Topic 18 - Inherited Changes Flashcards
Define allele.
One different form of the same gene located at a specific position on a specific chromosome.
Define homologous chromosome
Pair of chromosomes that have same gene loci and determine same features - not identical.
Define homozygous dominant
Organism with two dominant alleles
Define nucleotide
Organic compound made up of nitrogenous base, a sugar, and a phosphate group.
Define homozygous recessive
Organisms with two recessive alleles.
Define chromosome
Structure within nucleus of eukaryotic cells that bear genetic material as a threadlike linear strand of DNA bonded to histone proteins.
Define gene
A section of DNA that determines a single characteristic of an organism.
Define gamete
A reproductive sex cell that fuses with another gamete during fertilisation.
Define co-dominance
Both alleles contribute to the phenotype
Define fertilisation
Nucleus of a sperm cell fuses with nucleus of an ovum. Fusion of these gametes results in a zygote, which has 46 chromosomes. 23 inherited from mother, 23 inherited from father.
What is monohybrid inheritance?
Inheritance of a single gene.
What are expected ratios?
There are ratios of expected genotypes and phenotypes for each cross.
In practice this does not always happen - it’s down to chance.
The larger the sample, the more likely you are to find ratios closer to the theoretical value.
What is dihybrid inheritance?
Explanation for how 2 characteristics are determined by 2 genes located on different chromosomes.
What are multiple alleles?
Describes a situation when a gene has more than two alleles.
E.g. there are three alleles that are associated with the immunoglobulin gene I.
I^A
I^B
I^o
I^A and I^B are co-dominant
I^o is recessive to both
Why is sex inheritance (sex linkage) ‘unlike’ other features of inheritance?
Sex is determined by a chromosome, not a gene.
Which gender are sex linked characteristics most likely to appear in?
Males as the X chromosome carried the allele. Males only have one X chromosome so only need one recessive allele, females have two X chromosomes so need two recessive alleles. The Y chromosome doesn’t carry an allele.
What is a pedigree chart?
Used to trace the inheritance of characteristics, which can be sex-linked or not.
What is autosomal linkage?
Two genes are on the same chromosome and gametes are no longer produced in equal proportions.
What is epistasis?
The allele of one gene affects or masks the expression of another gene in the phenotype.
