Year 10 Science · Unit 1 · Lesson 4

Genes, Alleles and Punnett Squares

Foundation Worksheet

Name

Date

Class

Learning Goals

Identify whether statements about carriers, Punnett squares and codominance are true or false.
Use key vocabulary to describe how Punnett squares predict offspring.
Distinguish between genotype, phenotype, carrier, and codominance.

Warm Up

True or False? Fix the false ones

Circle T or F for each statement. If the statement is false, rewrite it correctly on the line below.

A carrier of cystic fibrosis has the disease and shows symptoms.

Correct it:

Two tall parents (both Tt) can have a short child.

Correct it:

Codominance means one allele is dominant over the other.

Correct it:

Punnett squares tell us the exact number of offspring that will be born with each genotype.

Correct it:

Your Turn

Fill the gap

Choose the correct word from the word bank to complete each sentence. Not all words are used.

Punnett square genotype phenotype carrier codominance sex-linked allele chromosome nucleus

A version of a gene is called an . The genetic makeup of an organism, for example, Tt or BB, is its , while the physical trait you can see is called its . A person who is heterozygous for a recessive disease but does not show symptoms is called a . Scientists use a grid to predict the probability of offspring inheriting different genotypes. When both alleles are expressed equally in the same individual, the pattern is called . Colour blindness is an example of a trait, because the gene sits on the X chromosome.

Show What You Know

1. A tongue-rolling father (Rr) and a non-rolling mother (rr) have children. State the genotype ratio and phenotype ratio of their offspring. (Hint: R = can roll tongue.)

Recall 2 marks

2. A person has blood type AB. Explain what this tells us about their two alleles and why this is an example of codominance rather than simple dominance.

Recall 2 marks

Wrap Up

In one sentence, what was the main idea of this lesson?