Inheritance & EvolutionDefinitions

Key Definitions

Part of Sex Determination · GCSE GCSE Biology revision

This definitions covers Key Definitions within Sex Determination for GCSE Biology. Sex chromosomes and sex determination mechanisms It is section 5 of 11 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.

Topic position

Section 5 of 11

Practice

26 questions

Recall

12 flashcards

Key Definitions

Sex chromosome: One of the 23rd pair of human chromosomes that determines the biological sex of an individual. Females have two X chromosomes (XX); males have one X and one Y chromosome (XY).

Autosome: Any chromosome that is not a sex chromosome. Humans have 22 pairs of autosomes (44 chromosomes), which carry genes for non-sex-related characteristics.

X chromosome: A sex chromosome present in both males and females. Females have two X chromosomes; males have one. The X chromosome is much larger than the Y chromosome and carries many genes unrelated to sex determination.

Y chromosome: A sex chromosome present only in males. It is much smaller than the X chromosome and carries fewer genes, including the SRY gene that triggers male sex development.

Sex-linked disorder: A genetic condition caused by an allele on a sex chromosome (usually the X chromosome). Because males have only one X chromosome, they are more likely to be affected by X-linked recessive conditions than females, who have two X chromosomes.

Carrier (sex-linked): A female who is heterozygous for an X-linked recessive allele (X^A X^a). She does not show the condition because her second X chromosome carries the dominant allele, but she can pass the recessive allele to her children.

Keep building this topic

Read this section alongside the surrounding pages in Sex Determination. That gives you the full topic sequence instead of a single isolated revision point.

How It Works: XX and XY Determine Sex Common Misconceptions Sex Chromosomes Inheritance of Sex

Practice Questions for Sex Determination

What determines the sex of a human baby?

A. The sex chromosomes inherited from the parents
B. The number of genes the baby has
C. Environmental factors during pregnancy
D. The age of the mother

1 markfoundation

Use a genetic diagram to show how sex is inherited in humans.

3 marksstandard

Quick Recall Flashcards

How do you remember XX = female and XY = male?

XX: the two X's look like chromosomes that pair up perfectly — females have a matching pair. XY: the Y looks like a little man standing with arms out — males have the odd one out. 'Why are boys different? Because of Y!'

What sex chromosomes do females and males have?

Females: XX (two X chromosomes). Males: XY (one X and one Y chromosome). These are the 23rd pair of chromosomes in humans.

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How It Works: XX and XY Determine Sex

Common Misconceptions