Chapter 9: Patterns of Inheritance

Practice flashcards covering vocabulary and key concepts from Chapter 9 on Patterns of Inheritance, including Mendelian laws, human genetic disorders, and chromosomal basis of inheritance.

Pangenesis

An early explanation for inheritance proposed around $400$ BCE by Hippocrates, suggesting that particles called pangenes from all parts of an organism travel to eggs or sperm.

Blending hypothesis

A $19\text{th}$-century idea suggesting that hereditary materials mix in forming offspring, which was later rejected because it failed to explain how traits could reappear in later generations.

Heredity

The transmission of traits from one generation to the next.

Genetics

The scientific study of heredity, which began in the $1860\text{s}$ with the work of Gregor Mendel.

Character

A heritable feature that varies among individuals, such as flower color.

Trait

Each variant for a character, such as purple or white flowers.

True-breeding

Varieties for which self-fertilization produces offspring all identical to the parent.

Hybrids

The offspring of two different varieties.

Genetic cross

The process of cross-fertilization, also known as hybridization.

P generation

The true-breeding parental plants in a genetic study.

F1 generation

The hybrid offspring of the P generation.

F2 generation

The offspring resulting from a cross of the F1 plants.

Monohybrid cross

A cross between two individuals that differ in only a single character.

Alleles

Alternative versions of genes that account for variations in inherited characters.

Homozygous

A genotype in which an organism has two identical alleles for a gene.

Heterozygous

A genotype in which an organism has two different alleles for a gene.

Dominant allele

The allele that determines the organism’s appearance when the two alleles of an inherited pair differ.

Recessive allele

The allele that has no noticeable effect on the organism’s appearance when paired with a dominant allele.

Phenotype

The physical appearance or expression of a trait in an organism.

Genotype

The genetic makeup of a trait in an organism.

Law of segregation

Mendel's law stating that a sperm or egg carries only one allele for each inherited character because allele pairs separate from each other during gamete production.

Punnett square

A diagram used to show the four possible combinations of alleles that could occur when gametes combine.

Locus

The specific location of a gene along a chromosome.

Dihybrid cross

A mating of parental varieties that differ in two characters.

Law of independent assortment

Mendel's law suggesting that the inheritance of one character has no effect on the inheritance of another.

Testcross

A mating between an individual of unknown genotype and a homozygous recessive individual to determine the unknown genotype.

Rule of multiplication

A rule of probability where the probability of a compound event is the product of the separate probabilities of the independent events.

Rule of addition

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

Wild-type traits

Traits that prevail in nature, which are not necessarily specified by dominant alleles.

Pedigree

A family tree that shows the inheritance of a trait in a family through multiple generations.

Carriers

Heterozygous individuals who do not display a recessive disorder but can pass the recessive allele to their offspring.

Inbreeding

Mating between close relatives, which increases the probability of offspring inheriting two recessive alleles for a disease.

Cystic fibrosis (CF)

The most common fatal genetic disease in the United States, characterized by excessive thick mucus secretions and carried by approximately $1$ in $31$ Americans.

Achondroplasia

A dominant human disorder that results in dwarfism.

Huntington’s disease

A dominant degenerative disorder of the nervous system that usually strikes in middle age.

Amniocentesis

A technique for detecting genetic conditions in a fetus by extracting amniotic fluid for karyotyping and biochemical tests.

Chorionic villus sampling (CVS)

A procedure that removes a sample of placental tissue to perform karyotyping and biochemical tests on a fetus.

Ultrasound imaging

The most common fetal imaging procedure, using sound waves to produce a picture of the fetus to check for anatomical deformities.

Complete dominance

A type of inheritance where the phenotypes of the heterozygote and the dominant homozygote are identical.

Incomplete dominance

A condition where the appearance of F1 hybrids falls between the phenotypes of the two parental varieties, such as pink flowers from red and white parents.

Codominance

A condition in which both alleles are expressed in heterozygous individuals, such as in the AB blood group.

Pleiotropy

A situation where one gene influences multiple characteristics, as seen in sickle-cell disease.

Polygenic inheritance

An inheritance pattern where a single phenotypic character results from the additive effects of two or more genes, such as human skin color.

Chromosome theory of inheritance

The theory stating that genes occupy specific loci on chromosomes and that chromosomes undergo segregation and independent assortment during meiosis.

Linked genes

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

Recombination frequency

The percentage of recombinant offspring produced in a genetic cross.

Sex chromosomes

The X and Y chromosomes that determine an individual’s sex in many species.

Hemophilia

A sex-linked recessive disorder characterized by excessive bleeding due to a lack of one or more blood-clotting proteins.

Red-green color blindness

A sex-linked recessive disorder involving the malfunction of light-sensitive cells in the eyes.

Duchenne muscular dystrophy

A sex-linked recessive condition characterized by progressive muscle weakening and loss of coordination.