Bio 8.1 and 8.2

Chromosomes

Structures within cells that contain genetic information.

Alleles

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

Segregation

The process by which alleles separate during gamete formation.

Independent Assortment

The process where different genes independently separate from one another when reproductive cells develop.

Homozygous Genotype

A genotype consisting of two identical alleles for a trait.

Heterozygous Genotype

A genotype consisting of two different alleles for a trait.

Dominant Allele

An allele that expresses its phenotype even in the presence of a recessive allele.

Recessive Allele

An allele that expresses its phenotype only when two copies are present.

Punnett Square

A diagram used to predict the genotype and phenotype of offspring from a genetic cross.

Incomplete Dominance

A genetic situation in which one allele does not completely dominate another allele, resulting in a new phenotype.

Codominance

A genetic scenario where both alleles in a heterozygote are fully expressed.

ABO Blood System

A classification system for blood based on the presence or absence of antigens on the surface of red blood cells.

Sex Determination

The biological mechanism that determines the development of sexual characteristics in an organism.

Sex-Linked Genes

Genes located on sex chromosomes that can exhibit different inheritance patterns.

Genetic Pedigree

A diagram that shows the occurrence and appearance of phenotypes of a particular gene or organism and its ancestors.

Newborn Screening

Mandatory testing performed 24 hours after birth to detect certain genetic disorders.

False Positive

A test result that indicates a disease is present when it is not.

Early Detection

Identifying a disorder at an early stage to allow for timely treatment.

Krabbe Disease

A rare genetic disorder that affects the nervous system, included in some newborn screening panels.

Phenylketonuria (PKU)

a genetic disorder that results in the inability to metabolize phenylalanine.

Central Dogma of Biology

The process by which DNA is transcribed to RNA and then translated into proteins.

Gene

A segment of chromosome that contains code required to direct the manufacture of a polypeptide or RNA molecule.

Proteins

What molecules do genes generally "code" for?

Genome

All the genes of an organism known collectively.

Prokaryotes

Organisms with single, circular chromosomes.

Eukaryotes

Organisms with multiple linear chromosomes.

Genetic information

The amount of genetic information in an organism does not correlate to its complexity; Stalked adder's tongue (plant) has 1260 chromosomes, but not more complex than humans.

Instruction manual analogy

Genes are analogous to words in an instruction manual for building a human; chromosomes are analogous to instruction manual pages.

Allele

One specific form of a gene, differing from other alleles by one or only a few base pairs and occupying the same gene locus as other alleles of the gene.

Locus

The specific physical location of a gene or other DNA sequence on a chromosome, like a genetic street address.

Genetic variation

Produced by copying and transmittal of parental genes to the next generation.

DNA replication

Produces duplicate DNA molecules, analogous to 'rewriting' an instruction manual page.

Mutation

Mistakes in copying DNA, analogous to a typographical error in an instruction manual.

Homologous pairs

Equivalent chromosomes; pairs contain one chromosome received from each parent.

Body cell

Has two complete copies of the manual, 23 page copy from mom + 23 page copy from dad = 46 total pages.

Random alignment

The uncoordinated 'lining up' of maternal and paternal homologous chromosome pairs before the first division of meiosis.

Gregor Mendel

Considered the first genetic scientist who accurately described simple rules of inheritance.

Mendel's Experiments

Controlled mating between pea plants, involving 30,000 plants over 10 years, describing patterns of inheritance for traits from single genes with a few alleles.

Phenotype

Physical traits of an individual, e.g. eye color, hair color, height.

Genotype

Genetic composition of an individual; describes alleles.

Homozygous

Carries two copies of the same allele (e.g., RR, rr, GG, gg, PP, pp).

Heterozygous

Carries two different alleles (e.g., Rr, rR, Gg, gG, Pp, pP).

Dominant Phenotype

The phenotype is seen when homozygous or heterozygous.

Recessive Phenotype

The phenotype of an allele is seen only when homozygous.

Pure Breeds

Organisms that are homozygous for a trait.

Heterozygotes

Organisms that have two different alleles for a trait.

Genetic Diseases in Humans

Rare, serious diseases caused by mutant alleles, mostly recessive alleles following Mendelian rules, screened for in newborn testing.

Pleiotropy

A single gene causes multiple effects on an individual's phenotype.

Galactosemia

Inability to digest sugar causes sugar accumulation in various organs.

Carriers

Heterozygotes for a recessive disease who are not affected by the disease but can pass the trait to the next generation.

Cystic fibrosis

Most common recessive disease in Europeans, affecting 1 in 2500, with 1 in 25 as heterozygous carriers; defect in chloride ion transport produces thick mucus.

Congenital hypothyroidism (C H)

Inadequate production of thyroid hormones, mostly caused by recessive mutations, may also be due to a dominant allele.

Dihybrid cross

Mating crosses that involve two traits, determining the possible gametes for pea seeds.