Terminology Chapter 23-24

genetics

the study of heredity and the variation of inherited characteristics. focuses on how traits and characteristics are passed from parent to offspring

inheritance

the process by which genetic information is passed from parents to offspring. involves the transmission of genes, - units of heredity

mendelian inheritance - follows specific patterns - dominant and recessive traits

non-mendelian inheritance - incomplete dominance and codominiance

DNA

A complex molecule containing the genetic information that makes up the chromosomes.

Genes

A segment of DNA on a chromosome that codes for a specific trait; can exist in various forms called alleles - contribute to genetic variation

Allele

any one of two or more genes that may occur alternatively at a locus on a chromosome; may occur in pair or there may be multiple alleles affecting the organisms phenotype

Chromosome

threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins - primarily histones - humans have 46 chromosomes arranged in 23 pairs

Genotype

genetic makeup of an organism, combination of alleles inherited from both parents; environmental factors can influce the expression of a genotype

Phenotype

the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.

Gregor Mendel

Augustinian monk and botanist whose experiments in breeding garden peas led to his eventual recognition as father of modern genetics, formulated the laws of segregation and independent assortment, established the concept of dominant and recessive traits

Law of Segregation

states that the pairs of homologous chromosomes (alleles) separate during gamete formation so that only one pair from each pair is present in each gamete; each gamete carriers one allele for each gene - law applies to traits goverened by signle genes with two alleles

Law of Independent Assortment

stating that allele pairs separate from one another independently during gamete formation, this principal applies to genes located on different chromosomes or far apart on the same chromosome; dihybrid or polyhybrid crosses

Law of Dominance

In many traits one allele is dominant over the other allele. The "weaker (recessive)" allele is only expressed when it is paired with another recessive allele

Recessive

trait of an organism that can be masked by the dominant form of a trait but is expressed when paired with another recessive allele

Law of Unit Characters

Factors (alleles), which always occur in pairs, control the inheritance of various characteristics; states that traits are determined by genes (inherited independently from one anther during gamete formation)

Homozygous

An organism that has two identical alleles for a specific gene (Dominant (AA) or Recessive (aa) , individuals that are homologous express the same trait for that gene

Heterozygous

An organism that has two different alleles for a specific gene, (Aa) one allele is typcially dominant while the other is recessive; contributes to the diversity within a population

Punnett Square

A chart that shows all the possible combinations of alleles that can result from a particular genetic cross

Gene Linkage

Refers to the tendency of genes located close together on a chromosome to be inherited toghter, linked genes do not assort independently during meiosis (affecting genetic variation) the closer the genes are on a chromosmoe the higher the likelihood they will be inherited together

Recombination

the process by which genetic material is rearranged during cell division, occurs primarly during meiosis leading to genetic diversity in offspring; homologous chromosomes exchange segments of DNA through crossing over, introduces new genetic variations

Crossing Over

Genetic process during meiosis; involves the exchange of chromosome segements between homologous chromosomes; occurs during Prophase I of meiosis, results in new allele combinations

X Linked Inheritance

Refers to traits determined by genes located on the X chromosome; males are (XY) and are more likely to express Z-linked traits since they have only one X chromosome; females (XX) can be carriers of X-linked traits without expressing them if the other X chromosome is normal (common x-linked traits are hemophilia and color blindness) affected fathers pass the trait to all daughters but none of their sons

Karyotype

A visual display of the chromosome pairs of a cell arranged by size and shape.

Aneuploidies

genetic disorder caused by an abnormal number of chromosomes; can result from nondisjunction during cell division, leading to extra or missing chromosomes, (common types include trisomy (3 copies of a chromosome) and monosomy (one copy of a chromosome) they can lead to developement disorders and various helath issues such as down syndrome (trisomy 21) disgnosis is often made through kayrotyping or genetic testing

Nondisjunction

Error in meiosis in which homologous chromosomes fail to separate.

Phenotypic Ratio

the relative frequency of different phenotypes in a population; expressed as a ration based on observable traits, the ratio arises from the combination of alleles during inheritance

Dominant Inheritance (AA)

A pattern of inheritance in which the phenotypic effect of one allele is completely expressed within a homozygous and heterozygous genotype, the individual only needs one copy of a dominant allele to express the trait, traits goverened by dominant alleles can be passed from one generation to the next.

Recessive Inheritance

A pattern of inheritance in which the phenotypic effect of one allele is only expressed within a homozygous genotype. In a heterozygous condition with a dominant allele, it is not expressed in the phenotype; recessive alleles can be carried without being expressed, known as being a carrier; traits goverened by recessive alleles can skip generations if carriers do not express the trait, (common examples of recessive inheritance include cystic fibrosis and sickle cell anemia)

Incomplete Dominance

Genetic phenomenon where neither allele is completely dominant, the resulting phenotype is a blend of the two parental traits, occurs in heterozygous individuals with two different alleles, (example of this would be the flower color of snapdragons, where red and white flowers produce pink offspring, differs from complete dominance where one allele completely masks the other

Codominance

Genetic scenario in which both alleles in a heterozygous individual are both expressed, the phenotype that displays characteristics of both alleles simultaneously, (example is the ABO blood group system, where both A and B alleles are expressed in AB blood type) differs from complete dominance but contrasts with incomplete dominance where the phenotype is a blend of the two alleles

Multiple Allele Inheritance

Involves more than two alleles for a single gene, each individual carries only two alleles (one from each parent) alleles can exhibit dominance, codominance or incomplete dominance; this patter leads to a variety of phenotypes in a population, (example is the ABO blood group system in humans)

Pedigree

A diagram that shows the occurrence of a genetic trait in several generations, represents the lineage or ancestory of an individual

male - square

female - circle

unaffected - open

affected - shaded in

Genotypic ratio

the relative frequencies of different genotypes in offspring, typical derived from a punnett square of a genteic cross (common ratios include 1:2:1 for heterozygous crosses and 3:1 for dominant recessive traits) reflects the genetic makeup rather than the physical traits

Monohybrid Cross

A type of genetic cross between two individuals with homozygous genotypes of a single character or trait, often resulting in an opposite phenotype

Dihybrid Cross

A type of genetic cross between two individuals with either homozygous or heterozygous genotypes of two characters or traits