| A | B |
|---|
| Mendel | monk who tested pea trait heredity |
| P generation | parental generation--the first parents crossed |
| genotype | the two alleles for a gene that are present in somatic cells--for example, Ss or SS or ss |
| phenotype | A description of an individual's trait--e.g., trait: hair color phenotype: brown hair color or blonde hair color |
| trait | a measurable characterisitic, such as height or hair color or pea seed shape or flower color |
| homozygous | Two of the same alleles in a genotype--AA or aa |
| allele | Slightly different forms of the same gene--for example, for the seed shape controlling gene R for the dominant round allele, r for the recessive wrinkled allele |
| gene | a part of a chromosome whose nucleotide sequence codes for a protein whose role controls trait(s) |
| DOMINANT | an allele which codes a protein that is present in the cells and that is able to carry out a job--Mendel described the dominant alleles as "masking" or "covering up" the recessive allele. e.g., for the Seed shape gene, R for the dominant allele controlling a round seed shape |
| recessive | an allele that codes for very little or no protein activity; Mendel described the dominant alleles as "masking" or "covering up" the recessive allele. e.g., for the Seed shape gene, r for the recessive allele controlling a wrinkled seed shape |
| heterozygous | two different alleles in the genotype--for example, Aa or Ss or Xx |
| F1 generation | First filial generation--the offspring of the parental generation; their genotypic ratios are predicted inside the Punnett Square for the parental generation cross |
| F2 generation | The offspring of two F1 individuals mated to each other; the F2 genotypic ratios are predicted inside the Punnett Square for the mating of the two F1 individuals |
| Punnett Square | a grid that places each possible male gamete allele above each column and each female gamete allele next to each row. Squares contain the possible genotypes of the offspring of the male and female, and the fractions of each genotype are called the genotypic ratio |
| genotypic ratio | The likely fraction or % of offspring that will have each genotype predicted possible by a Punnett Square |
| phenotypic ratio | The possible trait descriptions predicted for the offspring of a particular genetic cross. For example, The punnett square for the cross Aa x Aa shows that 1/4 will have the homozygous dominant genotype and the associated phenotype (angled head dominant, round head recessive) 2/4 will have a heterozygous genotype and an angled head phenotype, and 1/4 will have the aa genotype and round head phenotype. |
| law of simple dominance | Mendel concluded that the dominant allele masks the recessive allele, so that the homozygous dominant phenotype should be the same as the heterozygous phenotype |
| co-dominance | An exception to Mendel's law of simple dominance. For some genes, more than one dominant allele exists, and these can work together to control the phenotype. For example, for blood type, both A and B dominant alleles exist, while only one recessive allele called O exists. Blood type phenotype can be A, B, or AB. |
| incomplete dominance | An exception to Mendel's law of simple dominance: sometimes, the heterozygote has a phenotype in-between that of a homozygous dominant individual and homozygous recessive individual. For example, RR red, Rr pink, rr white. |
| Pedigree | A chart showing inheritance of a trait through several generations. |
| Mendel's law of random segregation | Mendel found that two alleles are present in a somatic cell for every gene. A parent passes one or the other, but not both, of his alleles to a gamete. |
| Mendel's law of independent assortment | Mendel found that different traits are coded by different genes. He found that it is not possible to predict what combinations of alleles for different unlinked genes will be inherited. For example, it is not possible to predict whether a blue eyed girl will also inherit brown or black or blonde hair. |
| Monohybrid cross | Mating two parents then predicting the phenotypic and genotypic ratios for only one trait using a 2 X 2 Punnett square. |
| recessive phenotype | a trait description present only when two recessive alleles are in the genotype |
| carrier | a person who is a heterozygote for a gene, for example Aa |
| linked genes | genes on the same chromosome. They do not obey Mendel's law of independent assortment. |
| Sex linked genes | genes on the X chromosome. Males have only once copy of each of them. |
