Genetics Terminology and Pedigree Analysis

Mr. Stellakis Guided Notes - Genetics

allele

A variant form of a gene.

codominance

A genetic scenario where both alleles in a heterozygote are fully expressed.

dominant

An allele that expresses its phenotype even in the presence of a recessive allele.

epistasis

A form of gene interaction where one gene masks or suppresses the expression of another gene.

genotype

The genetic constitution of an individual, represented by alleles.

heterozygous

Having two different alleles for a particular gene.

homozygous

Having two identical alleles for a particular gene.

Hybrid

An organism that is the offspring of genetically distinct parents.

incomplete dominance

A genetic situation where the phenotype of heterozygotes is intermediate between the phenotypes of the two homozygotes.

law of independent assortment

The principle that alleles for different traits are distributed to sex cells (& offspring) independently of one another.

law of segregation (bio)

The principle stating that allele pairs separate during gamete formation, and randomly unite at fertilization.

Locus

The specific physical location of a gene on a chromosome.

multiple allele system

A situation where three or more alleles exist for a particular gene.

Pedigree

A diagram that shows the occurrence of a genetic trait in several generations of a family.

Phenotype

The observable physical or biochemical characteristics of an organism, as determined by both genetic makeup and environmental influences.

Polygenic inheritence

A type of inheritance where multiple genes determine the phenotype of a trait.

Purebred

An organism whose ancestors are genetically uniform.

Recessive

An allele that only expresses its phenotype when two copies are present.

On a pedigree are males squares or circles

Males are represented by squares.

On a pedigree are females squares or circles

Females are represented by circles.

If a shape is shaded in a pedigree it means…

The individual has the trait being studied.

if a shape is half shaded it means…

The individual is a carrier of the trait.

9:3:3:1 Ratio in Punnet Squares

Genotype for both parents: AaBb

In a dihybrid cross, the 9:3:3:1 ratio results from the independent assortment of alleles, leading to nine offspring exhibiting both dominant traits, three with one dominant and one recessive trait, three with the other dominant trait and a recessive trait, and one with both recessive traits.

Dihybrid Cross

A genetic cross involving two traits, each represented by two alleles, demonstrating the inheritance patterns and ratios of offspring phenotypes.EX: AaBb x AAbb

Blood Type A

I^AI^A or I^Ai

Receives from A or O

Can donate to A or AB

Blood Type B

I^BI^B or I^Bi

Receives from B or O

Can donate to B or AB

Blood Type AB

I^AI^B

Receives from A, B, AB, or O

Blood Type O

ii **(RECESSIVE BLOOD TYPE)

Receives only from O

Donates to ALL types

Sex-Linked Traits

Sex-linked traits are characteristics determined by genes found on the sex chromosomes (X and Y). These traits often exhibit different inheritance patterns in males (XY) and females (XX) due to the varying numbers of X chromosomes.

*Relates to the X chromosome being the reason it is present

Autosomal

traits are controlled by genes located on autosomes (non-sex chromosomes) and follow Mendelian inheritance patterns.

X-Linked Traits

X-linked traits are characteristics determined by genes located on the X chromosome, typically exhibiting different inheritance patterns in males and females.