Lab 24 Vocabulary Appendix
Alleles: Form of a gene. An individual inherits two alleles for each gene, one from each parent.
Autosomal Chromosomes: Any chromosome that is not a sex chromosome. Humans have 46 total
chromosomes: 44 autosomal and 2 sex chromosomes.
Back cross: Crossing of a heterozygous individual with one of its parents.
Carrier: Heterozygous genotype that has both a normal and a mutant allele. While carriers have the
heterozygous genotype for a given gene, their phenotype is caused by the dominant allele.
Chance: Possibility of occurrence.
Chromosomes: A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists
of one very long DNA molecule and associated proteins.
Co-dominance: A kind of dominance in which the dominant allele is only partially expressed, and
usually resulting in a heterozygous offspring that shows both alleles.
Complete or Simple Dominance: A kind of dominance where the dominant allele completely masks the
effect of the recessive allele in heterozygous condition.
Diploid: Containing two complete sets of chromosomes, one from each parent. Humans have 46
chromosomes or 23 pairs.
Dominant Allele: Appears in the phenotype, if it appears in the genotype. Does not mean it is more
prevalent in the population. An upper case letter is used to denote a dominant allele.
F1 Generation: The first filial generation, which is comprised of offspring resulting from a cross
between strains of distinct genotypes.
F2 Generation: The second filial generation, which is comprised of offspring resulting from a cross of
the members of F1 generation.
Gamete: A mature haploid male or female sex cell that is able to unite with another in sexual
reproduction to form a zygote.
Genes: A section of a chromosome that codes for a trait or specifically a protein.
Genotype: Genetic makeup of an organism. Two letters of the same type are used to express the
genotype. Example BB, Bb, or bb.
Haploid: Having a single set of unpaired chromosomes.
Heterozygous: A genotype with two different alleles of a gene. Example Bb.
Homologous Chromosomes: Chromosome pairs of the same length that carry the same genes but
different alleles. One homolog is inherited from the father, the other from the mother.
Homozygous: A genotype with the same alleles of a gene. Example BB (homozygous dominant) or bb
(homozygous recessive).
Hybrid: Synonymous with heterozygous.
Incomplete Dominance: A kind of dominance in which the dominant allele is only partially expressed,
and usually resulting in a heterozygous offspring that shows a blending of the alleles.
Linkage: The tendency of alleles that are located close together on a chromosome to be inherited
together during meiosis. Genes whose are nearer to each other are less likely to be separated onto
different chromatids during crossing over, and are therefore said to be genetically linked.
Mendelian Genetics: Inheritance of biological features that follows the laws proposed by Gregor
Mendel.
Meiosis: A two-stage type of cell division in sexually reproducing organisms that results in gametes
with half the chromosome number of the original cell.
Multiple Alleles: A type of inheritance where more than two alleles code for a trait.
Multiple Genes: A type of inheritance where more than one gene codes for a trait.
Phenotype: Observable characteristics of an individual resulting from the interaction of its genotype
with the environment.
Phenotypic Ratio: Relative number phenotypes produced in a Punnett Square. For example ¾ red: ¼
green.
Principle of Segregation: During gamete formation, alleles of a gene separate and therefore each gamete
receives one copy of each allele. For example Aa will separate into A and a
Principle of Independent Assortment: During gamete formation, alleles of two traits will separate
independently allowing for all variations in the gametes. For example AaBb will separate into AB, Ab,
aB, and ab.
Punnett Square: The Punnett square is a diagram that is used to predict an outcome of a particular cross
or breeding experiment. The diagram is used by biologists to determine the probability of an offspring
having a particular genotype.
Recessive Allele: Appears in the phenotype only if paired with another recessive allele in the genotype. A
lower case letter is used to denote a recessive allele.
Sex Chromosome: A chromosome involved with determining the sex of an organism, typically one of
two kinds.
Sex Linkage: A type of inheritance where the alleles are located on the sex chromosomes. The
phenotypic ratio is not the same for males and females, unlike the inheritance of traits on autosomal
chromosomes, where both sexes have the same probability of inheritance.
Somatic Cells: Body cells
XY: Genotype for a male
XX: Genotype for a female