BIO201A Cell Biology

Lecture 37

Monday 04/23/07

Important Announcements:

– Friday, April 27, will be a review of the lab material.– Monday, April 30, will be the last day of classes and will

be carried out as a recitation. No new material will be presented. If you have questions about the lecture material, that is the time to ask about it.

– Next exam will be the Final. 34 questions over section 3 and 14 lab questions. This is 48 total questions worth 140 total points.

– Final exam is May 8th, 11:45AM to 2PM in four rooms:

NSC 201 (lab sections A1-A4)NSC 218 (lab sections A5-A8) Norton 112 (lab sections A9-A12)OBrian 109 (lab sections A13-A16). Please note which room you will need to attend.

Aneuploidy

1. Autosomal polyploidy. This is usually fatal except in the case of trisomy 21 (three chromosome #21)

2. Autosomal monosomy. Only one of the autosomes instead of two. This is usually fatal

1. Sex chromosome polyploidy.

XXY is male with Kleinfelter’s syndrome

XYY is male and was previously thought to have criminal tendencies because of being “too male”

4. Sex chromosome monosomy.XO is female with Turner syndrome

All of these are caused by nondisjunctions during meiosis

Aneuploidy in a cancer cell

Cross-over recombination and chiasmata

Two sources of genetic variability in Meiosis:

1. Crossing over and recombination.

This happens in pacytene of prophase I

1. Independent Assortment of genetic traits (maternal and paternal)

This happens in Anaphase I of meiosis

It produces genetic diversity

What does this do?

20_07_recombination.jpg

Crossing-over and recombination occurs

between non-sister chromatids in pachytene

Recombination

Chiasmata in Diplotene phase of meiotic prophase I

chiasmata

Chiasmata are covalent linkages between two non-sister chromatids. This helps to keep bivalents together after cohesion

linkages are broken

20_08_Chiasmata.jpgSegregation of chromatids modified by recombination

20_09_kinetochore_pull.jpgThe chromatids of each gamete are different in this case

The DNA sequences of each chromatid is different. Each gamete can get different genetic information.

20_11_reassortment.jpgIndependent Assortment Recombination

Different strategies for mitosis and meiosis

Gametic or terminal

Fungi. Zygotic or initial

1n 1n

2n

1n 1n

Fertilization

Meiosis

Plants, Sporic or intermediate

+Pollen (1n)

Egg (1n) 2n zygote

fertilization

mitosis

2nsporophyte

1n 1n

meiosis

Spores (haploid gametophytes)

Haploid

Mitosis

Haploid adults

Primary spermatocytes (2n4x4c)

Meiosis I

Secondary spermatocyte (1n2x2c)

Spermatids (1n1x1c)

Meiosis II

Sperm cells (1n1x1c)

Differentiation

Primary oocyte (2n4x4c)

Secondary oocyte (1n2x2c)

Differentiation

Meiosis I

THEN

Polar body (1n1x1c)

Egg (1n1x1c)

Meiosis II

Summary Mitosis produces daughter cells with the same genotype as

the mother cell

No genetic segregation or independent assortment in mitosis

Meiosis produces cells with different mixtures of maternal and paternal genes because of:

Independent assortmentGenetic recombination

Independent assortment and recombination happen in meiosis, not mitosis

Cloning animals nextFrom genetic variation to genetic uniformity