Text lesson

Unit 3 — Variation of Traits in Living Organisms

Science — Third Preparatory

1.1 Why are family members alike but not identical?

Look at a family photograph.
Children resemble their parents in some features and differ in others.
Genetics is the science that explains these similarities and differences by studying how genetic information passes from parents to offspring.

The genetic information is stored in a chemical substance called the genetic material, deoxyribonucleic acid (DNA).
In a cell, the genetic material is in the nucleus.
A DNA molecule is extremely long, so it is coiled around protein molecules to form thread-like chromosomes.
The genetic material of a chromosome is divided into sections; each section is a gene.
A gene is a segment of the genetic material (DNA) that carries the information responsible for a specific inherited trait, such as eye colour, hair texture or height.
So cell → nucleus → chromosomes → genes (DNA).

Unit 3 — Variation of Traits in Living Organisms · 2 / 22

1.1 Why are family members alike but not identical?