Biology unit 3 (Genetics)

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Biology unit 3 (Genetics) by Mind Map: Biology unit 3  (Genetics)

1. Genes

1.1. Chromosomes, genes and alleles

1.1.1. Gene locus refers to the specific position of a gene on a chromosome.

1.1.2. Alleles are the various, specific forms of a gene that usually vary from each other by one or a few bases.

1.1.3. The whole of the genetic information of an organism is its genome.

1.1.4. A gene is a short stretch of DNA that influences a specific characteristic.

1.2. Sickle cell anemia

1.2.1. Sickle cell anemia is a common genetic disease in areas where malaria is endemic

1.2.2. The DNA strand that is not transcribed is called the sense strand and has the same sequence of bases as the mRNA molecule except for thymine being replaced by uracil. The transcribed strand is known as the antisense strand and is complementary to the mRNA molecule.

2. Chromosomes

2.1. Prokaryotic chromosomes

2.1.1. Prokaryotes are microscopic, single-celled organisms without specialised compartments inside the cell. Prokaryotes include two of the three domains of life: eubacteria and archaea.

2.2. Eukaryotic chromosomes

2.2.1. Eukaryotic species can be unicellular or multicellular. They separate their genetic material from the cytoplasm by containing it in the membrane-bound nucleus.

2.3. Diploidy and haploidy

2.3.1. Diploid means when the nucleus contains two copies of each chromosome – 23 homologous pairs, for a total of 46 chromosomes.

2.3.2. Haploid nuclei contain only one chromosome from each pair. They are found only in your gametes, or sex cells (sperm and ova). Haploid cells are produced from diploid cells by meiosis.

2.4. Karyotyping

2.4.1. A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length.

3. Meiosis

3.1. Meiosis is a form of nuclear division that produces four haploid nuclei from one diploid nucleus.

3.2. stages of meiosis

3.2.1. MEIOSIS I Diploid (2n) →Haploid (n) Prophase I Metaphase I Anaphase I Telophase I

3.2.2. MEIOSIS II (n → n) Prophase II Metaphase II Anaphase II Telophase II

3.3. Prophase I and crossing over

3.3.1. In all ‘prophase’ stages in meiosis and mitosis, chromosomes condense by supercoiling. In prophase I, chromosomes also show behavior called crossing over.

3.3.2. Homologous chromosomes pair up and form a tetrad or bivalent.

3.3.3. Prophase I is the longest phase of meiosis. It involves: Pairing of homologous chromosomes Crossing over followed by condensation of DNA into highly organised chromosomes.

3.4. Metaphase I and random orientation

3.4.1. During metaphase I, the pairs of homologous chromosomes (also called bivalents or tetrads) that crossed over in prophase I align along the equatorial plate of the cell

3.5. Genetic variation

3.5.1. Sexual reproduction promotes genetic variation by: Crossing over between homologues in prophase I Random orientation of tetrads in metaphase I Fusion of gametes from two individuals

3.6. Fetal karyotyping

3.6.1. A karyogram is an image of a cell’s homologous chromosome pairs ordered by decreasing size.

4. Inheritance

4.1. Dominant alleles always mask the effects of the recessive alleles. When both a dominant and a recessive allele are present in the genotype, only the dominant allele affects the phenotype.

4.2. the dominant allele is represented by a capital letter and the recessive allele by the lowercase form of the same letter

4.3. Genetic diseases

4.3.1. Cystic fibrosis and Huntington's disease

4.3.2. Red-green colour blindness and hemophilia

5. Genetic modification and biotechnology

5.1. Gel electrophoresis

5.1.1. Gel electrophoresis is a technique used to separate proteins or fragments of DNA according to size.

5.2. PCR

5.2.1. PCR, or polymerase chain reaction, is a technique that repeatedly copies fragments of DNA

5.3. DNA profiling

5.3.1. DNA profiling is a technique that examines variable portions of DNA to create a profile or ‘fingerprint’ that is unique to the individual.

5.4. Genetic modification is carried out by gene transfer between species and this is possible because of the universality of the genetic code.

5.5. Clones

5.5.1. Clones are groups of genetically identical organisms, derived from a single original parent cell