Ib Biology 1

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genetics

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the scientific study of heredity and hereditary variations

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self-fertilize

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the fusion of sperm and egg produced by the same individual organism

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cross-fertilization

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the fusion of sperm and egg derived from two different individuals

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true-breeding

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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

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hybrid

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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

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cross

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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

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P generation

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the parent individuals from which offspring are derived in studies of inheritance; P stands for parental

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F1 generation

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the offspring of two parental (P generation) individuals; F1 stands for first filial

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F2 generation

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the offspring of the F1 generation; F2 stands for second filial

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monohybrid cross

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an experimental mating of individuals differing at one genetic locus

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allele

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an alternative form of a gene

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homozygous

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having two identical alleles for a given gene

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heterozygous

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having two different alleles for a given gene

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dominant allele

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in a heterozygote, the allele that determines the phenotype with respect to a particular gene

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recessive allele

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in a heterozygote, the allele that has no noticeable effect on the phenotype

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law of segregation

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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

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punnett square

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a diagram used in the study of inheritance to show the results of random fertilization

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phenotype

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the expressed traits of an organism; the appearance of an organism

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genotype

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the genetic makeup of an organism

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dihybrid cross

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an experimental mating of individuals differing at two genetic loci

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law of independent assortment

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a general rule 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

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testcross

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the mating between an individual of unknown genotype for a particular characteristic and an individual that is homozygous recessive for that same characteristic

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rule of multiplication

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a rule stating that the probability of a compound event is the product of the separate probabilities of the independent events

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rule of addition

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a rule stating that the probability that an event can occur in two or more alternative ways is the sum of the separate probabilities of the different ways

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pedigree

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a family tree representing the occurrence of heritable traits in parents and offspring across a number of generations

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carriers

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an individual who is heterozygous for a recessively inherited disorder and who therefore does not show symptoms of that disorder

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cystic fibrosis

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recessive disorder; a genetic disease that occurs in people with two copies of a certain recessive allele; characterized by an excessive secretion of mucus and vulnerability to infection; fatal if untreated

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inbreeding

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mating between close relatives

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achondroplasia

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dominant disorder; a form of human dwarfism caused by a single dominant allele; the homozygous condition is lethal

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Huntington's disease

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dominant disorder; a human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10 to 20 years after the onset of systems

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amniocentesis

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a technique for diagnosing genetic defects while a fetus is in the uterus; a sample of amiotic fluid, obtained via a needle inserted into the amnion, is analyzed for telltale chemicals and defective fetal cells

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chorionic villus sampling

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a technique used 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

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ultrasound imaging

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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

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complete dominance

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a type of inheritance in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable

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incomplete dominance

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a type of inheritance in which the phenotype of a heterozygote is intermediate between the phenotypes of the two types of homozygotes

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ABO blood group

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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

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codominant

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inheritance pattern in which a heterozygote expresses the distinct trait of both alleles

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pleiotropy

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the control of more than one phenotypic characteristic by a single gene

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polygenic inheritance

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the additive effect of two or more gene loci on a single phenotypic characteristic

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chromosome theory of inheritance

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a basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns

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linked genes

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genes located on the same chromosome that tend to be inherited together

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recombination frequency

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with respect to two given genes, the number of recombinant progeny from a mating divided by the total number of progeny; recombinant progeny carry combinations of alleles different from those in either of the parents as a result of independent assortment of chromosomes crossing over

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sex chromosomes

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chromosome that determine whether an individual is male or female

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sex-linked gene

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a gene located on a sex chromosome

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red-green color blindness

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a category of common, sex-linked human disorders involving several genes on the X chromosome; characterized by a malfunction of light-sensitive cells in the eyes; affects mostly males but also homozygous females

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hemophilia

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a human genetic disease cause by a sex-linked recessive allele; characterized by excessive bleeding following injury

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turner syndrome

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a chromosome disorder in females that is characterized by the absence of all or part of a second sex chromosome in some or all cells

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klinefelter syndrome

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also known as the XXY condition, is a term used to describe males who have an extra X chromosome in most of their cells

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down syndrome

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a common chromosome disorder due to an extra chromosome number 21