Chapter 13/14 important terms

Genotype

The particular set of alleles that is carried by an individual’s chromosomes.

Phenotype

An individual’s observable traits.

Homozygous

Having two identical alleles at the same locus on homologous chromosomes.

Heterozygous

Having two different alleles at the same locus on homologous chromosomes.

hybrid/carrier

A heterozygous individual.

Dominant

Refers to an allele that masks the effect of a recessive allele paired with it in heterozygous individuals.

Recessive

Refers to an allele with an effect that is masked by a dominant allele on the homologous chromosome.

Monohybrid

Cross between two individuals identically heterozygous for one gene; for example Aa × Aa.

Dihybrid

Cross between two individuals identically heterozygous for two genes; for example, AaBb × AaBb.

Trait

a specific characteristic or feature of an organism. These traits can be inherited from parents and are passed down through genes. They can be observable (like eye color or height) or internal (like the ability to digest milk).

Allele

Forms of a gene with slightly different DNA sequences; may encode different versions of the gene’s product.

law of segregation

When parents make sperm or egg cells, they separate the two copies of a gene (called alleles) so that each sperm or egg cell only gets one copy. This way, when the sperm and egg cells combine during fertilization, the offspring receives one allele from each parent for each trait. 

law of independent assortment

The alleles of two (or more) different genes get sorted into gametes independently of one another. (When you mix and match traits from parents, the traits don't influence each other).

punnett square

Diagram used to predict the genotypic and phenotypic outcomes of a cross.

test cross

Method of determining the genotype of an individual with a dominant phenotype

linkage group

All of the genes on a chromosome.

Codominant

Effect in which the full and separate phenotypic effects of two alleles are apparent in heterozygous individuals. (like white and red spots on something together)

incomplete dominance/intermediate inheritance

Inheritance pattern in which one allele is not fully dominant over another, so the heterozygous phenotype is an intermediate blend between the two homozygous phenotypes. (red + white = pink).

multiple allele systems

The presence of three or more alternative forms of a gene at a specific locus within a population. This concept is illustrated through various examples, such as the ABO blood group system in humans, which includes four distinct blood types: A, B, AB, and O.

Epistasis

Polygenic inheritance, in which a trait is influenced by multiple genes.A classic example is Labrador retriever coat color, where one gene determines if pigment is produced at all, and another determines the color (black or brown) if pigment is produced. 

Pleiotropic

Refers to a gene that affects multiple traits. Sickle Cell Anemia: A mutation in the hemoglobin gene can cause red blood cells to become sickle-shaped and also affects other traits like blood flow, fatigue, and malaria resistance. 

continuous variation

Traits that can change gradually and smoothly within a population, like height or weight, rather than falling into distinct categories. It's a range of differences, with many intermediate values between the extremes. Imagine a line with different people on it. Some are very tall, some are very short, and many are in between.

short tandem repeats

In chromosomal DNA, sequences of a few nucleotides repeated multiple times in a row. Used in DNA profiling.

bell curve

Bell-shaped curve; typically results from graphing frequency versus distribution for a trait that varies continuously.

Pedigree

Chart of family connections that shows the appearance of a phenotype through generations.

Sex-linkage

traits determined by genes located on sex chromosomes (X and Y), resulting in different inheritance patterns between males (XY) and females (XX)

Autosomal dominance

a single copy of a mutated gene is sufficient to cause a trait or disorder

autosomal recessive

a trait or disease is carried on a non-sex chromosome (autosome) and requires two copies of a mutated gene for the condition to manifest

Duplications

Repeated section of DNA in a chromosome.

Inversions

Structural rearrangement of a chromosome in which part of the DNA has become oriented in the reverse direction.

Translocations

In genetics, structural rearrangement in which a broken piece of chromosome has become reattached in the wrong location

Nondisjunction

Failure of chromosomes to separate properly during nuclear division.

Polyploidy

A condition where an organism or cell contains more than two complete sets of chromosomes. It can arise from errors in cell division, such as during meiosis, or through the fertilization of an egg by more than one sperm. Example: Could have 3n (triploid) or 4n (tetraploid) sets of chromosomes. 

Aneuploidy

Condition of having too many or too few copies of a particular chromosome. Example: A human normally has 46 chromosomes (2n). It could involve having 45 chromosomes (monosomy) or 47 chromosomes (trisomy). Can specifically occur from nondisjunction