SEXUAL REPRODUCTION AND MEIOSIS

Question 1

What is sexual reproduction

Answer 1

Occurs when two different parents reproduce together to form unique offspring different from each parent and siblings
* When gametes join to form a zygote

Question 2

Gametes

Answer 2

Reproductive cells (sperm, egg)

Question 3

Zygote

Answer 3

Egg fertilized w sperm
* Develops into body cells

Question 4

Chromatin

Answer 4

DNA w associated proteins as its found in nucleus

Question 5

Chromosome

Answer 5

One particular bundle of DNA
* Can be coiled up during cell division (easier to move w/o getting tangled up)
* Copied during interphase
* Every species has its own number of chromosomes
* Humans have 46 (23 pairs)

Question 6

Sister chromatids

Answer 6

Identical chromosomes bound together by a centromere

Question 7

If we combine chromosomes from each parent during sexual reproduction, why doesn’t the chromosome number double

Answer 7

Gametes must have half number of chromosomes as body cells (23 + 23 = 46_
* This means each cell in body has one copy of DNA from each parent
* Gametes get half number of chromosomes by process of meiosis

Question 8

Why would sexual reproduction have developed? Why not simply reproduce by mitosis?

Answer 8

Variation

Question 9

Variation mechanisms

Answer 9

• Mitosis produces identical daughter cells
• Meiosis has build in mechanisms to share and exchange DNA to create more variation in offspring

Question 10

Homologous Chromosomes

Answer 10

• Homologous chromosomes are not identical, but code for the same traits
• Not identical because one from mother and one from father

Question 11

Meiosis I

Answer 11

Stages:
* Prophase Ihomologous chromosomes form a tetrad (all four chromosomes are connected)
* Metaphase I: completely unique DNA created via independent assortment
* Anaphase I
* Telophase I: Nuclear membrane starts to reform

At the end of telophase I, cell is now diploid

Question 12

Independent assortment

Answer 12

Line up homologous chromosomes, forms independent chromosomes
* Homologous chromosomes from mom and dad cross over, exchange genetic information

Question 13

Meiosis II

Answer 13

Stages:
* Prophase II: DNA is not copied
* Metaphase II
* Anaphase II: only single chromatid
* Telophase II: four unique haploid cells

Meiosis II is like mitosis

Question 14

End Result of Meiosis

Answer 14

4 unique cells created from one body cell
* Each cell has half normal number of chromosomes (gametes)

Question 15

Key Features of Meiosis I and Meiosis II

Answer 15

Meiosis I
* Copy chromosomes
* Line up homologous chromosomes
* Crossing over between homologous chromosomes

Meiosis II
* Normal cell division (mitosis) without copying chromosomes

Question 16

Synapsis

Answer 16

aligning of homologous chromosomes during prophase I in meiosis I
* Spindle apparatus forms in prophase I (after crossing over)
* Centromeres only split in meiosis II anaphase II