Inheritance and Sexual Life Cycles

1
Inheritance and Sexual Life Cycles

• Chapter 13
• p. 238-247

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 100s to 1,000s genes
• Locus a genes 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. (2n46)
• 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. (n23)
• Created through meiosis (this cuts chromos. in ½)
• Fertilization joining of sperm ova ? zygote
• Results in diploid cell (2n46)

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. 243-249

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. 244-245 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 gt8 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