Cell division / Asexual reproduction Mitosis produce cells with same information identical daughter cells exact copies clones same amount of DNA same number of chromosomes same genetic information Aaaargh! I’m seeing double!

Mitosis & Asexual reproduction Single-celled eukaryotes yeast (fungi) Protists Paramecium Amoeba Simple multicellular eukaryotes Hydra budding budding What are the disadvantages of asexual reproduction? What are the advantages?

+ 46 46 92 How about the rest of us? What if a complex multicellular organism (like us) wants to reproduce? joining of egg + sperm Do we make egg & sperm by mitosis? No! What if we did, then…. 46 + 46 92 egg sperm zygote Doesn’t work!

This is where we start talking about MEIOSIS MEIOSIS - Cell division that leads to creation of Egg and Sperm cells – ________________! This leads us into a discussion of how traits are passed from one generation to the next ______________________ The scientific study of heredity and hereditary information

Note! When we pass on traits… We certainly do pass on similarities, but we are not CLONES! ___________________ exists as well MEIOSIS is one important key in ensuring that VARIATION exists (at least among sexually reproducing organisms) What’s the big deal About variation??

Units of Heredity… ___________________ SEGMENTS or regions of our long DNA molecules Each chromosome is ________ long strand of DNA If the chromosome has been replicated, it is ______ long strands of DNA joined at the centromere… Highly coiled (remember __________________ proteins) Genes Program our _________________________ May be ____________s of genes on a single chromosome Each chromosome is subdivided into many GENES Specific location of a gene on a chromosome __________________________ Genes have predictable “addresses” or loci on chromosomes Generally the same from person to person…though there is VARIATION sometimes ALL the genes contained in an organism ___________________________

What is a Karyotype? A display that shows the chromosomes from an individual cell arranged in pairs starting with the longest chromosome pair.

What does a human karyotype tell us about chromosomes? How many? _____ Arranged in PAIRS that are SIMILAR, though NOT IDENTICAL. _________________________ How many pairs? ______ Also, Staining methods and general visual inspection can tell us if a chromosome is “normal” Banding patterns Length of “arms”, etc.

What is the origin of each member of a homologous pair? One member of each pair comes from the organism’s… _________________ The other member of each pair comes from the organism’s… THEREFORE, while each homologous pair will contain genes for the same general trait (for example, eye color), they may _______ carry _________________ information for that trait. For example mom may pass a chromosome with the gene for _________ eyes, while dad may pass a chromosome with the gene for ______________ eyes. ____________ but not ___________________!

Homologous chromosomes Paired chromosomes both chromosomes of a pair carry “matching” genes control same (actually, just similar) inherited characters homologous = same (similar) information _________ stranded homologous chromosomes __ phase of interphase – csomes are replicated Gene for “eye color” __________ stranded homologous chromosomes

Karyotypes also tell us about SEX… ____________________ “normal” chromosomes that EVERYONE shares in common, regardless of gender In humans, pairs ___-____ are autosomes Sex Chromosomes Chromosomes that are associated with a particular gender Two types ____ and _____ Females have ____ and _____ Males have _____ and _____ X and Y are _________ homologous!! X is MUCH ____________ than Y Codes for LOTS of important stuff that has nothing to do with sex. Y codes pretty much only for genes that cause “____________” No Y? You’re _______________. X Y

Ploidy N = number of chromosomes in ONE set – Varies according to species __________________ ____n Cell with ___ complete ______ of chromosomes 1 set from _________ = ______ chromosomes ________________ cells are diploid So are cells that are ____________ to become _______________ (that are going to undergo meiosis), but haven’t done so yet. ________________ ______ Cell with only ___ complete set of chromosomes __________ of ______________ GAMETES - Sperm or egg! What’s the diploid # for humans? What’s the haploid # for humans?

How do we make sperm & eggs? Must reduce _____ chromosomes  _____ must reduce the number of chromosomes by _____ 23 46 23 ________ 46 egg 23 ________ 46 23 ____________ sperm gametes

Meiosis: production of gametes ____________ stages chromosome number must be __________ _________  ________ 2n  n humans: 46  23 ____________ reduces chromosome number makes ___________ fertilization __________ chromosome number _______  __________ n  2n haploid diploid

Sexual reproduction lifecycle 2 copies diploid 2n 1 copy haploid 1n 1 copy haploid 1n fertilization meiosis In the next generation… We’re mixing things up here! A good thing? gametes gametes

Meiosis ____________________ special cell division for sexual reproduction reduce ___n  ___n _______  ________ “two”  “half” makes gametes sperm, eggs Warning: meiosis evolved from mitosis, so stages & “machinery” are similar but the processes are radically different. Do not confuse the two!

Overview of meiosis I.P.M.A.T.P.M.A.T 2n = ____ interphase 1 prophase 1 metaphase 1 anaphase 1 n = ___ n = ___ prophase 2 metaphase 2 anaphase 2 telophase 2 n = ___ telophase 1

Double division of meiosis DNA replication Repeat after me! I can’t hear you! Meiosis 1 _____ division of meiosis separates _________________ Meiosis 2 _____ division of meiosis separates _________________

___________ for meiosis ____ of Interphase __________ of DNA Why bother? meiosis evolved after mitosis convenient to use “machinery” of mitosis DNA replicated in S phase of interphase of MEIOSIS (just like in mitosis) 2n = 6 single stranded 2n = 6 double stranded M1 prophase

Meiosis ___ _____ division of meiosis separates _______________ single stranded Meiosis ___ _____ division of meiosis separates _______________ ___n = 4 double stranded prophase 1 _________ ___n = 4 double stranded metaphase 1 ________ reduction ___n = 2 double stranded telophase 1 Repeat after me! I can’t hear you!

