Biology - 9201 OxfordAQA

Genetic Disorders

Resumen

Most of what your genes do passes unnoticed. Occasionally a single faulty instruction, or one chromosome too many, produces an effect large enough to shape a whole life. These are the genetic disorders, and they are among the few places in biology where a family tree, a fraction and a set of symptoms all describe the same thing. Learn to move between those three descriptions and this topic becomes arithmetic rather than memory.

In this lesson you will meet three inherited conditions that the specification names by example, and you will see why one of them shows up in every generation of a family while another can hide for decades in people who feel completely well. You will then look at a different kind of cause altogether, where nothing is wrong with any individual allele and the problem is simply that a cell finished up with the wrong number of chromosomes. By the end you will be able to read a family diagram, fill a Punnett square, quote a probability and explain the biology sitting behind the number.

Objetivos

  1. Some disorders are inherited. Students should be able to interpret data relating to genetic disorders such as polydactyly, cystic fibrosis, and sickle cell anaemia.
  2. Some inherited conditions are caused by inheritance of abnormal numbers of chromosomes, eg Down’s Syndrome is caused by the presence of an extra chromosome.

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Nota de la lección

A human body cell carries around twenty thousand genes, and for almost all of them it makes no practical difference which version you inherited. Then there are the handful where it makes every difference. A single altered allele can thicken the mucus lining an airway, change the shape of a red blood cell, or add a sixth finger to a hand. Nothing about the way that allele is passed on is special: it travels in a gamete, obeys the same rules as eye colour in a textbook cross, and lands in a Punnett square exactly where you would predict. What makes genetic disorders worth a topic of their own is that the predictions matter to real families, so the examiner expects you to produce them precisely and to say what they do and do not mean.

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Evaluación de la lección

Felicitaciones por completar la lección del Genetic Disorders. Ahora que has explorado el conceptos e ideas clave, es hora de poner a prueba tus conocimientos. Esta sección ofrece una variedad de prácticas Preguntas diseñadas para reforzar su comprensión y ayudarle a evaluar su comprensión del material.

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  1. Cystic fibrosis is caused by a recessive allele f. The working allele is F. What is the genotype of a carrier of cystic fibrosis? A. FF B. Ff C. ff D. A carrier has no alleles for the gene Answer: B
  2. Polydactyly is caused by a dominant allele. Which statement is correct? A. A person needs two copies of the allele to have the condition B. A person with one copy of the allele has the condition C. The condition always skips a generation D. Only females can have the condition Answer: B
  3. How many chromosomes are found in a body cell of a person with Down's syndrome? A. 23 B. 45 C. 46 D. 47 Answer: D
  4. Two carriers of cystic fibrosis have a child. What is the percentage chance that the child has cystic fibrosis? A. 0% B. 25% C. 50% D. 75% Answer: B
  5. Which of the following describes the event that leads to Down's syndrome? A. A dominant allele is inherited from one parent B. A recessive allele is inherited from both parents C. A pair of chromosomes fails to separate during meiosis D. A chromosome is lost during mitosis in the adult Answer: C

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