CH 15 Genetic Variation Reading Guide

Question 1

Define Genotype

Answer 1

The genetic makeup of a cell

Question 2

Define phenotype

Answer 2

an individuals observable characteristics or traits

Question 3

How did differences in genotype between individuals originate?

Answer 3

Mutations

Question 4

Does a difference

in genotype between two individuals necessary translate into a difference in phenotype?

Answer 4

No

Question 5

Define polymorphism

Answer 5

Genetic difference among individuals that is sufficiently common ie. present in a group of 50 randomly chosen people

Question 6

Define allele

Answer 6

Different forms of any gene that correspond to different DNA sequences

Question 7

What is the maximum number of alleles of a given gene that you can carry? Explain.

Answer 7

2. You can be homozygous AA of heterozygous Aa

Question 8

Define homo and heterozygous

Answer 8

Homozygous: Has the two same types of alleles AA
Heterozygous: Has two different alleles Aa

Question 9

What determines whether you are homozygous or heterozygous for a particular gene?

Answer 9

It depends what alleles you inherit from your parents

Question 10

Is at always
best to be homozygous for a given allele? or is it always better to be heterozygous? Can
we make such a ‘rule of thumb’ when it comes to allelic combinations in general?

Answer 10

No. Some homozygous pairings can lead to life threatening conditions like sickle cell anemia

Question 11

Define nondisjunction

Answer 11

is the failure of a pair of chromosomes to separate during anaphase. Results in one daughter cell receiving an extra set of chromosomes and one daughter receive no copy of that chromosome

Question 12

Which checkpoint in the cell cycle is there to prevent nondisjunction from happening?

Answer 12

Spindle assembly checkpoint

Question 13

If nondisjunction happens during meiosis, does it matter for the outcome if the error
happens in the first or the second meiotic division?

Answer 13

Yes.
In the first-division non disjunction you get two daughter cells with an extra set of chromosome and two empty daughter cells
In the second-division non disjunction you get 1 daughter cell with an extra chromosome, 1 empty daughter cell and 2 normal daughter cells

Question 14

If nondisjunction happens in meiosis I, what is it that fails to separate properly from
each other?

Answer 14

The homologous chromosomes fail to seperate

Question 15

If nondisjunction happens in meiosis II, what is it that fails to separate properly from
each other?

Answer 15

The sister chromatids

Question 16

What causes down syndrome?

Answer 16

An extra chromosome of one of the smallest sets. Usually a trisomy of chromosome 21

Question 17

Why don’t we observe trisomy of chr 1, 2, 3, etc in live born infants?

Answer 17

Because trisomies involving these chromosome result in still births

Question 18

What makes human males male? Is it the presence of the Y chromosome or the fact that
they just have a single X chromosome?

Answer 18

It’s because of the presence of a Y chromosome

Question 19

What explanation does the textbook give for the fact that XYY males are phenotypically
normal?

Answer 19

The extra Y chromosome contains only a few functional genes that an extra Y is essentially non detectable.

Question 20

What explanation does the textbook give for the fact that XXX females are phenotypically
normal?

Answer 20

Due to X-inactivation

Question 21

What causes Turners Syndrome?

Answer 21

45 chromosomes with just one X chromosome

Question 22

What causes Klinefelter syndrome?

Answer 22

Two X and one Y chromosome on 47