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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