Genetic Variation
Tahquitz High School
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How does genetic variation occur?
EQ: How do parents with the same genes make
offspring that are so different?
How does genetic variation occur?
• Meiosis: the process
by which the number
of chromosomes per
cell is cut in half the
the separation of
homologous
chromosomes in a
diploid cell
How does genetic variation occur?
Meiosis
• Step 1: Chromosome Duplication
– Each chromosome is copied in the nucleus of the
cell
Meiosis
Question: The average human has 23 pair of
chromosomes. How many pairs will a cell have
after chromosome duplication?
Meiosis
Question: The average human has 23 pair of
chromosomes. How many pairs will a cell have
after chromosome duplication? 46 pairs
Meiosis
Question: The average Time Lord has 68 pair of
chromosomes. How many pairs will a cell have
after chromosome duplication?
Meiosis
• Step 2: Crossing Over
– Homologous chromosomes pair together and
gene alleles are able to switch with the
neighboring chromosome.
Meiosis
• Step 2: Crossing Over
– Homologous: chromosomes with same genes, one
from each parent
– Alleles: one of a number of different forms of a gene
Meiosis
• Step 3: Meiosis I
– Homologous chromosomes are separated into 2
sister cells
Status Check: How many chromosomes at this stage
for the average human? Time lord?
Meiosis
• Step 4: Meiosis II
– Homologous chromosome pairs are separated into
2 sister cells with half the amount of chromosome
as the original cell.
Status Check: How many chromosomes at this stage
for the average human? Time lord?
Meiosis
• Step 4: Meiosis II
– Creates 4 genetically different haploid cells
– Genes are randomly separated into the 4 different
cell which is the Principle of Independent
Assortment
Meiosis
• Step 4: Meiosis II
– Haploid cells: (Greek haplous means single)
contain ½ the amount of chromosomes
– Diploid cells: (diplo- means double) contains both
sets of homologous chromosomes
Your Turn
• Create a Flow Chart showing the steps of
meiosis for a mosquito. A mosquito has 6
chromosomes.
– Tip: Refer back to your
notes
– Due: Tomorrow
• EQ: How do parents
with the same genes make
offspring that are so different?