Notes

Chapter 17 – Simple Patterns of Inheritance p. 327 – 350

Inheritance: The acquisition of traits by their transmission from parent to offspring.

*1761-1766   Joseph Kolreuter studied inheritance in tobacco plants

Blending inheritance: An early hypothesis of inheritance that started that the genetic material that dictates hereditary traits blends together from generation to generation, and the blended traits are then passed to the next generation.

*Concept developed by Jean Baptiste Lamarck – he also believed use or disuse cause changes in offspring genetics

Particulate inheritance: The idea that the determinants of hereditary traits are transmitted intact from one generation to the next.

*Concept by Gregor Mendel (“Father of Genetics”) in the 1860s that didn’t become popular until after his death

*Hugo deVries of Holland, Carl Corrans of Germany, and Erich von Tschermak of Austria and rediscovered Mendel’s work in the 1900s.

*Why did Mendel choose pea plants?

         1)  the pea was available in many varieties and easily recognizable characteristics

         2)  peas are normally self-fertile

         3)  It is easy to cross pollinate because of the large flowers

Hybridization: A situation in which two individuals with different characteristics are mated or crossed to each other; the offspring are referred to as hybrids.

Characters: A characteristic of an organism, such as the appearance of seeds, pods, flowers, or stems.

Trait: An identifiable characteristic; usually refers to a variant.

Self-fertilization: Fertilization that involves the union of a female gamete and male gamete from the same individual.

True-breeding line: A strain that continues to exhibit the same trait after several generations of self-fertilization or inbreeding.

Cross-fertilization: Fertilization that involves the union of a female gamete and a male gamete from different individuals.

Monohybrid cross: A cross in which the inheritance of only one trait is followed.

Single-factor cross: Another name for monohybrid cross. A cross in which the inheritance of only one trait is followed.

P generation:  The parental generation in a genetic cross.

F1 generation: The first filial generation in a genetic cross.

Monohybrid: The F1 offspring, also called single-trait, of true-breeding parents that differ with regard to a single trait.

F2 generation:  The second filial generation in a genetic cross.

*(p.330) Mendel’s Postulates from his studies:

         1)  traits exist in two forms: Dominant and Recessive

         2) An individual carries two genes for a given characteristic

                     *genes have variant forms called alleles

         3)  The two alleles of a gene separate during gamate formation so that each sperm and egg receives only one allele

Dominant: A term that describes the displayed trait in a heterozygote.

Recessive: A term that describes a trait that is masked by the presence of a dominant trait in a heterozygote.

Gene: A unit of heredity that contributes to the characteristics or traits of an organism. At the molecular level, a gene is composed of organized sequences of DNA.

Allele: A variant form of a gene.

Segregate: To separate, as in chromosomes during mitosis.

Law of segregation: States that two copies of a gene segregate from each other during gamete formation and during transmission from parent to offspring.

Genotype – genetic composition of an individual

Homozygous: A individual with two identical copies of an allele.

Heterozygous: An individual with two different alleles of the same gene.

Phenotype: The characteristics of an organism that are the result of the expression of its genes.

Punnett square: A common method for predicting the outcome of simple genetic crosses.

Testcross: A cross to determine if an individual with a dominant phenotype is a homozygote or a heterozygote. Also, a cross to determine if two different genes are linked.

Dihybrid cross: A cross in which the inheritance of two different traits is followed.

Two-factor cross: Another name for a dihybrid cross. A cross in which the inheritance of two different traits is followed.

Dihybrid: An offspring that is a hybrid with respect to two traits.

Law of independent assortment: States that the alleles of different genes assort independently of each other during gamete formation.

The Chromosome Theory of Inheritance

Chromosome theory of inheritance: An explanation of how the steps of meiosis account for the inheritance patterns observed by Mendel.

*Group Question on p. 334

Locus: The physical location of a gene on a chromosome.

16.3 – Pedigree analysis of human traits

Pedigree analysis: An examination of the inheritance of human traits in families.

*Cystic fibrosis (CF) recessive allele.

*Homozygous recessive individuals include abnormalities of the pancreas, intestines, sweat glands and lungs

Autosomes: All of the chromosomes found in the cell nucleus of eukaryotes except for the sex chromosomes.

*Huntington’s disease is a dominant trait

*Appears when people are 30-50 yrs old and includes uncontrollable jerking movements of limbs, trunk and face. Progressive loss of mental ability

16.4 – Sex Chromosomes and X-linked Inheritance Patterns

Sex chromosomes: A distinctive pair of chromosomes that are different in males and females.

*First study that confirmed certain genes on specific chromosomes

X-linked gene: A gene found on the X chromosome but not on the Y.

*x chromosomes have over 1,000 genes while the Y carries less than 100 genes

Sex linked: Refers to genes that are found on one sex chromosome but not on the other.

Hemizygous: The term used to describe the single copy of an X-linked gene in a male.

*A male mammal is said to be hemizgous for an X-linked trait

16.5 – Variations in Inheritance Patterns and their Molecular Basis

Mendelian inheritance: The inheritance patterns of genes that segregate and assort independently.

Simple Mendelian inheritance: The inheritance pattern of traits affected by a single gene that is found in two variants, one of which is completely dominant over the other.

X-linked inheritance: The pattern displayed by pairs of dominant and recessive alleles located on X chromosomes.

Wild-type allele: One or more prevalent alleles in a population.

*Most cases have a wild-type allele encoding a protein that is made in proper amount to function normally.

Mutant allele: An allele that has been altered by mutation.

*these tend to be rare in a population

*Most of these recessive alleles decrease or eliminate the synthesis or functional activity of a protein.

(p.342)

Pleiotropy: The phenomenon in which a mutation in a single gene can have multiple effects on an individual’s phenotype.

Incomplete dominance: The phenomenon in which a heterozygote that carries two different alleles exhibits a phenotype that is intermediate between the corresponding homozygous individuals.

Multiple allele: Refers to the occurrence of a gene that exists as three of more alleles in a population.

Codominance: The phenomenon in which a single individual expresses two alleles.

Sex-influenced inheritance: the phenomenon in which an allele is dominant in one sex but recessive in the other.

Norm of reaction: A description of how a trait may change depending on environmental conditions.

Probability: chance that an event will have a particular outcome

Random Sampling Error: the deviation between observed and expected outcomes

Product Rule: the probability that two or more independent events will occur in equal to the product of their individual probabilities.

Sum Rule: the probability that one of two or more mutually exclusive outcomes will occur is the sum of the probabilities of the individual outcomes.

Group Questions (p.334)

1)  List 5 fundamental principles of the chromosome theory of inheritance

2)  List 10 organisms and explain how genes determine if they are male or female/have male or female organs.

*several are in the reading*