Topic 7: Inherited Change Flashcards
Define:
- Genotype
- Phenotype
- All the alleles an organism has
- The observable or biochemical characteristics of an organism
Define:
- Gene
- Allele
- A section of DNA that determines a single polypeptide or characteristic
- One of the different forms of a gene that are found at the same locus
Define:
- Homologous chromosomes
- Codominance
- A pair of chromosomes with the same gene loci and determine the same features, one maternal one paternal.
- Where both alleles contribute to the phenotype
What is monohybrid inheritance?
How are the generations named?
The inheritance of a single gene.
The F1 (first fillial) generation is the 1st generation of offspring. The F2 generation is the offspring’s offspring.
What is dihybrid inheritance?
The inheritance of a phenotype due to two genes found on different chromosomes
What are autosomes?
The 22 chromosomes that are not sex chromosomes
What is autosomal linkage?
When 2 or more genes exist in the same autosome. All the genes on a single chromosome form a linkage group.
A basic assumption is that no crossing over occurs, so all the linked genes remain together during meiosis, and so pass into the gametes and offspring together.
What is codominance and how is it written?
When both alleles are dominant so both are expressed.
Alleles are written as superscripts (upper and lowercase would not work as both are dominant)
What is multiple alleles?
When a gene has more than 2 alleles.
Only 2 alleles can still be present in an organism at one time, as there are only 2 homologous chromosomes so 2 gene loci
What is an example of multiple alleles?
Human blood groups.
IA = antigen A
IB = antigen B
IO = antigen O
IA and IB are codominant alleles, IO is recessive to both
Why is sex inheritance unlike other inheritance?
It is determined by a chromosome not a gene. Females have the genotype XX while males are XY, so females always produce gametes with the X chromosome, and male gametes have either X or Y
What is sex linkage?
The inheritance of any gene carried on the sex chromosomes.
What group of individuals is most likely to inherit a sex-linked disease and why?
Males
The X chromosome is much longer than the Y, so for many sex-linked genes on the X chromosome there is no homologous portion on the Y. This means that when a recessive characteristic is inherited by a male, it is always expressed since there is no dominant allele on the Y.
What is an example of a sex-linked disorder?
Haemophilia
What is epistasis?
When the allele of one gene affects or masks the expression of another in the phenotype.
What is one way epistasis can occur?
By genes acting in sequence by determining the function/non-function of enzymes in a biochemical pathway.
