AP Biology Analyzing Pedigrees Objectives I can determine

AP Biology Analyzing Pedigrees

Objectives • I can determine inheritance pattern for a genetic trait/disorder • I can analyze a pedigree for genotypes

Inheritance Pattern: How the gene is transmitted/passed on.

Two Question Pedigree Approach: 1. Are there any children who are shaded differently than both of their parents? A. This determines dominant vs recessive phenotypes B. Yes = that child represents the recessive phenotype C. No = shaded trait is probably dominant 2. Are there any girls with the recessive phenotype who have a father/son with the dominant phenotype A. This determines if trait is sex-linked B. Yes = trait is NOT sex linked C. No = trait may be sex linked

Example 1: practice the two question method • Question 1: Are there any children who are shaded differently than both of their parents?

Example 1 continued • Question #1 was yes – Person III-12 MUST be the recessive genotype. – Persons II-5 and II 6 MUST be heterozygous shaded = recessive unshaded = dominant

Example 1 continued • Question #2: Are there any girls who are recessive, that has a father or son who is dominant? – Yes = not sex linked – No = probably sex linked

Example 1: Question 2 continued • Girl III – 12 would have to be Xb. Xb if this was sex linked. There is no way for that to happen if her father is XBY

Final Decision: Example 1 • Question 1 – showed us that the shaded trait is recessive • Question 2 – showed us that the shaded trait cannot be sex linked • Inheritance pattern = autosomal recessive

Example 2: • Question 1 = No. Therefore it is probably dominant • Question 2 = Girl III 3 has a father (II-1) who is dominant. Therefore it is not sex linked. Autosomal Dominant

Example 3: • Question 1: yes – boy III-9 represents the recessive • Question 2: no – the recessive females all have recessive fathers or sons. X-linked Recessive

Example 4: • Question 1: NO – the shaded trait is probably dominant • Question 2: NO – all recessive females only have recessive sons or fathers – Probably sex linked X-linked Dominant

Example 5: • Question 1: Yes. Boy II-7 represents the recessive. So shaded trait is dominant. • Question 2: Yes. Girl II-8 has a dominant father so not sex linked. Autosomal Dominant

Double Check Yourself: • Autosomal Recessive – Typically skips generations – Pedigree may show carriers • Autosomal Dominant – Usually doesn’t skip generations – No carriers • X-linked recessive – Skips generations – More males than females • X-linked Dominant – Usually doesn’t skip generations – More females than males

Autosomal Recessive • Skips generations • Affects males/females equally • Pedigree may show carriers

Autosomal Dominant • There will not be carriers – those with the gene will be “affected” • Will probably not skip generations • Will affect males/females equally

Sex-Linked (X-Linked) Recessive • More males affected than females • Skips generations

Sex – linked Dominant • Doesn’t skip generations • More females than males

Pedigree Practice: • How is the trait inherited? Autosomal Recessive • What is the genotype of person II-3? Carrier - heterozygous • Should persons II-1 and II-2 get checked to see if they are carriers? Yes

Pedigree Practice: • How is the trait inherited? Autosomal Dominant • What is the genotype of person II-3? Homozygous recessive • Are there carriers for this trait? No

• What is the most likely inheritance pattern for this trait?

How is the trait most likely inherited?

How is the trait most likely inherited?