Chapter 13: Modern Understanding of Genetics:

Chromosomal Theory of Inheritance

Proposed by Sutton and Boveri, it states that genes are located on chromosomes.

Linked genes

Genes that are located close together on the same chromosome and are usually inherited together.

Independent assortment

Mendel's law that genes on different chromosomes segregate independently during gamete formation.

Crossing over

The process during meiosis where linked genes swap parts, creating genetic diversity.

Genetic mapping

The process of mapping genes on chromosomes based on recombination frequencies.

Centimorgan (cM)

Unit used to measure recombination frequency; 1% recombination corresponds to 1 cM.

Three-point test cross

A method to determine the order and distances between three genes.

Recombinant progeny

Offspring that exhibit new allele combinations due to crossing over.

Parental types

Offspring that inherit the same allele combination as their parents.

SNPs

Single-nucleotide polymorphisms, variations in a single base of a gene locus.

Karyotype

The number and appearance of chromosomes in a cell.

Karyogram

An image of an individual’s chromosomes arranged by size.

Nondisjunction

The failure of chromosomes to separate properly during meiosis.

Aneuploidy

An abnormal number of chromosomes, resulting from nondisjunction.

Trisomy

Condition where there is an extra chromosome, e.g., Down Syndrome (Trisomy 21).

Monosomy

Condition where one chromosome is missing in the pair.

Klinefelter Syndrome

A syndrome resulting from an extra X chromosome in males (XXY).

Turner Syndrome

A condition where only one X chromosome is present in females (XO).

Deletions

Chromosomal abnormalities where part of a chromosome is missing.

Duplications

Chromosomal abnormalities involving extra copies of a gene.

Inversions

Chromosomal abnormalities where gene order is reversed.

Translocations

Segments of one chromosome that move to another non-homologous chromosome.

True-breeding plants

Plants that, when self-fertilized, always produce offspring with the same trait.

F1 generation

The first filial generation, offspring from a cross between two true-breeding plants.

Dominant trait

A trait that masks the expression of a recessive trait in the phenotype.

Recessive trait

A trait that is masked by the presence of a dominant trait.

Law of Segregation

The principle that alleles separate during gamete formation.

Genotype

The genetic constitution of an individual, including alleles present.

Phenotype

The observable physical or biochemical characteristics of an organism.

Dihybrid cross

A cross that examines the inheritance of two different traits at the same time.

Testcross

A cross between an organism with a dominant phenotype and a homozygous recessive to determine the genotype.

Polygenic inheritance

A trait controlled by multiple genes, showing continuous variation.

Pleiotropy

A single gene that affects multiple traits or systems.

Codominance

A form of inheritance where both alleles are expressed in the heterozygote.

Incomplete dominance

A form of inheritance where the heterozygote displays a blend of both traits.

Mutation

A change in DNA sequence that can affect phenotype.

Probabilities of independent events

Calculated by multiplying the probabilities of each event occurring.

Rule of addition

Used to calculate the probability of mutually exclusive events.

Chiasmata

Microscopic structures that signify crossing over during meiosis.

Gene linkage

The tendency of genes located close together on a chromosome to be inherited together.

Aneuploid zygote

A zygote with an abnormal number of chromosomes due to nondisjunction.

Orphan alleles

Alleles that have no corresponding allele in a population, often resultant from mutations.

Genetic diversity

Variety of genetic characteristics within a population.

Homologous recombination

Exchange of genetic material between homologous chromosomes during meiosis.

Centromere

The region of a chromosome where the two sister chromatids attach.

Alleles

Different forms of a gene that may exist at a specific locus.

Random assortment

The process by which alleles segregate independently, leading to variation.

Banding patterns

Distinct patterns on chromosomes that help identify them during a karyotype analysis.