How to predict result of the cross
Punnett Square Definition A Punnett square is a graphical representation of the possible genotypes of an offspring arising from a particular cross or breeding event. Creating a Punnett square requires knowledge of the genetic composition of the parents. The various possible combinations of their gametes are encapsulated in a tabular format. Therefore, each box in the table represents one fertilization event. The inherent assumption is that each trait is determined by a single gene locus and that various traits assort independently from one another. Though this is true for many useful traits, especially when choosing characters for plant or animal breeding, there are many exceptions. This tool was created in the twentieth century, much after Mendel’s seminal experiments on genetics. However, they are now commonly used to explain the results that Mendel obtained, especially when combined with our current knowledge of DNA, genes and chromosomes. Common Terms in Genetics Some terms are often used in the study of genetics and these are particularly useful in understanding the function of Punnett squares. Among these is the term ‘allele’ and is used to denote a variant of a gene. For example, a pea plant can have red or white flowers and the gene variants coding for each of these is called an allele. When an organism contains two copies of the same allele, its genetic composition or genotype is said to be homozygous. These are also called true-breeding specimens. For instance, plants with white flowers are homozygous at the genetic loci coding for flower color. Individuals who have two different alleles are said to be heterozygous at that locus. Many plants that have red flowers can have one allele for red color and another for white color. The externally observed characteristic of an individual is called the phenotype. The phenotype in a heterozygous individual is said to be the ‘dominant’ form of the gene and the trait that is suppressed is considered as the ‘recessive’ allele. In the example of flower color, the allele coding for red color is dominant over the one for white. In a cross between a dominant homozygote and a recessive homozygote, all the offspring will have a heterozygous genotype and a dominant phenotype. Some gene loci are on sex chromosomes and are called sex-linked traits, while all the others are said to be autosomal. Functions of Punnett Squares In large-scale experiments, such as those conducted by Mendel, Punnett squares can accurately predict the ratios of various observable traits as well as their underlying genetic composition. For instance, when a true-breeding tall pea plant is cross fertilized with pollen from a true-breeding short pea plant, the Punnett square can predict that all the offspring will be tall, and all of them will be heterozygous with both the allele for shortness and tallness. It can further predict that if these heterozygous plants are allowed to self-fertilize, approximately seventy-five percent of the second generation plants will be tall, and the remaining twenty-five percent will be short. Among the tall plants, one-third will remain true-breeding while the remaining two-thirds will be heterozygous. This tool is therefore used by plant and animal breeders to choose appropriate specimens in order to obtain offspring carrying a desired trait. They are also used in genetic counseling to help couples make the decision about having children. For example, in cases where both parents are carriers for an autosomal recessive disease such as cystic fibrosis, there is a twenty-five percent chance of their child suffering from the illness and a fifty-percent chance that their offspring will be carriers. However, if one parent has the disease and the other is neither a carrier nor suffering from the illness, the couple can be reassured that their child will not develop cystic fibrosis since she will carry only one copy of the abnormal gene. Types of Punnett Squares T... #protein #Genetics101 #Cancer #genes #codons #locus #dnaMolecule #geneExpression #enzyme #Heterozygous #dominant #alleles #GeneStructure #prokaryotes #genome #GeneticExamQuestionsSolutions #eukaryotic #genotype #rRNA #aminoAcid #homozygous #Allele #centromeres #genetics #chromosomes #eukaryotes #genomes #RNA #genomics #chromosome #GeneticsLecture #GeneticTesting #phenotype #proteins #molecularBiology #GeneticsExamQuestionsSolutions #gene #geneticCode #transcription #DNA #NikolaysGeneticsLessons https://www.youtube.com/watch?v=XAu-VeOmP3M
Punnett Square Definition A Punnett square is a graphical representation of the possible genotypes of an offspring arising from a particular cross or breeding event. Creating a Punnett square requires knowledge of the genetic composition of the parents. The various possible combinations of their gametes are encapsulated in a tabular format. Therefore, each box in the table represents one fertilization event. The inherent assumption is that each trait is determined by a single gene locus and that various traits assort independently from one another. Though this is true for many useful traits, especially when choosing characters for plant or animal breeding, there are many exceptions. This tool was created in the twentieth century, much after Mendel’s seminal experiments on genetics. However, they are now commonly used to explain the results that Mendel obtained, especially when combined with our current knowledge of DNA, genes and chromosomes. Common Terms in Genetics Some terms are often used in the study of genetics and these are particularly useful in understanding the function of Punnett squares. Among these is the term ‘allele’ and is used to denote a variant of a gene. For example, a pea plant can have red or white flowers and the gene variants coding for each of these is called an allele. When an organism contains two copies of the same allele, its genetic composition or genotype is said to be homozygous. These are also called true-breeding specimens. For instance, plants with white flowers are homozygous at the genetic loci coding for flower color. Individuals who have two different alleles are said to be heterozygous at that locus. Many plants that have red flowers can have one allele for red color and another for white color. The externally observed characteristic of an individual is called the phenotype. The phenotype in a heterozygous individual is said to be the ‘dominant’ form of the gene and the trait that is suppressed is considered as the ‘recessive’ allele. In the example of flower color, the allele coding for red color is dominant over the one for white. In a cross between a dominant homozygote and a recessive homozygote, all the offspring will have a heterozygous genotype and a dominant phenotype. Some gene loci are on sex chromosomes and are called sex-linked traits, while all the others are said to be autosomal. Functions of Punnett Squares In large-scale experiments, such as those conducted by Mendel, Punnett squares can accurately predict the ratios of various observable traits as well as their underlying genetic composition. For instance, when a true-breeding tall pea plant is cross fertilized with pollen from a true-breeding short pea plant, the Punnett square can predict that all the offspring will be tall, and all of them will be heterozygous with both the allele for shortness and tallness. It can further predict that if these heterozygous plants are allowed to self-fertilize, approximately seventy-five percent of the second generation plants will be tall, and the remaining twenty-five percent will be short. Among the tall plants, one-third will remain true-breeding while the remaining two-thirds will be heterozygous. This tool is therefore used by plant and animal breeders to choose appropriate specimens in order to obtain offspring carrying a desired trait. They are also used in genetic counseling to help couples make the decision about having children. For example, in cases where both parents are carriers for an autosomal recessive disease such as cystic fibrosis, there is a twenty-five percent chance of their child suffering from the illness and a fifty-percent chance that their offspring will be carriers. However, if one parent has the disease and the other is neither a carrier nor suffering from the illness, the couple can be reassured that their child will not develop cystic fibrosis since she will carry only one copy of the abnormal gene. Types of Punnett Squares T... #protein #Genetics101 #Cancer #genes #codons #locus #dnaMolecule #geneExpression #enzyme #Heterozygous #dominant #alleles #GeneStructure #prokaryotes #genome #GeneticExamQuestionsSolutions #eukaryotic #genotype #rRNA #aminoAcid #homozygous #Allele #centromeres #genetics #chromosomes #eukaryotes #genomes #RNA #genomics #chromosome #GeneticsLecture #GeneticTesting #phenotype #proteins #molecularBiology #GeneticsExamQuestionsSolutions #gene #geneticCode #transcription #DNA #NikolaysGeneticsLessons https://www.youtube.com/watch?v=XAu-VeOmP3M