1. Inheritance and Sexual Life Cycles
Chapter 13 p

2. Intro to Genetics Genetics: the study of heredity
Heredity: passage of traits from parents to offspring (“inheritance”)
Leads to variation of species

3. Offspring acquire genes from parents
Gene: hereditary unit in form of DNA
Code for specific traits by controlling cell protein production
Composed of specific sequence nucleotides
Each chromosome contains 100’s to 1,000’s genes
Locus: a gene’s location on a chromos.
Human Genome Project

4. Asexual vs. Sexual Reproduction
Asexual: 1 parent cell
Copy entire genome → offspring
Produces clone (genetically identical being)
Unicell = Mitosis or Binary Fission; multicell = “budding”
Sexual: 2 parent cells
½ genome from each parent → offspring
Produces genetically different offspring
↑ genetic variation of species

5. The Human Life Cycle “Life Cycle” – conception → produce offspring
1) Somatic Cells: all cells except reproductive
44 autosomes in pairs & 2 sex chromosomes in a pair
Determine sex of offspring
Male: XY; Female: XX
Homologous Chromosomes: pair of chromos. carrying genes for same trait
Diploid: cell w/ 2 sets chromos. (2n=46)
Karyotype: chart of autosomes arranged in homologous pairs

6. The Human Life Cycle 2) Gametes: “sex cells” sperm & ovum
23 unpaired chromosomes
Haploid: 1 set chromos. (n=23)
Created through meiosis (this cuts chromos. in ½)
Fertilization: joining of sperm & ova → zygote
Results in diploid cell (2n=46)

7. Variety of Sexual Life Cycles
Differ in timing of meiosis & fertilization
1) Animals: meiosis produces gametes; diploid zygote divides by mitosis
2) Fungi & Protists:
Gametes fuse → diploid zygote
Meiosis produces haploid cells
Haploid cells divide by mitosis → adult orgnsm.

8. Variety of Sexual Life Cycles
3) Plants & some algae: “Alternation of Generations”
Alternate btwn diploid/haploid stages
1) Sporophyte: diploid stage
Meiosis occurs, making haploid spores
Spores develop into adult orgnsm. (gametophyte)
2) Gametophyte: haploid stage
Undergoes mitosis to make gametes
2 gametes fuse → diploid zygote (spororphyte)

9. Meiosis & Genetic Variation
Ch 13 p

10. Meiosis Reduces Chromos. # from Diploid → Haploid
Meiosis occurs in 2 stages, resulting in 4 genetically different daughter cells
1) Inherit 1 set chromos. from each parent (pair up to form homologous chromos.)
2) during Interphase, copy each chromos. → sister chromatids of each
3) Meiosis I: homol. chromos. separate → diploid cell
4) Meiosis II: sister chromatids separate → haploid cell w/ unreplic. chromos.

11. Meiosis Overview
Refer to p for the stages of Meiosis

12. Unique Meiosis Events
1) Synapsis: pairing of duplicated chromos. w/ homologue
Held completely together by synaptonemal complex
At end of Prophase I, 4 individual chromatids appear as tetrad
Sometimes non-sister chromatids overlap, creating X-shaped region called chiasmata

13. Unique Meiosis Events
2) Metaphase I: homologous chromos. line up (not sister chromatids)
3) Anaphase I: homo. chromos. separate (not sisters)
4) Meiosis II: separates sister chromatids → 4 genetically different daughter cells
Almost identical to mitosis

14. Genetic Variation
Meiosis results in genetic variation of species populations by:
1) Independent Assortment
2) Crossing Over
3) Random Fertilization

15. Independent Assortment
When chromos. line up along metaphase plate, they do so independently of one another
i.e.: D M OR D M
D M M D
D M D M
D M M D
# possible combos = 2n
(humans = 223 = >8 mill)

16. Crossing Over
Produces Recombinant Chromosomes: contain DNA from BOTH parents
Begins in Prophase I, before synaptonemal complex forms btwn homologous chromos.
Non-sister chromatids exchange portions of DNA
No longer identical sister chromatids assort independently

17. Random Fertilization ANY ovum may be fertilized by ANY sperm
# possible ovum = ~8 mill
# possible sperm = ~8 mill
# possible zygotes = 8 mill x 8 mill ~ 64 trillion

18. Genetic Variation Determines Evolutionary Adaptation
Populations of species evolve through the reproductive success of individuals
Organisms best adapted to environment have best success
Genes good for that environment get passed
Makes evolution possible