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Unit 4 Meiosis and Genetics
Objectives
1.
Understand offspring acquire genes by inheriting
chromosomes from parents
2.
Fertilization and meiosis alternate in a sexual life cycle
3.
Meiosis reduces the number of chromosome sets
4.
Meiosis and sexual reproduction are responsible for
genetic variation, which is necessary for evolution
Sexual Reproduction
-Two parents produce offspring
-Offspring have shared traits with family
Asexual Reproduction
Inheritence of Genes
-Genes are…
-Asexual reproduction produces two offspring from a
single parent
1. Genetic software that codes for specific proteins
-Offspring are identical or Clones
2. Read much like a book with letters
-Genetic variation is minimal and due to mutations
3. Responsible for the raw material that is a species
(Nature via Nurture)
4. Located on Chromosomes called a locus
-Inheritence relies on…
1. Precise replication of DNA
2. Meiosis to maintain a chromosomal number
specific to a species
The Behavior or Chromosomes is responsible for Genetic Variation in
Sexually Reproducing Organisms
-Chromosomes alternate between fertilization (2n or
Diploid) and Meiosis (1n or Haploid)
-Somatic Cells are all cells except sex cells
-Sex Chromosomes determine male and female gender
-All other chromosomes are called Autosomes
Other Sexually Reproducing Organisms
Alternation of
Generations
No multi-cellular
diploid cell
How does Meiosis differ
from Mitosis???
(p. 254 – 255)
Homologs line
up in the middle
Homologs
Separate
d
Origins of Genetic Variation
1. Crossing Over
-Occurs in Prophase 1 (average of 1-3 events/chromosome)
-Creates Recombinant chromosomes
-Cross overs occure between nonsister homologs
2. Independent Assortment of
Chromosomes
-One Paternal and one Maternal chromosome goes to each
daughter cell
-Occurs in Metaphase 1
-With 23 chromosomes there are 8.4 million different combinations
3. Random Fertilization