Chapter 2 - Genetics and Patterns of Inheritance

Double-stranded DNA

Consists of two chains of purine/pyrimidine pairs where each strand mirrors the other

Replication

Process of making two identical strands from one.

Gene

A functional unit of heredity, consisting of a discrete segment of a DNA strand at a specific region within a chromosome

Polymorphism

Variability in specific genes among individuals

Chromosome

A single, linear double strand of DNA with associated proteins

In the nucleus of every cell, there are ___ (or ____ pairs) of chromosomes:

___ pairs of autosomes (nonsex) chromosomes

__ pair of sex chromosomes

• 46 or 23 pairs

• 22 autosomes

• 1 pair sex chromosomes

Autosomes

Chromosome pairs from 1 to 22

Numbered in order of length (longest is 1; shortest is 22).

Centromere

Area of constriction for each chromosome

Metacentric chromosomes

The centromere is in the middle of the chromosome

Submetacentric chromosomes

The centromere is off center, leading to a short and a long arm

A “p” (or petit) arm

Short arm and/or arm above the centromere on each side

A “q” arm

: Long arm and/or arm below the centromere on each side

Karyotype

A picture of a person’s chromosomes that is derived from a blood sample.

Genome

A complete set of instructions in the chromosomes for a particular organism or species (e.g., human genome, mouse genome, etc.)

Phenotype

Observable characteristics of an individual resulting from the interaction of its genotype with other genetic and environmental factors

Chromosomal abnormalities

Duplications: When a part of a chromosome is duplicated

Deletions: When part of a chromosome becomes separated and lost, sometimes bent

Translocations: When there is a transfer of genetic material between two or more chromosomes

Contiguous gene syndromes: Caused by deletions that contain several genes

Fluorescence in situ hybridization (FISH)

A method where submicroscopic segments of DNA can be identified using a fluorescent dye.

Ideogram

A visual representation of specific segments of a chromosome that are seen through staining.

Autosomal recessive inheritance conditions

Inheritance occurs when both parents contribute an affected allele on the chromosome

25% recurrent risk when there are two affected parents

Autosomal dominant conditions

Inheritance is the same as with gender where one parent (the father in the case of gender) contributes the affected allele on the chromosome half of the time

50% recurrent risk when there is one affected parent

Non-Mendelian inheritance types

Multifactorial inheritance

Anticipation

Imprinting

Multifactorial inheritance

When disorders result from an interaction of multiple genes with environmental influences (e.g., clefts)

Teratogens

Environmental factors known to increase risks for birth defects

Two categories of multifactorial inheritance

Continuous variation abnormalities

threshold abnormalities

Continuous variation abnormalities

include traits on a continuum that are subjective and arbitrary in their expression

Threshold abnormalities

As risk factors increase, the additive risk may cross a threshold, resulting in expression of the trait

Anticipation

A tendency in certain inherited disorders to have more severe manifestations or an earlier age of onset with succeeding generations

Imprinting

The tendency for some genes to function differently, depending on whether they were inherited maternally or paternally