4/17 Flashcards
what did Mendels work on a single gene cross reveal?
it supported the law of segregation where two copies of a gene will separate into separate gametes
How did Mendel show dominant/ recessive traits?
by crossing true-breeding individuals, the complete disappearance of a trait showed which traits were dominant and which were recessive
what does it mean to be true bred?
homozygous for a particular trait
when the F1 generation from a true-breeding cross is self-crossed, what was the outcome?
the outcome was a 3:1 ratio of the dominant and recessive traits
what did Mendel’s 3:1 ratio support?
it supported the law of segregation where two copies of a gene separated into separate gametes
what is the purpose of a test cross?
an individual with a dominant phenotype is crossed with a homozygous recessive individual to identify the genotype of the dominant parent
when we have a recessive individual, we immediately know their genotype
true
true or false, the purpose of a test cross is to determine whether a trait is dominant or recessive
false, it is to identify the genotype of a parent
If you have a tall plant (Tt or TT) crossed with a short plant (tt) in a test cross, what will the resulting phenotypic ratios be in the offspring if the tall plant was homozygous dominant? (TT)
the offspring will all be 100% tall
if you have a tall plant (Tt or TT) crossed with a short plant (tt) in a test cross, what will the resulting phenotypic ratios be if the tall plant was heterozygous dominant? (Tt)
the ratios would be 1/2 tall and 1/2 short
how many gametes can form from this parent? YyRRTt
it depends on 2^n, where n= the number of heterozygote loci
Since there are two heterozygotes (Yy and Tt) n=2 and the number of gametes is 4
what were the two hypothesis for gamete formation?
the linked hypothesis where genes were always associated with eachother (ex. YYRR would have YR gametes when crossed with yyrr)
the independent assortment hypothesis where two different genes randomly segregate
in a sister chromatid, which chromosomes will undergo recombination
only the inner chromosomes will
when will parent phenotypes be in the majority?
when the genes are so close that they rarely recombine
for linked transmission, what type of phenotype is in the majority vs minority?
the parent type will always be in the majority while the recombinant/ non parent type will be in the minority
under conditions of linked genes, will the phenotypic ratios follow the law of independent assortment?
no, often times the parents will be in the majority while the recombinants are in the minority
if you have a dihybrid for two different genes (heteozygote for both) and they are found on the same chromosome, then recombination between the genes is the only way that you can get all four gamete combinations like you would have true independent assortment
true, if you did not have a recombination event, you would only get the parent type of genes
what does mendels 3:1 ratio tell us
it supports the law of segregation where the dominant phenotype is present 3 times as often as the recessive trait in the F1 selfcross of a heterozygote
what does the 9:3:3:1 ratio tell us
in a dihybrid cross, the two traits are inherited independently of each other, this means the alleles for one trait do not influence the inheritance for another trait
