mendelian inheritance 2, pedigrees and statistics- lecture 9 Flashcards
monohybrid cross
“A monohybrid cross is the hybrid of two individuals with homozygous genotypes which result in the opposite phenotype for a certain genetic trait.” “The cross between two monohybrid traits (TT and tt) is called a Monohybrid Cross.” Monohybrid cross is responsible for the inheritance of one gene
what is the only way you can get segregated offspring from two dominant phenotype parents
if they’re both heterozygotes
chi square
sum of (observed-expected)^2/expected (for each trait and observed kid)
gives us an indication of whether our observations can reasonably be expected to have just been generated by chance sampling error or if there is something else going on
degree of freedom
n-1 of phenotypic categories
p value
probability of getting this departure (given null hypothesis) by random sampling error
associated with a chi-square value is the
probability that the null hypothesis is consistent with the observations, even with the observed deviation from the expected results. This p-value can be determined by looking up your calculated χ2 value in a table of critical values. But to look up the p-value you must first determine the degrees of freedom (DF). The degree of freedom represents the numbers
of ways in which the expected classes are free to vary. A quick method rule of thumb for determining degrees of freedom is: # of phenotypic classes -1 = Degrees of freedom.
Looking up 14.61 with one degree of freedom in the chi square critical values table gives a p-value of < 0.001. This p-value, or probability value, tells us how likely the observed deviation from the expected values
is simply due to chance. If the p-value is high (p>0.05), then we conclude that chance alone could be responsible for producing deviations from
the expected results. If the p-value is low, then this tells us that the deviations are so great that it is likely that some factor other than chance is responsible for the observed results. It is convention in science to use the 0.05 (5%) probability level as the cutoff value. This means that if the pvalue is greater than 5% then you would fail to reject the null hypothesis.
It’s important to note that rejecting the null hypothesis is not equivalent to accepting the alternative hypothesis – it simply lends
support to the alternative hypothesis
pedigree analysis
autosomal recessive
autosomal dominant
x linked recessive
x linked dominant
y linked trait
Hemizygosity
Describes an individual who has only one member of a chromosome pair or chromosome segment rather than the usual two. Hemizygosity is often used to describe X-linked genes in males who have only one X chromosome
linkage
This phenomenon is called genetic linkage. When genes are linked, genetic crosses involving those genes will lead to ratios of gametes (egg and sperm) and offspring types that are not what we’d predict from Mendel’s law of independent assortment.
Mendel’s second law
The results of Mendel’s second set of experiments led to his second law. This is the law of independent assortment. It states that factors controlling different characteristics are inherited independently of each other
dihybrid test cross
