(a)+The+topics

__**4.1 Chromosomes, genes, alleles & mutations**__ 4.1.1 Eukaryotic chromosomes are found in the nucleus. They contain DNA and proteins.

4.1.2

4.1.3 A permanent change in the sequence of base pairs in the DNA that makes up a gene. e.g. A mutation occurs in the Manx cat where some are born without tails.

4.1.4    >>> not true.      <span style="color: #0000ff; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;"> <span style="color: #0000ff; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;"> <span style="color: #0000ff; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;"> <span style="color: #0000ff; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;"> <span style="color: #0000ff; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;"> <span style="color: #0000ff; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;"> <span style="color: #0000ff; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;"> <span style="color: #0000ff; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;"> >>> Test before having children <span style="color: #0000ff; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;"> __** TOK: **__ There is a clear casual link in frequency of the sickle-cell allele is correlated with the prevalence of malaria. There is natual selection in favour of the sickle-cell allele in malarial areas (cause severe anemia in the homozygos >>> frequeences of the sickle - cell and the normal hemoglobin alleles: balance the twin risks of anemia and malaria <span style="color: #008000; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;">__**4.2 Meiosis**__ <span style="color: #008000; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;">4.2.1
 * 1) <span style="direction: ltr; font-family: Calibri; font-size: 16px; font-style: normal; normal margin-top: 0px; margin-bottom: 0in; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">**__ Mutation and DNA: __**
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.375in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> Old opinion: Mutation which involves a smaller number of nitrogenous bases in the DNA will be less significant than one where a large number of bases is changed
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.75in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> Example: Sickle-cell anemia: only 1 base leads to a protein with one amino acid changed and >>> cause disease of sickle-cell anemia
 * 1) <span style="direction: ltr; font-family: Calibri; font-size: 16px; font-style: normal; normal margin-top: 0px; margin-bottom: 0in; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">**__ Hemoglobin __**
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.375in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> Made of 4 polypeptide chains: 2 α and 2 β
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.375in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> When an A to T base substitution occurs, GAG has GTG causing glutamic acid to be replaced by valine and hence sickle -cell
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.375in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> Common hemoglobin: HbS (normal level of Oxygen) >< 'normal' Hemoglobin HbA (makes it crystallize at low oxygen levels)
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.375in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> HbA >>> the erythrocyte change from a biconcave shape into a sickly-cell shape >>> less efficient at transporting oxygen as keeping their stickle shape
 * 1) <span style="direction: ltr; font-family: Calibri; font-size: 16px; font-style: normal; normal margin-top: 0px; margin-bottom: 0in; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">__** Symptoms of Sickle cell anemia: **__
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.375in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> Acute anemia >>> physical weakness; cause damage to the heart and kidney >>> might cause death (in homozygous individually)
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.375in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> The gene for sickle cell anemia is co-dominant with the normal allele although the latter is expressed more strongly in the heterozygous individual.
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.375in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> Plasmodium ( cause malaria) cannot reproduce in erythrocytes with HbS >>> help to reduced chance of contracting malaria.
 * 1) <span style="direction: ltr; font-family: Calibri; font-size: 16px; font-style: normal; normal margin-top: 0px; margin-bottom: 0in; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">**__ Natural selection and effect on young generation __**
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.375in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> Sickle cell trait is more common than malaria infested area such as west Africa.
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.375in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> Carriers often don’t know if they possess the sickly cell allele >>> may pass in to their children. 2 carriers have 25% chance of the child having the disease.
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.375in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> If the pregnant mom and the father are both carrying sickle cell, they should test the child using amniocentesis or chorionic villi sampling. If the child have sickle cell >>> may decide to discontinue the pregnancy
 * <span style="direction: ltr; margin-bottom: 0in; margin-bottom: 0px; 0.375in margin-top: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> >>> Ethical issues relating to screening of fetuses and abortion of those found of have a genetic disease.

<span style="color: #0000ff; font-family: Arial,Helvetica,sans-serif; font-size: 110%; margin: 0in;">**Meiosis is a reduction division of a diploid nucleus to form haploid nuclei:**


 * <span style="color: #0000ff; direction: ltr; font-family: Arial,Helvetica,sans-serif; font-size: 15px; margin-bottom: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Meiosis is called a "reduction division" because:
 * <span style="color: #0000ff; direction: ltr; font-family: Arial,Helvetica,sans-serif; font-size: 15px; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0px; unicode-bidi: embed; vertical-align: middle;">The daughter cells have only half of the number of chromosomes as the original parent cell.

