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Our Biolory course requires that a research paper be written and submitted for evaluation Due to the nature of this EXERCISE 13.6 many people, the term peodigree brings about imags of championship dogs and thoroughbred horses. 'sentially Developing Pedigrees everything from fruit flies to watermelons has a pedygree. To geneticists, howevet, a pedigree is a valuable tool resembling a family tree used to display family relationships and to track traits through a family In mehal pedigrees are helpful in understanding how disorders appear in families. Pedigrees are particularly valuable in understanding the inheritance of unifactorial (sin gle-gene) traits such as albinism cystic fibrosis, and hemophilia. A pedigree can be used to visually represent Mendelian inheritance of a trait. A typical pedigree con sists of universally accepted sym Normal female, male Parents Femaie, male who expresses trait Female, male who carries an Adoption slele for the trait but does not express it tcarrie) Dead temale, male - identicali twins bols connected by either horizon numerals represent gencrations Sex unspecified tal or vertical lines. Roman Stwbirth Fraternal twi SB SB and Arabic numerals representPregnancy Parents closely related individuals. Filled shapes repre- sent individuals who express a trait, and half-shaded shapes rep by blood) lFormer relationship - Spontaneous abortion miscarriag0) resent carriers. A few common - Person who prompted (shade if abnormal) pedigreo analysis (proband symbols appear in Figure 13.6. FICURE 13.6 Pedigree symbols. Procedure 1 Using and Constructing Pedigrees 13 Using a pedigree, autosomal recessive traits, such as cystic fibrosis, are casy to follow through the generations. With your knowledge of pedigrees, explain the inheritance of cystic fibrosis in two children of the third generation in Figure 13.7 1 FIGURE 13.Z Cystic fibrosis pedigree. 190 Exploring Biology in the Laboratory

Explanation / Answer

Cystic fibrosis is an autosomal recessive disorder. Lets say the dominant allele for this F and the recessive allele for this is f. Now the individual who will have a genotype of ff will be positive with cystic fibrosis, FF and Ff will not have cystic fibrosis.

So in the 2nd generation both the parent are heterozygous for the cystic fibrosis gene. So they both have Ff genotype.

The 3rd generation: Ff X Ff

FF

cystic fibrosis negative

Ff

cystic fibrosis negative heterozygous

Ff

cystic fibrosis negative heterozygous

ff

cystic fibrosis positive

cystic fibrosis negative = 25%

cystic fibrosis negative heterozygous= 50%

cystic fibrosis positive= 25%

So there is 25% chance for each person in the 3rd generation to have cystic fibrosis. So the two children in the 3rd generation have cystic fibrosis with ff genotype.

F f F

FF

cystic fibrosis negative

Ff

cystic fibrosis negative heterozygous

f

Ff

cystic fibrosis negative heterozygous

ff

cystic fibrosis positive

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