Name: per:
chromosomes are made
of DNA wound tightly.
A normal human cell is ________, and has 46
chromosomes.
A gamete (_____ or _____)
is haploid, and has ____ chromosomes.
h
1. Sexual reproduction: chromosomes are
chromosomes are combined, 1 set from mom, 1 set from dad, during fertilization to create a unique zygote
zygote.
2. Independent assortment: each chromosome
can split independently of the next chromosome,
so that every gamete is a different mix of the
chromosomes inherited from mom and dad.
light: mom chromosome 1,
dark: dad chromosome 1
3. Crossing over: i
during prophase I the chromosomes line up next to each other and cut and paste to form new combinations
Mitosis is the process
cells use to make
genetically
__________
cells.
Meiosis is the process
cells use to make
genetically
_____________
cells, eggs and sperm
called ____________
They copy their DNA
once, (S phase), and
then divide once
Mitosis (__ __ __ __)
They copy their DNA
once, (S phase), and
then divide twice
__ __ __ __ __ __ __ __
Mistakes can be made in meiosis
during crossing over:
A picture of the chromosomes in a
cell is called a “karyotype”
normal human
male karyotype
before S phase
normal human
male karyotype
after S phase
ex: 1 copy of chromosome 1 is from mom, one copy of
mom, one copy of chromosome 1 is from dad
ex: each “X” is two copies of chromosome 1 from mom, twp copies of chromosome 1 is from dad
meiosis mistake: anaphase… one parent’s gamete contains two copies of chromosome b
copies of chromosome b
trisomy 21: “Down’s syndrome”… when anaphase in meiosis does
anaphase in meiosis does not occur correctly, and one parent’s gametes contains two copies of chromosome 21. Baby ends up with 3
Baby ends up with 3 copies… extra DNA means extra dose of proteins coded for by genes on chromosome 21.
Physical characteristics: distinct facial features, varying impairments of mental development, muscle tone problems, heart problems, early onset Alzheimer’s
meiosis mistake: anaphase… one parent’s g
gamete does not contain a sex chromosome, or father’s sperm contains both X and Y.
Turner’s syndrome: XO (female)
girl is missing one X chromosome. Leads to less of a dose of gender related proteins. Physical characteristics: normal mental development, webbed neck, short stature, almost always with fertility problems.
Kleinfelter’s syndrome: XXY (male)
boy has extra X chromosome. Leads to increase in dose of X proteins, infertility, and lower testosterone production
Physical characteristics: problematic mental development, low testosterone levels, infertility, longer limbs than normal