Biology Exam - Genetics

Allele

A variant form of a gene.

Autosome

A chromosome that is not a sex chromosome.

Autosomal dominance

A pattern of inheritance where one copy of a dominant allele is sufficient to express the trait.

Carrier

An individual who has one copy of a recessive allele but does not express the trait.

Chromatid

Two identical copies of a chromosome joined together.

Chromosome

A structure containing DNA and proteins, found in the nucleus of eukaryotic cells.

Codominance

A pattern of inheritance where both alleles are expressed equally.

Dihybrid cross

A cross between individuals heterozygous for two traits.

DNA

Deoxyribonucleic acid, the molecule that carries genetic information.

Dominant allele

An allele that masks the expression of a recessive allele.

Gene

A unit of heredity that is transferred from a parent to offspring and determines some characteristic of the offspring.

Genotype

The genetic makeup of an individual.

Heterozygous

Having two different alleles for a particular gene.

Homologous chromosomes

Pairs of chromosomes that have the same genes but may have different alleles.

Homozygous

Having two identical alleles for a particular gene.

Incomplete dominance

A pattern of inheritance where the heterozygote phenotype is a blend of the two homozygous phenotypes.

Law of independent assortment

During gamete formation, alleles for different genes segregate independently of each other.

Law of segregation

During gamete formation, each pair of alleles segregates so that each gamete receives only one allele for each gene.

Meiosis

A type of cell division that produces gametes (sex cells) with half the number of chromosomes.

Mitosis

A type of cell division that produces two identical daughter cells.

Phenotype

The observable characteristics of an individual.

Punnett square

A diagram used to predict the genotypes and phenotypes of offspring from a genetic cross.

Recessive allele

An allele that is masked by a dominant allele.

Recombination

The process of exchanging genetic material between homologous chromosomes during meiosis.

Sex chromosome

A chromosome that determines an individual's sex (e.g., X and Y chromosomes in humans).

Trait

A characteristic or feature of an organism.

Test cross

A cross between an individual with an unknown genotype and a homozygous recessive individual.

Interphase

The phase of the cell cycle characterized by growth (G1), DNA replication (S), and preparation for division (G2).

Cytokinesis

Division of the cytoplasm during cell division.

Nondisjunction

The failure of chromosomes to separate properly during meiosis.

Karyotype

Visual representation of an individual's chromosomes.

Phenotypic ratio

The ratio of different phenotypes in the offspring of a genetic cross.

Genotypic ratio

The ratio of different genotypes in the offspring of a genetic cross.

X-linked inheritance

Inheritance of genes located on the X chromosome.

Autosomal recessive

Inheritance pattern in which two copies of a recessive allele are required for expression.

Punnett squares for monohybrid and dihybrid crosses.

Used to predict genotype ratios from one (monohybrid) or two (dihybrid) traits.

Klinefelter's Syndrome

A genetic condition resulting from an extra X chromosome in males (XXY).