Year 10 - Science
The inheritance of biological sex and sex-linked genetic disorders
Inheritance, genotype and phenotype
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
This unit covers key genetic terms, single-gene inheritance, and genetic crosses, including probability and ratios. It explores how most traits result from multiple genes and sex determination in humans. The unit also includes interpreting data and using models to solve problems.
Lesson Summary
You will learn to explain how the inheritance of chromosomes determines biological sex in humans, and the inheritance of sex-linked genetic disorders.
Key Notes
- During sexual reproduction, an individual's biological sex is determined by the chromosomes they inherit.
- In humans, the 23rd pair of chromosomes are sex chromosomes; XX in females and XY in males.
- A gene on the Y chromosome triggers the development of testes, which make male sex hormones (androgens).
- Interpreting, completing and constructing Punnett squares showing the inheritance of human sex chromosomes.
- Some disorders are caused by alleles on the sex chromosomes, so have sex-linked inheritance.
Vocabulary To Learn
- sexual reproduction: The process of producing offspring where a male and a female provide half the genetic material via gametes.
- biological sex: Male or female as determined by the combination of sex chromosomes inherited (i.e. XX female, XY male).
- sex chromosome: The chromosomes that determine the reproductive and secondary sexual characteristics (i.e. X and Y).
- sex hormone: Chemical messengers, secreted by glands, that help to control the reproductive and secondary sexual characteristics.
- sex-linked disorder: An inherited condition determined by alleles carried by the X or Y chromosome.
Common Mistakes To Avoid
- Males only have Y chromosomes, only males inherit sex-linked conditions.
3 Quick Questions (With Answers)
1. Explain the scientific idea in this lesson using two key points.
During sexual reproduction, an individual's biological sex is determined by the chromosomes they inherit. In humans, the 23rd pair of chromosomes are sex chromosomes; XX in females and XY in males.
2. Define this scientific word and use it in context. 'sexual reproduction'
The process of producing offspring where a male and a female provide half the genetic material via gametes. Include the word in a full scientific explanation, not as a single label.
3. Correct this common scientific misunderstanding.
Mistake: Males only have Y chromosomes, only males inherit sex-linked conditions. Correction: Males have one Y and one X chromosome, males only need one recessive allele to suffer from a sex-linked genetic disorder, whereas females need two and therefore the condition is less common in females.
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