Chromosomal Basis of Inheritance

Question 1

what are x linked genes?

Answer 1

-genes found on the x chromosome that code for characteristics other than sex
-males have one x , females have two

Question 2

what is a barr body?

Answer 2

the inactivated x chromosome in females. because they have two x’s, one x will get deactivated in every cell of their body

Question 3

what are linked genes?

Answer 3

-genes on the same chromosome, meaning they cannot sort independently
-can only separate during prophase 1 crossing over

Question 4

how does the distance between genes affect their linkage?

Answer 4

-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

Question 5

what are recombinants?

Answer 5

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

Question 6

what is genetic mapping?

Answer 6

-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

Question 7

what are the units of gene mapping?

Answer 7

-centimorgans: 1 unit = 1% recombination frequency to a max of 50%. if greater than 50%, genes not linked

Question 8

what are linkage maps?

Answer 8

visual representations for the order of genes along a chromosome

Question 9

what is nondisjunction?

Answer 9

-a chromosome error when homologous pairs or sister chromatids fail to separate, causing a cell to have an extra chromosome

Question 10

what is aneuploidy?

Answer 10

-an abnormal number of chromosomes

Question 11

what is trisomy?

Answer 11

-3 copies of a chromosome, if this occurs on chromosome #21 a person will have down syndrome

Question 12

what is monosomy?

Answer 12

-having only one copy of a chromosome, usually lethal

Question 13

what is polyploidy?

Answer 13

-having more than 2 sets of chromosomes. commonly found in plants

Question 14

what is chromosomal deletion?

Answer 14

-a segment of a chromosome is removed / deleted

Question 15

what is chromosomal duplication?

Answer 15

-a segment of a chromosome is repeated / duplicated

Question 16

what is chromosomal inversion?

Answer 16

-a segment of a chromosome is reversed / inversed (ABCDE -> ADCBE)

Question 17

what is chromosomal translocation?

Answer 17

-when a segment of one chromosome is moved to a segment of a nonhomologous chromosome, and vice versa

Question 18

what is genomic imprinting?

Answer 18

-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

Question 19

how did thomas morgans experiments prove the existence of x linked genes?

Answer 19

-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)

Question 20

how can a female express an x linked recessive trait?

Answer 20

-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