Meiosis Division of Sex Cells

Meiosis vocabulary: Diploid __________ = a cell containing TWO sets of chromosomes one set inherited from each parent 2n (number of chromosomes) _____________ (somatic cells) Diploid body cells

Meiosis vocabulary: Haploid __________ = a cell with only ONE set of chromosomes. 1n (number of chromosomes) _____________ (gametes) Haploid sex cells

Meiosis vocabulary: Gamete __________ = sex cells _______ = male gamete _____ = female gamete Gamete Sperm Egg

Meiosis vocabulary: _______________ _______________ = paired chromosomes that have genes for the same traits arranged in the same order. One homologous chromosome is inherited from the organism’s father, the other from the mother. Homologous chromosomes

Meiosis vocabulary: Meiosis __________ = a two stage type of cell division that results in gametes with half the number of chromosome number as the body cells. Meiosis

Meiosis vocabulary: Crossing over _______________ = when nonsister chromatids of homologous chromosomes exchange genetic information Results in a new combination of genes. Crossing over

Meiosis vocabulary: ___________ = the process of joining gametes. _________ = when sperm (haploid) fertilizes egg (haploid), the resulting cell is the zygote (diploid) Fertilization Zygote

I. Genes, Chromosomes and numbers: In humans, each ______________ (any cell other than a sperm or egg) has ____ chromosomes. somatic cell 46

46 chromosomes → __________ (humans get ________ from each parent) 23 1 pair

XX = ________ XY = ________ _________________ - determine the sex of an individual Last pair of chromosomes – 23rd pair for humans XX = ________ XY = ________ Sex chromosomes female male

A thousand or more genes are lined up on a chromosome at one time. The _______________________ for an organism is NOT related to the ____________ of that organism! A thousand or more genes are lined up on a chromosome at one time. number of chromosomes complexity Ex: A dog has 78 body chromosomes and humans have 46 body chromosomes.

Diploid & haploid numbers: Each ______________ of an organism contains ________ chromosomes somatic cell paired

Half of each pair came from each parent Half of each pair came from each parent. These cells are said to have 2n chromosomes or a full set. They are DIPLOID.

Each __________ of organisms contains only _________ a chromosome set. These cells are HAPLOID and have 1n chromosomes. Ex: Humans have ____ chromosomes in their gametes (egg or sperm cell) sex cell half of 23

Sex cells will fuse with another sex cell during fertilization to create an _____________ organism

So if human sperm and egg both have ____ chromosomes, after fertilization and embryo has ____ chromosomes! 23 46

2 Reasons why meiosis is significant!! 1. _________ is another form of cell division that ______________________ to be used for reproduction. Meiosis creates haploid cells Female Egg Cell Male Sperm Cells

2 Reasons why meiosis is significant!! If mitosis was the only form of cell division, then new offspring would always have _________ as many _____________ as their parents. 2 times chromosomes

2 Reasons why meiosis is significant!! Eventually, there would be so many chromosomes, the organism would ____________ or be severely _________. not survive mutated

2 Reasons why meiosis is significant!! 2. Meiosis provides ____________________ - the reshuffling of genes carried by the individual members of a population. GENETIC VARIATION

II. Meiosis vs. Mitosis Remember: _________ = asexual division of diploid body cells mitosis

II. Meiosis vs. Mitosis

Meiosis I Separates __________________ of chromosomes, NOT sister chromatids or individual chromosomes. homologous pairs

Interphase I Metabolic activities & replicate chromosomes

Prophase I __________ occurs – the pairing of homologous chromosomes. Each pair of ____________ chromosomes come together to form a _________ ( 4 part structure) Synapsis homologous tetrad

Genetic material is exchanged in a process called _______________ (swapping portions of adjacent DNA) crossing over Must be done with great precision so that neither chromatid gains or loses any genes!

