Chapter 10:Patterns of inheritance

Inheritance – definitions and terms • Mendel and his pea plants • Punnett squares – Monohybrid – Dihybrid • Linkage • Incomplete dominance, codominance, pleiotropic traits • Sex linked traits, X inactivation • Diseases

Inheritance

The process in which genetic material is passed from parents to their offspring.

Genes

DNA segments that serve as the key functional units in hereditary transmission.

Allele

Different forms of a gene

Homozygous

Having two identical alleles for a particular gene (GG or gg)

Heterozygous

An organism that has two different alleles for a trait
(Gg)

dominant allele

An allele whose trait always shows up in the organism when the allele is present.

recessive allele

An allele that is masked when a dominant allele is present

polygenic inheritance

An additive effect of two or more genes on a single phenotypic character.

Pleotropic

one gene affects many characteristics

P generation

Parental generation, the first two individuals that mate in a genetic cross
True breeding parents

F1 generation

hybrid offspring of the P generation

F2 generation

Offspring resulting from interbreeding of the hybrid F1 generation.

carriers

heterozygous individuals who carry the recessive allele but are phenotypically normal

Phenotype

An organism's physical appearance, or visible traits.

Genotype

genetic makeup of an organism

monohybrid cross

A cross between individuals that involves one pair of contrasting traits

Genotypic ratio

the ratio of the genotypes that appear in offspring
1:2:1

Phenotypic ratio

the ratio of phenotypes produced by a cross
3:1

Law of Segregation

Mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete

sex-linked alleles

-Y chromosome does not carry alleles for X-linked traits
-Males always receive X from female parent, Y from male parent

independent assortment

One of Mendel's principles that states that genes for different traits can segregate independently during the formation of gametes

Incomplete dominance

A pattern of inheritance in which two alleles, inherited from the parents, are neither dominant nor recessive. The resulting offspring have a phenotype that is a blending of the parental traits.

Codominance

situation in which both alleles of a gene contribute to the phenotype of the organism

Pleiotropy

The ability of a single gene to have multiple effects.

Epistasis

A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.

A=aa

Ao

B=BB

Bo

AB

Ab

O

OO

A=B>O

O is able to go into each type

X inactivation

one of two X chromosomes is randomly inactivated and remains coiled as a Barr body