Genetically determined classes of human blood that are based on the presence or absence of carbohydrates A and B on the surface of red blood cells. The ABO blood group phenotypes, also called blood types, are A, B, AB, and O.
An alternative form of a gene.
A technique for diagnosing genetic defects while a fetus is in the uterus. A sample of amitotic fluid, obtained via a needle inserted into the amnion, is analyzed for telltale chemicals and defective fetal cells.
Pair of homologous chromosomes split up
Same as mitosis, sister chromatids separate
Condition of having an abnormal number of certain chromosomes
A neuro-genetic disorder characterized by intellectual and developmental delay, sleep disturbance, seizures, jerky movements especially hand-flapping, frequent laughter or smiling, and usually a happy demeanor.
A chromosome not directly involved in determining the sex of an organism; in mammals, for example, any chromosome other than X or Y.
An individual who is heterozygous for a recessively inherited disorder and who therefore does not show symptoms of that disorder.
The region of a chromosome where two sister chromatids are joined and where spindle microtubules attach during mitosis and meiosis. The centromere divides at the onset of anaphase during mitosis and anaphase II during meiosis.
The microscopically visible site where crossing over has occurred between chromatids of homologous chromosomes during prophase I of meiosis.
chorionic villus sampling (CVS)
A technique for diagnosing genetic defects while the fetus is in the uterus. A small sample of the fetal portion of the placenta is removed and analyzed.
The combination of DNA and proteins that constitutes chromosomes; often used to refer to the diffuse, very extended form taken by the chromosomes when a eukaryotic cell is not dividing.
chromosome theory of inheritance
A basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns.
A threadlike, gene-carrying structure found in the nucleus of a eukaryotic cell and most visible during mitosis and meiosis; also, the main gene-carrying structure of a prokaryotic cell. Chromosomes consist of chromatin.
Inheritance pattern in which a heterozygote expresses the distinct trait of both alleles.
A type of inheritance in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.
Cri du Chat
Deletion on chromosome 5.
The fusion of sperm and egg derived from two different individuals.
The exchange of segments between chromatids of homologous chromosomes during synapsis in prophase I of meiosis; also, the exchange of segments between DNA molecules in prokaryotes.
The division of the cytoplasm to form two separate daughter cells. Cytokinesis usually occurs during telophase of mitosis, and mitosis and cytokinesis make up the mitotic (M) phase of the cell cycle.
The loss of one or more nucleotides from a gene by mutation; the loss of a fragment of a chromosome.
An experimental mating of individuals differing at two genetic loci.
In an organism that reproduces sexually, a cell containing two homologous sets of chromosomes, one set inherited from each parent; a 2n cell.
In a heterozygote, the allele that determines the phenotype with respect to a particular gene.
A human genetic disorder resulting from the presence of an extra chromosome 21; characterized by heart and respiratory defects and varying degrees of mental retardation.
Repetition of part of a chromosome resulting from fusion with a fragment from a homologous chromosome; can result from an error in meiosis or from mutagenesis.
The offspring of two parental (P generation) individuals; F1 stands for first filial.
The offspring of the F1 generation; F2 stands for second filial.
The union of the nucleus of a sperm cell with the nucleus of an egg cell, producing a zygote.
Involves inserting a thin fiber-optic scope into the uterus, done at the 18th week.
A sex cell; a haploid egg or sperm. The union of two gametes of opposite sex (fertilization) produces a zygote.
The production, by crossing over and/or independent assortment of chromosomes during meiosis, of offspring with allele combinations different from those in the parents. The term may also be used more specifically to mean the production by crossing over of eukaryotic or prokaryotic chromosomes with gene combinations different from those in the original chromosomes.
The scientific study of heredity and hereditary variations.
A complete (haploid) set of an organism's genes; an organism's genetic material.
A genetic phenomenon by which certain genes are expressed in a parent-of-origin-specific manner.
The genetic makeup of an organism.
germ line (germ cell)
Germline of a mature or developing individual is the line (sequence) of germ cells that have genetic material that may be passed to a child.
For example, sex cells such as the sperm or the egg, are part of the germline. So are the cells that produce sex cells, called gametocytes, the cells that produce those, called gametogonia, and all the way back to the zygote, the cell from which the individual developed.
In the life cycle of an organism that reproduces sexually, a cell containing a single set of chromosomes; an n cell.
