Pedigree Charts The family tree of genetics Overview

Pedigree Charts The family tree of genetics

Overview I. What is a pedigree? a. b. II. Definition Uses Constructing a pedigree a. b. III. Symbols Connecting the symbols Interpreting a pedigree

Terms § Autosomal gene- a gene found on any chromosome except for the sex chromosome. These are chromosomes numbered 1 -22. § Sex-linked or X-linked gene- a gene found on a chromosome designated as a sex chromosome (X or Y).

Sex-linked Traits § When the traits (genes) is located on the sex chromosomes § Sex chromosomes are X and Y § XX genotype for females § XY genotype for males § Many sex-linked traits carried on X chromosome

Sex-linked Traits Example: Color blindness Sex Chromosomes Trait for color blindness XX chromosome - female Xy chromosome - male

X-Linked Recessive Inheritance § Males show disorder more than females § Son cannot inherit disorder from his father; has to come from mother

Sex-linked Trait Problem § Example: Color blindness (color blind male) x (color blind female) X b. Y x X b § Remember: the Y chromosome in males does not carry traits. Xb Xb BB = normal Bb = normal bb = color blind XY = male XX = female Xb Y

Sample Colorblind Tests 4 Sex-Linked Traits: 1. Normal Color Vision: A: 29, B: 45, C: --, D: 26 2. Red-Green Color-Blind: A: 70, B: --, C: 5, D: -3. Red Color-blind: A: 70, B: --, C: 5, D: 6 4. Green Color-Blind: A: 70, B: --, C: 5, D: 2

Terms § Dominant- Refers to an allele that is expressed phenotypically and masks any recessive counterpart. § Recessive- An allele that is not phenotypically expressed when its counterpart is dominant.

Example § What does a pedigree chart look like?

What is a Pedigree? § A pedigree is a chart of the genetic history of family over several generations. § Scientists or a genetic counselor would find out about your family history and make this chart to analyze.

Constructing a Pedigree § Female § Male

Connecting Pedigree Symbols Examples of connected symbols: § Married Couple § Children

Symbols in a Pedigree Chart

Symbols used in pedigree charts A marriage with five children, two § § § Normal male Affected male Normal female Affected female Marriage daughters and three sons. The middle child is affected by the condition. Eldest child Youngest child © 2007 Paul Billiet ODWS

Organizing the pedigree chart § A pedigree chart of a family showing 20 individuals © 2007 Paul Billiet ODWS

Organizing the pedigree chart – Generations are identified by Roman numerals I II IV © 2007 Paul Billiet ODWS

Organizing the pedigree chart § Individuals in each generation are identified by Arabic numerals numbered from the left I II IV © 2007 Paul Billiet ODWS

Organizing the pedigree chart § Individuals in each generation are identified by Arabic numerals numbered from the left I 1 II III 2 1 1 2 3 7 6 5 4 IV © 2007 Paul Billiet ODWS 1 2 3 4 5

Terms § Autosomal gene- a gene found on any chromosome except for the sex chromosome. These are chromosomes numbered 1 -22. § Sex-linked or X-linked gene- a gene found on a chromosome designated as a sex chromosome (X or Y).

Interpreting a Pedigree Chart § When interpreting a pedigree chart of a family with a disease like muscular dystrophy, it is important to consider two steps. § The first is to determine if the disorder is autosomal or X-linked.

Interpreting a Pedigree Chart 1. Determine if the pedigree chart shows an autosomal or X-linked disease. – If most of the males in the pedigree are affected the disorder is X-linked – If it is a 50/50 ratio between men and women the disorder is autosomal.

§ To determine if a pedigree is illustrating the inheritance of a sex-linked trait, there are three characteristics you should look for: – More males than females are affected – Only females are carriers – Trait is usually passed from mother to son

Female Carriers copyright cmassengale 26

Royal Hemophilia Pedigree

Autosomal or x-linked

Example of Pedigree Charts § Is it Autosomal or X-linked?

Answer § Autosomal

Terms § Dominant- Refers to an allele that is expressed phenotypically and masks any recessive counterpart. § Recessive- An allele that is not phenotypically expressed when its counterpart is dominant.

Interpreting a Pedigree Chart 2. Determine whether the disorder is dominant or recessive. – If the disorder is dominant, one of the parents must have the disorder. – If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

Autosomal Dominant Pedigree Chart

Example of Pedigree Charts § Dominant or Recessive? § Sex-linked/autosomal?

Answer § Dominant & Autosomal Bb bb Bb or BB bb bb Bb Bb bb bb Bb bb

Autosomal Recessive Pedigree Chart

Example of Pedigree Charts § Dominant or Recessive? § Sex-linked or autosomal?

Answer § Recessive & Autosomal Bb B? bb Bb Bb Bb or BB Bb bb bb Bb Bb bb B?

Summary § Pedigrees are family trees that explain your genetic history. § Pedigrees are used to find out the probability of a child having a disorder in a particular family. § To begin to interpret a pedigree, determine if the disease or condition is autosomal or Xlinked and dominant or recessive.

Pedigree Checklist § Autosomal or Sex-linked? – 50/50 or greater females affected (autosomal) – More male affected than females (sex-linked) § Dominant or Recessive trait? – Does it skip a generation- two unaffected parents have an affected child (recessive) § Affected will have 2 little letters (bb) § Unaffected will have (BB or Bb) – Does every generation have it? (dominant) § Affected will have a Capital letter (BB or Bb) § Unaffected will have (bb)