How to solve pedigree probability problems

More of my videos on the topic:
How to read a pedigree like a pro youtube.com/watch?v=5OlpOEC9vQ8
How to read a pedigree like a pro - 2 youtube.com/watch?v=Vxl-18BaUag
How to read a pedigree like a pro - 3 youtube.com/watch?v=0pYj00896p4
How to read a pedigree like a pro - 4 youtube.com/watch?v=kHlxYBlM3fA
How to read a pedigree like a pro - 5 youtube.com/watch?v=3Dia_W0ky-I
How to read a pedigree like a pro - 6 youtube.com/watch?v=0CXI3r0NC2Q

A pedigree chart is a diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next, most commonly humans, show dogs, and race horses.

The word pedigree is a corruption of the French "pied de grue" or crane's foot, because the typical lines and split lines (each split leading to different offspring of the one parent line) resemble the thin leg and foot of a crane.

A Pedigree results in the presentation of family information in the form of an easily readable chart. Pedigrees use a standardized set of symbols, squares represent males and circles represent females. Pedigree construction is a family history, and details about an earlier generation may be uncertain as memories fade. If the sex of the person is unknown a diamond is used. Someone with the phenotype in question is represented by a filled-in (darker) symbol. Heterozygotes, when identifiable, are indicated by a shade dot inside a symbol or a half-filled symbol.

Relationships in a pedigree are shown as a series of lines. Parents are connected by a horizontal line and a vertical line leads to their offspring. The offspring are connected by a horizontal sibship line and listed in birth order from left to right. If the offspring are twins then they will be connected by a triangle. If an offspring dies then its symbol will be crossed by a line. If the offspring is still born or aborted it is represented by a small triangle.

Each generation is identified by a Roman numeral (I, II, III, and so on), and each individual within the same generation is identified by an Arabic number (1, 2, 3, and so on). Analysis of the pedigree using the principles of Mendelian inheritance can determine whether a trait has a dominant or recessive pattern of inheritance. Pedigrees are often constructed after a family member afflicted with a genetic disorder has been identified. This individual, known as the proband, is indicated on the pedigree by an arrow.