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'Tall' is an example of a phenotype.

Unit 2 - Construct Genetic Diagrams (H)

This GCSE Biology quiz checks how well you can use genetic diagrams and Punnett squares to predict inherited traits and calculate simple probabilities.

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Fascinating Fact:

Genetic diagrams can be used to calculate the probability of a child inheriting a particular condition, often expressed as fractions, ratios, or percentages.

In GCSE Biology, genetic diagrams are used to show how alleles are inherited from parents to offspring. You draw Punnett squares, label genotypes, and interpret ratios and probabilities for different traits.

Key Terms

Genetic diagram: A model that shows how alleles from parents can combine to produce possible genotypes in their offspring.
Punnett square: A grid used in genetics to predict the possible allele combinations and their probabilities in offspring.
Genotype: The combination of alleles an organism has for a particular gene, such as Bb or bb.

Frequently Asked Questions (Click to see answers)

How do you draw a genetic diagram in GCSE Biology?

To draw a genetic diagram, write the parental genotypes, show the possible gametes, combine them in a Punnett square, then read off the genotypes and their ratios or percentages.

What is the difference between genotype and phenotype in genetics?

The genotype is the alleles an organism has for a gene, for example Bb. The phenotype is the physical characteristic shown, for example brown eyes.

How are probabilities worked out from a Punnett square?

Probabilities are calculated by counting how many squares show a particular genotype or phenotype, then expressing this as a fraction, ratio, or percentage of the total number of squares.

Try These Related Quizzes

1 .

What is the ratio of Tall:short if Tt is crossed with tt? Use a genetic diagram to predict the outcome.

2:1

3:1

4:1

1:1

Using a Punnett square:
          T          t
t        Tt         Tt
t        tt           tt      2 Tall Tt and 2 short tt cancels to 1:1, Equal numbers of Tall to short in the offspring

2 .

Alleles are different forms of the same...

allele

gene

code

egg

In some inherited diseases, like cystic fibrosis or Huntingtons disease, one of the alleles is faulty

3 .

Phenotype is the expression of what?

The face

The genotype

The eyes

The zygote

Phenotype is usually described as 'what you look like'! Blue eyes or brown hair, tall or short. The genes (alleles) in the genotype dictate what we look like

4 .

Genotype describes which of the following?

All alleles present in a population

One allele

Alleles present in a single organism, for a particular feature

Four genes

It can also refer to an individual's collection of genes

5 .

Which word describes Tt?

Heterozygous

Homozygous

Heterogametic

Homogametic

Since the alleles are different, you can immediately rule out the two options beginning with 'homo'

6 .

Which word describes TT?

Heterozygous

Heterogametic

Homozygous

Homogametic

Since the alleles are the same, it could only be one of the last two alternatives

7 .

Using a Punnett square, predict the ratio of tall to short when Tt is crossed with Tt. The allele for tall is T and the allele for short is t.

2:1

4:1

3:1

1:1

The gametes are T or t. The Punnett Square looks like this:
          T          t
T       TT      Tt
t        Tt         tt      3 Tall (either TT or Tt) and 1 short (tt), hence a 3:1 ratio Tall:short

8 .

'Tall' is an example of which of the following?

A genotype

An allele

A gene

A phenotype

Phenotypes are descriptions of the effects of alleles

9 .

What does homozygous mean?

That the alleles are the same

That the alleles are different

That the alleles are varied

That the alleles are mutated

The prefix homo always means the same e.g. homologous, homogenous

10 .

Which of the following is an example of a heterozygous genotype?

The same letter of the alphabet is used for each feature (gene) - T in this case - so Tc is incorrect

You can find more about this topic by visiting BBC Bitesize - Genetic inheritance

Author: Donna Davidson (GCSE Biology Teacher & Examiner, Quiz Writer)

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