Having two different alleles for a given gene.
Having two identical alleles for a given gene.
The offspring of parents of two different species or of two different varieties of one species; the offspring of two parents that differ in one or more inherited traits; an individual that is heterozygous for one or more pairs of genes.
A type of inheritance in which the phenotype of a heterozygote (Aa) is intermediate between the phenotypes of the two types of homozygotes (AA and aa).
A period of rest that cells enter during meiosis. It is the abbreviated interphase that occurs between meiosis I and II. No DNA replication occurs during this stage of Meiosis. Many plants skip telophase I and interkinesis, going immediately into prophase II. Each chromosome still consists of two chromatids.
A change in a chromosome resulting from reattachment of a chromosome fragment to the original chromosome, but in a reverse direction. Mutagens and errors during meiosis can cause inversions.
XYY. Males that are usually taller and aggressive but are still fertile and intelligent.
A display of micrographs of the metaphase chromosomes of a cell, arranged by size and centromere position.
XXY. Male sex organs with abnormally small testes. Sterile, feminine body contours, and breast enlargement, usually normal intelligence.
law of independent assortment
A general rule in in inheritance that when gametes form during meiosis, each pair of alleles for a particular characteristic segregate independently; also known as Mendel's second law of inheritance.
law of segregation
A general rule in inheritance that individuals have two alleles for each gene and that when gametes form by meiosis, the two alleles separate, and each resulting gamete ends up with only one allele of each gene; also known as Mendel's first law of inheritance.
A cancer of the blood or bone marrow characterized by an abnormal increase of blood cells, usually leukocytes (white blood cells).
The particular site where a gene is found on a chromosome. Homologous chromosomes have corresponding gene loci.
In a sexually reproducing organism, the division of a single diploid nucleus into four haploid daughter nuclei. meiosis and cytokinesis produce haploid gametes from diploid cells in the reproductive organs of the parents.
Tetrads line up.
Chromosomes line up.
An experimental mating of individuals differing at one genetic locus.
Aneuploid cell missing a chromosome.
Any of a set of three or more alleles, or alternative states of a gene, only two of which can be present in a diploid.
An accident of meiosis or mitosis in which a pair of homologous chromosomes or a pair of sister chromatids fail to separate at anaphase.
The scan is carried out at 11–13+6 weeks pregnancy and assesses the amount of fluid behind the neck of the fetus - also known as the nuchal fold or 'the nuchal translucency.
The formation of ova (egg cells).
An unfertilized egg, or female gamete.
The parent individuals from which offspring are derived in studies of inheritance (P stands for parental).
The expressed traits of an organism.
A cell structure found inside an ovum. Both animal and plant ova possess it. It is also known as a polar cell.
An organism whose cells have more than two complete sets of chromosomes.
Missing 7 genes chromosome 15 on the paternal chromosome, appetite low, muscle tone, emotional instability, immature physical features.
Homologous chromosomes pair and exchange segments.
The nuclear envelope breaks down and the spindle apparatus forms.
A diagram used in the study of inheritance to show the results of random fertilization.
In a heterozygous individual, the allele that has no noticeable effect on the phenotype.
THe fusion of sperm and egg produced by the same individual organism.
A chromosome that determines whether an individual is male or female.
One of the two identical parts of a duplicated chromosome in a eukaryotic cell.
The formation of sperm cells.
The pairing of two homologous chromosomes that occurs during meiosis. It is a form of chromosomal crossover. Synapsis takes place during prophase I.
2 haploid cells form; chromosomes are still double.
Haploid daughter cells form.
The mating between an individual of unknown genotype for a particular characteristic and an individual that is homozygous recessive for that same characteristic.
A change in a chromosome resulting from a chromosomal fragment attaching to a nonhomologous chromosome; can occur as a result of an error in meiosis or from mutagenesis.
Referring to organisms for which sexual reproduction produces offspring with inherited traits identical to those of the parents; the organisms are homozygous for the characteristics under consideration.
One less chromosome, usually lethal. XO. Short stature, at puberty, secondary sexual characteristic fail to develop. Sterile.
A technique for examining a fetus in the uterus. High-frequency sound waves echoing off the fetus are used to produce an image of the fetus.
The fertilized egg, which is diploid, that results from the union of a sperm cell nucleus and an egg cell nucleus.