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Samenvatting DNA & Evolutie
- Vak
- DNA & Evolutie
- Instelling
- Avans Hogeschool (Avans)
hier is een zelfgemaakte samenvatting van DNA en Evolutie. Ik heb dit vak afgerond met een 7,3. Hopelijk jij ook!
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DNA en Evolutie13.1 – Offspring acquire genes from parents by inheriting
chromosomes
Inheritance of genes
• Genes: A discrete unit of hereditary information consisting of a specific nucleotide
sequence in DNA.
- Program specific traits that emerge as we develop from fertilized eggs into adults.
• Most genes program cells to synthesize specific enzymes and other proteins, whose
cumulative action produces an organism’s inherited traits.
• Gametes; reproductive cells that transmit genes from one generation to the next.
• During fertilization, male and female gametes (sperm and eggs) unite, passing on
genes of both parents to their offspring.
• 46 chromosomes in their somatic cells.
• Locus; A specific place along the length of a chromosome where a given gene is
located.
• Genome; consists of the genes and other DNA that make up the chromosomes we
inherited from our parents.
Comparison of Asexual and sexual reproduction.
• In Asexual reproduction a single individual is the sole parent and passes copies of all
its genes to its offspring without the fusion of gametes.
- The genomes of the offspring are exact copies of the parent’s genome.
• Clone; A group of genetically identical individuals.
• Sexual reproduction: Two parents give rise to offspring that have unique
combinations of genes inherited from the two parents.
- Offspring vary genetically from their siblings and both parents.
13.2-fertilazation and meiosis alternate in sexual life cycles
Life cycle:
The generation-to-generation sequence of stages in the reproductive history of an organism
from conception to production of its own offspring.
Sets of chromosomes in Human cells
• Each somatic cell has 46 chromosomes.
• During Mitosis, chromosomes are condensed → can be distinguished from one
another.
• Two chromosomes of each 23 types.
, • Karyotype; A display of the chromosome pairs of a cell arranged by size and shape.
• Homologous chromosomes; two chromosomes of a pair have the same length,
centromere position and staining pattern.
• Both chromosomes of each pair carry genes controlling the same inherited
characters.
• Human females → homologous pair of X chromosomes (XX)
• Males → X chromosome and Y chromosome (XY)
- Sex chromosomes
• Others → autosomes
• We inherit one chromosome of a pair from each parent.
- A maternal set from our mother and a paternal set from our father.
• Diploid cell; Any cell with two chromosome sets.
- 2n (2n = 46)
• When chromosomes are duplicated → still diploid (2n)
• Haploid cells; Gametes which contain a single set of chromosomes.
- n (n = 23)
- 22 autosomes plus single sex chromosome.
Behavior of chromosomes sets in the human life cycle
• Human life begins with a haploid sperm from the father and a haploid egg from the
mother.
• Fertilization; The union gametes, culminating in fusion of their nuclei.
- Zygote; fertilized egg → diploid.
• Mitosis of the zygote and its descendant cells generates all the somatic cells in the
body.
- Chromosomes sets + genes are passes with precision to the somatic cells.
- Gametes are not produced by mitosis.
• Gametes develop from specialized cells (germ cells) in the gonads; ovaries in females
and testes in males.
• Meiosis; type of cell division that reduces the number of sets of chromosomes from
two to one in gametes, counterbalancing the doubling that occurs at fertilization.
- Each human sperm and egg is haploid (n = 23)
, - Fertilization restores the diploid condition by combining two sets of
chromosomes and the human life cycle is repeated, generation after generation.
• Fertilization and meiosis alternate in sexual life cycles, maintaining a constant
number of chromosomes in each species from one generation to the next.
The variety of sexual life cycles
• Gametes are the only haploid cells.
• Meiosis occurs in germ cells during the production of gametes, which undergo no
further cell division prior to fertilization.
- After fertilization, the diploid zygote divides by mitosis, producing a multicellular
organism that is diploid.
• Alternation of generations; second life cycle of plants and some species of algae.
- Sporophyte; the multicellular diploid stage.
*Meiosis produces haploid cells → spores
*spores doesn’t fuse with another cell
*divides mitotically
- Gametophyte; multicellular haploid stage.
* Cells give rise to gametes by mitosis
* Fusion of 2 haploid gametes at fertilization results in a diploid zygote.
- The sporophyte generation produces a gametophyte as its offspring
- The gametophyte generation produces the next sporophyte generation.
• Third life cycle → in most fungi and protists.
- After gametes fuse and form a diploid zygote, meiosis occurs without a
multicellular diploid offspring developing.
- Meiosis produces not gametes but haploid cells that then divide by mitosis and
give rise to either unicellular descendants (nakomelingen) or a haploid
multicellular adult organism.
- Haploid organism carries out further mitoses, producing the cells that develop
into gametes.
- Diploid stage → single-cell zygote
• Either haploid and diploid cells can divide by mitosis depending on the life cycle.
, 13.3 – Meiosis reduces the number of chromosomes sets from diploid
to haploid
Meiosis: Preceded by the duplication of chromosomes.
- Meioisis I
- Meioisis II
The two chromosomes of a homologous pair are individual chromosomes that were
inherited from each parent.
o Homologs may have different versions of genes at corresponding loci.
o Each version is called an allele of that gene.
Meiosis I
Prophase I:
o Spindle formation, nuclear envelope breakdown.
o Chromosomes condense
o Crossing over; The reciprocal (onderling) exchange of genetic material between
nonsister chroma-tids
- Chiasmata; X-shaped regions where crossovers have occurred.
o Microtubules from one pole or the other attach to the kinetochores, one at the
centromere of each homolog.
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