CHAPTER 13 MEIOSIS AND SEXUAL LIFE CYCLES

• __________ is the study of heredity (transmission of traits from one generation) and variation.

• Genes

• are segments of _____.

• program cells to synthesize specific enzymes and other proteins that produce an organism’s inherited traits

• Consist of four __________________

• program specific traits that emerge as we develop from fertilized eggs into adults.

• The transmission of hereditary traits has its molecular basis in the precise __________ of DNA

• Most DNA in a eukaryotic cell is subdivided into _________________ in the nucleus.

• Some DNA exists in ___________ and ____________.

• Every living species has a characteristic number of chromosomes.

• Humans have 46 in almost all of their cells.

• Chromosomes consist of a single ____ molecule in association with various ________.

• Each chromosome has hundreds or thousands of genes, each at a specific location, it’s _____.

• ________________- occurs mostly in single-cell eukaryotes, by

mitotic cell division to produce two identical daughter cells

•_________________- results in greater variation among offspring than does _________reproduction.

•Offspring of sexual reproduction vary _____________ from their siblings and from both parents.

Figure not in text

• Humans contain 46 chromosomes in each _____________ (all cells except germ cells) and 23 in the ________ (sperm or ovum).

1. Fertilization and ___________

•We have ____________

________________ pairs that carry genes that control the same inherited characters.

•An exception - the _____ ___________ (X and Y).

•Females are XX and males are XY

Know these terms!

Fig. 13.3

_____________ - an ordered displays of an individual’s chromosomes - used to detect large abnormalities

Fig. 13.3

________ - Germ cells with one set of chromosomes (22 __________ and an X or a Y in humans).

________ - Somatic cells with two sets of chromosomes (46 total in humans)

_______ - The fertilized egg with two haploid sets of chromosomes- one from mom, one from dad

Fig. 13.5

Gametes develop by _________ instead of mitosis in which the chromosome number is halved.

In meiosis, there are two consecutive cell divisions, __________ and ___________ which results in four haploid daughter cells.

2. Meiosis reduces chromosome number from diploid to haploid

Fig. 13.7

How??- By copying chromosomes once, but dividing twice.

Meiosis I – separates ____________________

Meiosis II-separates ______________________

• 4 phases: prophase, metaphase, anaphase, and telophase.

___________ - Previously replicated chromosomes join together at many locations to exchange DNA

Meiosis I

These exchange points are called _________

Spindles form from ___________

Metaphase, anaphase and telophase are similar to those in __________

Metaphase Anaphase

End result- 2 ________cells

Fig. 13.8

• Meiosis II is very similar to mitosis

• BUT- DNA is not ___________ first.

Meiosis II

Prophase, metaphase, anaphase or telophase occur

End result- 4 _____ cells

Fig. 13.8

Comparison of mitosis and meiosis

End result ___ ____

Daughter cells ________________

Chiasmata?

Meiosis Mitosis

_________

____________ are the physical manifestation of crossing over, a form of genetic rearrangement.

# of divisions __ __

Purpose ________ _________

• Mitosis produces two _________ daughter cells, but meiosis produces 4 very different cells.

Fig. 13.8

• Four mechanisms contribute to genetic variation:

3. Sexual life cycles produce genetic variation among offspring

• A fifty-fifty chance that a particular daughter cell of _______ will get the maternal chromosome of a certain homologous pair

Gametes

1. _____________________

• For humans with n = 23, there are about 8 ________ possible combinations of chromosomes. Fig. 13.9

2. ___________________-

• Four mechanisms.. (Cont.)

Fig. 13.11

-homologous portions of two nonsister chromatids trade placesin meiosis I.

• produces ____________

____________ which combine genes inherited from each parent.

•For humans, this occurs ______ ________ per chromosome pair.

3. _____________________

Any sperm can fuse with any egg.

• A zygote produced by mating of a woman and man has a unique genetic identity.

• A given ovum and sperm each have 223 (8 million)

________________________

• A zygote is composed of 1 in 70 trillion (223 x 223) possible combinations of chromosomes.

• __________________ adds even more variation to this.

• Four mechanisms.. (Cont.)

This results in adaptation, the accumulation of favorable genetic variations.

4. _ __________________

New genetic _________________ that work best in the new conditions will produce more offspring and these genes will increase.

• Four mechanisms.. (Cont.)