Topic H: Linkage and Mapping

Question 1

Mendel observed a phenotypic ratio of 9:3:3:1 in his dihybrid F2 progeny. This ratio is indicative of ________ assortment

Answer 1

INDEPENDENT

Question 2

F1 dihybrids are capable of producing two classes of gametes:

Answer 2

• Parental
• Recombinant

Question 3

What are parental gametes?

Answer 3

Having the same allelic combinations (genotypes) of the gametes made by the true-breeding (homozygous) parents of the F1 (parent generation)

Question 4

What are Recombinant gametes?

Answer 4

having different allelic combinations (genotypes) from the gametes made by the true-breeding (homozygous) parents of the F1 (parent generation)

Question 5

When there is independent assortment, parental and recombinant gametes are made in ______ ______

Answer 5

EQUAL PROPORTIONS

Question 6

Mendel observed a phenotypic ratio of __________ in his dihybrid testcross progeny. This ratio is indicative of ____ _____

Answer 6

1:1:1:1

INDEPENDENT ASSORTMENT

Question 7

A tester is always

Answer 7

HOMOZYGOUS RECESSIVE

Question 8

Genes which are unlinked assort independently, as described by Mendels ______________-

Answer 8

second law of inheritance

Question 9

Non-Syntenic? Syntenic?

Answer 9

Non-syntenic: “on different chromosomes”

syntenic: “the same chromosome”

Question 10

Two genes may demonstrate independent assortment because they are _______________

Answer 10

physically located on different chromosomes (non-syntenic)

Question 11

If a dihybrid F2 progeny does not appear with the typical 9:3:3:1 ratio that is expected with independent assortment, we assume that ….

Answer 11

the two different genes do NOT assort independently, and thus are linked.

Question 12

In a dihybrid cross:

• if we are unsure if two genes are linked or unlinked, we write a ____ between the genes
• If we think they are unlinked, we write a ______ between the genes

Answer 12

• if we are unsure if two genes are linked or unlinked, we write a ● between the genes
• If we think they are unlinked, we write a ; between the genes

Question 13

a plus sign beside a gene indicates it is ___

Answer 13

Dominant.

ex. (pr+/pr) would be (dominant/recessive)

Question 14

When a dihybrid F2 phenotypic ratio deviates from 9:3:3:1 , or when the F1 x tester testcross progeny phenotypic ratio deviates from 1:1:1:1, then __________

Answer 14

LINKAGE IS ASSUMED

Question 15

If we deem two loci to be linked, they will be ______

Answer 15

Syntenic (on the same chromosome)

Question 16

If there is a greater proportion of parental testcross progeny than recombinant testcross progeny, in a dihybrid cross between F1 and a tester, what do we assume?

Answer 16

that the two genes are syntenic and linked

Question 17

What does ( A/a) mean?

Answer 17

a forward slash symbolically separates two homologous chromosomes

Question 18

What does (A/a; B/b) mean?

Answer 18

Genes KNOWN to be UNLINKED are separated by a semi-colon

Question 19

what does (Ac/aC) mean?

Answer 19

alleles known to be linked (on the same homolog) have no punctuation

Question 20

What does (A/a ● F/f) mean?

Answer 20

Genes of UNKNOWN linkage are shown with a dot

Question 21

If two dihybrid genes are completely linked, what would we observe in the testcross progeny?

Answer 21

If they are completely linked, this would prevent crossing over from occurring between the two genes, and NO recombinant gametes would be produced. We would only see equal proportions of the two parental gametes

Question 22

If two dihybrid genes are linked, (but not completely), what would we observe in the testcross progeny?

Answer 22

If they were not completely linked, crossing over would occur between the two loci and all four testcross progeny classes would be observed, but with MORE PARENTAL than recombinant types

Question 23

When genes are UNLINKED we expect ____% of the F1 gametes to be recombinant

Answer 23

50% (this is mendelian inheritance)

Question 24

When genes are COMPLETELY LINKED we expect ____% of the F1 gametes to be recombinant

Answer 24

0%

Question 25

When genes are linked we expect ____% of the F1 gametes to be recombinant

Answer 25

0-50% (The distance BETWEEN the two genes)

Question 26

As the interval between two linked genes increases, the _______ the chance of a cross-over or recombinant event will be

Answer 26

GREATER
(So the further the two genes are away from one another, the more likely they will cross over during meiosis)

Question 27

the recombination frequency (RF) between two genes is proportional to……

Answer 27

proportional to the distance between the two genes

Question 28

the recombination frequency (RF) between two genes can be used to determine:

Answer 28

• if genes are unlinked or linked
• if linked, can be used to estimate the distance between the two genes

Question 29

How do you calculate recombinant frequency ?

Answer 29

(Using numbers from the test cross progeny):
RF= # of recombinant progeny / total # of testcross progeny

Question 30

A recombinant frequency value can never exceed ___, which means….

Answer 30

50% , which means you can NEVER HAVE MORE RECOMBINANTS THAN PARENTALS