8- transfer of genetic variation Flashcards
origins of genetic variation
• Mutations.
• Meiosis (crossing over, independent assortment).
• Random fertilisation.
allele
An alternative form of a gene.
genotype
The alleles present within cells of an organism.
phenotype
The observable characteristics of an organism.
homozygote
Two identical alleles of a gene.
heterozygote
Two different alleles of a gene.
dominance
An allele that is always expressed in the phenotype.
recessive
An allele that is only expressed in the phenotype if two copies are present.
codominance
Both alleles contribute to the phenotype without mixing, and are equally expressed.
multiple alleles
More than two possible versions of an allele.
genetic crosses and pedigree diagrams
• Used to predict the genotypes and phenotypes of offspring.
• The first set of offspring is the F1 generation, the second set is the F2 generation.
Monogenic / monohybrid
inheritance
The inheritance of a characteristic controlled by a single gene.
dihybrid inheritance
• The inheritance of 2 characteristics controlled by different genes.
• Expected ratios and actual ratios may be different due to chance or linked genes
two non interacting unlinked genes
Unlinked genes are on different chromosomes (non-homologous).
two linked genes
Linked genes are on the same chromosome, and leads to autosomal linkage.
recombinants
• Recombinants have phenotypes different from the original parents.
• Recombinants show that crossing over has taken place.
• The number of recombinants depends on the frequency of crossing over. The frequency of crossing over is higher the further apart two genes are.
sex linkage
• Inheritance of genes located on sex chromosomes.
• X-linked genes: Present on the X chromosome.
• Y-linked genes: Present on the Y chromosome, less common due to their smaller size.
sex determination
• Females have two X chromosomes (XX).
• Males have one X and one Y
chromosome (XY).
X-linked inheritance
Characteristics caused by recessive alleles on the X chromosome occur more in males.
haemophilia
• A group of blood disorders caused by mutations in genes that code for proteins for clotting.
• Those with haemophilia lack factor VIII (blood clotting factor).
• They are X-linked recessive disorders.
Males are affected more. Females are usually carriers.
null hypothesis
• It states that there is no significant difference between the observed and expected results.
• The aim is to either support or reject the hypothesis.
chi squared test
• It is done to see if there is a significant difference between the observed and expected results.
• It determines the possibility of results being due to chance.
• It is used for discontinuous variation data.
• It is only done when the sample size is sufficiently large (>20).
