Reproduction key terms

Allele

A variant form of a gene that occupies a specific position on a chromosome and can influence a particular trait.

Inherited disorder

A disease or condition that arises when a harmful allele is passed from parent to offspring.

polydactyly

In Inherited disorders, polydactyly means the specific Unit 4.6 idea used to answer this objective: students must describe polydactyly as an inherited disorder caused by a dominant allele. Keep the term curriculum-specific by applying this boundary: DNA is the molecule; a gene is a functional section of that molecule. Do not use polydactyly as a vague inheritance word; link it to Reproduction and explain the exact role it plays in AQA GCSE Biology.

dominant allele

A gene variant that is expressed in the phenotype even when only one copy is present.

cystic fibrosis

An inherited disorder that affects the cell membranes, caused by a recessive allele.

recessive allele

An allele that is expressed only when two copies are present and no dominant allele is present.

Dominant allele

A form of a gene that is expressed in the phenotype when present in a single copy, masking the effect of a recessive allele.

Recessive allele

A form of a gene that is expressed in the phenotype only when two copies are present and no dominant allele is present.

embryo screening

A medical procedure used to identify genetic disorders in embryos before implantation.

ethical issues

Moral considerations and implications related to the practices and consequences of embryo screening.

Embryo screening

In Inherited disorders, Embryo screening means the specific Unit 4.6 idea used to answer this objective: students must consider that embryo screening and gene therapy may alleviate suffering but raise ethical issues. Keep the term curriculum-specific by applying this boundary: DNA is the molecule; a gene is a functional section of that molecule. Do not use Embryo screening as a vague inheritance word; link it to Reproduction and explain the exact role it plays in AQA GCSE Biology.

Gene therapy

A medical intervention that modifies or replaces defective genes to treat or prevent disease.

chromosome pairs

Ordinary human body cells contain 23 pairs of chromosomes, which include 22 pairs that control characteristics and one pair that determines sex.

human body cells

Cells in the human body that contain genetic material organized into 23 pairs of chromosomes.

chromosome pairs

Pairs of chromosomes that contain genes controlling various characteristics of an organism.

sex determination

The process by which the sex of an organism is established, determined by the presence of specific sex chromosomes.

XX sex chromosomes

The pair of sex chromosomes found in female humans, consisting of two X chromosomes.

female sex determination

The genetic mechanism by which the presence of two X chromosomes (XX) results in the development of female characteristics.

Sex chromosomes

Chromosomes that determine the sex of an individual, with females having two X chromosomes (XX) and males having one X and one Y chromosome (XY).

XY chromosome pair

The combination of one X chromosome from the mother and one Y chromosome from the father that identifies a male individual.

genetic cross

A diagrammatic representation of the possible combinations of alleles from two parents, used to predict the distribution of traits in offspring.

sex inheritance

The pattern by which sex chromosomes (XX or XY) are transmitted from parents to offspring, determining the sex of the individual.

Genetic cross

A diagrammatic representation, such as a Punnett square, that shows the possible combinations of alleles from two parents and predicts the genotypic and phenotypic ratios of their offspring.

Direct proportion

A relationship in which the ratio of two quantities remains constant; in sex‑determination crosses it means that the proportion of male to female offspring is fixed by the parental genotypes.