Chromosomes Review

1
(No Transcript)
2
Chromosomes Review

• Every organism has traits (eye color, hair color,
  height, etc) passed on to them by their parents.
• The instructions for each trait is found within a
  gene that is found on chromosomes

3
(No Transcript)
4
Review!

• Humans somatic cells (body cells) have how many
  total chromosomes?
• How many pairs?
• Half of your chromosomes come from your father
• Half of your chromosomes come from your mother

46
23
5
46 Total Chromosomes 23 pairs of chromosomes
6
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

7
(No Transcript)
8
Chromosome Number

• 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

9
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

10
Chromosomes

• 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

11

• A cell with 2n chromosomes is called a diploid
• A fertilized egg is called a zygote
• In humans the haploid number is?
• In humans the diploid number is?
• How many chromosomes in a human gamete?
• How many chromosomes in a human zygote?

23
46
23
46
12
(No Transcript)
13
LETS MAKE A BABY!!!!
X
Haploid (n)
Y
Haploid (n)
14
LETS MAKE A BABY!!!!
X
Haploid (n)
Y
Haploid (n)
15
LETS MAKE A BABY!!!!
X
Y
Haploid (n)
Haploid (n)
16
LETS MAKE A BABY!!!!
X
Y
Haploid (n)
Haploid (n)
17
LETS MAKE A BABY!!!!
X
Y
Haploid (n)
Haploid (n)
18
LETS MAKE A BABY!!!!
X
Y
Haploid (n)
Haploid (n)
19
LETS MAKE A BABY!!!!
Y
X
Haploid (n)
Haploid (n)
20
LETS MAKE A BABY!!!!
Y
X
21
LETS MAKE A BABY!!!!
Y
X
22
LETS MAKE A BABY!!!!
Y
X
23
LETS MAKE A BABY!!!!
Y
X
24
LETS MAKE A BABY!!!!
Y
X
25
LETS MAKE A BABY!!!!
Y
X
26
LETS MAKE A BABY!!!!
27
LETS MAKE A BABY!!!!
Diploid (2n)
28
Awww! WE MADE A ZYGOTE!
Diploid (2n)
29
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

30
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

31
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

32
(No Transcript)
33
Review Challenge!

• Interphase
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I
• Prophase II
• Metaphase II
• Anaphase II
• Telophase II

Which stage does DNA Replication occur? Does
Meiosis replicate DNA twice?
During Interphase (the S phase)
No! That is why is meiosis you end up with HALF
of the original chromosome number
34
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.
• B) Crossing-over DNA is exchanged

35
Genetic Variation

• Independent assortmenthomologous chromosomes are
  randomly sorted/distributed during meiosis
• Leads to several possible combinations of genes
  (why siblings arent always identical)

36
(No Transcript)
37
Genetic Variation

• Random-fertilizationthe fertilization of an egg
  and sperm is random
• Each sperm can have a different combination of
  genes (from independent assortment)
• It is random which combination of genes will
  fertilize the egg

38
Genetics Variation

• 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

39
(No Transcript)
40
(No Transcript)
41
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).

42
Mitosis Vs. Meiosis

• Meiosis
• 2 divisions 4 cells
• Daughter cells different (crossing over
  independent assortment)
• Haploid cells (n)23
• Gametes (sex cellseggs or sperm)
• Sexual reproduction

• Mitosis
• 1 division2 cells
• Daughter cells identical
• Diploid cells (2n)46
• Body/Somatic cells
• Asexual reproduction

43
Meiosis Animation

• http//www.sinauer.com/cooper5e/animation1607.html

44
Meiosis Animation

• http//www.youtube.com/watch?vD1_-mQS_FZ0