Inheritance Flashcards
What is genetics?
Study of inheritance and variation.
What are the sources of variation in genetics?
- Mutation
2. Meiosis - cross-over and random assortment
What are genotype and phenotype?
- Genotype = set of genes responsible for a particular trait (DNA).
- Phenotype = physical expression of a particular trait (protein).
What do the terms homozygous, heterozygous and hemizygous mean?
- Homozygous = 2 alleles of a gene are the same
- Heterozygous = 2 alleles of a gene are different
- Hemizygous = only 1 allele of a gene on the X chromosome, i.e. Males only
What do the terms dominant and recessive mean?
- Dominant = allele determining the phenotype in a heterozygote
- Recessive = non-dominant allele in a heterozygote
What is co-dominance?
2 alleles are expressed equally, creating a new phenotype.
Give an example of a gene that can show co-dominance of alleles.
- Human isoglutamin gene codes for glycoproteins on RBC surface - determines ABO blood types.
- Gene I has 3 alleles: A, B and O:
- allele A is dominant over allele O
- allele B is dominant over allele O
- alleles A and B are co-dominant
- 4 possible genotypes: blood group A, B, AB and O.
What is polygenic inheritance?
More than 1 gene involved in producing a phenotype (e.g. Multiple genes coding for multiple enzymes required for a single product).
Give an example of a polygenic trait that may result in disease.
Albinism is inherited in a recessive manner but is polygenic - even if 2 parents are inherited, offspring may not be is parents are affected in different genes.
What is genome complementation?
2 genomes complement each other if heterozygous for each allele.
What is the difference between linked and unlinked genes?
- Linked: genes are on the same chromosomes - do not show independent assortment at meiosis
- Unlinked: genes are on different chromosomes
What does recombination frequency between 2 linked genes depend on?
The distance between genes:
- genes close together are tightly linked.
- genes that are apart on the same chromosome almost behave as unlinked genes due to crossing over.
What is the ration of linked and unlinked genes in gametes?
- Unlinked genes: 1:1:1:1
- Linked genes not 1:1:1:1 as rate dependent on how often cross-over occurs, itself dependent on distance between genes on chromosomes.