Genetics

genetics

the study of heredity

heredity

the passing of traits from one generation to the next

trait

a specific characteristic that varies from one individual to another

gene

sequence of DNA that codes for a protein and thus determines a trait

genome

the entire "library" of genetic instructions in DNA that an organism inherits

Gregor Mendel

father of genetics

allele

alternative form of a gene (one member of a pair) located at a specific position on a specific chromosome (a letter)

dominant allele

an allele that produces the same phenotype whether its paired allele is identical or different (capital letter)

recessive allele

an allele that produces its characteristic phenotype only when its paired allele is identical (lowercase letter)

genotype

the combination of alleles located on homologous chromosomes that determines a specific characteristic or trait (the allelic combination such as Bb)

phenotype

the observable physical or biochemical characteristics of an organism, as determined by the genotype (the expressed trait such as brown eyes)

homozygous

term used to refer to an organism that has two identical alleles for the same trait (ex. BB or bb)

heterozygous

term used to refer to an organism that has two different alleles for the same trait (ex. Bb)

Punnett square

diagram showing the gene combinations that might result from a genetic cross

gamete (sex cell)

specialized cell involved in sexual reproduction (sperm or egg)

probability

the possibility of different outcomes (percentage or ratio)

monohybrid cross

a one-trait cross (ex. color)

dihybrid cross

a two-trait cross (ex. color & shape)

P generation

parental generation is the first generation involving two individuals that are mated to predict or analyze the genotypes of their offspring

F1 generation

first filial generation is the generation resulting immediately from a cross of the first set of parents (P generation)

F2 generation

second filial generation is the generation resulting from a cross between two F1 individuals

purebred

offspring that are the result of mating between genetically similar kinds of parents; opposite of hybrid; same as true breeding

hybrid

offspring that are the result of mating between two genetically different kinds of parents; opposite of purebred

Principle of Dominance

when individuals with contrasting traits are crossed, the offspring will express only the dominant trait

Law of Segregation

states that allele pairs separate, or segregate, during gamete formation

Law of Independent Assortment

states that genes for different traits can segregate independently during the formation of gametes

non-Mendelian inheritance

refers to any pattern of inheritance in which traits do not segregate in accordance with Mendel's laws (ex. incomplete dominance, codominance, multiple alleles, polygenic traits, sex-linked traits)

incomplete dominance

when one allele is not completely dominant over the other, or blending occurs (ex. Red + White = Pink)

codominance

occurs when BOTH alleles of a gene are expressed in an individual (ex. Black + White = Black & White Speckled)

multiple allele traits

traits that are controlled by more than two alleles (ex. ABO blood typing = A allele, B allele, & O allele)

polygenic traits

a trait controlled by two or more genes; produce a wide range of phenotypes

sex-linked traits

a trait genetically determined by an allele located on the sex chromosome

pedigree chart

a diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next

chromatin

unraveled and long DNA (during interphase)

chromosome

condensed, coiled, and shorted DNA (this occurs during mitosis and meiosis)

chromatids

the two identical halves of a single replicated eukaryotic chromosome and joined at the centromere

homologous chromosomes

chromosome pairs of approximately the same length, centromere position, and staining pattern, with genes for the same characteristics at corresponding places (one homologous chromosome is inherited from the mother; the other from the father)

daughter cells

new cells

mitosis

a type of cell division that results in two genetically identical daughter cells each with the same number of chromosomes of the parent cell

meiosis

a type of cell division that results in four genetically different daughter cells each with half the number of chromosomes of the parent cell (also known as reduction division)

sexual reproduction

process by which two cells from different parent unite to produce the first cell of a new organism

asexual reproduction

process by which a single parent reproduces by itself

crossing over

process in which homologous chromosomes exchange portions of their chromatids during meiosis (also called gene shuffling)

genetic variation

genetic differences within a species

fertilization

a process in sexual reproduction in which a sperm unites with an egg to make the first cell of a new organism, or zygote

zygote

fertilized egg

somatic cell

body cell (non-sex cell)

haploid (N)

term used to refer to a cell that contains only a single set of chromosomes and therefore only a single set of genes (Humans N = 23)

diploid (2N)

term used to refer to a cell that contains both sets of homolgous chromosomes (Humans 2N = 46)

chromosomal mutation

mutation that affects the number or structure of whole chromosomes

deletion chromosomal mutation

a mutation that involves the loss of all or part of a chromosome

duplication chromosomal mutation

a mutation that produces extra copies of parts of a chromosome

inversion chromosomal mutation

a mutation that reverses the direction of parts of a chromosome

translocation chromosomal mutation

a mutation that occurs when part of one chromosome breaks off and attaches to a different chromosome

nondisjunction

the most common error in meiosis and occurs when homologous chromosomes fail to separate

trisomy

a condition in which an extra copy of a chromosome is present in the cell nuclei, causing developmental abnormalities

polyploidy

condition in which an organism has extra sets of chromosomes because a complete set of chromosomes failed to separate during meiosis (ex. 3N or 4N)

DNA fingerprinting

an individual's unique sequence of DNA base pairs, determined by exposing a sample of the person's DNA to molecular probes

genetic engineering

the process of making changes in the DNA code of living organisms

genetically modified organism (GMO)

one that has artificially acquired one or more genes from the same or different species

plasmid

circular DNA found in bacteria

recombinant DNA

DNA produced by combining DNA from different organisms (DNA is cut out of one organism and recombined with another organism's DNA)

enzyme

protein that speeds up chemical reactions in organisms

restriction enzyme

DNA-cutting enzymes found in bacteria

biotechnology

the use of living organisms or other biological systems in the manufacture of drugs or other products or for environmental management, as in waste recycling

karyotype

a picture of an organism's genome and can be used for chromosomal anlysis