wk6-1.12-sexual reproduction,meoisis,genetic recombination

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wk6-1.12-sexual reproduction,meoisis,genetic recombination by Mind Map: wk6-1.12-sexual reproduction,meoisis,genetic recombination

1. reproduction

1.1. asexual reproduction

1.1.1. no genetic recombination

1.1.2. used for proliferation

1.1.3. produces genetically identical cells

1.1.4. widespread in nature mitotic division of unicellular organisms budding of offspring from a multicellular parent's body regeneration of whole organisms/piece of parent organisms

1.1.5. efficient as long as environmental conditions are constant if environment changes asexual reproduction cannot aid organisms to adapt

1.1.6. binary fission division in half reproductive process undergone by prokaryotes in which cells grow to double its size and then divides into two cells process chromosome replication begins replication continues replication finishes two daughter cells result

1.2. sexual reproduction

1.2.1. able to allow organism to adapt

1.2.2. allows genetic info from parents to be mixed together>produce genetically different offspring

1.2.3. offspring are unpredictably dissimilar

2. Meosis

2.1. keywords

2.1.1. living organisms reproduce to produce offspring of their own kind

2.1.2. hereditary transmission of traits from one generation to the next generation

2.1.3. variation offspring differ from parents and siblings

2.1.4. homologous chromosomes two members of each chromosome pair carry same genes but might have different alleles

2.1.5. sex chromosomes look different under LM determine whether individual is male or female XX / XY

2.1.6. diploid cell or organism with two sets of chromosomes 2n 46

2.1.7. haploid cell or organism with a single set of chromosomes n 23 one set of chromosomes from each parent

2.1.8. gene locus place on a chromosome that contains the DNA sequence for a particular gene

2.1.9. allele versions of a gene

2.1.10. genetic recombination physical exchange of parts of DNA molecules exchange of DNA segments between two different sources

2.2. Human life cycle

2.2.1. begins with fertilization haploid sperm fuses with haploid egg>zygote(fertilized egg) zygote=diploid=46

2.2.2. human develops into sexually mature adult mitosis of zygote and descendent cells>all somatic cells of body all genes in zygote passed to somatic cells

2.2.3. gametes only cells not produced by mitosis produced by meiosis develop from germ cells ovaries in female testes in males

2.3. role of meiosis

2.3.1. allows chromosome number to remain constant from generation to generation

2.3.2. reduces the chromosome number from diploid to haploid

2.4. process

2.4.1. one round of chromosomal DNA replication

2.4.2. no intervening DNA synthesis or chromosome duplication only one Interphase(I) may be a short interphase interphase not accompanied by DNA replication

2.4.3. 2 successive nuclear divisions meiosis I homologous chromosomes separate sister chromatids remain attached 2 chromosomes of each homologous pair join during prophase to exchange genetic info 2 chromosomes of each homologous pair bind together during prophase I and behave like a single unit bivalents align at the spindle equator process meiosis II sister chromatids separate form 4 haploid cells with 2 chromosomes each very similar to mitosis process

2.4.4. forms 4 daughter nuclei contain haploid set of chromosomes per nucleus

3. genetic variation

3.1. independent assortment of chromosomes

3.1.1. random orientation of homologous pairs at the metaphase I plate each consists of one maternal and one paternal chromosome 50% chance that a particular daughter cell of meiosis I will get a maternal chromosome/paternal chromosome each pair of homologous chromosomes is positioned independently of the others at the plate 1st meiotic division=each pair sorting its maternal and paternal homologs into daughter cells independently of every other pair

3.1.2. number of possible combinations when chromosomes sort independently during meiosis=2^n n=haploid number of organism humans n=23

3.2. crossing over

3.2.1. produces recombinant chromosomes =individual chromosomes that carry genes derived from two different parents

3.2.2. average of 1-3 crossovers occur/chromosome pair depends on size of chromosomes and position of centromeres

3.2.3. begins in early prophase I homologous chromosomes pair loosely along their lengths each gene on one homolog is aligned precisely with the corresponding gene on the other homolog single crossover event DNA of two nonsister chromatids

3.2.4. metaphase II chromosomes that contain 1/more recombinant chromatids can be oriented into two alternative non equivalent ways with respect to the other chromosomes sister chromatids no longer identical

3.3. random fertilisation

3.3.1. in humans each male and female gamete represents one of about 8.4 million (2^23) possible combinations due to independent assortment fertilization=a zygote with any of 70 trillion (2^23 x 2^23)

4. non disjunction

4.1. members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis II

4.2. one gamete receives two of the same type of chromosome and another gamete receives no copy

4.2.1. aberrant gamete

4.3. aneuploidy

4.3.1. if either of aberrant gametes unite with a normal one during fertilization

4.3.2. trisomy chromosome is present in triplicate in the zygote cell has 2n+1 chromosomes (n+1)+(n) Down's syndrome extra chromosome 21 2n+1=47 chromosomes also known as Trisomy 21 symptoms frequency increases with age of mother

4.3.3. monosomy involves a chromosome that has no copy of a particular chromosome leads to a missing chromosome in the zygote cell has 2n-1 chromosomes (n-1)+(n) Monosomy X(Turner's syndrome) 1/2500 female births only known monosomy in humans X0 individuals phenotypically female sterile as sex organs dont mature normal intelligence

4.3.4. zygote will have an abnormal number of a particular chromosome

4.4. polyploidy

4.4.1. more than one complete set of chromosomes in all somatic cells

4.4.2. triploidy (3n) 3 chromosomal sets may arise by fertilization of an abnormal diploid egg produced by nondisjunction of all chromosomes

4.4.3. tetraploidy (4n) 4 chromosomal sets failure of 2n zygote to divide after replicating its chromosomes mitotic divisions=4n

5. meiosis and mitosis comparison

5.1. Meiosis

5.1.1. form of nuclear division

5.1.2. single round chromosome duplication followed by 2 chromosome segregation meiosis I homologs separated homolog meiosis II sister chromatids are separated

5.2. mitosis

5.2.1. homologs dont pair up

5.2.2. sister chromatids separate in a single division