Ib Biology Hl Notes

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Genes and Genetics
1. 2.

each chromosome exists as two genetically identical chromatids attached to their centromere. Each chromosome appears as two chromatids attached to a centromere. In the first meiotic division chromosomes align in homologous pairs. Points of contact form between members of the same homologous pair. The points of contact or crossing over between members of a homologous pair are the chiasmata.

3. The homologous pairs move to the equator of the cell. Equal lengths of the chromatids of the same homologous pair have broken off and crossed over. The chromosomes align at random and independantly. Only one possible arrangement is shown. 4. Homologous pairs align at random at the equator of the cell. This shows the early separation of the chromosomes of each of the homologous pairs. 5. Homologous pairs are separated. This shows the cell at an early stage of meiotic division. The cell membrane is starting to pinch inwards. 6. The cell divides to form two cells each with a haploid set of chromosomes. Cell division is complete and two cells containing a haploid set of chromosomes are formed. 7. In the second meiotic division the chromosomes in each cell align independently and randomly at the equator of the cell. 8. The chromatids in each cell are separated. The chromatids are pulled towards the opposite poles of the cell. 9. The cells divide. The cell membrane is starting to pinch inwards. 10. Cell division is complete, resulting in the formation of four cells each with the haploid number. 11.

Meiosis - Functions

Halving the chromosome number - meiosis consists of two nuclear divisions (meiosis I and meiosis II) but the chromosomes replicate once. Producing four daughter cells. Each are haploid Producing Genetic Variety - through prophase I and through random assortment during metaphase I. In addition, random fertilisation also produces variety since any gamete has an equal chance on combining.

Crossing Over - during prophase one, homologous chromosomes combine to form bivalent so maternal and paternal chromosomes are adjacent. Homologous pairs contain same genes but different alleles. They line up and non-sister chromatids break then they rejoin in corresponding position on other chromatid. Region this occurs is called the chiasma (chiasmata). Point where this is in random but not all chromatids form a chiasma and some dont happen at all.Therefore, chromatids keep alleles. Monohybrid and Dihybrid Inheritance0 There Codominance - both alleles have an effect on a phenotype neither allele is recessive multiple allels - 3 alleles in blood typed these are Ia , Ib and 'i' (Io) these 3 alleles make up the phenotype and genotypes in the blood gene. Sex Link Genes Autosome (normal chromosome) pairs are said to be linked. Meaning they contain the same locus on a gene. HOMEWORK 2 b) Genotypes Gametes F1 Genotypes Phenotypes



4 b) Bw Tl Male Gametes- B,w T,l ww ll Female Gametes - w,w,l,l B w w Bw Bw w ww ww

3) Polygenic inheritance of skin colour - Depends on the amount of pigment that is produced in the skin. Melanin synthesis is controlled by genes. The degree of pigmentation can range from very dark to very pale. Several genes are involved in skin colour determination and these produce continuous variation. Each gene has two alleles so there are numerous outcomes for example when three genes are involved there are seven outcomes. One allele M contributes to melanin. 7.4.6  

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Ribosomes are made of two subunits, large and small Small subunits binds to the first codon on the mRNA. This is the initiation part of translation. The first codon is usually AUG and codes for the amino acid methionine. Large Sub-units will now bind and two binding sites for tRNA sit over the first two codons Transfer RNA with the correct with the correct anticodon will lock into the first tRNA binding site and form hydrodgen bonds to...
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