Lesson 3 Flashcards
What is sexual reproduction?
Sexual reproduction is the production of offspring from the fusion of two cells, usually from two different parents. The genetic makeup of the offspring is different from the parents.
How is genetic information inherited in sexual reproduction?
Offspring obtain half of their genetic information from each parent.
What is meiosis?
Meiosis is a two-stage cell division in which the resulting daughter cells have half the number of chromosomes as the parent cell. This process produces gametes (sperm and egg cells).
What happens during fertilization?
Fertilization is the process where gametes (sperm and egg) fuse to produce a zygote, which restores the diploid chromosome number.
What are homologous chromosomes?
Homologous chromosomes are matching pairs of chromosomes that are similar in size and carry genetic information for the same genes. One comes from the mother, and the other comes from the father.
What happens during Prophase I of meiosis?
Chromosomes condense. Microtubules/spindle fibers begin to form. Centrosomes move to opposite sides of the cell. Homologous chromosomes pair up to form a tetrad (synapsis).
What happens during Metaphase I of meiosis?
Homologous chromosomes (tetrads) line up at the metaphase plate, and independent assortment occurs, which increases genetic variation.
What happens during Anaphase I of meiosis?
Spindle fibers shorten, pulling one chromosome from each tetrad to opposite sides of the cell. The chromatids are still attached at the centromere.
What happens during Telophase I of meiosis?
The spindles break down, and the nuclear envelope forms around each set of chromosomes.
What is Cytokinesis in meiosis I?
Cytokinesis splits the cytoplasm equally, resulting in two cells, each with one copy of each chromosome, making them haploid (n=2).
What happens during Prophase II of meiosis?
Chromosomes condense again, and microtubules/spindle fibers begin to form. Centrosomes begin to move to opposite sides of the cell.
What happens during Metaphase II of meiosis?
Chromatids line up at the metaphase plate in both haploid cells.
What happens during Anaphase II of meiosis?
Spindle fibers shorten, separating the chromatid pairs and pulling individual chromatids (now chromosomes) to opposite poles of the cell.
What happens during Telophase II of meiosis?
The spindles break down and the nuclear envelope forms around each set of chromosomes.
What is Cytokinesis in meiosis II?
Cytokinesis splits the two cells, resulting in a total of four haploid cells, each with half the number of chromosomes they started with (n=2).
What are the number of chromosomes and chromatids at different stages of meiosis in humans?
Before Meiosis I: 2n = 46 chromosomes, 92 chromatids. After Meiosis I: n = 23 chromosomes, 46 chromatids. After Meiosis II: n = 23 chromosomes, 23 chromatids.
Where does meiosis occur in humans?
Meiosis occurs in the gonads: the ovaries in females and the testes in males.
What are alleles?
Alleles are different forms of a gene. For example, the gene for eye color can have a blue allele from one parent and a brown allele from the other parent.
What is independent assortment in meiosis?
Independent assortment refers to the random arrangement of homologous chromosomes during Metaphase I, which increases genetic variation.
Which division of meiosis is most similar to mitosis?
Meiosis II is most similar to mitosis because chromosomes line up on the metaphase plate and move towards opposite poles of the cell.
How is metaphase I in meiosis different from metaphase in mitosis?
In metaphase I, homologous chromosomes (tetrads) line up in pairs at the metaphase plate (23 pairs in humans). In metaphase of mitosis, chromosomes line up single-file at the metaphase plate (46 chromosomes in humans).
Why is independent assortment important in meiosis?
Independent assortment leads to increased genetic variation because the chromosomes line up in different combinations, resulting in diverse combinations in the gametes.
