HEREDITY BIO 101 STUDY GUIDE IMPROVE YOUR SKILLS

HEREDITY BIO 101 STUDY GUIDE
IMPROVE YOUR SKILLS

HEREDITY

SOME TERMINOLOGIES IN GENETICS
Alleles
Alternate forms or varieties of a gene. The alleles for a trait occupy the same locus or
position on homologous chromosomes and thus govern the same trait. However, because
they are different, their action may result in different expressions of that trait.
Carrier
An individual who is heterozygous for a trait that only shows up in the phenotype of
those who are homozygous recessive. Carriers often do not show any signs of the trait
but can pass it on to their offspring. This is the case with hemophilia.
Chromosomes
Thread-like, gene-carrying bodies in the nucleus of a cell. Chromosomes are composed
primarily of DNA and protein. They are visible only under magnification during certain
stages of cell division. Humans have 46 chromosomes in each somatic cell and 23 in
each sex cell.
Codominance
The situation in which two different alleles for a trait are expressed unblended in the
phenotype of heterozygous individuals. Neither allele is dominant or recessive, so that
both appear in the phenotype or influence it. Type AB blood is an example. Such traits
are said to be codominant.

Cross-pollination
The mating of two genetically different plants of the same species. Usually, the term is
used in reference to the crossing of two pure breeding (homozygous) plants.
 Dominant allele
 An allele that masks the presence of a recessive allele in the phenotype. Dominant
alleles for a trait are usually expressed if an individual is homozygous dominant or
heterozygous.

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,HEREDITY BIO 101 STUDY GUIDE
IMPROVE YOUR SKILLS
 DNA (Deoxyribonucleic acid)
 A large organic molecule that stores the genetic code for the synthesis of proteins. DNA
is composed of sugars, phosphates and bases arranged in a double helix shaped molecular
structure. Segments of DNA in chromosomes correspond to specific genes.
 Evolution
 Genetic change in a population of organisms that occurs over time. The term is also
frequently used to refer to the appearance of a new species.
 F1 generation
 The first offspring (or filial) generation. The next and subsequent generations are
referred to as f2, f3, etc.
 Gene pool
 All of the genes in all of the individuals in a breeding population. More precisely, it is
the collective genotype of a population.
 Genes
 Units of inheritance usually occurring at specific locations, or loci, on a chromosome.
Physically, a gene is a sequence of DNA bases that specify the order of amino acids in an
entire protein or, in some cases, a portion of a protein. A gene may be made up of
hundreds of thousands of DNA bases. Genes are responsible for the hereditary traits in
plants and animals.
 Genetic drift
 Evolution, or change in gene pool frequencies, resulting from random chance. Genetic
drift occurs most rapidly in small populations. In large populations, random deviations in
allele frequencies in one direction are more likely to be cancelled out by random changes
in the opposite direction.
 Genetics
 The study of gene structure and action and the patterns of inheritance of traits from parent
to offspring. Genetic mechanisms are the underlying foundation for evolutionary
change. Genetics is the branch of science that deals with the inheritance of biological
characteristics.
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, HEREDITY BIO 101 STUDY GUIDE
IMPROVE YOUR SKILLS
 Genome
 The full genetic complement of an individual (or of a species). In humans, it is estimated
that each individual possesses approximately 2.9 billion base units in his or her DNA.
See Human Genome Project.
 Genome imprinting
 An inheritance pattern in which a gene will have a different effect depending on the
gender of the parent from whom it is inherited. Genome imprinting is also known as
genetic imprinting.
 Genotype
 The genetic makeup of an individual. Genotype can refer to an organism's entire genetic
makeup or the alleles at a particular locus.
 Heterozygous
 A genotype consisting of two different alleles of a gene for a particular trait (Aa).
Individuals who are heterozygous for a trait are referred to as heterozygotes. See
homozygous.
 Homologous chromosomes
 Chromosomes that are paired during the production of sex cells in meiosis. Such
chromosomes are alike with regard to size and also position of the centromere. They also
have the same genes, but not necessarily the same alleles, at the same locus or location.
 Homozygous
 Having the same allele at the same locus on both members of a pair of homologous
chromosomes. Homozygous also refers to a genotype consisting of two identical alleles
of a gene for a particular trait. An individual may be homozygous dominant (AA) or
homozygous recessive (aa). Individuals who are homozygous for a trait are referred to as
homozygotes. See heterozygous.
 Hybrids
 Offspring that are the result of mating between two genetically different kinds of
parents--the opposite of purebred.

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