Unit 5.8

• Biologie
• WO
• Studiejaar 3

Unit 5.8

Learning goal

You can describe what homozygous, heterozygous, dominant and recessive mean.

Planning

Instruction 

Practicing some exercises together

Make ex. 1 to 3 (BS5.8)

Body cells, chromosomes, DNA

Gene and allele

Example: 

Gene: 

Eyecolour

Allele (=gene variant): 

- Brown eyes

- Blue eyes

- Green eyes 

Homozygous and heterozygous

• 2 similar alleles: homozygous
• 2 different alleles: heterozygous 

What about the phenotype when heterozygous...

• Usually one allele 'wins' from the other. The stronger allele determines which trait (phenotype) you have. We call this allele: dominant. 

• The trait that 'loses' and does not become visible is called recessive. 

Which allele is dominant? 

Which allele is dominant? 

Symbols 

To conclude

1. Homozygous: 2 identical alleles 

2. Heterozygous: 2 different alleles

3. Dominant gene: gene that 'wins' 

4. Recessive gene: gene that 'loses'/is being suppressed 

To practice

Joep has brown eyes. He received the allele for brown eyes from his mother. From this father he received the allele for blue eyes. 

- Is Joes homozygous or heterozygous for eye colour?

- Is "brown eyes" dominant of recessive?

In guinea pigs, short hair is dominant and long hair is recessive.

-What is the genotype of a guinea pig with long hair?

1. AA
2. aa
3. Aa

In guinea pigs, short hair is dominant and long hair is recessive.
Which genotype(s) can a guinea pig with short hair have?

1. AA or Aa
2. aa or Aa
3. Aa

T

Allele

Dominant

Genotype

Heterozygote

Homozygote

Recessive

Phenotype

Same gene: different forms

Two of the same genes

The weaker allele

Appearance

Two different alleles

The stronger allele

Genetic constitution: the alleles that you have