Aufgabe 3 - Humangenetik, Gendiagnostik und Gente… · Abitur NRW Biologie GK · Haupttermin · bilingual Englisch 2021

Material A: Warmblood Fragile Foal Syndrome in Horse Breeding

Warmblood fragile foal syndrome (WFFS) is a hereditary disease in horses which leads to an incurable connective tissue disorder. Foals affected by WFFS show symptoms immediately after birth. Already in the first hours of life, they contract injuries in the ligaments, tendons and bones, which hardly heal and are eventually fatal. WFFS is inherited in an autosomal recessive pattern.

Although WFFS has been in existence for an estimated 170 years, an increase in cases has been documented since 2011. Between six and eleven percent of all horses are carriers of this gene defect. Horses which have been bred for equestrian sports 1 are especially affected. In breeding, one breeding stallion 2 is mated with several female horses. Scientists suspect a connection between the mutation underlying WFFS and the traits desired in the breeding of sports horses, such as a high level of agility.

1 Pferdesport

2 Zuchthengst

Material B: Molecular genetic causes of WFFS

Connective tissue consists mostly of collagen. Collagen is a fibrous protein which is involved in the production of connective tissues – such as in the skin, blood vessels, tendons and cartilage – as well as in the production of bones and teeth. Up to 25 % of the protein in a human or animal body consists of collagen. The gene PLOD1 codes for the enzyme lysyl-hydroxylase 1 (LH1), which is involved in an intermediate step in the synthesis of stable collagen fibres. In order to gain insights into the molecular genetic causes of WFFS, the PLOD1 gene was sequenced (Table 1).

Table 1 Section of the non-template strand of the PLOD1 gene of a healthy foal and a foal affected by WFFS. · Number of triplet

691 · 692 · 693 · 694 · 695 · 696 · 697

Normal allele · TAC · GAG · GGC · GGG · GGC · TGT · CGG · 5' → 3'

Mutated allele · TAC · GAG · GGC · AGG · GGC · TGT · CGG · 5' → 3'

Material C: Detecting WFFS

When breeding horses, it is recommended to test the horses. For this purpose, DNA is isolated from the blood or other tissues of the animals to be tested. Then, the procedure shown in Figure 1 is used to detect the mutation with the help of a specialised PCR. In this type of PCR, two additional probes are used which do not serve as primers. Each nucleotide of the probes is complementary to the nucleotides of the DNA sequence investigated, either with or without the mutation. Both probes are attached to different fluorescent dyes at their 5' ends, whereas quenchers 3 are attached at their 3' ends. If both the dye and the quencher of the probe are bound, the quencher inhibits the fluorescence of the dye.

3 hier: Entleuchter

During PCR, the fluorescence of the PCR sample is measured. Figure 2 gives exemplary values of the fluorescence which would be expected over the course of such a PCR for horses with different PLOD1 genotypes.

Material D: Diagram and Codon Table of the Genetic Code

Teilaufgabe 3

Describe the main stages of the PCR method and illustrate what role the fluorescent probes play in detecting the WFFS alleles shown in Figure 1 (Material C). Building on this, analyse and evaluate the findings of the study in Figure 2 (Material C). Providing reasons, derive measures that could help to lower the number of WFFS cases among sports horses (Materials A to C). [26 Punkte]

a)

b)

c)

d)