Biology Genetics Graded A+

Biology Genetics Graded A+ Trait Characteristic that is inherited; can be either dominant or recessive. P Generation The parent organisms that are bred to make offspring so that scientists can study inheritance; P stands for "parental." Brainpower Read More F1 generation The first offspring born from a parental (P generation) cross. F2 generation The offspring resulting from interbreeding (or self-pollination) of the F1 generation. The Law of Segregation Mendel's first law, stating that the two alleles in a pair segregate (separate from each other) into different gametes during gamete formation. Allele Any of the alternative versions of a gene that may produce distinguishable phenotypic effects. (For example, wrinkled seeds or smooth seeds in a pea plant) Dominant Allele An allele that is fully expressed in the phenotype of a heterozygote (for example, the big T in Tt). Only need 1 copy of dominant allele to show dominant trait. Recessive Allele An allele whose phenotype is not expressed in a heterozygote (for example, the little r in Rr) - it is "masked" or hidden. Need 2 copies of recessive allele to show recessive trait (rr). Genotype The genetic makeup, or set of alleles, of an organism. (Ex: PP, Pp or pp) Phenotype The EXPRESSED/observable physical and physiological traits of an organism, which are determined by its genetic makeup. Punnett Square A diagram used in the study of inheritance to show the predicted genotypic results of random fertilization in genetic crosses between individuals of known genotype. Homozygous Having two identical alleles for a given gene. Heterozygous Having two different alleles for a given gene. The Law of Independent Assortment Mendel's second law, stating that each pair of alleles segregates, or assorts, independently of each other pair during gamete formation (production of sex cells like sperm or egg); applies when genes for two characters are located on different pairs of homologous chromosomes or when they are far enough apart on the same chromosome to behave as though they are on different chromosomes. Dihybrid Cross A cross between two organisms that are each heterozygous for both of the characters being followed (or the self-pollination of a plant that is heterozygous for both characters).