Heredity — Part 2: How traits are expressed, and sex determination: visual lesson, CBSE Class 10 Science

Lesson

How traits are expressed, and boy or girl?

Part 2 — how a gene actually makes a plant tall, why chromosomes come in pairs, and what decides whether a baby is a boy or a girl.

In this lesson you will

Explain how genes control traits through proteins, using plant height as an example
Explain why each germ cell carries one chromosome of each pair
Explain sex determination in humans using X and Y chromosomes
Describe other ways in which sex is determined in some animals

Concept

Genes make proteins

Cellular DNA carries the information for making proteins. A section of DNA that provides the information for one protein is a gene. Many proteins are enzymes, which control the chemical reactions that build the body and its features.

Table of DNA, gene, protein and enzyme with their meanings
Term	Meaning
DNA	The information store in the nucleus
Gene	A section of DNA with the information for one protein
Protein	Made using a gene’s information; does a job in the cell
Enzyme	A protein that speeds up a particular chemical reaction

Diagram

From gene to plant height

Plant height depends on the amount of a growth hormone. The hormone is made with the help of an enzyme. If the gene for this enzyme makes an efficient enzyme, plenty of hormone is made and the plant grows tall. If the gene is altered so the enzyme is less efficient, less hormone is made and the plant stays short.

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