Genetics and Pedigrees

Genotype

Genetic makeup.

Phenotype

Physical expression.

Dominant

Expressed when present.

Recessive

Only shown when homozygous.

Punnett Square

Diagram predicting offspring ratios.

Pedigree

Chart of inheritance.

What is a gene?

A sequence of DNA that codes for a protein.

What is an allele?

Different version of a gene.

What is the Law of Segregation?

Alleles separate during gamete formation.

What is the genotype ratio of Aa x Aa?

1 AA : 2 Aa : 1 aa.

What is phenotype ratio of Aa x Aa?

3:1 dominant : recessive.

What is a test cross?

Unknown genotype × homozygous recessive.

Autosomal dominant traits appear…

In every generation.

Autosomal recessive traits often…

Skip generations.

X-linked traits affect mostly…

Males.

What symbol represents a female?

Circle.

What symbol represents a male?

Square.

What does a shaded shape mean?

Affected individual.

Gregor Mendel

Father of Genetics; Studied inheritance of traits in pea plants. He found that plants' offspring retained traits of the parent

Trait

any characteristic that can be passed from parent to offspring

Homozygous

gene combination involving two dominant or two recessive genes (e.g RR or rr); also called pure

Heterozygous

gene combination of one dominant and one recessive allele (e.g Rr); also called as hybrid

Monohybrid cross

a cross involving single trait (e.g. flower color)

Dihybrid cross

cross involving two traits (e.g. flower color and plant height)

Law of Dominance (complete dominance)

Mendel's first law that states that in a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation.

Law of segregation

Mendelian law stating that two alleles for each trait separate during meiosis; Alleles for a trait will then "recombine" at fertilization producing the genotype for the traits of the offspring

Law of independent assortment

Alleles for different traits are distributed ) independently of one another; Inheritance of one trait does not affect inheritance of the other = law of independent assortment. This law is best illustrated using a Dihybrid Cross

Incomplete Dominance

Situation in which one allele is not completely dominant over another allele; Cross between organisms with two different phenotypes produces offspring with a third phenotype, usually a blend in color
(e.g Red x White = Pink Flowers)

Codominance

A condition in which both alleles for a gene are fully expressed; Phenotype of both alleles is expressed
(e.g Red hair x White hair = Roan)

Sex-linked Traits

Traits carried by the sex chromosomes (e.g Hemophilia and color blindness)

X-linked traits

The gene is found on the x chromosomes
Example: Color blindness

Y-linked trait

The gene is found on the y chromosomes
Example: Hypertrichosis pinnae auris

sex-influenced traits

Expression of trait is affected by an individual's biological sex
Example: Baldness (Baldness is dominant in males and recessive in female)

pedigree

A chart or "family tree" that tracks which members of a family have a particular trait