Bellwork #23 Genetic Diversity
Cells that are formed by 1 __________ are identical to each other and to the parent cell. Conversely,
2 ________ increases genetic diversity because every sperm or egg is a little bit different. No two offspring
are exactly the same. Genetic diversity causes some organisms to be more fit to survive and reproduce.
Genetic diversity is essential for the 3 ______________ of species. With very little gene variation within the
species, healthy reproduction becomes increasingly difficult.
Crossing over during meiosis allows recombination of genes between 4 ___________ chromosomes.
This alters the linkage between genes on the same chromosome. Crossing over occurs frequently during
5 _______________ of meiosis, when homologous chromosomes associate with each other in a structure
called a 6 ___________. Recall that one member of each pair of 7 ___________ chromosomes came from
one parent, and the other member came from the other parent. Without crossing over, each 8 ____________
cell produced will inherit a chromosome with the same combination of genes as was on one of the parental
chromosomes. Crossing over is important because it results in new 9 _________________ of genes that are
different from either parent, contributing to genetic diversity.
During 10 ____________, the homologous chromosomes line up 11 _______________ in the middle
of the cell. Therefore, there is a 12 ____% chance of the maternal or paternal chromosomes going to either
side of the cell. 13 ______________________ is the process where chromosomes randomly segregate
towards either side of the cell during 14 ______________ of meiosis resulting in the production of
genetically unique 15 ________________.
16 _____________ is an error in meiosis when homologous chromosomes fail to separate properly
during 17 ____________ or one 18 ___________ fail to separate in anaphase II. Recall that during meiosis
I, one chromosome from each 19 ___________ pair moves to each pole of the cell. In nondisjunction, both
chromosomes of a homologous pair move to the same pole of the cell. Nondisjunction will result in two
kinds of 20 ___________. One gamete will have an extra chromosome, and the other gamete is missing a
chromosome. For example, when a gamete with an extra chromosome is fertilized by a normal gamete, the
21 ________will have an extra chromosome. This condition is called 22 ________. In humans, if a gamete
with an extra chromosome number 21 is fertilized by a normal gamete, the resulting 23 ______has 24 ____
chromosomes instead of 25 ____. This zygote will develop into a baby with 26 ________________.
_______________________________________________
WORD BANK__________________________________________________
a. 46
b. 47
c. 50
d. combinations
e. evolution
f. gametes (x2)
g. haploid
h. homologous (x3)
i. anaphase I (x2) j. nondisjunction
k. tetrad
l. metaphase I
m. mitosis
n. meiosis
o. chromatid
p. prophase I
q. zygote (x2)
r. randomly
s. trisomy
t. Down syndrome
u. independent assortment