Cheat sheet 7 : Heredity and Genetic Inheritance

A basic unit or sequence of genetic material that encodes a trait.

Gene

Carrying the same alleles on each homologous chromosome.

Homozygous

Having only one copy of a gene instead of two, such as in the sex chromosomes of males.

Hemizygous

The specific location of a gene within a genome.

Locus

The set of observable characteristics in an individual resulting from the expression of genotype.

Phenotype

A variant form of a gene.

Allele

The normal version of an allele.

Wild type

An allele with an altered DNA sequence.

Mutant

Carrying one dominant allele and one recessive allele on homologous chromosomes.

Heterozygous

A pair of chromosomes, one from each parent, that contain the same genes in the same locations.

Homologous chromosomes

The alleles an individual carries.

Genotype

Principles that describe how traits are inherited through generations.

Mendel's Laws of Inheritance

A genetic cross between a homozygous recessive individual and an individual of unknown genotype to determine the latter's genotype.

Test Cross

The principle stating that pairs of alleles are separated when gametes are formed.

Law of Segregation

The principle stating that pairs of alleles are sorted independently of one another during gamete formation.

Law of Independent Assortment

The principle stating that one dominant allele can mask the effect of a recessive allele.

Principle of Dominance

A pattern of inheritance where many genes interact to shape a single phenotype.

Polygenic Inheritance

A condition where a single gene controls the expression of multiple phenotypic traits.

Pleiotropy

A genetic situation where the heterozygous phenotype is a blend of the two homozygous phenotypes.

Incomplete Dominance

More than two typical alleles exist for a gene (e.g., A, B, O alleles in the ABO human blood type system)

Multiple Alleles

One gene affects

the phenotypic expression

of an independently

inherited gene (e.g.,

baldness: 1st gene controls whether one is bald or not, and the 2nd controls the hair color)

Epistasis

: both alleles are

completely expressed

[e.g., (R Red) x (W White) = (RW Red

& White speckled)]

x = x =Gametes from RrYy parent

Codominance

The occurrence of an abnormal number of chromosomes, often caused by nondisjunction.

(Trisomy 21)

Aneuploidy

The failure of chromosomes or chromatids to separate properly during cell division.

Nondisjunction

: During embryonic

development in female mammals, one of

the two X chromosomes is inactivated,

forming a highly condensed chromosome

(Barr body)

X-inactivation

The proportion of individuals with a specific genotype that express the corresponding phenotype.

Penetrance

The degree to which a genotype is expressed in an individual's phenotype.

Expressivity

A single copy

of the mutated gene is enough to express the condition

Autosomal Dominant

Two copies of

the mutated gene must be present to express the condition

Autosomal Recessive

A single copy of

the mutation of a gene on the X chromosome is enough to cause the

condition in both males & females

X-linked Dominant

Two copies of the

mutated gene on the X chromosomes causes the condition in females; one

copy will cause the condition in males

X-linked Recessive

Genes located on the Y

chromosome cause the

condition/trait

Y-linked

Changes in chromosome number or structure, including inversions, deletions, translocations, and duplications.

Chromosomal Aberrations

A chromosome

segment is

rearranged in

the reverse of

its original

orientation

Inversions

A chromosome

segment is

missing or

deleted

Deletions

segment is moved

to another; it can be

reciprocal or

nonreciprocal

(substitution)

Translocation

A chromosome

segment is

repeated on the

same chromosome

Duplication

arrests mitosis by interfering with mitotic spindle formation; it can prevent cells from replicating and has anticancer effects

Colchicine

stimulate normal growth; if mutated become oncogenes (cancer-causing genes)

Proto-oncogenes

make proteins that help control cell growth; if mutated may lead to cancer

Tumor suppressor genes