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Samenvatting GENOMICA uitgewerkte leerdoelen H13 en H14 Universiteit Utrecht
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In dit document staan de uitgewerkte leerdoelen voor de hoofdstukken 13 en 14 uit het boek Campbell Biology; a global approach.
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GenomicaJaar 1, periode 4
Bevat alle uitgewerkte leerdoelen van H13 en H14
Meiosis: Campbell Chapter 13
• Distinguish the roles of the soma and the germ line in the life cycle of a typical multicellular organism. Explain why
mammalian gametes are haploid and somatic cells are diploid.
Germ line: The cells that form eggs in females and sperm in males. Germline cells contain the genetic information
that is passed down from one generation to the next.
Soma: All the living matter of an animal or a plant except the reproductive, or germ, cells.
In humans, ovaries and testes produce haploid gametes by meiosis, each gamete containing a single set of 23
chromosomes (n = 23). During fertilization, an egg and sperm unite, forming a diploid (2n = 46) single-celled zygote,
which develops into a multicellular organism by mitosis, these somatic cells are of course, diploid.
• Describe the difference between sister chromatids and homologous chromosomes.
Sister Two copies of a duplicated chromosome attached to each other by proteins at the
chromatids centromere and, sometimes, along the arms. While joined, two sister chromatids make up
one chromosome. Chromatids are eventually separated during mitosis or meiosis II.
Homologous A pair of chromosomes of the same length, centromere position, and staining pattern that
chromosomes possess genes for the same characters at corresponding loci. One homologous
(or homologs) chromosome is inherited from the organism’s father, the other from the mother.
• Diagram the process of homologous recombination during meiosis and explain how it can lead to new combinations of
linked alleles.
Homologous recombination is a type of genetic recombination during Meiosis I which starts with synapsis. Synapsis
is the pairing of two chromosomes that occurs during meiosis. It allows matching-up of homologous pairs prior to their
segregation, and possible chromosomal crossover between them. X- shaped areas, called chiasmata, are the sites of
crossovers. This exchanging of DNA is an important source of the genomic variation seen among offspring.
,Crossing over vindt plaats tijdens profase I, de zusterchromatiden worden bij elkaar gehouden door eiwitten genaamd
cohesines. De non-zusterchromatiden worden op exact dezelfde posities geknipt. Een ritssluiting-achtige structuur
genaamd het ‘synaptomenal complex’ houdt de homologen strak bij elkaar. De DNA-breuken worden gerepareerd
waarbij het DNA van niet-zusterchromatiden met elkaar wordt verbonden. De homologen zijn nu in synapsis
• Describe the phenomena of linkage and independent assortment of alleles during meiosis.
Because each pair of homologous chromosomes is positioned independently of the other pairs at metaphase I of
meiosis I, the first meiotic division results in each pair sorting its maternal and paternal homologs into daughter cells
independently of every other pair. This is called independent assortment.
Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together
during the meiosis phase of sexual reproduction.
• Explain how the process of meiosis increases genetic diversity within the offspring and why it is essential for evolution
to occur.
Three events in sexual reproduction contribute to genetic variation in a population: independent assortment of
chromosomes during meiosis I, crossing over during meiosis I, and random fertilization of egg cells by sperm. During
crossing over, DNA of nonsister chromatids in a homologous pair is broken and rejoined.
NUMBERS:
Independent assortment: Het aantal mogelijke combinaties wanneer chromosomen onafhankelijk van elkaar in
gameten worden ingedeeld is 2n waarbij n het haploïde getal is. Voor mensen (n=23) zijn er dan meer dan 8 miljoen (2 23)
mogelijke combinaties van chromosomen.
Random fertilization: Elke spermacel kan samensmelten met elke eicel. De fusie van twee gameten (elk met 8.4 miljoen
mogelijke chromosoomcombinaties uit independent assortment) produceert een zygote met ongeveer 79 biljoen
diploïde combinaties. Crossing-over zorgt dan vervolgens voor nóg meer variatie.
• List similarities and differences between mitosis and meiosis.
Drie gebeurtenissen zijn uniek voor meiose en alle drie komen voor in meiose I:
- Synapsis en crossing-over in profase I: Homologe chromosomen verbinden fysiek en wisselen genetische
informatie uit.
- Homologen paren op de metafase plaat
- Scheiding van homologen tijdens anafase I
, • Explain the possible impact of disjunction errors on a gamete, an embryo and an individual.
Nondisjunction: An error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of
sister chromatids fail to separate properly from each other.
Meiosis: In nondisjunction, one gamete receives two of the same type of chromosome and another gamete receives no
copy. The other chromosomes are usually distributed normally.
Mitosis: Nondisjunction can also occur during mitosis. If such an error takes place early in embryonic development, then
the aneuploid condition is passed along by mitosis to a large number of cells and is likely to have a substantial effect on
the organism.
When a normal gamete unites with one containing two copies or no copies of a particular chromosome, the resulting
zygote and its descendant cells either have one extra copy of that chromosome (trisomy, 2n + 1) or are missing a copy
(monosomy, 2n - 1). Polyploidy (extra sets of chromosomes) can result from nondisjunction of all chromosomes
(mitosis).
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