Dihybrid inheritance and Gene Interaction Flashcards
what is the study of dihybrid inheritance?
-the study of the inheritance of two traits in the one cross
what is the typical ratio of each genotype of the offspring from crossing two heterozygous plants that are tall (T) or short (t) and have either round (R) or wrinkled (r) seeds?
-9:3:3:1
-9 being tall and round seeds
-3 tall with wrinkled seeds
-3 short with round seeds
-1 short with wrinkled seeds
what is Mendel’s second law, the law of independent assortment?
-during the formation of gametes, the segregation of the alleles of one gene is independent to the segregation of the alleles of any other genes
how are genes independently inherited?
-if the genes are on different chromosomes then they will be independently inherited
what is the ratio a dihybrid cross produces when a double heterozygous is crossed with a double homozygous recessive?
-1:1:1:1
what does the term gene interaction mean?
-when two genes that are on different chromosomes if certain allele combinations occur from the different forms of the same gene, they can interact to produce a range of phenotypes
what are the 2 forms of gene interaction?
-epistasis
-polygenic inheritance
what does the term epistasis mean?
-when one gene inhibits the action of another gene
what does polygenic inheritance mean?
-where a trait is influenced by a range of genes rather than just one
what type of variation does polygenic inheritance lead to?
-continuous as traits are controlled by multiple genes
how else is the phenotype of an organism effected other than its genotype?
-the environment
how does the environment effect the phenotype of an organism? (example of plant with tall gene)
-an plant which has a gene for tallness will only grow tall if it has enough nutrients, light, space etc
what are the 3 assumptions made when a monohybrid (3:1) and a dihybrid cross (9:3:3:1) produce their expected ratios?
-independent assortment has occurred
-no sex linkage
-codominance does not occur
what is the equation used that links expected a nd observed ratios of inheritance crosses? why is it used?
-chi-squared
-used to decide if the differences between the actual set of results and the expected set of results are statistically significant or are they just due to chance
what is the formula for chi-squared?
-look in booklet and be able to say what each letter stand for
what must be made first before calculating chi-squared? what does this prediction state?
-make a Null hypothesis first
-this states that there will be no significant difference between the expected and observed ratios
what must the chi-squared value lie between for the null hypothesis to be accepted/ rejected?
-if the value is less than the probability value of 0.05 then the null hypothesis is accepted
-if it is greater an 0.05 then is it usually rejected