Crossing over:

3. Metaphase I __________________________ line up at the __________ in pairs. Homologous chromosomes equator

4. anaphase I Homologous chromosomes separate and move to opposite ends of the cell. This occurs because the _____________ do NOT split like in mitosis. centromeres

4. anaphase I This ensures that each __________ will receive only ________________ for each homologous pair. new cell one chromosome

5. Telophase I The new cells are _________ so another division is required to create _________ cells. diploid haploid

Meiosis I: Separate the Homologues

Meiosis II The mechanisms of ____________ is almost the same as _________. However, the chromosomes DO NOT replicate between meiosis I and meiosis II, the final outcome of meiosis is _________ the number of chromosomes per cell. Meiosis II mitosis halving

Allows the new cells to become _________. 1. Interphase II No replication ______________ Allows the new cells to become _________. haploid

Same as Prophase I except NO _________ are formed. tetrads 2. Prophase II Same as Prophase I except NO _________ are formed. tetrads

Chromosomes line up at the _________. equator 3. MetapHase II Chromosomes line up at the _________. equator

___________________ move to the opposite ends of the cell. 4. Anaphase II ___________________ move to the opposite ends of the cell. Sister chromatids

Creates 4 _________ cells. (gametes) haploid 5. Telophase II Creates 4 _________ cells. (gametes) haploid

But wait . . . there’s more! Meiosis II: Separate the Sister Chromatids

http://www.sumanasinc.com/web content/animations/content/meio sis.html Meiosis Animation http://www.sumanasinc.com/web content/animations/content/meio sis.html

Meiosis provides genetic variation in 2 ways Independent assortment 1. ____________ ____________ of homologous chromosomes during meiosis I The amount of different chromosomes that can be produced increases greatly as the number of chromosomes an organism has.

Meiosis provides genetic variation in 2 ways A pea plant has 7 pairs of chromosomes. Each pair can line up 2 different ways. Therefore, each gamete can have 27 = 128 possibilities!! Humans: n=23; so the number of different kinds of eggs or sperms a person can produce is more than 8 million (223).

Meiosis provides genetic variation in 2 ways When fertilization occurs, 223 x 223 zygotes are possible or 70 trillion!! No wonder brothers and sisters can be so different.

Meiosis provides genetic variation in 2 ways 2. ______________ between homologous chromosomes during prophase of meiosis I. Increases the number of genetic variations. Crossing over

Meiosis is NOT flawless It is estimated that from 10-20% of all human fertilized eggs contain chromosome abnormalities, and these are the most common cause of pregnancy failure (35% of the cases) http://www.sumanasinc.com/webcontent/animations/content/mistakesmeiosis/mistakesmeiosis.html

These chromosome abnormalities: Arise from errors in meiosis, usually ________. Occur more often (90%) during ______________ than during sperm formation. Become more frequent as a woman _______. meiosis I egg formation ages

Down syndrome Two copies of an autosomal chromosome fail to separate during meiosis so three copies of that chromosome are made. Trisomy 21

Turner’s Syndrome A female with Turner’s Syndrome usually inherits only one X chromosome. Women with Turner’s syndrome are sterile which means they are unable to reproduce.

Klinefelter’s syndrome In males nondisjunction may cause Klinefelter’s syndrome, resulting in the inheritance of an extra X chromosome, which interferes with meiosis and usually prevents these individuals from reproducing.

Androgen insensitivity syndrome Every fetus, whether genetically male (XY) or female (XX), starts life with the capacity to develop either a male or female reproductive system.   In AIS the child is conceived with male (XY) sex chromosomes and normal embryonic testes (known as the fetal gonads) develop and start to produce masculinizing androgens.  However with AIS, a rare genetic condition carried on the X chromosome means that the fetus has no receptors for these male hormones, and his/her body can't "see" or acknowledge them.   Lacking the effect of these androgens, the external genitals develop along female rather than male lines.  Unfortunately however, another hormone produced by the fetal testes simultaneously suppresses the development of female internal organs (uterus and ovaries).