Download Genes, Alleles, and Meiosis PowerPoint

GENES, ALLELES, AND CHROMOSOMES
• All living things carry their genetic information in DNA
• Sections of DNA with instructions for making proteins
are called genes
• DNA coils up to form structures called chromosomes
• Chromosomes come in pairs, one from mom and one
from dad
REVIEW:
WHAT DO WE KNOW ABOUT
MITOSIS?
1. It makes more cells!
2. It begins with one cell, ends with two identical cells
BIG BANG THEORY CLIP…
https://www.youtube.com/watch?v=HV5kPiDYC3M
But…
• Why can’t Sheldon actually reproduce
through mitosis?
MITOSIS:
•
Essential for growth and repair of plant, animal, and
human tissue.
•
Results in TWO daughter cells that are IDENTICAL
HOMOLOGOUS CHROMOSOMES
• Chromosomes that carry the same genes
• One from mom and one from dad
• Remember- genes are instructions for making
proteins, and proteins determine traits
ALLELES
• So each of the homologous
chromosomes has one copy of a gene
from mom and one from dad
• These copies are called alleles and may
be the same or different versions
• Green peas or yellow peas
• Smooth seeds or wrinkled seeds
• Tall plant or short plant
KARYOTYPE
• A photo of the chromosomes in a dividing cell
that shows an individual’s chromosomes
arranged by size.
HUMAN KARYOTYPE SHOWING
23 PAIRS OF HOMOLOGOUS
CHROMOSOMES
KARYOTYPE CONT’D
• Each of a human’s 46 chromosomes has
thousands of genes, so the presence of all
chromosomes is essential for normal
functioning
Humans who are missing a chromosome
don’t survive past the embryo stage
Humans with more than two copies of a
chromosome may survive but will not
develop properly (this is called trisomy).
SO WHAT’S MEIOSIS???
MEIOSIS
• We can’t use SOMATIC cells (body cells with homologous
chromosomes) to reproduce sexually
• We need special cells called GAMETES (sperm and egg)
• Gametes only have ONE chromosome from each
homologous pair
• The process of separating homologous chromosomes
and making gametes is called meiosis
WHY MEIOSIS?
•
No meiosis = no sperm or
eggs.
•
No sperm or eggs = no
fertilization.
•
No fertilization = no sexual
reproduction
SPERM AND EGG CELLS ARE:
• Reproductive Cells
• Also called Gametes
• Haploid (n)- only have half of the normal
chromosome number
• The normal number found in somatic cells is
called diploid (2n)
PHASES OF MEIOSIS
• Meiosis occurs in two parts:
•Meiosis I - homologous chromosomes
are separated, the cell splits in 2
•Meiosis II - each sister chromatid is
separated, both cells split in 2 for a total
of 4
RESULT OF
MEIOSIS:
4
HAPLOID
DAUGHTER
CELLS!
FERTILIZATION:
Human
Sperm
cell
+
Human
Egg Cell
=
Fertilized Egg
Zygote
Embryo
23
chromosomes
23
chromosomes
46
chromosomes
(haploid, n)
(haploid, n)
(diploid, 2n)
MITOSIS
MEIOSIS
Makes somatic (body) cellsskin, blood, liver
Makes gametes- Sperm & Egg
Divide Once =2 Diploid Cells (2n)
Divide Twice= 4 Haploid Cells (n)
One division, four Phases:
Two divisions, four phases each:
 Prophase
 Metaphase
 Anaphase
 Telophase/ cytokinesis
 Meiosis I
 Prophase I, Metaphase I, Anaphase I,
Telophase I/ cytokinesis
 Meiosis II
 Prophase II, Metaphase II, Anaphase II,
Telophase II/ cytokinesis
CROSSING OVER
• When homologous chromosomes pair up early in
meiosis I, they can swap pieces (sections of DNA)
• This results in a new combination of alleles and
increases genetic diversity
MITOSIS AND MEIOSIS SIMULATIONS
http://sepuplhs.org/high/sgi/teachers/genetics_act3_si
m.html
Mitosis
Meiosis
Makes 2 daughter cells
Makes somatic cells
Both
makes 4 daughter
cells
DNA replicates
during interphase
Makes gametes
Daughter cells are
identical to parent
Daughter cells
are diploid (2n)
one round
of division
individual
chromosomes line
up during
metaphase
One parent cell
divides
Prophase
Metaphase
Anaphase
Telophase
Daughter cells are
different
Daughter cells
are haploid (n)
two rounds
of division
homologous pairs line
up in metaphase I
YOUTUBE VIDEO
http://www.youtube.com/watch?v=zGVBAHAsjJM&safe=active