GENETICS: PATTERNS OF INHERITANCE

ALLELE One of the two or more forms of the gene for a specific trait Represented by letters S – Smooth seed s – wrinkled seed

AUTOSOMES The first 22 sets of of chromosomes are called autosomes.

CHROMOSOME A strand of DNA carrying many different genes.

CODOMINANCE Case in which both alleles contribute to the phenotype of the offspring

Hybrid pink and white azalea (Rhododendron sp., fam. Ericaceae)

CROSSING-OVER Homologous chromosomes within the tetrad exchange portions of their chromatids, occurs during Prophase 1

DIPLOID Two sets of chromosomes

DIHYBRID CROSS (Two-Factor Cross) A genetic cross in which two pairs of contrasting traits are studied.

DOMINANT The trait that hides the expression of another trait. T

F 1 GENERATION The first filial generation that results from a cross between two purebred parents.

F 2 GENERATION When flowers of the F 1 generation were allowed to self-pollinate, their offspring became the second filial generation or F 2 generation

GAMETE Sex cells (egg or sperm)

GENE A unit of DNA that produces a specific trait in an individual.

GENETICS The scientific study of heredity

GENOTYPE The genetic makeup of an organism TT

GREGOR MENDEL Austrian monk who studied mathematics and science As a boy he could predict the possible types of flowers and fruits that would result from crossbreeding two plants in his father’s garden

GREGOR MENDEL cont’d Curiosity about the connection between the color of a pea flower and the type of seed that same plant produced inspired him to begin experimenting with garden peas in Made careful use of scientific methods, which resulted in the first recorded study of how traits pass from one generation to the next.

HAPLOID One set of chromosomes

HETEROZYGOUS Having two different alleles for a trait.

HOMOZYGOUS Having two identical alleles for a trait.

HOMOLOGOUS CHROMOSOMES

Human Chromosomes Humans have 46 pairs of chromosomes: 23 from the father + 23 from the mother

HYBRID An individual that is heterozygous for a specific trait.

INCOMPLETE DOMINANCE Cases in which one allele is not completely dominate over another; the offspring will have a phenotype between that of its parents

MEIOSIS The process of cell division that leads to gamete formation During meiosis, the number of chromosomes per cell is cut in half.

MONOHYBRID CROSS (One-Factor Cross) A genetic cross in which only one pair of contrasting traits is studied

NONDISJUNCTION During nondisjunction, the chromosomes fail to divide properly during meiosis. Abnormal numbers of chromosomes may find their way into gametes.

PEDIGREES A “family tree” Constructed by studying the phenotypes of family members from one generation to the next.

EXAMPLE OF A PEDIGREE

P GENERATION The parental generation with two pure-bred parents

PHENOTYPE The physical traits that appear in an organism as a result of it genes. White hair

Principle of Dominance The principle of dominance states that some alleles are dominant and others are recessive.

Principle of Independent Assortment The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.

Principle of Probability The principles of probability can be used to predict the outcomes of genetic crosses.

PROBABILITY The likelihood that a particular event will occur

PUNNETT SQUARE A diagram used to predict the probability that certain traits will be inherited by offspring

RECESSIVE The trait that is hidden Recessive traits only appear when homozygous. t

SEGREGATION The separation of alleles during gamete formation

SEX CHROMOSOMES The last pair of chromosomes in the karyotype are called sex chromosomes because they determine a whether a person will be male (xy) or female (xx).

TEST CROSS A genetic cross between an unknown genotype for a trait and a homozygous recessive genotype for the same trait; the phenotypes of the resulting generation reveal the unknown genotype.

TETRAD The pairing of homologous chromosomes, occurs during Prophase 1

TRAIT A genetically determined characteristic, such as eye color.

Mendel’s 7 garden pea traits.

TRUE-BREEDING Plants that when crossed produce offspring identical to themselves every time.