Week 2 Online Module 2 Flashcards
What is the inheritance in organelle genes?
Organelle genes have a special mode of inheritance called uniparental inheritance
• Progeny inherit organelles gene exclusively from one parent, in most cases the
mother (maternal inheritance).
• This is because the egg contributes the bulk of the cytoplasm
what is mendel’s law of independent assortment?
- A heterozygote for a single gene (A/a) is sometimes called a monohybrid
- A double heterozygote (A/a B/b) is sometimes called a dihybrid
- From studying dihybrid crosses, Mendel came up with the law of independent assortment
A 9:3:3:1 ratio is diagnostic of
independent assortment
what is a testcross?
a testcross is a cross to a homozygous recessive individual
this individual can only produce recessive gametes
When a dihybrid is testcrossed a 1:1:1:1 phenotypic ratio is expected
if the gene loci are independently assorting
R/r ; Y/y (round yellow) x r/r ; y/y (wrinkled green)
1 round yellow (R/r ; Y/y)
1 round green (R/r ; y/y)
1 wrinkled yellow (r/r ; Y/y)
1 wrinkled green (r/r ; y/y)
what are the possibilities of independent assortment?
When a monohybrid is testcrossed a 1:1 phenotypic ratio is expected
- When a monohybrid is selfed a 3:1 phenotypic ratio is expected
- When a dihybrid is testcrossed a 1:1:1:1 phenotypic ratio is expected
- When a dihybrid is selfed a 9:3:3:1 phenotypic ratio is expected
Explain the process of Meiosis
interphase. chromosomes are unpaired.
prophase. chromosomes and centromeres have replicated, but centromeres have not split
homologs synapse.
anaphase. centromeres attach to spindle and are pulled to poles of the cell.
telophase. two cells form
second anaphase. New spindles form and centromeres finally divide.
end of meiosis. four cells produced.
how do we detect the input and output gamete’s genotypes in recombination?
The production of new allele combinations is called recombination
The genotypes of input or output gametes cannot be detected directly in diploids but
these can be inferred by:
- using pure-breeding diploid parents because they can produce only one gamete type
- detecting recombinant output gametes by testcrossing the diploid and observing it’s progeny
The recombinant frequency can be used to test whether two genes are on different
chromosomes
• For genes on separate chromosomes, the 1:1:1:1 ratio that we have seen before is
observed. Recombinants are 50% of the total progeny.
• A recombination frequency of 50% indicates the genes are independently assorting
and are most likely on different chromosomes
in what different ways can we predict progeny ratios?
predicting progeny ratios from parents of known genotypes can be performed by:
punnett squares
branch diagrams
statistical approaches: chi-square test or product rule
what is the chi-square test?
The chi-square test is a statistical test used to see if the monohybrid and dihybrid ratios generated from a cross are as expected
• The X2 test is a way of quantifying if deviations are due to chance in a hypothesis (rejected as false if there is a probability of less than 5%)
• In order to decide if an X2 value of 0.84 is significant
we use a X2 table to calculate probability (p).
• We use p>0.05
• The degrees of freedom is the number of independent variables in the data – 1, In this case df=2-1=1
what is the product rule?
The product rule states that the probability of independent events occurring together is the product of their individual probabilities.
Want to obtain a/a ; b/b ; c/c ; d/d ; e/e progeny from:
A/a ; b/b ; C/c ; D/d ; E/e x A/a ; B/b ; C/c ; d/d ; E/e
From A/a x A/a, 1⁄4 of the progeny will be a/a
From b/b x B/b, 1⁄2 of the progeny will be b/b
From C/c x C/c, 1⁄4 of the progeny will be c/c
From D/d x d/d, 1⁄2 of the progeny will be d/d
From E/e x E/e, 1⁄4 of the progeny will be e/e
Overall probability = 1/4 x 1/2 x 1/4 x 1/2 x 1/4 = 1/ 256
