Name____KEY______Per_____

PAP Biology & Biology I Meiosis, Chromosomes, & Karyotype NOTES

Meiosis Notes

Chromosomes Review

•  Every organism has traits (eye color, hair color, height, etc.) passed on to them by their _offspring____.

•  The instructions for each trait are found within a gene that is found on chromosomes

•  Humans’ somatic cells (body cells) have how many total chromosomes?__46___

•  How many pairs? ___23___

–  Half of your chromosomes come from your father

–  Half of your chromosomes come from your mother

Homologous Chromosomes

•  A _pair___ of chromosomes (one from mom and one from dad) are called homologous chromosomes.

–  They are the __same__ length and have the centromere in the same place.

–  They also carry genes for the same __traits____ at the same place

•  They “read” the same genes in the same places

Chromosomes

·  The number of chromosomes does not change from generation to generation

–  You have the _same____ number of chromosomes as your __parents___

•  Gametes are sex cells (__sperm_____ and egg) that contain___half ___ the number of chromosomes

–  Since you get half from mom and half from dad this guarantees each generation has the same number of chromosomes

•  The symbol n represents the _number______of chromosomes.

–  A cell with n number of chromosomes is called haploid

–  In humans n = 23

–  Gametes are __haploid_____

•  The process in which one haploid gamete joins______with another haploid gamete is called fertilization.

–  After fertilization the cell has 2n chromosomes

•  n from the _female______parent plus n from the __male______parent

•  A cell with 2n chromosomes is called a diploid cell

•  A fertilized __egg___ is called a zygote

–  In humans the haploid number is?___23_____

–  In humans the diploid number is? ___46_____

–  How many chromosomes in a human gamete? __23____

–  How many chromosomes in a human zygote?___46____

Cell Division

•  Recall that somatic cells are formed by __mitosis______

–  In mitosis the chromosome number stays the __same___

•  However, sex cells need __half______the chromosomes so a different type of cell division is needed

–  Gametes are formed during meiosis

Meiosis

•  Meiosis is a type of cell division that produces __gametes______

–  This produces sex cells, which are _not___ genetically identical, through a series of cell divisions.

–  In Meiosis the nucleus divides __twice___

•  Important because it creates genetic variation (a variety in genes/traits)

–  Because the nucleus divides twice meiosis creates _four___ daughter cells

Stages of Meiosis

•  There are 2 divisions of the nucleus in meiosis

–  Interphase

–  Prophase I

–  Metaphase I

–  Anaphase I

–  Telophase I

–  Prophase II

–  Metaphase II

–  Anaphase II

–  Telophase II

Genetic Variation

•  Meiosis allows for __new______genetic combinations

•  The ways this can occur

–  Independent assortment: of the chromosomes. About 8 million combinations can be made from the original cell

–  Random Fertilization: Zygotes form by random joining of gametes.

–  Crossing-over: DNA is exchanged

Independent assortment

·  homologous chromosomes are _randomly____ sorted/distributed during meiosis

•  Leads to several possible combinations of genes (why siblings aren’t always identical)

Random-fertilization

·  the fertilization of an egg and sperm is __random____

•  Each sperm can have a different combination of genes (from independent assortment)

•  The combination of genes that will fertilize the egg is random.

Crossing-over

·  the exchange___ of genetic material that can occur between

homologous chromosomes during Prophase I

–  Part of one chromatid is broken and exchanged with the

corresponding chromatid of the other homologous chromosome

–  Crossing over provides __new_____ combinations of genes

that are __different__ from either parent

How is Meiosis Different from Mitosis?

•  There are 2 divisions in meiosis

–  Meiosis I and meiosis II

•  The result is ____4_____ cells instead of 2

•  In meiosis II, the DNA is ___not____ replicated again. (No interphase)

•  The ending number of chromosomes is 23 in humans (egg has 23 and sperm has 23).This is haploid (n).

Mitosis Vs. Meiosis

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Mitosis

•  1 division=2 cells

•  Daughter cells identical

•  Diploid cells (2n)=46

•  Body/Somatic cells

•  Asexual reproduction

Meiosis

•  2 divisions = 4 cells

•  Daughter cells different (crossing over; independent assortment)

•  Haploid cells (n)=23

•  Gametes (sex cells—eggs or sperm)

•  Sexual Reproduction

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Chromosomal Mutations and Karyotypes- Notes

Chromosomes

Humans have 46 chromosomes (_diploid =2N)

·  2 of them are _sex___ chromosomes (the last pair)

o  X and Yà they determine what sex you are

§  XX = female

§  XY = male

·  44 of them are autosomes

o  they do _not_ determine the sex of an individual

o  code for everything else

Differences among species

Each organism has a characteristic number of chromosomes

·  The number is __constant____ with the species

o  potatoes, plums, and chimpanzees all have 48 chromosomes

o  oats, raccoon dogs, rats, wheat and wolverines all have 42 chromosomes

If multiple organisms can have the same number of chromosomes, why do they look so different?

·  The _order______ of the DNA nucleotides found on their chromosomes determines an organism’s traits

·  The number of chromosomes does _NOT__ determine intelligence

o  Some plants, for example, can have over 100 chromosomes- this doesn’t mean they are more intelligent than an organism with 46 chromosomes

Karyotypes

·  A karyotype is a picture of an organisms chromosomes

·  During __mitosis___, a picture of a cell is taken

·  The chromosomes are sorted into identical pairs and arranged from _biggest______to smallest

·  The 2 sex chromosomes are put at the end (_pair_ 23)

·  We can determine the _sex____ of an organism, chromosome number, as well as if it has mutations or a nondisjunction

·  Karyotypes from a somatic cell will show 2 of each chromosome since they are diploid. Karyotypes from a gamete (egg or sperm) will show only 1 of each chromosome since they are haploid.

Chromosomal Mutations

·  Mutations are changes made to an organism’s _genetic______material

·  These changes may be due to _errors_____ in DNA replication or transcription. Changes can also be caused by exposure to radiation, viruses, or other things.

·  In protein synthesis we talked about _SMALL______scale mutations that involved changes in nucleotides

·  There are also __LARGE___ scale mutations that can change entire segments of a chromosome

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-  deletion

-  duplication

-  inversion

-  translocation

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Original Chromosome:

Deletion- when a piece of chromosome breaks off completely

Duplication- occurs when a segment of a chromosome is __doubled______

Inversion- when a piece of DNA is removed from the chromosome, inverted/_flipped____ and then placed back into the chromosome

Translocation- when the chromosome piece attaches to a nonhomologous chromsome

Nondisjunction

Sometimes during meiosis, the chromosomes fail to separate correctly during anaphase I or anaphase II.

This is called nondisjunction.

·  When a gamete has only 1 copy of the affected chromosome it is called monosomy

·  When the other gamete has

3 copies of one chromosome it is called trisomy

Edwards Syndrome:

·  autosomal

·  trisomy 18

·  30% of babies die by 1 month

·  learning disabilities, congenital heart

defects and malformations of digestive tract,

urinary tract and genitals

Practice:

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