Gregor Mendel’s Discoveries

1. Lecture 9: Genetics Gregor Mendel’s Discoveries

2. Second: The law of independent assortment • Mendel’s experiments that followed the inheritance of flower color or other characteristics focused on only a single characteristic via monohybrid cross التزاوج أحادي الصفة • Mendel also analyzed the inheritance pattern of two traits at the same time via a dihybrid cross التزاوج ثنائي الصفة. For example, he examined plants that differed in both the shape and color of their peas. • He crossed homozygous plants that produced yellow, round seeds (YYRR) with plants that produced green, wrinkled seeds (yyrr). He founds that: • Yellow seeds (Y) was dominant to green seeds (y). • Round seeds (R) was dominant to wrinkled seeds (r)

3. Dihybrid cross التزاوج ثنائي الصفة • It is a mating تزاوجbetween two parent plants different in two characteristics. • The two pairs of alleles segregate independently of each other. • When the F1 plants were self-fertilized, they produced an F2 generation of plants that had all four phenotypic ratios (9:3:3:1) of the two seed characteristics: • 9 plants with yellow, round seeds. • 3 plants with green, round seeds. • 3 plants with yellow, wrinkled seeds. • 1 plants green, wrinkled seeds.

4. Genetic disorders in human • A) Recessive genetic disordersالاعتلالات الوراثية المتنحية • Thousands of genetic disorders اعتلالات وراثية, including disabling الإعاقةor deadly genetic diseases الأمراض الوراثية المُميتة, are inherited as simple recessive traits صفات مُتنحية. • Heterozygotes have a normal phenotype because one “normal” allele produces enough of the required factors (for normal trait). • Thus, individuals who lack the disorder are either homozygous dominant or heterozygous. • Heterozygous member may have no clear phenotypic effects, but is a carrier who may transmit a recessive allele to their offspring. • Two carriers have a 1/4 (25%) chance of having a child with the disorder, 1/2 (50%) chance of a carrier, and 1/4 (25%) free. • Recessive genetic disorders include albinism البهاق, cystic fibrosis التليفالكيسي,Tay-Sachs disease مرض تاي ساكسand sickle cell anemia الأنيمياء المجلية

5. 1- Albinismالبهاق • X-linked recessiveمتنحي مرتبط بكروموسوم اكس • Absence of melanin pigment صبغة الميلانينin the hair, skin and eyes. • Albinism results from inheritance of recessive gene alleles. • Albinism is caused by an alteration of the gene that makes the melaninpigment • Albinism is associated with vision الرؤيةproblems and skin cancer سرطان الجلد . • 2- Cystic Fibrosisالتليف الكيسي • Autosomal recessive متنحي جسدي , gene located in chromosome 7 • It is caused by the presence of mutations in both copies of the gene for the protein Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). • CFTR gene controls chloride ion movement in and out of the cell. • It affects mostly the lungs but also the pancreas, liver and kidneys. • Without treatment, affected children die before five, but with treatment can live between 37 and 50years.

6. Cystic fibrosis is inherited in the autosomal recessive pattern

7. 3- Tay-Sachs diseaseمرض تاي ساكس أو البله المميت • Autosomal recessive متنحي جسدي • Tay–Sachs results from mutations in the HEXA gene on chromosome 15 • Mutation of HEXA gene leads to accumulate lipids in the brain's nerve cells leading to the death of the cells. • The symptoms الأعراضbegin with seizures ,نوبة عصبية blindness عمى, and mental and physical disabilities إعاقة عقلية وجسدية six months after birth and usually results in death by the age of four. • 4- Sickle-cell anemiaالأنيمياء المجلية • Autosomal recessive متنحي جسدي • Sickle cell anemia results from mutations in the HBB gene هيموجلوبين بيتاon chromosome 11 • It is caused by the substitution استبدالof a single amino acid in hemoglobin. • People with sickle-cell anemia have abnormal hemoglobin in their red blood cells. • Hemoglobin is a protein that carries oxygen throughout the body. • Doctors can use regular blood transfusions نقل الدمto prevent brain damage and new drugs to prevent or treat other problems.

9. B) Dominant genetic disordersالاعتلالات الوراثية السائدة • 1- Achondroplasiaالقزمية • Autosomal dominantسائد جسدي • Achondroplasia is caused by a mutation in fibroblast growth factor receptor 3(FGFR3) geneon chromosome 4 • People with achondroplasia have short stature قصر القامة, with an average adult height of 131 centimeters for males and 123centimeters for females. • Heterozygous individuals have the dwarf قزمphenotype. • Lethal dominant alleles الأليلات السائدة المميتةare much less common أقل شيوعاًthan lethal recessives, because if a lethal dominant kills an offspring before it can mature and reproduce, the allele will not be passed on future generations أجيال المستقبل .

10. 2- Huntington’s diseaseمرض هنتنغتون • Autosomal dominantسائد جسدي • Huntington’s disease is caused by a mutation in HD gene. • HD gene is located in chromosome 4 • The dominant lethal allele has no obvious phenotypic effect until an individual is about 35 to 45 years old. • Huntington's disease is an inherited condition that damages nerve cells in the brain. • Huntington's disease results in an losing of both mental and physical control.

11. Summary of the human genetic disorders • Dominant traitالصفة السائدة : Describes a trait that is expressed when only one copy of the allele is present in the genotype. • Recessive trait الصفة المتنحية: Describes a trait that is masked by the dominant trait and is only expressed in the homozygous condition. • Autosome الكروموسوم الجسدي: Any chromosome that is not a sex chromosome. • Humans have 22pairs of autosomes and one pair of sex chromosomes (the X and Y). • Genetic disorders caused by genes on autosomes are called autosomal disorders. • Some genetic disorders are autosomal dominant سائد جسدي • An individual with AA has the disorder • An individual with Aa has the disorder • An individual with aa does not have disorder • Other genetic disorders are autosomal recessive متنحي جسدي • An individual with AA does not have disorder • An individual with Aa does not have disorder, but is a carrier حامل • An individual with aa has the disorder