Chapter 15: The Chromosomal Basis of Inheritance

Question 1

What is a sex-linked gene?

Answer 1

Any gene located on either the X or the Y chromosome

Question 2

Are males and females affected differently by sex-linked genes?

Answer 2

Yes

Question 3

What is the notation for red green colourblindness? (X-linked recessive trait)

Answer 3

N = Normal vision
n = colour blind 

Females:
XN XN = normal
XN Xn = normal
Xn Xn = colourblind

Males:
XN Y = normal
Xn Y = colourblind

Question 4

X-linked disorders are more common in ________?

Answer 4

Males

Question 5

In terms of haploid and diploid:

Females are _____ for each X-linked trait.
Males are _____ for each X-linked trait.

Answer 5

Females are diploid

Males are haploid

Question 6

What is X inactivation?

Answer 6

When one of the Xs in a female is inactivated and it’s genes cannot be read.

Question 7

What are linked genes?

Answer 7

When two genes are on the same chromosome.

|R |
|y |

Rather than:

|R |y
| |

Question 8

Drosophila have __ homologous pairs.

Answer 8

4

Question 9

Describe the naming system for drosophila.

Answer 9

b+b+ = grey 
b+b   = grey 

bb = black

Question 10

What does it mean when a fly is wildtype?

Answer 10

It displays the normal phenotype

Question 11

What does it mean when a fly is mutant?

Answer 11

It displays the unusual phenotype.

Question 12

How do you test whether two traits are linked or unlinked?

Answer 12

Do a testcross of the two parents.

If the results are 1:1, they are unlinked.
If the results vary, they are linked.

Question 13

What are recombinant offspring?

Answer 13

Offspring that look nothing like the parent.

Question 14

Recombinant offspring are ______ common.

Answer 14

Less

Question 15

Recombinant offspring originate from ____________.

Answer 15

Crossing over

Question 16

If the genes are close together on a chromosome, it is ______ likely that there will be a crossover.

Answer 16

Less

Question 17

If the genes are far apart on a chromosome, it is ______ likely that there will be a crossover.

Answer 17

More

Question 18

What is recombination frequency?

Answer 18

The frequency of which a single crossover takes place

Question 19

How do you calculate recombination frequency?

Answer 19

recombinants
__________________ x 100
total offspring

Question 20

The higher the recombination frequency, the ________ the genes are on the chromosome.

The higher the recombination frequency, the _______ crossing over there was.

Answer 20

Further

More

Question 21

What is nondisjunction?

Answer 21

When chromosome fail to separate during Meiosis

Question 22

What is aneuploidy?

Answer 22

The abnormal number of chromosomes at the end of nondisjunction Meiosis

Question 23

What will happen if one of these nondisjunction eggs gets fertilized?

Answer 23

Genetic disorders (like Down syndrome)

Question 24

What are the 4 other methods where genetic disorders can occur?

Answer 24

1. Deletion
   
   • piece of chromosome is lost
2. Duplication
   
   • piece of chromosome is copied x2
3. Inversion
   
   • piece of chromosome pops out and is put back in backwards
4. Translocation
   
   • two chromosome broken off at the same time and rejoined to the other one