Chromosomal Basis of Inheritance Flashcards
what are x linked genes?
-genes found on the x chromosome that code for characteristics other than sex
-males have one x , females have two
what is a barr body?
the inactivated x chromosome in females. because they have two x’s, one x will get deactivated in every cell of their body
what are linked genes?
-genes on the same chromosome, meaning they cannot sort independently
-can only separate during prophase 1 crossing over
how does the distance between genes affect their linkage?
-genes close together on the same chromosome are “linked” and do not sort independently
-genes on different chromosomes, or very far apart on the same chromosome, are unlinked and can assort independently
what are recombinants?
offspring that have new combinations neither parent had
-if 50% or more of offspring are recombinants, the genes are independently assorted. if 50% or more are the parental type, the genes are linked
what is genetic mapping?
-a mapped sequence of linked genes on a chromosome, done by using recombinant frequencies
-greater distance between 2 genes = more room for crossing over = more likely to be separated during crossing over
what are the units of gene mapping?
-centimorgans: 1 unit = 1% recombination frequency to a max of 50%. if greater than 50%, genes not linked
what are linkage maps?
visual representations for the order of genes along a chromosome
what is nondisjunction?
-a chromosome error when homologous pairs or sister chromatids fail to separate, causing a cell to have an extra chromosome
what is aneuploidy?
-an abnormal number of chromosomes
what is trisomy?
-3 copies of a chromosome, if this occurs on chromosome #21 a person will have down syndrome
what is monosomy?
-having only one copy of a chromosome, usually lethal
what is polyploidy?
-having more than 2 sets of chromosomes. commonly found in plants
what is chromosomal deletion?
-a segment of a chromosome is removed / deleted
what is chromosomal duplication?
-a segment of a chromosome is repeated / duplicated
what is chromosomal inversion?
-a segment of a chromosome is reversed / inversed (ABCDE -> ADCBE)
what is chromosomal translocation?
-when a segment of one chromosome is moved to a segment of a nonhomologous chromosome, and vice versa
what is genomic imprinting?
-a phenomenon where the expression of certain traits depends on which parent the gene was received from (imprinted genes). one allele is “silenced” through methylation and the other is expressed
how did thomas morgans experiments prove the existence of x linked genes?
-two true breeding red/white eye flies get crossed
-all F1 offspring have red eyes
-F2 offspring have a 3:1 ratio of red to white eyes, but only the males have white eyes. therefore, eye colour must be an x linked gene and the female F2 flies were able to suppress their white eye gene due to having 2 x chromosomes (one is red dominant)
how can a female express an x linked recessive trait?
-by having 2 copies of the x linked gene. if she has one dominant gene, it will be expressed over the recessive. because of this, x linked recessive conditions are rarer in females than in males
