Lecture 20: meiosis and inheritance of traits

Question 1

homologous

Answer 1

two of the same alleles for the gene

-AA or aa, a’a’ or a”a”

Question 2

heterozygous

Answer 2

two different alleles for the gene

-Aa or aa’ or Aa’ or Aa” or aa”

Question 3

multiple alleles exist in the rabbit population at the locus for coat color. How many alleles for coat color does an individual rabbit have?

Answer 3

2

Question 4

males are more often affected by sex-linked traits than females because

Answer 4

males have only one x chromosome

Question 5

X-inactivation

Answer 5

only one x is expressed in the cell

Question 6

XX mosaic

Answer 6

some cell expresses the maternal X and other the pattern X

Question 7

an inactivated x is normally found in the nucleus of which kind of human cell

Answer 7

somatic cells of a female only

Question 8

female calico cats are XX for two different color alleles. Can male tortoise shell cat exist?

Answer 8

rarely, if the male has 2 x’s and 1 y: XXY

Question 9

three mechanisms of meiosis and fertilization that contribute to genetic variation

Answer 9

• crossing over
• random alignment of homologous pairs
• random fertilization

Question 10

result of crossing over

Answer 10

4 unique chromatids on homologous chromatids

Question 11

crossing over

Answer 11

increases genetic diversity

Question 12

assume that an animal has a diploid chromosome number of ten (2n=10)

a. how many chromosomes would it have in a somatic cell?
b. how many chromosomes would be present in a cell at the beginning of meiosis 1?
c. how many chromatids would be present at the beginning of meiosis 1?
d. how many chromosomes would be present in each gamete?

Answer 12

10, 10, 20, 5

Question 13

assume that a plant has a tetraploid chromosome number of 20 (4N= 20)

a. how many chromosomes would it have in a somatic cell?
b. how many chromosomes would be present in a cell at the beginning of meiosis 1?
c. how many chromatids would be present in the cell at the beginning of meiosis I?
d. how many chromosomes would be present in each gamete?
e. is the gamete 1N 2N or 4N?
f. how many different kinds of chromosomes are there(n=)?

Answer 13

20, 20, 40, 10, 2N, 5

Question 14

meiosis 1

Answer 14

from 1 cell (2n=8) to two cells (n=4)

Question 15

end of meiosis 1

Answer 15

two cells each n=4

Question 16

meiosis 2

Answer 16

two cells (n=4) divide to form four cells (n=4)

Question 17

end of meiosis 2

Answer 17

result is 4 cells with half the chromosomes as the parent cell

Question 18

how do cells at the completion of meiosis compare with cells that have replicated their DNA and are just about to begin meiosis?

Answer 18

they have half the number of chromosomes and 1/4 the amount of DNA

Question 19

if the somatic cells of an animal have 23 chromosomes, how many chromosomes would be found in a gamete?

Answer 19

none, meiosis cannot occur