Download Meiosis 11.4

Meiosis
 Where do the alleles come from that we inherit?
 We get them from mom and dad in the form of egg
and sperm
Meiosis Vocabulary
 Remember, genes carry the information to code for
specific traits
 These genes are found on structures called
chromosomes (DNA)
 Humans have 46 chromosomes
 We receive 23 from mom and 23 from dad
 There are 23 pairs of
chromosomes
 Homologous
chromosomes are
structurally the
same. They carry
the same genes.
However, each
chromosome may
carry a different
form of a gene.
 Humans are diploid
 Di = two
 Ploid = sets
 We have two of each chromosome (one from mom and
one from dad) in each body cell
 A body cell is a cell that makes up part of our body,
such as a skin cell, liver cell, heart cell
 A gamete is a sex cell
 Gametes are haploid, meaning they only have one copy
of each chromosome
 Two haploid gametes make a diploid cell through
fertilization
How do we make these haploid cells?
 Meiosis
 Cell division that creates gametes (sex cells)
 One cell divides and becomes four haploid gametes
 The parent cell is diploid or (2N) it has two sets of
chromosomes
 Each daughter cell is haploid or (1N)
Stages of Meiosis
In Meiosis I, the
homologous
chromosomes
separate (2n1N)
In Meiosis II, the
sister chromatids
separate like
mitosis
Crossing Over
 Homologous chromosomes pair up and sister
chromatids cross over each other
 When the sister chromatids are separated, some of the
genetic material becomes switched
 This increases genetic variation
Important Points of Meiosis
 Sexual reproduction is important for genetic variation
 Sexual reproduction is only possible by cutting the
number of chromosomes in half through meiosis
 Each egg and sperm contains 23 chromosomes, when
combined through fertilization, they produce an
offspring with 46 chromosomes