Unit 5: Hereditary

Gametes

Sex cells that are haploid and combine from two parents to form a diploid zygote.

Haploid

A cell that contains one complete set of chromosomes.

Diploid

A cell that contains two complete sets of chromosomes, one from each parent.

Zygote

The fertilized egg that develops from the merging of two gametes.

Gregor Mendel

The monk known as the Father of Genetics who discovered the principles of heredity.

Locus

The specific position of a gene on a chromosome.

Homologous chromosomes

Pairs of chromosomes that are the same size, shape, and carry the same genes, but may contain different alleles.

Alleles

Different versions of a gene.

Homozygous

An organism with two identical alleles for a particular trait.

Heterozygous

An organism with two different alleles for a particular trait.

Phenotype

The physical appearance of an organism as a result of its genotype.

Genotype

The genetic makeup of an organism, comprising the alleles it possesses.

Dominant allele

An allele that is expressed in the phenotype even in the presence of a recessive allele.

Recessive allele

An allele that is only expressed in the phenotype if two copies are present.

Punnett square

A diagram used to predict the genotype and phenotype combinations in genetic crosses.

Law of Dominance

The principle stating that one trait can mask the effects of another trait.

Law of Segregation

Each gamete gets only one copy of each gene, resulting in allele separation during gamete formation.

Law of Independent Assortment

Genes for different traits are inherited independently of one another.

Monohybrid cross

A genetic cross that examines the inheritance of a single trait.

Dihybrid cross

A genetic cross that examines the inheritance of two traits simultaneously.

Test cross

A method used to determine an organism’s genotype by crossing it with a recessive phenotype.

Linked genes

Genes that are located on the same chromosome and tend to be inherited together.

Recombinants

Offspring that exhibit a combination of traits that differ from those of either parent due to recombination.

Sex-linked traits

Traits that are associated with genes located on sex chromosomes, often the X chromosome.

Barr bodies

Inactive X chromosomes in females that are condensed and visible in the nucleus.

Incomplete dominance

A form of inheritance where neither allele is dominant, resulting in a blended phenotype.

Codominance

A form of inheritance where both alleles are fully expressed in the phenotype.

Polygenic inheritance

A form of inheritance where multiple genes interact to determine a single trait.

Meiosis

A type of cell division that results in four haploid daughter cells, producing gametes.

Spermatogenesis

The process of producing sperm cells through meiosis.

Oogenesis

The process of producing egg cells (ova) through meiosis.

Nondisjunction

The failure of chromosomes to separate correctly during meiosis, resulting in an abnormal number of chromosomes.

Aneuploidy

A condition involving an abnormal number of chromosomes, such as Down syndrome.