Content 15 Cell Division Part B: Meiosis

After mitosis, each daughter human cells will be haploid and have 23 chromosomes. True or false?

false

After meiosis, how many chromosomes end up in each human gamete cells (egg or sperm)?

23

In human cells, 23 chromosomes are inherited from father and 23 chromosomes are inherited from mother. true or false

true

  A zygote is a single cell that is formed after egg and sperm are fertilized.  The zygote will undergo many cell divisions to develop into an embryo.  How many chromosomes are in a human zygote?

46

Homologous chromosomes carry the same genes but may have different_____

alleles

In the homologous chromosome above, a total of _______ copies of the gene are present before DNA replication.

2

n the homologous chromosome above, a total of ______copies of the gene are present after DNA replication.

4

Which of the following are sister chromatids?

Two identical copies of the orange allele after DNA replication.

Non-sister chromatids can have different alleles, such as:_______

orange and green

Which phase of the cell cycle is DNA replication completed?

Given the description, guess the phases of meiosis I.

Flip card to find the correct answer.

“Chromosomes condense, homologous chromosomes pair up, and crossing over occurs.”

Prophase I

Given the description, guess the phases of meiosis I.

Flip card to find the correct answer.

“Homologous chromosome pairs align at the metaphase plate”

Metaphase I

Given the description, guess the phases of meiosis I.

Flip card to find the correct answer.

“Homologous chromosomes are pulled apart and move to opposite poles of the cell.”

Anaphase I

Given the description, guess the phases of meiosis I.

Flip card to find the correct answer.

“The cell divides into two new cells, each with half the original number of chromosomes, followed by cytokinesis.”

Telophase I

Crossing over

Crossing over is the process where non-sister chromatids of homologous chromosomes exchange segments of genetic material during prophase I of meiosis.

• It occurs between non-sister chromatids of homologous chromosomes (one from each parent).

• The exchange happens at points called chiasmata (singular: chiasma).

• Crossing over increases genetic variation by creating new combinations of alleles.

• It ensures that the resulting gametes (sperm or egg) are genetically unique.

Independent assortment

Independent assortment is the process during metaphase I of meiosis where homologous chromosome pairs line up randomly along the metaphase plate, and are then separated independently into daughter cells.

• Each chromosome pair’s orientation is independent of others.

• This random alignment leads to many possible combinations of maternal and paternal chromosomes in gametes.

• It is a major source of genetic variation in reproducing organisms.

Replicated homologous chromosomes (Tetrads) lines up at the metaphase I plate. true or false

true

Sister chromatids exchange parts during crossing over. true or false

false

During Meiosis II, the sister chromatids are separated.

true

DNA replication occurs again between meiosis I and meiosis II.

false

Meiosis II

Given the description, guess the phases of meiosis II.

Flip card to find the correct answer.

“Chromosomes condense and become visible, the nuclear envelope breaks down, and the spindle apparatus forms.”

Prophase II

Meiosis II

Given the description, guess the phases of meiosis II.

Flip card to find the correct answer.

“Chromosomes align at the metaphase plate, and spindle fibers attach to the centromeres of the sister chromatids.”

Metaphase II

Meiosis II

Given the description, guess the phases of meiosis II.

Flip card to find the correct answer.

““Sister chromatids are pulled apart toward opposite poles of the cell.” “

Anaphase II

Meiosis II

Given the description, guess the phases of meiosis II.

Flip card to find the correct answer.

“Chromatids arrive at the poles, the nuclear membrane reforms, and the cell undergoes complete separation, resulting in four haploid daughter cells.”

Telophase II and Cytokinesis 

After meiosis I, ____ haploid daughter cells are made.

two

Each daughter cells contain _____replicated chromosomes.

three

After meiosis II, ____ haploid daughter cells are made.

four

Each daughter cells contain ______ unduplicated chromosomes.

three