Download Meiosis

Meiosis
Honors Biology
Summary of your notes already taken
• We already went over meiosis
• We went over spermatogenesis
• I believe we went through oogenesis
• That will bring us to comparing and contrasting oogenesis and
spermatogenesis (VII. On your outline)
VII. Spermatogenesis vs. Oogenesis
• In your notes, make a 3 column T chart (we usually make this when
we compare 2 processes)
• List 5 differences between spermatogenesis and oogenesis
• Then list 3 similarities
• Be sure to leave space, we will go over these and possible add more
VIII. Random Fertilization
• During meiosis, the genetic combination for gametes depends on how the
chromosomes divide (randomly)
• The reason you don’t look identical to your sibling or parent is because there
is 2 23 combinations for genetic material or 8 million different ways genetics
can be combined
• That is just one human gamete, now consider when two humans unite
haploid cells (8 million x 8 million = 64 million combinations are possible
IX. Mutations
• Mutation – mistake in the genetic make up
• A karyotype is used to detect genetic defects of a chromosome’s size, shape
or number
A. Process of Karyotype
• Collect sample of cells from amniotic fluid / or blood cell if already born
• Centrifuge cells to separate them
• Put cells in hypotonic solution to make them swell up and then centrifuge
them again to separate the one that are swollen.
• Stain and examine cells and take a picture of the chromosomes inside the
cell
• Compare the chromosome size, shape and number to a “normal”
karyotype to see if any defects
Typical Karyotype
B. 3 Types of Defects (mutations)
1. Somatic – effects body cells
2. Germ – effects gametes
3. Lethal – kills prior to birth
There are also 2 levels at which these chromosomes occur:
1. chromosomal
2. gene (also called point mutation)
C. Chromosomal mutations (there are 4 of
these you need to know
1. Nondisjunction:
• chromosomes don’t separate properly (during meiosis or mitosis)
• can be somatic or germ
a. Germ chromosomal disorders due to
nondisjunction
• XXY – Klinefelters – sterile, breast enlargement, small testicles
(1/2000 men)
•
• XYY – taller, aggressive, big teeth, acne – common in criminals
(1/2000 men)
•
• XXX – normal female (1/1000 females)
•
• XO – Turners syndrome – short, web neck, sterile, poor breast
development, sex organs not fully developed (1/5000 females)
b. Somatic chromosomal nondisjuction
• Trisomy 21 - Downs Syndrome
• Trisomy (3 chromosomes stuck together) can happen with any of the
autosomal chromosomes (1-22)
2. Deletion – fragment of chromosome is lost
3. Inversion – less likely to be harmful. Piece of chromosome detaches and
reattaches in reverse order
4. translocation – part of a chromosome breaks off and reattaches to
another non-homologous chromosome. Can be harmful or not harmful
• ex. Part of chromosome 17 breaks off and reattaches to chromosome 1
Gene Mutations (point mutations)
1. Deletion – gene that codes for a trait is missing
Ex. Lactose intolerance, sickle cell anemia
2. Duplication – 2 copies of a gene that codes for a trait
3. Inversion – gene that codes for a trait is inverted
The chromosome looks the same, gene sequence is different
4. Silent mutation - DNA mutations that do not significantly alter the
phenotype of the organism.
5. Nonsense mutation - is the substitution of a single base pair that creates
stop codon
4 ways genetic variation occurs during sexual
reproduction
1.
2.
3.
4.
Cross overs
Independent sorting of chromosomes
Random fertilization
mutations
You now have all the notes from this chapter and are able to start the
meiosis review that is posted on my page.
Your review will be due on Friday.