7A - Genetics Flashcards
Define a gene.
A sequence of bases on a DNA molecule that codes for a protein (polypeptide) which results in a characteristic.
Define an allele.
A different version of a gene.
How many alleles can there be for a gene?
Several.
What makes different alleles different?
The order of bases in the gene.
Define genotype.
The alleles an organism has for a certain gene.
Define phenotype.
An organism’s characteristics as a result of the expression of the genotype.
Define dominant.
The allele that is expressed in the heterozygous genotype.
Define recessive.
The allele that is expressed only in the homozygous genotype.
How are dominant alleles represented?
Uppercase letters
How are recessive alleles represented?
Lowercase letters
Define codominant.
Alleles that are both expressed in the heterozygous. Neither one is recessive.
Define locus.
The fixed position of a gene on a chromosome.
Define homozygote.
An organism that carries two copies of the same allele.
Define heterozygote.
An organism that carries two different alleles.
Define carrier.
A person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring.
Are humans haploid or diploid?
Diploid - We have two sets of chromosomes, so we have two alleles for each gene.
What can be used to predict the genotypes and phenotypes of offspring produced in genetic crosses?
Genetic diagrams
What is monohybrid inheritance?
The inheritance of a characteristic controlled by a single gene.
What things must be shown in a Punnet square question?
1) List the parents’ genotypes.
2) List the gametes’ alleles.
3) Draw the square to show the cross between the gametes.
4) Write out the proportions of resulting genotypes and phenotypes.
5) Answer the question.
Remember to revise monohybrid cross diagrams.
Pg 168 and 169 of revision guide.
What are the F1 and F2 phenotypes?
- F1 - First generation phenotypes
* F2 - Second generation phenotypes
Give an example of codominance.
Sickle-cell anaemia
How is codominance represented in genetic diagrams?
- A large, capital letter is given for the gene (e.g. H)
- A superscript capital latter is given for each allele
Example genotypes: HSHN (where S and N are superscript)
Explain genetic inheritance for sickle-cell anaemia.
- Homozygous for normal haemoglobin = HNHN -> Don’t have the disease
- Homozygous for sickle haemoglobin = NSHS -> All blood cells are sickle-shaped
- Heterozygous = HNHS -> Sickle-cell trait with some normal and some sickle haemoglobin