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2 Pages

Natural Science
Course Code
NATS 1690
Barbara Czaban

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Gene linkage - Linked genes tend to be inherited together because the chromosome is passed along as unit – located on the same chromosome - Each chromosome has hundreds or thousands of genes, arranged linearly - Results of crosses with linked genes deviate from those expected according to independent assortment - Independent assortment = non-linked genes A Full linkage – genes that are close together on the chromosome - Results in equal ratios of 2 types of gametes - The 2 genes with their respective alleles act as a unit during segregation  Incomplete linkage – genes that are far apart on the chromosome - Results in unequal ratios of 4 types of gametes - The 2 genes are usually segregated as a unit - BUT crossing over may re-combine the alleles, thus shifting the ratios - Ratios of recombinant gametes will vary depending on chance Crossover Frequency - Proportional to the distance that separates genes - Crossing over will disrupt linkage between A and B more often than between C and D  The closer together 2 genes are on a chromosome, the less likely they are to cross over Genetic sex determination - Plants and animals have a quite similar mechanism - Females heterogametic (ZW), males homogametic (ZZ)  Birds, butterflies and some frogs - Females X, males O  Grasshoppers and roaches - Males heterogametic (XY), females homogametic (XX)  Humans and mamm
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