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Meiosis -
Chapter 10.1 and 11.3
Sexual Reproduction
Sexual reproduction creates genetic
variability. That is why we all look different
and you look different from your siblings!
Define the following words…
• Meiosis:
– Sexual reproduction-production of gametes
• Gamete:
– Sex Cells (egg = females & sperm = males)
– contain half the number of chromosomes (23)
• Somatic Cells:
– Body Cells
– Contain 46 chromsomes
• Haploid:
– Half the chromosome number (n)
– 1 of each pair of chromosomes (23)
– Gametes are haploid
• Diploid:
– 2 of each type of chromosome (2n)
– Somatic cells are diploid
• Fertilization:
– Sperm enters egg
• Zygote:
– Fertilized egg (diploid)
How many chromosomes do
we have in our cells?
▪ Human body cells have 46 chromosomes
▪ Each parent contributes 23 chromosomes
▪ Homologous chromosomes - a pair of
chromosomes that have the same genes
Homologous Chromosomes
▪ Carry the same genes that
control the same inherited
traits
▪ Alleles are the variations of
one gene
–Ex: eye colors can brown,
blue, green, hazel, etc….
▪ You inherit one chromosome
from each parent!
DNA Replication any cell divides, All
DNA must be replicated
Unduplicated homologous
chromosomes
Duplicated homologous
chromosomes
Meiosis
• The sexual life cycle in animals involves meiosis
• Meiosis produces
gametes (23
chromosomes).
• When gametes
combine in
fertilization, that
creates a zygote.
• A zygote has 46
chromosomes
Meiosis
• 2 Divisions
Meiosis I - separation of homologous chromosomes
Meiosis II - separation of sister chromatids
DO NOW
Label the following structures:
Do Now
What are ways that increase genetic
diversity during meiosis?
Meiosis 1
1. Crossing over occurs
1. Homologous
chromosomes
separate, randomly!
46
Duplicated
23
duplicated
Crossing over = the exchange of genes between
homologous chromosomes, resulting in a mixture of
parental characteristics in offspring.
Crossing over
• The same genes “switch”, which allows for
unique gametes to form, different from the exact
chromosomes given from the mother and father.
• Occurs during Meiosis 1, Prophase 1
Meiosis 2
1. Sister chromatids
separate into 4
different gametes,
randomly.
Each gamete has a
unique combination
of genes!
23
duplicated
23 unduplicated chromosomes in each gamete
What creates genetic variability?
1. Crossing over - switching of genes during
meiosis 1 creates a unique combination of genes
1. Independent Assortment - chromosomes
separate into gametes randomly during meiosis
1 and meiosis 2
1. Random Fertilization - random sperm and egg
combine to make a unique gamete
•http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#
Meiosis 1 & 2 - Oogenesis (Eggs) and
Spermatogenesis (Sperm)