Genetics Vocabulary

Sex-linked gene

. A particularly important category of genetic linkage has to do with the X and Y sex chromosomes. These not only carry the genes that determine male and female traits but also those for some other characteristics as well. Genes that are carried by either sex chromosome are said to be sex linked.

Hemophilia

. An X-linked recessive genetic disease, caused by a mutation in the gene for clotting factor VIII (hemophilia A) or clotting factor IX (hemophilia B), which leads to abnormal blood clotting.

Cystic fibrosis

A common grave genetic disease that affects the exocrine glands and is characterized by the production of abnormal secretions, leading to mucus buildup that impairs the pancreas and, secondarily, the intestine.

Klinefelter's syndrome

A condition in males who have XXY sex chromosomes, rather than the usual XY. Some also have additional X chromosomes, or more than one Y chromosome. XXY is one of the most common chromosomal abnormalities. It occurs in 1 in 500 male births.

Down syndrome

A congenital disorder, caused by the presence of an extra 21st chromosome, in which the affected person has mild to moderate mental retardation, short stature, and a flattened facial profile. Also called trisomy 21, trisomy 21 syndrome.

Codominance

A form of dominance in which the alleles of a gene pair in a heterozygote are fully expressed thereby resulting in offspring with a phenotype that is neither dominant nor recessive

Sickle cell anemia disease

A genetic blood disease due to the presence of an abnormal form of hemoglobin, namely hemoglobin S. Hemoglobin is the molecule in red blood cells that transports oxygen from the lungs to the farthest areas of the body.

Fertilization

A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.

Sex chromosome

A type of chromosome in the genome that is involved in the determination of the sex as well as the development of sexual characteristics in an organism. It occurs in pairs in somatic cells while singly in sex cells (gametes)

Homozygous

Alternative forms of a given gene are called alleles, and they can be dominant or recessive. When an individual has two of the same allele, whether dominant or recessive, they are homozygous. Heterozygous means having one each of two different alleles

Dominant allele

An allele or a gene that is expressed in an organism's phenotype, masking the effect of the recessive allele or gene when present. (2) (Of, or pertaining to) An organism that expresses the dominant gene (or allele).

Pedigree

An ancestral line or chart depicting the lineage or descent of an individual. (2) (genetics) A diagram showing the lineage or genealogy of an individual and all the direct ancestors, usually to analyze or follow the inheritance of trait.

Hybrid

An offspring resulting from the cross between parents of different species or sub-species. ... Of or pertaining to the offspring produced from crossbreeding. Supplement. (biology): For instance, a mule is an animal produced by breeding animals of different breeds, particularly a cross between a horse and a donkey

Autosome

Any chromosome not considered as a sex chromosome, or is not involved in sex determination. It occurs in pairs in somatic cells and singly in sex cells (gametes

Greg Mendel

Augustinian monk and botanist whose experiments in breeding garden peas led to his eventual recognition as founder of the science of genetics (1822-1884) Synonyms: Johann Mendel, Mendel Example of: botanist, phytologist, plant scientist. a biologist specializing in the study of plants.

Muscular dystrophy

Duchenne muscular dystrophy (pseudohypertrophic muscular dystrophy) is the most common form. It is due to a sex-linked recessive allele and this is expressed as an absence of the protein dystrophin, the disease in boys shows extensive but insufficient muscle fibre reformation from satellite cells.

Law of dominance

Mendel's third law (also called the law of dominance) states that one of the factors for a pair of inherited traits will be dominant and the other recessive, unless both factors are recessive. See more at inheritance.

Gene

The fundamental, physical, and functional unit of heredity. Supplement. It is because a gene is a segment of DNA (on a specific site on a chromosome) that is responsible for the physical and inheritable characteristics or phenotype of an organism

Heterozygous

The genetics term heterozygous refers to a pair of genes where one is dominant and one is recessive — they're different. Like all words with the prefix hetero, this has to do with things that are different — specifically genes. ... If you inherited the same gene from both parents, it's homozygous — the same.

Colorblindness

The inability to perceive colors in a normal fashion. The most common forms of colorblindness are inherited as sex-linked (X-linked) recessive traits. Females are carriers and males are affected. As a result, approximately 1 in 8 males is colorblind as compared to less than 1 in 100 females.

Law of Segregation

The principles that govern heredity were discovered by a monk named Gregor Mendel in the 1860's. One of these principles, now called Mendel's law of segregation, states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization

Genetics

The study of heredity, or how the characteristics of living things are transmitted from one generation to the next. Every living thing contains the genetic material that makes up DNA molecules. This material is passed on when organisms reproduce. The basic unit of heredity is the gene.

