PEDIGREE ANALYSIS PART #1: AUTOSOMAL TRAITS

Vertical lines extending downward from a couple represent their children Roman numerals (I, II, III, etc.) symbolize generations. Arabic numerals (1,2,3, etc.) symbolize birth order within each generation Circle individual II 3

A pedigree is a diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships. A square represents a male A circle represents a female If the individual exhibits the condition in question, example colour-blindness, the symbol is FILLED IN  or A horizontal line between two symbols represents a mating (Ex. )

I II The purpose of a pedigree is to analyze the pattern of inheritance of a particular trait. Mating Normal Female Normal Male I 1st born II Affected Siblings

Conventional symbols used in depicting human pedigrees

In part 1, we will learn the patterns of the inheritance of autosomal traits or conditions, when the affected genes are on the autosomes (non-sex chromosomes). In part 2, we will learn the patterns of the inheritance of sex-linked traits or conditions, when the affected genes are on sex chromosomes X or Y.

1. Autosomal Dominant Example: Huntington disease

AUTOSOMAL because males and females are equally affected LOOK FOR: DOMINANT because affected individuals have at least one affected parent the phenotype generally appears every generation two unaffected parents will only have unaffected offspring AUTOSOMAL because males and females are equally affected

2. Autosomal Recessive Example: Cystic fibrosis

LOOK FOR: Recessive because it skips generations, since heterozygous (carrier) parents, who do not show the trait (unaffected), can have an affected offspring Autosomal because both males and females are equally affected

PRACTICE PROBLEM #1 Determine the pattern of inheritance.

Autosomal Dominant Both genders equally affected = Autosomal But how do we know whether it is dominant or recessive?

Autosomal Recessive WE DON’T ! There is not enough information. Either pattern is possible. You should be able to explain this.

PRACTICE PROBLEM #2 Determine the pattern of inheritance.

Autosomal Recessive In generation II, unaffected parents have an affected child = recessive Both sexes affaected = autosomal (usually)

HOMEWORK (SECTION 5.3) Page 223 Learning Check # 17 to 22 Page 227 #2, 3, 5, 7 to 9 Page 236 # 23, 24

PEDIGREE ANALYSIS PART #2: SEX-LINKED TRAITS We will focus on X-linked traits. Maleness is Y-linked.

3. X-linked recessive Example: Red/Green Colour Vision Deficiency LOOK FOR: Condition predominantly affects MALES A son’s X is inherited from mother, his Y is inherited from father, so affected males cannot pass trait to male offspring Often, a carrier mother passes it to her son

What do you see?

4. X-linked dominant Example: Rett syndrome LOOK FOR: Affected males always pass the condition to daughters and never pass the condition to sons… WHY???

SUMMARY FOUR PATTERNS AUTOSOMAL DOMINANT AUTOSOMAL RECESSIVE X-LINKED DOMINANT X-LINKED When analyzing a pedigree, you must explain both parts, ie. Why the pattern is autosomal or X-lnked AND why it is dominant or recessive. Sometimes there is not enough information to make a conclusive decision between the four patterns and more than one pattern may be possible, so be careful.

The grandparents had two children, a son and a daughter. Analyze this pedigree: The grandparents had two children, a son and a daughter. The son had the trait in question. One of his 3 sons has the trait

HOMEWORK (Section 6.2) Page 258 # 17 Page 259 #10 to 15 Page 273 #5 - provide a full analysis P.274 #18 P.277 #17 P.283 #37