Unit 5: Heredity

Allele

A version of a gene found at a specific location on a chromosome

Autosome

A chromosome that is not a sex chromosome

Barr body

An inactivated X chromosome found in the cells of female mammals

Chloroplast DNA (cpDNA)

DNA located in the chloroplast, usually inherited from the mother in plants

Codominance

A form of inheritance where both alleles are fully and equally expressed

Crossing over

The exchange of genetic material between homologous chromosomes during meiosis

Daughter cell

A new cell formed as a result of cell division

Dihybrid cross

A genetic cross involving two traits

Diploid

A cell that contains two sets of chromosomes, one from each parent

Dominant

An allele that is expressed even if only one copy is present

Epistasis

A phenomenon where one gene affects the expression of another gene

Fertilization

The fusion of a sperm and an egg to form a zygote

Gamete

A haploid sex cell such as a sperm or egg

Genetic disorders

Diseases or conditions caused by changes or mutations in DNA

Genetic diversity

The total variety of genetic characteristics in a population

Genetic linkage

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

Genetics

The study of heredity and variation in living organisms

Genotype

The genetic makeup of an organism in terms of its alleles

Haploid

A cell containing only one complete set of chromosomes

Heterozygous

Having two different alleles for a gene

Homozygous dominant

Having two identical dominant alleles for a gene

Homozygous recessive

Having two identical recessive alleles for a gene

Incomplete dominance

A form of inheritance where the phenotype is a blend of both alleles

Karyotype

A picture showing an organism's chromosomes arranged in pairs

Law of independent assortment

Mendel's principle that genes for different traits are inherited independently

Law of segregation

Mendel's principle that two alleles for a gene separate during gamete formation

Lethal allele

An allele that can cause the death of an organism if present in a certain genotype

Linkage map

A genetic map showing the relative locations of genes on a chromosome

Linked genes

Genes located close together on the same chromosome that are inherited together

Locus (loci)

The specific physical location of a gene on a chromosome

Map unit

A unit of distance on a chromosome equal to a 1 percent recombination frequency

Meiosis (I and II)

The two-part cell division that results in four genetically unique gametes

Mendels Laws

The foundational principles of heredity established by Gregor Mendel

Mitochondrial DNA (mtDNA)

DNA found in mitochondria that is inherited from the mother

Monohybrid cross

A genetic cross involving one trait

Monosomy

A condition where an individual has only one copy of a chromosome instead of two

Multiple alleles

More than two possible alleles exist for a gene in a population

Non nuclear inheritance

The inheritance of DNA found outside the nucleus such as in mitochondria or chloroplasts

Nondisjunction

The failure of chromosomes to separate properly during meiosis

P F1 F2 Generations

The parental first filial and second filial generations used in genetic crosses

Pedigree

A diagram that shows how a trait is inherited over several generations

Phenotype

The observable traits or characteristics of an organism

Phenotypic plasticity

The ability of one genotype to produce different phenotypes in different environments

Polygenic inheritance

A trait controlled by two or more genes

Polyploidy

A condition in which an organism has more than two complete sets of chromosomes

Punnett square

A chart used to predict the genetic outcomes of a cross

Random assortment

The random distribution of chromosomes into gametes during meiosis

Recombinant chromosome

A chromosome that has undergone crossing over and contains genes from both parents

Recombination

The rearrangement of genetic material through crossing over or independent assortment

Rules of probability

Mathematical principles used to predict the likelihood of genetic outcomes

Sex chromosome

A chromosome that determines an individual's biological sex

Sex linked trait

A trait associated with a gene carried on a sex chromosome

Sexual reproduction

Reproduction involving the combination of genetic material from two parents

Somatic cell

Any body cell that is not a gamete

Test cross

A genetic cross used to determine an unknown genotype by crossing with a homozygous recessive

Tetrad

A group of four chromatids formed during meiosis by the pairing of homologous chromosomes

Trait

A specific inherited characteristic of an organism

Trisomy

A condition where an organism has three copies of a chromosome instead of two

True breeding

Organisms that produce offspring identical to themselves when self fertilized

X chromosome

A sex chromosome found in both males and females

X Inactivation

The process by which one of a female's X chromosomes becomes inactive

X linkage

A gene located on the X chromosome

Y chromosome

The sex chromosome found only in males

Zygote

A fertilized egg cell formed by the fusion of a sperm and an egg