Patterns of inheritance Flashcards
Define phenotype
The expression of an organisms genetic constitution combined with it’s interaction with environment
How can meiosis bring about genetic varaiation
Crossing over of chromatids before the first division
(Independent assortment) Random arrangement of chromosomes lining up
How does fertilization bring about genetic variation?
Sex cells (gametes) are haploid meaning they only contain half of an organisms DNA. Two individuals thus will produce genetically different offspring. (random nature of fertilization)
Define monogenic inheritance
One phenotypic characteristic is controlled by a single gene
Define dihybrid inheritance
Two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time
e.g Mendel’s peas!
What is meant by sex linkage?
An allele is located on one of the sex chromosomes meaning expression depends on the sex of the individual
What are co-dominant alleles?
Two dominant alleles that contribute to the phenotype either by showing a ‘blend’ of characteristics or the two characteristics appearing together
What is autosomal linkage?
Two or more genes are located on the same non sex chromosome.
What is epistasis?
Where two non linked genes interact, with one gene masking or suppressing the other gene
What is the Chi Squared test?
Statistical test to find out whether the difference between observed and expected characteristics is due to chance, or real effect. Used to compare phenotypic ratios.
How is the Chi Squared test performed?
The formula results in a number which is compared to a critical value. If it’s greater than or equal to the critical value then there is no significant difference so it’s down to chance.
How can the number of genes coding for a characteristic influence variation?
If determined by one gene it is discontinuous variation (monogenic)
If determined by more than one gene it’s continuous variation (polygenic)
What is stabilizing selection?
Occurs when environmental conditions stay the same. Individuals closest to the mean are favored and any new characteristics are selected against. Results in low diversity.
What is directional selection?
Occurs when environmental conditions change. Individuals with phenotype suited to the new conditions will survive and pass on their genes. Over time the population will move towards these characteristics.
What is genetic drift?
A change in a population’s allele frequency that occur due to chance. May cause gene variants to disappear completely
