1. Chapter 11:
Meiosis and sexual reproduction

2. Sexual vs. Asexual Reproduction
Sexual:
2 parents
Offspring are genetically different from parent – mix of traits
Union of egg & sperm
Asexual:
1 parent
Offspring are identical to parent
Binary fission in bacteria
Regeneration in worms

3. In sexual reproduction, each parent produces a reproductive cell called a gamete
Male gamete – sperm
Female gamete – egg
Zygote – formed when sperm fertilizes egg
Fertilization – process in which sperm and egg fuse together

4. Examples of asexual reproduction:
Fragmentation – body breaks into several pieces, each of which regrows into an adult
Budding – new individuals split off from existing ones
Parthenogenesis – a female makes a viable egg that grows into an adult without being fertilized by a male
Binary fission – a type of cell division used by prokaryotic cells

5. Advantage of sexual reproduction:
Produces offspring that are different from their parents so they have a better chance of surviving changes in the environment, diseases, etc.
Advantages of asexual reproduction:
Simple and efficient
No need to find a mate
May produce many offspring in a relatively short period of time

6. Somatic cells – body cells such as skin, hair, muscle, bones, or organs that do no participate in sexual reproduction
Germ cells – cells that are specialized for sexual reproduction, such as eggs or sperm

7. Each species has a set number of chromosomes:
Humans – 46
Crayfish – 200
Corn – 20
Adder’s tongue fern – 1262
Chimpanzee - 48
Sand dollar – 52
Dog – 78
Cat - 32

8. Viewing the Chromosomes
Karyotype - a photograph of the chromosomes in a dividing cell
Shows the gender of the child
Shows abnormalities in chromosome number or structure.
Humans have 23 pairs of homologous chromosomes (chromosomes with the same genes; similar in size and shape), or 46 chromosomes total.
You get 1 of each chromosome from mom, and 1 from dad.

9. Of the 23 pairs of chromosomes:
1 pair are sex chromosomes – determine your gender; may determine other traits as well
Females are XX
Males are XY
22 pairs are autosomes – all other pairs of chromosomes; do NOT determine gender

10. How is karyotyping done?
Cells are taken from the fetus of a pregnant woman
Chemicals added to the cells make them divide
Another chemical stops division at the midpoint
The stained cells are photographed and can be paired based on cross-bands, size, and shape.

11. Human karyotype preparation

12. Normal male karyotype

13. Down syndrome karyotype

14. Body cells contain the diploid (2n) number of chromosomes – contain 2 chromosomes of each kind (1 from each parent)
Sex cells (eggs and sperm) contain only 1 chromosome of each kind – haploid (1n) number of chromosomes

15. Meiosis – form of cell division that produces
daughter cells with half the number of
chromosomes that are in the parent
Produces sex cells (gametes)
Female gamete – egg
Male gamete - sperm
Reduces the chromosome number
Egg or sperm cells each have only one of each kind of chromosome
Diploid cells (2n)  haploid cells (1n)

20. Overview of meiosis

21. Meiosis involves two cell divisions (meiosis I and II)
Produces four haploid cells.

22. Meiosis I
Original cell produces 2 new cells
Splits homologous chromosomes so that each new cell has 1 chromosome from each homologous pair
Diploid cells (2n) create haploid cells (1n)
Crossing over (chromosomes exchange genetic material) can occur

24. Meiosis II
Each of the 2 cells made in meiosis I splits
2 haploid cells divide to make 4 haploid cells
Chromatids of chromosomes are separated
Errors in meiosis can result in missing or extra chromosomes

26. Changes in Chromosome Number
Occurs when:
In meiosis I, homologous pair both go into the same daughter cell or
In meiosis II, the sister chromatids both go into the same gamete.
The result is either:
Trisomy (3 copies of a single chromosome)
Monosomy (1 copy of a single chromosome)

27. Nondisjunction in meiosis I

28. Nondisjunction in meiosis II

29. Types of chromosomal mutations:
Deletion – a piece of a chromosome is lost
Duplication – a chromosome with a repeated section attached
Inversion –a section of chromosome is flipped in the reverse direction
Translocation – a chromosome piece ends up on another non-homologous chromosome
Gene rearrangement – an entire gene moves to a different location on the same chromosome

30. Ex. of deletion: Williams syndrome
Chromosome 7 loses an end piece
Children have a pixie look (turned-up noses, wide mouth, small chin, large ears)
Poor academic skills, good verbal and musical abilities
Skin ages prematurely from lack of the gene that controls the production of elastin (also affects cardiovascular health).

32. Ex of duplication: An inverted duplication in chromosome 15 causes inv dup 15 syndrome
Poor muscle tone, mental retardation, seizures, curved spine, and autistic characteristics

33. Duplication

34. Ex of translocation: Alagille syndrome results from a deletion of chromosome 20 or a translocation that disrupts an allele on chromosome 20.
The symptoms for Alagille syndrome range from mild to severe, so people may not be aware they have the syndrome.
Distinctive face, abnormalities of eyes & internal organs, and severe itching.

35. Translocation

36. Meiosis in males vs. females:
Occurs in testes
Spermatogenesis
Makes 4 haploid sperm
Females:
Occurs in ovaries
Oogenesis
Makes 1 large egg & 3 polar bodies (that die) – cells divide unevenly

37. Spermatogenesis

38. Oogenesis

39. Meiosis vs. Mitosis Mitosis Body cells
Diploid cells make diploid cells
End result 2 cells
No variation in cells produced
Meiosis
Sex cells
Diploid cells make haploid cells
End result up to 4 cells
Cells made are different from parent

40. Meiosis compared to mitosis

41. The Human Life Cycle
Requires both mitosis and meiosis.
In males, meiosis occurs as spermatogenesis and produces 4 haploid sperm.
In females, meiosis occurs as oogenesis and produces 1 egg cell.
Mitosis is involved in the growth of a child and repair of tissues during life.
Cell differentiation occurs at many times during development as cells take on specific roles

42. Life cycle of humans