<span style="color: #008000; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;">4.2.2

<span style="color: #0000ff; font-family: Arial,Helvetica,sans-serif; font-size: 110%; margin: 0in;">**Homologous chromosomes:**


 * <span style="color: #0000ff; direction: ltr; font-family: Arial,Helvetica,sans-serif; font-size: 110%; margin-bottom: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">They are 2 chromosomes - one from each parent that:


 * <span style="color: #0000ff; direction: ltr; font-family: Arial,Helvetica,sans-serif; font-size: 110%; margin-bottom: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Look the same


 * <span style="color: #0000ff; direction: ltr; font-family: Arial,Helvetica,sans-serif; font-size: 110%; margin-bottom: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Same size


 * <span style="color: #0000ff; direction: ltr; font-family: Arial,Helvetica,sans-serif; font-size: 110%; margin-bottom: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Show the same binding pattern in a karyotype


 * <span style="color: #0000ff; direction: ltr; font-family: Arial,Helvetica,sans-serif; font-size: 110%; margin-bottom: 0px; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Carry the same genes - not necessarily the same alleles

<span style="color: #0000ff; font-family: Arial,Helvetica,sans-serif; font-size: 110%; margin: 0in 0in 0in 0.375in;">Note: Homologous chromosomes will pair up and split during meiosis

<span style="color: #008000; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;">4.2.3 <span style="color: #008000; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;">4.2.4 <span style="color: #008000; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;">4.2.5 <span style="color: #008000; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;">4.2.6

State that karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for pre-natal diagnosis of chromosome abnormalities.

2 common pre-natal tests


 * <span style="direction: ltr; font-family: 'Times New Roman'; font-size: 21px; font-weight: bold; margin-bottom: 0px; margin-top: 0in; text-decoration: underline; unicode-bidi: embed; vertical-align: middle;">Chorionic villus sampling
 * <span style="direction: ltr; font-family: 'Times New Roman'; font-size: 16px; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0px; unicode-bidi: embed; vertical-align: middle;">Done at 11-12 weeks of pregnancy
 * <span style="direction: ltr; font-family: 'Times New Roman'; font-size: 16px; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0px; unicode-bidi: embed; vertical-align: middle;">Involves taking a sample of the chorionic villi to obtan cells from tissue that was originally from the zygote
 * <span style="direction: ltr; font-family: 'Times New Roman'; font-size: 16px; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0px; unicode-bidi: embed; vertical-align: middle;">Cells will have the same genetic composition as the unborn baby, so a karyotype can be made.

Diagram of chorionic villus sampling




 * <span style="direction: ltr; font-family: 'Times New Roman'; font-size: 21px; font-weight: bold; margin-bottom: 0px; margin-top: 0in; text-decoration: underline; unicode-bidi: embed; vertical-align: middle;">Amniocentesis
 * <span style="direction: ltr; font-family: 'Times New Roman'; font-size: 16px; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0px; unicode-bidi: embed; vertical-align: middle;">Done at 16 weeks of pregnancy
 * <span style="direction: ltr; font-family: 'Times New Roman'; font-size: 16px; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0px; unicode-bidi: embed; vertical-align: middle;">Sample of amniotic fluid is taken, and a culture is made.
 * <span style="direction: ltr; font-family: 'Times New Roman'; font-size: 16px; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0px; unicode-bidi: embed; vertical-align: middle;">When sufficient cells have been obtained, a karyotype can be done to detect chromosomal abnormalities
 * <span style="direction: ltr; font-family: 'Times New Roman'; font-size: 16px; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0px; unicode-bidi: embed; vertical-align: middle;">The dividing cells are photographed, and from the photographs the chromosomes are arranged in homologous pairs
 * <span style="direction: ltr; font-family: 'Times New Roman'; font-size: 16px; margin-bottom: 0px; margin-left: 0.375in; margin-top: 0px; unicode-bidi: embed; vertical-align: middle;">Some genetic disorders can be detected this way (e.g. down syndrome)

Diagram of amniocentesis



<span style="color: #008000; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;">(We will complete the rest of this topic in class)

<span style="color: #008000; font-family: Verdana,Geneva,sans-serif; font-size: 12pt;">__**4.3 Theoretical genetics**__

4.3.1: Define //genotype, phenotype, dominant allele, recessive allele, codominant alleles, locus, homozygous, heterozygous, carrier// and //test cross//.

**Genotype:** the alleles of an organism. **Phenotype:** the characteristics of an organism. **Dominant allele:** an allele that has the same effect on the phenotype whether it is present in homozygous or heterozygous state. **Recessive allele:** an allele that only has an effect on the phenotype when present on the homozygous state. **Codominant alleles:** pairs of alleles that both affect the phenotype when present in a heterozygote. **Locus:** the particular position on homologous chromosomes of a gene. **Homozygous:** having two identical alleles of a gene. **Heterozygous:** having two different alleles of a gene. **Carrier:** an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele. **Test cross:** testing a suspected heterozygote by crossing it with a known homozygous recessive.

<span style="font-family: Verdana,Geneva,sans-serif; font-size: 12pt;">(We will complete the rest of this topic in class).