Meiosis and Sexual Life Cycles

1
Meiosis and Sexual Life Cycles
2
Reproduction

• Why do offspring closely resemble their parents
  and not unrelated individuals?
• Heredity

3
Reproduction

• Why do offspring closely resemble their parents
  and not unrelated individuals?
• Heredity passing of genes from parents to
  offspring
• variation

4
Reproduction

• Why do offspring closely resemble their parents
  and not unrelated individuals?
• Heredity passing of genes from parents to
  offspring
• variation inherited differences within a
  species
• DNA

5
Reproduction

• Why do offspring closely resemble their parents
  and not unrelated individuals?
• Heredity passing of genes from parents to
  offspring
• variation inherited differences within a
  species
• DNA Nucleic acid polymer with bases A,C,T, and
  G
• genes

6
Reproduction

• Why do offspring closely resemble their parents
  and not unrelated individuals?
• Heredity passing of genes from parents to
  offspring
• variation inherited differences within a
  species
• DNA Nucleic acid polymer with bases A,C,T, and
  G
• genes

7
Reproduction

• Why do offspring closely resemble their parents
  and not unrelated individuals?
• Heredity passing of genes from parents to
  offspring
• variation inherited differences within a
  species
• DNA Nucleic acid polymer with bases A,C,T, and
  G
• genes units of heredity made of DNA found on
  the chromosomes

8
Asexual Reproduction

• What occurs in asexual reproduction?
• Single individual is the parent which copies all
  of its genes into an identically cloned
  offspring.
• Limited variation with asexual reproduction.
• What nuclear division is involved in asexual
  reproduction?

9
Sexual Reproduction

• In order for 2 parents to combine their genes
  into one offspring, what must their genetic
  contribution be?
• Each parent must contribute 1/2 of their genes to
  the offspring.
• How does the process ensure that the offspring
  receives the correct genes from each parent?

10
Vocabulary of genetics and reproduction

• Somatic cell

11
Vocabulary of genetics and reproduction

• Somatic cell any cell other than sperm or egg.
  Human somatic cells have 46 chromosomes
• karyotype

12
Vocabulary of genetics and reproduction

• Somatic cell any cell other than sperm or egg.
  Human somatic cells have 46 chromosomes
• karyotype display of individuals somatic cell
  metaphase chromosomes.
• Homologous chromosomes

13
Vocabulary of genetics and reproduction

• Somatic cell any cell other than sperm or egg.
  Human somatic cells have 46 chromosomes
• karyotype display of individuals somatic cell
  metaphase chromosomes.
• Homologous chromosomes chromosomes that have
  same centromere position, same genetic loci, and
  same length.
• How, then, are homologous chromosomes different
  from one another?

14

• Homologous chromosomes have different alleles.
• Allele

15

• Homologous chromosomes have different alleles.
• Allele expression of a gene
• autosome

16

• Homologous chromosomes have different alleles.
• Allele expression of a gene
• autosome non-sex chromosome
• sex chromosome

17

• Homologous chromosomes have different alleles.
• Allele expression of a gene
• autosome non-sex chromosome
• sex chromosome dissimilar chromosomes that
  determine an individuals sex.
• How many autosomes and how many sex chromosomes
  are there in a normal human?
• How many homologous pairs of chromosomes?

18

• diploid

19

• diploid condition in which cell contains 2 sets
  of chromosomes abbreviated 2n
• haploid

20

• diploid condition in which cell contains 2 sets
  of chromosomes abbreviated 2n
• haploid condition in which cells contain 1 set
  ( no homologous pairs) of chromosomes
  abbreviated n
• gamete

21

• diploid condition in which cell contains 2 sets
  of chromosomes abbreviated 2n
• haploid condition in which cells contain 1 set
  9 no homologous pairs) of chromosomes
  abbreviated n
• gamete haploid reproductive cells, human
  gametes have 23 chromosomes
• fertilization

22

• diploid condition in which cell contains 2 sets
  of chromosomes abbreviated 2n
• haploid condition in which cells contain 1 set
  9 no homologous pairs) of chromosomes
  abbreviated n
• gamete haploid reproductive cells, human
  gametes have 23 chromosomes
• fertilization union of 2 gametes
• zygote

23

• diploid condition in which cell contains 2 sets
  of chromosomes abbreviated 2n
• haploid condition in which cells contain 1 set
  9 no homologous pairs) of chromosomes
  abbreviated n
• gamete haploid reproductive cells, human
  gametes have 23 chromosomes
• fertilization union of 2 gametes
• zygote diploid cell that results from fusion of
  gametes
• What sort of nuclear division must occur to
  produce haploid gametes?

24
(No Transcript)
25
Meiosis

• Must have a stage that results in the reduction
  of chromosome number.
• In meiosis the diploid parent cell produces
  haploid gametes

26
Interphase I

• What happens in interphase I?
• Chromosomes replicate
• centriole paris in animal cells also replicate
• In what way is interphase I from meiosis I
  different from interphase of mitosis?
• There is no difference.

27
Prophase I

• Synapsis occurs.
• Homologous chromosomes come together as pairs
• chromosomes appear as tetrads with 4 attached
  sister chromatids
• chiasmata form, they are sites where homologous
  non-sister chromatids cross over.
• 90 of meiosis is spent in prophase I

28
Metaphase I

• Tetrads allign at metaphase plate
• synaptic pair are alligned so that cnetromeres of
  homologues point to opposite poles
• each homologue is attached to kinetochore
  microtubules emerging from opposite poles, so
  that the 2 homologues are destined to separate
  during anaphase I

29
Anaphase I

• Homologous chromosomes are moved to opposite
  poles by spindle apparatus
• sister chromatids remain attached at the
  entromeres
• How does this differ from anaphase of mitosis?

30
Telophase I

• Spindle apparatus continues to separate
  homologous pairs of chromosomes
• each pole has a haploid set of chromosomes
• cytokinesis occurs and daughter cells are formed.
• What is the chromosome number in each daughter
  cell?

31
Telophase I

• Spindle apparatus continues to separate
  homologous pairs of chromosomes
• each pole has a haploid set of chromosomes
• cytokinesis occurs and daughter cells are formed.
• What is the chromosome number in each daughter
  cell? Haploid!

32

• What has been accomplished by the end of meiosis
  I?
• Homologous pairs of chromosomes have separated.
• Why isnt meiosis over, if haploid daughter cells
  have already been formed?
• We still need to separate sister chromatids!

33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
Genetic Variation

• How do independent assortment and random
  fertilization contribute to genetic variation?
• Orientation of homologous pairs of chromosomes
  with regard to each-other is random (metaphase I)
  
• there is a 50/50 chance that a particular
  daughter cell will receive a paternal or maternal
  chromosome

37

• There are 2n possible combinations of maternal
  and paternal chromosomes.
• In humans there are 223 possible different
  combinations or 8 million.
• Random fertilization has the random combining of
  egg and sperm. Each egg and sperm has one in 8
  million different possibilities. Thus the zygote
  can have one in 64 trillion possible diploid
  combinations.
• This number hasnt even accounted for crossing
  over, which has a random contribution to genetic
  variation!

38
Genetic Variation in all organisms

• In asexually reproducing organisms, mutations are
  the primary source of genetic variation
• In sexually reproducing organisms meiosis
  accounts for most of the variation.