What does this division look like? Meiosis ____ _____ division of meiosis separates _______ ________________ ____ = 2 double stranded prophase 2 What does this division look like? _____ = 2 double stranded metaphase 2 ___ = 2 single stranded telophase 2 _ cells

Steps of meiosis Meiosis 1 Meiosis 2 interphase prophase 1 metaphase 1 anaphase 1 telophase 1 Meiosis 2 prophase 2 metaphase 2 anaphase 2 telophase 2 1st division of meiosis separates homologous pairs (2n  1n) “_______________” 2nd division of meiosis separates sister chromatids (1n  1n) * just like ________ *

Trading pieces of DNA _________________ during ___________, sister chromatids ___________ _______________ ______ pieces of chromosome DNA breaks & re-attaches Also called ______________ prophase 1 synapsis tetrad

What are the advantages of crossing over in sexual reproduction? 3 steps ____________ __________ of DNA ___________ of DNA New combinations of traits Sexual reproduction is advantageous to species that benefit from genetic variability. However, since evolution occurs because of changes in an individual's DNA, crossing over and chromosome segregation is likely to result in progeny that are less well-adapted than their parents. On the other hand, asexual reproduction ensures the production of progeny as fit as the parent since they are identical to the parent. Remember the adage, “if it's not broken, don't fix it.” There are several hypotheses regarding the evolution of sexual reproduction. One is associated with repairing double-stranded DNA breaks induced by radiation or chemicals. The contagion hypothesis suggests that sex arose from infection by mobile genetic elements. The Red Queen hypothesis theorizes that sex is needed to store certain recessive alleles in case they are needed in the future. Along similar lines, eukaryotic cells build up large numbers of harmful mutations. Sex, as explained by Miller's rachet hypothesis, may simply be a way to reduce these mutations. The “whole truth” is likely a combination of these factors. Regardless of how and why, the great diversity of vertebrates and higher plants and their ability to adapt to the highly varied habitats is indeed a result of their sexual reproduction.

Mitosis vs. Meiosis

Mitosis vs. Meiosis Mitosis Meiosis __ division daughter cells genetically ________ to parent cell produces ____ cells ___n  ___n produces cells for ______ & ________ ____ crossing over Meiosis ___ divisions daughter cells genetically ______ from parent produces _____cells ___n  ___n produces __________ crossing over

Putting it all together… meiosis  fertilization  mitosis + development gametes 46 23 46 23 46 46 46 46 46 23 ________ 46 46 egg 46 46 23 zygote _________ _________ sperm development

The value of sexual reproduction Sexual reproduction introduces genetic _________! genetic ___________________ ______________________ of chromosomes in ___________ random alignment of homologous chromosomes in Metaphase 1 ____________________ mixing of alleles across homologous chromosomes ___________________________ which sperm fertilizes which egg? Driving evolution providing ____________ for natural selection metaphase1

Variation from __________________ Independent assortment of chromosomes meiosis introduces genetic variation gametes of ____________ do _____ have same combination of genes as gametes from ___________ random assortment in humans produces 223 (8,388,608) different combinations in gametes offspring from Mom from Dad new gametes made by offspring

Variation from _________________ Crossing over creates completely _______ ______________ of ______ on each ____________ creates an infinite ________ in __________

Variation from random fertilization Sperm + Egg = ? any 2 parents will produce a zygote with over ____________ (223 x 223) possible diploid combinations

Sperm production _____________________ continuous & prolific process Epididymis Testis germ cell (diploid) Coiled seminiferous tubules primary spermatocyte (diploid) MEIOSIS I secondary spermatocytes (haploid) MEIOSIS II Vas deferens spermatids (haploid) spermatozoa _____________________ continuous & prolific process each ejaculation = 100-600 million sperm Cross-section of seminiferous tubule

Egg production ________________ eggs in ovaries halted before Anaphase 1 Meiosis 1 completed during maturation Meiosis 2 completed after fertilization __ egg + _ polar bodies unequal divisions Meiosis 1 completed during egg maturation ovulation What is the advantage of this development system? Meiosis 2 completed triggered by fertilization

___________ triggers completion of ________ Advantages of Polar Bodies and Fertilization triggers for meiosis completion… __________________ Enables manufacture of one REALLY GOOD egg. All nutrition, organelles, etc. poured into one egg Quality, NOT quantity ___________ triggers completion of ________ Ensures that further resources will NOT be wasted on an egg that does NOT get fertilized.

Putting all your egg in one basket! Oogenesis MEIOSIS I MEIOSIS II first polar body second polar body ovum (haploid) secondary oocyte primary (diploid) germinal cell primary follicles mature follicle with secondary oocyte ruptured follicle (ovulation) corpus luteum developing follicle fertilization fallopian tube after fertilization

Differences across kingdoms Not all organisms use haploid & diploid stages in same way which one is ______________ (2n or n) differs but still alternate between haploid & diploid must for sexual reproduction