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• Defined: Tightly coiled
DNA
• Forms during cell
division
– New chromosomes
created for new cells
• 2 Parts:
– 1) Chromatids: two
identical parts of a
chromosome
– 2) Centromere:
Joins chromatids
together
Chromosomes condense at the start
of mitosis.
• DNA wraps around proteins (histones) that
condense it.
DNA double
helix
DNA and
histones
Chromatin
Supercoiled
DNA
• Defined: Picture of an
individuals chromosomes
– Identify sex & chromosome
defects
• Size of final pair identifies
sex
– Same size: XX = female
– Different size: XY = male
• Normal human will have
46 chromosomes
Down Syndrome: What’s Wrong?
• Writing notation:
– 1st: total
chromosome #
– 2nd: Sex
chromosomes
– 3rd: extra or
missing
• Down Syndrome:
47, XY, +21
Turner’s Syndrome: What’s Wrong?
• Write the notation
for Turner’s
Syndrome.
45, X, -23
or
45, XO, -23
Patau’s Syndrome: What’s Wrong?
• Write the notation
for Patau’s
Syndrome.
47, XY, +13
Klinefelter’s Syndrome: What’s Wrong?
• Write the notation
for Klinefelter’s
Syndrome.
47, XXY, +23
Body cells are diploid; gametes are haploid.
• Fertilization between
egg and sperm occurs in
sexual reproduction.
• Diploid (2n) cells have
two copies of every
chromosome.
– Body cells are diploid.
– Half the chromosomes
come from each parent.
• Diploid Cells = Cells
with the full set of
chromosomes
– Paired chromosomes
• Somatic (body, or nonsex) cells are diploid
• Created by mitosis
• Ex: Skin, Muscle, Nerve,
Blood Cells
What is the human diploid chromosome
number?
Remember…Diploid = total number of chromosomes
Answer = 46
What is the human somatic chromosome
number?
Remember…Somatic cells are non-sex cells…
…Somatic cells are diploid…
…Diploid cells have the full set of chromosomes
Answer = 46
How many chromosomes are in brain cells?
Remember…Brain cells are non-sex cells…
…Somatic cells are non-sex cells…
…Somatic cells are diploid…
…Diploid cells have the full set of chromosomes
Answer = 46
• Haploid (n) cells have one copy of every chromosome.
– Gametes are haploid.
– Gametes have 22
autosomes and 1 sex
chromosome.
• Haploid Cells = Cells with ½ the
total number of chromosomes
• Gametes (sex cells) are the only
haploid cells
– Ex: Sperm, Egg, Pollen
• Chromosome number is reduced
by meiosis
• How do humans get 46
chromosomes?
Haploid sperm cell (23) + Haploid egg cell (23) = Diploid zygote (46)
What is the human haploid chromosome
number?
Remember…Haploid = half number of chromosomes
Answer = 23 chromosomes
What is the human gamete chromosome
number?
Remember…Gamete cells are sex cells…
…Sex cells are haploid…
…Haploid cells have ½ the set of chromosomes
Answer = 23
How many chromosomes are in female egg
cells?
Remember…Egg cells are sex cells…
…Sex cells are gametes…
…Gamete cells are haploid…
…Haploid cells have ½ the set of chromosomes
Answer = 23
• What is the diploid chromosome number?
42
• What is the haploid chromosome number?
21
• How many chromosomes would be in somatic cells?
42
• How many chromosomes would be in brain cells?
42
• How many chromosomes would be in gamete cells?
21
• How many chromosomes would be in muscle cells?
42
• How many chromosomes would be in sperm cells?
21
• How many chromosomes would be in egg cells?
0- this is not a
female!
• Is this a male or female rat?
male
Quick Review
• Chromsomes are tightly coiled
strands of DNA
• Diploid (somatic) cells contain the
entire set of chromosomes
• Haploid (gametes) cells contain only
½ the total number of chromosomes