lec 10-1

Question 1

Principles of segregation

Answer 1

Alleles of a gene (R,r) separate independently

Question 2

Principle of independent assortment

Answer 2

Independent separation of non-homologous chromosomes

Question 3

Crossing over during meiosis

Answer 3

During late prophase, after replication, homologous chromosomes come very close to each other to make crossing over possible

Question 4

Crossing over

Answer 4

Exchange of DNA between non-sister chromatids

Question 5

Result of crossing over

Answer 5

Gamete chromosomes have different combinations of alleles than parental chromosomes, thus mixing of alleles on same chromosome

Question 6

Recombinant chromosomes/gametes/progeny

Answer 6

Is not the same as the parental

Question 7

non-recombinant chromosomes/gametes/progeny

Answer 7

same as the parental

Question 8

High frequency of crossing over means

Answer 8

Alleles of one gene would be inherited independently from many other genes

Question 9

Not all genes are inherited

Answer 9

Independently

Some are linked

Question 10

Recombination frequency depends on

Answer 10

How far away from each other two genes are on a chromosome

Question 11

Recombination frequency is higher

Answer 11

The farther apart two genes are

Question 12

Linkage group

Answer 12

Set of genes located closely together on the same chromosome and likely inherited together

Question 13

Notation for linked genes

Answer 13

A B a b
——– X ——–
A B a b

Line separates two homologous chromosomes

alleles of the same gene aligned vertically

Question 14

To test for linkage

Answer 14

Use a testcross with a plant that is heterozygous for both characteristics crossed to a plant that is homozygous recessive for both

Question 15

Testing for linkage using a testcross

Two extreme possibilities

Answer 15

Genes are completely unlinked (different ends of the chromosome)

Genes are completely linked very close to each other physically

Question 16

If alleles are completely un-linked

Answer 16

Crossing over will occur

Some gametes will be non-recombinant and recombinant (50-50 split theoretically)

Question 17

Completely un-linked results are

Answer 17

The same if two genes are on different chromosomes (Mendel’s dihybrid experiments)

Question 18

Testcross can not tell

Answer 18

If two genes are far apart on the same chromosome or on two different chromosomes

Question 19

If alleles are completely linked

Answer 19

Crossing over will not occur between genes and so alleles for two genes stay together

All gametes will be non-recombinant

Question 20

Completely linked means all progeny will be

Answer 20

Non-recombinant with 1/2 having geno/phenotype from each parent

Question 21

Partially linked genes

Answer 21

Genes are spread all along the chromosome so many would be partially linked

Question 22

Over many gametes the majority will be

Answer 22

Non-recombinant

Due to no crossing over making 100 percent non-recombinant while crossing over only makes 50 percent recombinant

Question 23

Majority of progeny will be what when some crossing over happens

Answer 23

Non-recombinant

Question 24

Max recombinant percentage is

Answer 24

50 percent as this would occur if genes were far enough apart on the chromosome or on completely different chromosomes

Question 25

Recombination frequency

Answer 25

recombinant progeny / #total progeny

X100

Question 26

Steps to predicting cross outcomes with linked genes when recombination frequency is given

Answer 26

Perform a testcross

Predict the frequency of the different progeny

Halve the recombination frequency and assign that to each gamete type of the recombinants

Halve the non-recombinant and assign that to each gamete type of the non-recombinants

Finally, homozygous parents will produce 100 percent non-recombinant gametes (meaning it will be 1)

Use multiplication rule to determine cross outcomes