17 Inheritance Flashcards
What is a gene
A length of DNA, sequence of nucleotide bases, that normally code for a particular polypeptide
How many alleles of a gene can occur at the locus
Only one allele of a gene can occur at the locus of any one chromosome
However in diploid organisms the chromosomes occur in pairs called homologous pairs, so two loci that each carry one allele of a gene
Pair of homologous chromosomes showing diff possible pairings of dominant and recessive alleles
INSERT PIC
SEE TXTBOOK PG 155
Summary of genotypes
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SEE TEXTBOOK PG 156
How to represent genetic crosses
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SEE TXTBOOK PG 157
Monohybrid inheritance
Inheritance of a single gene
The law of segregation
In diploid organisms, characteristics are determined by alleles that occur in pairs
Only one of each pair of alleles can be present in a single gamete
What is ratio
Measure of relative size of two classes that is expressed as a proportion
Why is actual not same as expected
Discrepancy due to statistical error
It is chance that determines which gametes fuse with which
Larger sample more likely to produce actual results near theoretical ones, more representative
Genetic cross for pure breeding
See card 1
Genetic explanation of Mendals intercross between plants of F1 generation
See card 2
Law of independent assortment
Each member of a pair of alleles may combine randomly with either of another pair
Multiple alleles
Where there are more than two alleles of which only two may be present at loci of individual’s homologous chromosomes
For codominant alleles how are letters written
See card 3
Inheritance of ABO blood groups
Three alleles associated with gene I (immunoglobulin gene), which lead to presence of different antigens on cell surface membrane of red blood cells:
See card 4
How many alleles present at one time
Although there may be three alleles e.g. ABO blood groups, only two can be present in individual at one time as there are only two homologous chromosomes and so only two gene loci
Comparison of gametes produced by organism that is heterozygous for 2 genes A and B when they are linked and not linked
INSERT PIC
SEE TXTBOOK PG 437
Example of autosomal linkage
See card 5
Example of epistasis
See card 5
Other forms of epistasis
Where genes act in sequence by determining enzymes in biochemical pathway
See card 6
Chi2 test used to
It’s used to test null hypothesis
Chi2 test can be used if certain criteria are met:
The sample size is relatively large, over 20.
Data must fall into discrete categories.
Only raw counts and not percentages, rates etc. can be used
It is used to compare experimental results with theoretical ones e.g. in genetic crosses with Mendelian ratios
What are degrees of freedom
Number of classes - 1
How to analyse calculated value for chi squared
Critical value is p= 0.05
If probability that the deviation is due to chance is equal to or greater than 0.05, deviation not significant, null hypothesis accepted.
If deviation is less that 0.05, deviation is significant, factor other than chance affecting results, null hypothesis rejected.
