Genetic Variation

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How does genetic variation occur? EQ: How do parents with the same genes make offspring that are so different?

• 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?

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 cellsStatus 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?