Principles of Biology I - Exam 4 (Ch. 13 - 15) - KEY TERMS

Heredity

the transmission of traits from one generation to the next

Genetics

the study of heredity and variation

Gene

a unit of heredity; a segment of DNA that codes for a specific trait

Allele

different version of the same gene

Gamete

a reproductive cell (egg or sperm) containing a single set of chromosomes

Somatic cell

any cell in the body that is not a gamete

Haploid

having a single set of chromosomes

Diploid

having two sets of chromosomes

Zygote

a fertilized egg; the cell formed when sperm and egg unite

Fertilization

the union of two gametes

Meiosis

cell division that reduces chromosome number by half, creating gametes

Mitosis

cell division that produces two identical daughter cells

Homologous chromosomes

two chromosomes that carry the same genes at the same loci

Sex chromosomes

chromosomes that determine sex (X and Y in mammals)

Autosomes

chromosomes that are not sex chromosomes

Karyotype

an ordered display of the pairs of chromosomes from a cell

Crossing over

the exchange of genetic material between homologous chromosomes during meiosis

Independent assortment

the random alignment of homologous chromosomes during meiosis

Sporophyte

the diploid multicellular stage in plants that makes haploid spores by meiosis

Gametophyte

the haploid multicellular stage in plants that makes gametes by mitosis

Centromere

the region where sister chromatids are joined

Sister chromatids

two identical copies of a chromosome joined at the centromere

Recombination

the production of new combinations of alleles as a result of crossing over

Genetic variation

differences in genetic makeup among individuals of a population

Mutation

a change in an organism's DNA; the original source of genetic diversity

True breeding

individuals that pass on specific traits to all of their offspring

Hybridization

crossing of two true breeding populations with different traits

P generation

parental generation in genetic crosses

F₁ generation

first filial (offspring) generation in genetic crosses

F₂ generation

second filial generation, offspring from crossing F₁ individuals

Dominant allele

an allele that determines the phenotype even when heterozygous

Recessive allele

an allele that only affects the phenotype when homozygous

Homozygous

having two identical alleles for a gene

Heterozygous

having two different alleles for a gene

Genotype

the genetic makeup of an organism; the combination of alleles

Phenotype

the observable traits of an organism

Monohybrid cross

a genetic cross tracking a single trait

Dihybrid cross

a genetic cross tracking two traits simultaneously

Testcross

crossing an individual with an unknown genotype with a homozygous recessive individual

Punnett square

a diagram used to predict the outcomes of a genetic cross

Law of segregation

allele pairs separate during gamete formation, and reunite randomly during fertilization

Law of independent assortment

genes for different traits segregate independently during gamete formation

Complete dominance

when the heterozygote phenotype is identical to the dominant homozygote

Incomplete dominance

when the heterozygote phenotype is intermediate between both homozygotes

Codominance

when both alleles are expressed in the heterozygote

Multiple alleles

when a gene has more than two possible alleles in a population

Pleiotropy

when one gene affects multiple phenotypic traits

Epistasis

when one gene affects the phenotypic expression of another gene

Polygenic inheritance

traits controlled by multiple genes that each contribute to the phenotype

Pedigree

a family tree showing the inheritance of traits across generations

Carrier

an individual who has a recessive allele but does not show the trait

Sex-linked gene

a gene located on a sex chromosome

X-linked trait

a trait determined by a gene on the X chromosome

Barr body

an inactivated X chromosome in female mammals

Linked genes

genes located on the same chromosome that tend to be inherited together

Genetic map

a diagram showing the relative positions of genes on a chromosome

Map unit

a unit of measurement for genetic distance; 1% recombination frequency

Nondisjunction

failure of homologous chromosomes to separate during meiosis

Aneuploidy

having an abnormal number of chromosomes

Monosomy

having only one copy of a particular chromosome instead of two

Trisomy

having three copies of a particular chromosome instead of two

Polyploidy

having more than two complete sets of chromosomes

Deletion

a chromosomal mutation where a segment is lost

Duplication

a chromosomal mutation where a segment is repeated

Inversion

a chromosomal mutation where a segment is flipped

Translocation

a chromosomal mutation where a segment moves to a non-homologous chromosome

Genomic imprinting

when the phenotype depends on which parent passed along the allele

Cytoplasmic inheritance

inheritance of genes in organelles such as mitochondria

SRY gene

gene on Y chromosome responsible for male development in mammals

Mosaicism

condition where different cells in the same individual have different genetic makeup

Parental phenotypes

phenotypes in F₂ generation that match those in the P generation

Recombinant phenotypes

new phenotypes in F₂ generation from genetic recombination

Life cycle

generation-to-generation sequence of stages in an organism's reproductive history

Crossover frequency

the percentage of recombinant offspring; indicates genetic distance

Multifactorial trait

trait determined by multiple genes and environmental factors