5.8 Dominant and recessive

• Biologie
• Middelbare school
• havo, vwo
• Leerjaar 4

Put them in the correct order from big to small.

Chromosome

Gene

Genome (biggest)

Nucleotide

nitrogenous base

Learning objectives

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

You have learned that an allele pair can contain two identical or two different alleles for a certain hereditary characteristic. In a non-identical allele pair, the stronger allele is reflected in the phenotype.

Gene en allele

gene = piece of DNA that codes for 1 protein = 1 trait

• chromosomes are in pairs and thus genes as well

allele = one of the variants of a gene

Mutation

A change in the DNA

mutant = organism in which a mutation can be seen in the phenotype

Causes mutation(mutagenic influences/carcinogens)

Cancer, how and why?

• Happens due to mutations
• Mutation makes cells divide continously      
• This creates a tumour:

       - Benign: divides slowly, stays at its spot

       - Malignant: divides quickly, disrupts tissues

• Metastasis > cancer cells are carried by blood/lymph. End up in different body parts and create more/new tumours

Homozygous: both alleles are the same

Heterozygoos: the alleles are different

homozygous = when an allele pair consists of two identical alleles

heterozygous = when an allele pair consists of two different alleles

dominant allele: allele that is always expressed in the phenotype

• A

recessive allele: allele that is only expressed in the phenotype if there is no dominant allele present

• a

Carrier

Een heterozygous is a carrier of the recessive allele

hair colour or a disease

Gene symbols

AA = homozygous dominant

aa = homozygous recessive

Aa = heterozygous

2 equal alleles for a trait is what we call

1. Homozygous
2. Heterozygous
3. Dominant
4. Recessive

Which characteristic is expressed in a heterozygous individual?

1. the dominant one
2. the recessive one

Pjotr his gene code for hair is Aa. His hair is brown. Is the colour of his hair dominant or recessive?

1. Dominant
2. Recessive

Aa is also described as:

1. Homozygoot dominant
2. Heterozygoot
3. Homozygoot recessief
4. Heterozygoot dominant

Which description fits best at the question mark?

1. Chromosomepair
2. Allele pair
3. Gene pair
4. Both gene pair and allele pair

True or not true:
A chromosome is a gene

1. True
2. not true

What is a allele?

1. the variant of a gene
2. One of the genes of a gene pair