If the sperm and egg had a full set of 46 chromosomes, how many would the zygote (fertilized egg) have? 46 92 46

What would happen to the chromosome number each generation if the sperm and egg had a full set of chromosomes? It would double! Sperm + egg 46 + 46 Sperm + egg 92 + 92 92 Sperm + egg 184 + 184 184

MEIOSIS Cell division that produces eggs and sperm the process of cell division in which the chromosome # is cut in half

46 46 diploid # of chromosomes meiosis sperm egg 23 23 monoploid # of male female 46 46 diploid # of chromosomes meiosis sperm egg 23 23 monoploid # of chromosomes fertilization zygote 46 (diploid #)

meiosis and fertilization keep the # of chromosomes constant from generation to generation

mitosis meiosis my toe eggs and sperm What kind of cell division occurs in the embryo?

Where does meiosis occur in humans?

Mitosis

Meiosis synapsis

disjunction

meiosis Diploid 2n monoploid n

4 3 2 1 1 (5) 4 (8) 3 (7) 2 (6)

1 7 3 4 6 2 5 8

Meiosis animation http://www.youtube.com/watch?v=D1_-mQS_FZ0&feature=related http://www.youtube.com/watch?v=MqaJqLL49a0&feature=related http://www.johnkyrk.com/meiosis.html http://www.youtube.com/watch?v=uh7c8YbYGqo

synapsis - coming together of homologous copied chromosomes - they line up in pairs

Meiosis synapsis

It increases genetic diversity crossing over – the exchange of segments between chromatids during synapsis Why is this important? It increases genetic diversity

Crossing Over

(e.g. red hair and freckles) Why are some traits always inherited together? (e.g. red hair and freckles)

What effect does linkage have on independent assortment? Gene Linkage – 2 or more genes located on the same chromosome; these genes are inherited together linkage group - all the genes that are on the same chromosome What effect does linkage have on independent assortment?

What effect does crossing over have on linkage?

Crossing over breaks linkage groups crossing over is an exception to linkage

Place the letters in the correct positions on each chromo-some b b B B F f F f b b B B F f F f b b B B F f F f

Mitosis vs. Meiosis http://www.pbs.org/wgbh/nova/miracle/divide.html

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Mitosis Meiosis         

MITOSIS MEIOSIS chrom.number chrom. number stays the same cut in half forms body cells forms sex cells from from body cells gonad cells (primary sex cells) 2 kinds of each 1 kind of each chrom. in each cell chrom.in each cell (2 sets) (1 set)

Comparison of Meiosis and Mitosis Homologous Homologous Chromosomes Chromosomes do not pair up pair up no crossing over crossing over 1 division 2 divisions forming 2 cells forming 4 cells new cells get the same cells get one half # and type of the # and type of chrom. chromosome (1 of each homologous pair) MITOSIS MEIOSIS

How does meiosis and fertilization increase genetic variation?

How does meiosis and fertilization increase genetic variation? crossing over random segregation of chromosome pairs fertilization many different possible combinations of genes in sperm and egg

Why is genetic variation important? If the environment changes some organisms may have the variations (inherited characteristics) needed to survive the change Variation creates new characteristics or new combinations of characteristics that help a species adapt to its environment

How is meiosis different in males and females?

Polar body

Why do women only produce 1 egg from every primary sex cell whereas men produce 4 sperm cells from every primary sex cell?

Why are polar bodies important? (What is the function of a polar body?)

Zygote (fertilized egg)

2 cells 4 cells 8 cells Where is this process occuring?

Where is the embryo getting the nutrients it needs as it passes down the oviduct?

Why are polar bodies important? (What is the function of a polar body?)

Function of a polar body Removes the extra set of chromosomes without taking away much cytoplasm from the egg …So the egg can be as large as possible and store nutrients for the embryo to use before the placenta is formed

https://www.youtube.com/watch?v=_5OvgQW6FG4 Fertilization activates egg Start at 4:08)

Oogenesis Spermatogenesis 1 egg cell produced; 4 sperm cells produced 3 polar bodies no polar bodies produced produced production occurs during production during development; occurs finishes during throughout a fertilization male's lifetime

spermatogenesis http://wps.prenhall.com/wps/media/objects/489/501016/CDA45_1/CDA45_1a/CDA45_1a.htm

oogenesis http://wps.prenhall.com/wps/media/objects/489/501016/CDA45_1/CDA45_1b/CDA45_1b.htm

Draw the chromosomes in each of the empty cells

Draw the chromosomes in each of the empty polar bodies and the egg

Eggs Sperm large, round small - head, acrosome, middlepiece, flagellum stored food – no stored food yolk (for developing animal) sessile motile cytoplasm, almost no cytoplasm, mitochondria mitochondria left outside fertilized egg

Kissing or Fighting?

http://www.youtube.com/watch?v=qhrZj2RuNgQ&feature=related