Nondisjunction

There are three forms of nondisjunction: failure of a pair of homologous chromosomes to separate in meiosis I, failure of sister chromatids to separate during meiosis II, and failure of sister chromatids to separate during mitosis. Nondisjunction results in daughter cells with abnormal chromosome numbers (aneuploidy).

Multiple alleles

Three or more alternative forms of a gene (alleles) that can occupy the same locus. However, only two of the alleles can be present in a single organism. For example, the ABO system of blood groups is controlled by three alleles, only two of which are present in an individual. "multiple alleles."

Achondroplasia

a genetic disorder disturbing normal growth of cartilage, resulting in a form of dwarfism characterized by a usually normal torso and shortened limbs, and usually inherited as an autosomal dominant trait.

Gamete

are the cells used during sexual reproduction to produce a new individual organism or zygote. The male gamete, sperm, is a smaller, mobile cell that meets up with the much larger and less mobile female gamete, egg or ova. Both sperm and egg are only haploid cells. They only carry half of the chromosomes needed

Turners syndrome

is a chromosomal disorder that affects only females. It involves a lack of part or all of a second sex chromosome in some or all cells. Girls are often short in stature, and they may have some emotional and learning difficulties, but most will have normal intelligence.

Punnett square

is a diagram that is used to predict an outcome of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach. The diagram is used by biologists to determine the probability of an offspring having a particular genotype.

Incomplete dominance

is a form of intermediate inheritance in which one allele for a specific trait is not completely expressed over its paired allele. This results in a third phenotype in which the expressed physical trait is a combination of the phenotypes of both alleles.

Huntington's disease

is an autosomal dominant disease, which means that it is a disease caused by a gene on an autosome and only one copy of the causative gene is needed to cause the disease. Since Huntington's disease is autosomal, it affects males and females equally.

Phenotype

is defined as an organism's expressed physical traits. Phenotype is determined by an individual's genotype and expressed genes, random genetic variation, and environmental influences. Examples: Examples of an organism's phenotype include traits such as color, height, size, shape, and behavior.

Allele

is one of the possible forms of a gene. Most genes have two alleles, a dominant allele and a recessive allele. If an organism is heterozygous for that trait, or possesses one of each allele, then the dominant trait is expressed. ... So a gene is a particular region of your DNA that controls a specific trait.

Albinism

is the "Congenital absence of any pigmentation or coloration in a person, animal or plant, resulting in white hair and pink eyes in mammals."

Genotype

is the set of genes in our DNA which is responsible for a particular trait. The phenotype is the physical expression, or characteristics, of that trait. For example, two organisms that have even the minutest difference in their genes are said to have different genotypes.

Probability

is used to measure the chances or likelihood of an event to occur, a hypothesis being correct, or a scientific prediction being true. In biology, it is used in predicting the outcome of a genetic cross or of a random experiment

Trait

or character is a feature of an organism. The term phenotype is sometimes used as a synonym for trait in common use, but strictly speaking, does not indicate the trait, but the state of that trait (e.g., the trait eye color has the phenotypes blue, brown and hazel).

Law of independent Assortment

originated by Gregor Mendel, stating that when two or more characteristics are inherited, individual hereditary factors assort independently during gamete production, giving different traits an equal opportunity of occurring together. Expand. Also called Mendel's second law, Mendel's law.

Polygenic trait

that is controlled by a group of nonallelic genes. Supplement. Polygenic traits are controlled by two or more than two genes (usually by many different genes) at different loci on different chromosomes. ... Examples of human polygenic inheritance are height, skin colour and weight.

Recessive allele

that produces its characteristic phenotype only when its paired allele is identical. Synonyms: recessive Type of: allele, allelomorph. (genetics) either of a pair (or series) of alternative forms of a gene that can occupy the same locus on a particular chromosome and that control the same character

True-breeding

that the parents will also pass down a specific phenotypic trait to their offspring. Remember that a phenotype is the outward appearance of something. True bred organisms will have a pure genotype (genetic expression of a trait) and will only produce a certain phenotype.

Karyotype

the number and visual appearance of the chromosomes in the cell nuclei of an organism or species

Segregation

the principle, originated by Gregor Mendel, stating that during the production of gametes the two copies of each hereditary factor segregate so that offspring acquire one factor from each parent. Expand. Also called Mendel's first law, Mendel's law.