
Genetics is the scientific study of genes and heredity—of how certain qualities or traits are passed from parents to offspring as a result of changes in DNA sequence. The traits of organisms are controlled by genes on chromosomes. A gene is the part of a chromosome that contains the genetic code for a particular protein. The position of a gene on a chromosome is called its locus. Each gene may have different versions, called alleles. In sexually reproducing species, chromosomes are present in cells in pairs. Chromosomes in the same pair are called homologous chromosomes. They have the same genes at the same loci. The genes may be present as the same or different alleles. During meiosis, when gametes are produced, homologous chromosomes separate and go to different gametes. Thus, the two alleles for each gene also go to different gametes. When gametes unite during fertilization, the resulting zygote inherits two alleles for each gene. One allele comes from each parent. The two alleles that an individual inherits make up the individual's genotype. The two alleles may be the same or different. An individual with two alleles of the same type is called a homozygote. An individual with two alleles of different types is called a heterozygote. The expression of an individual's genotype is called its phenotype. The phenotype refers to the individual's traits. Different genotypes may produce the same phenotype. This will be the case if one allele is dominant to the other. For example, if B is dominant to b, only the B allele will be expressed in a Bb heterozygote. The recessive b allele will be expressed only in a bb genotype.
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