7A - Inheritance Flashcards
What does ‘codes for’ mean?
Contains the instructions for.
Define gene:
A sequence of bases on a DNA molecule that codes for a protein (polypeptide), which results in a characteristic, e.g. a gene for eye colour.
Define allele:
A different version of a gene. There can be many different alleles of a single gene, but most plants and animals, including humans, only carry two alleles of each gene, one from each parent. The order of bases in each allele is slightly different - they code for different versions of the same characteristic.
Define genotype:
The genetic constitution of an organism - the alleles an organism has.
Define phenotype:
The expression of the genetic constitution and its interaction with the environment - an organism’s characteristics.
Define dominant:
An allele whose characteristic appears in the phenotype even when there’s only one copy. Dominant alleles are shown by a capital letter.
Define recessive:
An allele whose characteristic only appears in the phenotype if two copies are present. Recessive alleles are shown by a lower case letter.
Define codominant:
Alleles that are both expressed in the phenotype - neither one is recessive.
Define locus:
The fixed position of a gene on a chromosome. Alleles of a gene are found at the same locus on each chromosome in a pair.
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.
What do genetic diagrams show?
The possible genotypes of offspring.
Are human haploid or diploid organisms?
Diploid.
What does diploid mean?
Has two sets of chromosomes so have 2 alleles for each gene.
How many alleles for each gene do gametes have?
Only 1.
What is monohybrid inheritance?
The inheritance of a characteristic controlled by a single gene.
Whenever you do a monohybrid cross with 2 heterozygous parents, what ratio of dominant:recessive characteristic do you get?
3:1
What does a dihybrid cross show you?
How 2 different genes are inherited at the same time.
What is the phenotypic ratio?
The ratio of different phenotypes in offspring.
What is the phenotypic ratio in the F1 generation in a monohybrid cross?
All heterozygous offspring (e.g. Rr).
What is the phenotypic ratio in the F2 generation in a monohybrid cross?
3:1
dominant : recessive
What is the phenotypic ratio in the F1 generation in a dihybrid cross?
All heterozygous offspring (e.g. RrYy).
What is the phenotypic ratio in the F2 generation in a dihybrid cross?
9:3:3:1
dominant both : dominant 1st recessive 2nd : recessive 1st dominant 2nd : recessive both
What is the phenotypic ratio in the F1 generation in a codominant cross?
All heterozygous offspring.
What is the phenotypic ratio in the F2 generation in a codominant cross?
1:2:1
homozygous for one allele : heterozygous for the other allele.
What are the 3 main reasons why the phenotypic ratio is different from what is expected?
- Sex linkage.
- Autosomal linkage.
- Epistasis.
Explain the dominant and recessive alleles in blood groups
Io (blood group O) is recessive.
IA (blood group A) and IB (blood group B) are codominant.
Haploid
1 set of chromosomes.
Diploid
2 sets of chromosomes.
Polyploid
Many set of chromosomes (>2).
Codominant
When two/both alleles mask the expression of other/both are expressed.
Homologous chromosomes
Pairs of chromosomes with the same genetic sequence and loci.
Monohybrid inheritance
The study of the inheritance of alleles for one gene.
Dihybrid inheritance
The study of the inheritance of alleles for 2 genes at the same time.
