ch 11

Offspring are genetically identical to original cell or organism

Involves inheritance of all genes from one parent

produce new unicellular cells

heal wounds and replace damaged cells/tissues

grow and develop

plantae

animalia

Fungi

Protista

bacteria

archaea

(Diploid --->diploid)

• only one parent cell
• offspring are genetically identical to parent
• DNA replicated and evenly divided so 2 daughter cells get same DNA, TWO copies of each gene ='s Mitosis

Diploid--->Haploid--->Diploid

• offspring are genetically different from one another and from parents
• Gamete are combinded from two parents
• DNA replicated and divide up so each of 4 daughter cells gets ONE copy of each gene ='s MEIOSIS

Shuffling of gene forms (alleles)

random gamete fusion, mating choice

46

alternation of haploid and diploid stages

Longer diploid and haploid phases

Diploid state 

Zygote first undergoes mitosis to produce diploid cells

Diploid cells undergo meiosis to produce haploid gametes

Gametes combine to regenerate diploid zygote

• Diploid cells
• 2 copies of each autosome (1-22)
• 2 sex chromosomes: 2X or (1X +1Y)

• Haploids cells
• 1 copy of each autosome (1-22)
• 1 sex chromosome: 1X or 1Y

Gametogenesis

specialized form of cell division in gonads to produce gametes

Reduces number of chromosomes in each cell by one-half.

Homologous pairs

Human somatic cells have 22 pairs of autosomes, and one pair of sex chromosomes (2X or X+Y)

human gametes have one of each pair (22 autosomes plus 1X or 1Y)

• Prophase I
• Metaphase I
• Anaphase I
• Telophase I

homologous pairs come together

homologous pairs line up at equator

homologous pairs separate

nuclear envelope reforms

after an nterval of variable length

in Anaphase I Microtubules pull homologous chromosomes apart and sister chromatids are held together

In Anaphase in Mitosis microtubules pull sister chromatids apart

• Metaphase I:
•     -Chiasmata hold homologues together
•     -the kinetochores of sister chromatids fuse and function as one
•     -microtubules can attach to only one side of each centromere

• Metaphase:
•     -Homologues do NOT pair
•     -kinetochores of sister chromatids remain separate
•     -microtubules attach to both kinetochores on opposite side of centromere

• -Four cells contain haploid sets of chromosomes
• -in animals, develop directly into gametes
• -in plants, fungi, divide mitotically 
•     -produce greater number of gametes
•     -Adults with varying numbers of gametes

Shuffling of gene forms (alleles)  

random gamete fusion, mating choice

='s Synapsis 

Homologous chromosomes closely associate (sunaptonemal complexes)

-Tetrad= bivalent

exchange of equivalent portions of chromosomes between members of a homologus pair

Results in new types of gametes being formed

• 1. Homologous chromsosome
• 2. Chiasma (non sister chromatids join at chiasmata)
• 3. Recombinant chromatids 
•     -alleles of genes that were formerly on separate homologues can now be found on the same homologue

='s production of new combinations ofalleles due to crossing over

• Recobination 
•     -phrophase I: homologous pairs exchange genetic information 

• Independent Assorment
•     - Metaphase I

radom alignment of homologue, which homologue goes to which cell

• 1. Synapsis and crossing over
• 2. sister chromatids remain joined at their centromeres throughout meiosis I
• 3. Kinetochores of sister chromatids attach to same pole in meiosis I
• 4. DNA replication is suppressed btw meiosis I and Meiosis II

• -Chromosome pairs fail to separate during meiosis I
• - Chromosomes fail to separate at centromere during meiosis II

• Results:
• -gametes with incorrect chromosome number
• -zygote with incorrect chromosome number

Accidents in meiosis can alter chromsome number 

Failure of homologues or sister chromatids to separate properly during meiosis

Older women 

• -increased incidence of trisomic embryos in older women
• -Meiosis begin in all eggs b4 the woman is born, and finishes as each egg matures in the monthly cycle following puberty
• -Eggs of older women have been "within" meiosis longer

gain or loss of chromosome

Loss of chromosome

Gain of chromosome

Some of the smalles autosomes can present as 3 copies and allow individuals to survive 

• -13,15,18- severe defects, die w/in a few months to year
• -21 and 22- can survive to adulthood

Down Syndrome

Trisomy 21: 3 copies of chromosome 21

most common human chromosome abnormality (1/700 births)

Edwards Syndrome

• Trosomy 18: 3 copies of chromosome 18
•     -1/3,000 births
•     - incidence increases w/ maternal age
•     -50% are stillborn, 5-10% live to 1 year, 1% live to 10 years, rare to survive to adult

Patau syndrome

• Trisomy 13: 3 copies of chromosome 13
•    -incidence increases w/ maternal age
•    - 18% survive beyond 1 year, rare to survive to adult

Do not generally experience severe developmental abnormalities

Individuals have somewhat abnormal features, but often reach maturity and in some cases may be fertile

• XXX-triple X females
• XXY-males (Klinefelter syndrome)
• XO-females (Turner syndrome)
• OY-nonviable zygotes
• XYY- males (jacob syndrome)

Triple X females

Males (klinefelter syndrome)

females Turner Syndrome

nonvialbe zygotes

Males Jacobs syndrome

meiosis, mitosis, DNA replication, environmental damage

• Deletion
• Duplication
• Inversion
• Translocation

Gametes: birth defects/spontaneous abortion

Somatic cells: cancer