chapter 11: meiosis and sexual reproduction. sexual vs. asexual reproduction sexual: 2 parents...
TRANSCRIPT
Chapter 11:Meiosis and sexual reproduction
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
•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
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
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
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
•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
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.
•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
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.
Human karyotype preparation
Normal male karyotype
Down syndrome karyotype
•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
Meiosis – form of cell division tha 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)
• Meiosis involves two cell divisions (meiosis I and II)
• Produces four haploid cells.
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
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
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)
Nondisjunction in meiosis I
Nondisjunction in meiosis II
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
• 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).
• 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
Duplication
• 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.
Translocation
Meiosis in males vs. females:•Males:
•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
Spermatogenesis
Oogenesis
Meiosis vs. MitosisMitosis
•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
Meiosis compared to mitosis
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
Life cycle of humans