Chapter 4 Modern GeneticsSection 1Human InheritanceByMr Hamdy Karim
Human Inheritance and Genetic DisordersPolydactylyDown SyndromeHemopheliaProgeriaHypertrichosisSickle Cell Anaemia
Warm-up:Below is an actual photo of a persons full set of chromosomes. Usethe picture below to answer the following questions in your notebook:●How many chromosomes does each human have?●How any chromosomes does the person below have?●What might have caused this extra chromosome? (Hint: It happens during meiosis)●How do you predict this might affect the person?
Human InheritanceReview:●Every living thing (organism) is controlled by its DNA, which istightly bound in strands called chromosomes inside the nucleusof each cell.●Each individual trait (characteristic) of an organism is controlled bya gene which is a part of a chromosome.●Each gene is controlled by two allelles; one from mother, one fromfather.●Alleles are patterns of DNA that tell the body how to make certainamino acids which form proteins.●Proteins control how an organism looks and functions.
Human Inheritance●Some traits are controlled by just one gene, two alleles.A widows peak for example.●Multiple alleles are three or four forms of a gene that codefor a single trait. Our blood type is an example:●Still other traits are controlled by multiple genes. Skin type,eye color, hair color and many others are controlled bymultiple genes.
Sex Chromosomes●Sex Chromosomes are 1 pair of the 23 pairs of chromosomes inthe body.●Sex Chromosomes carry the genes that makes a person maleor female, but also carry genes which determine other traits.
Sex Chromosomes●The Y chromosome (male) is much smaller than theX chromosome.●Because the X is bigger, it carries a lot more genetic informationthan the Y●Sex-Linked Genes have alleles that pass from parent to child ona sex chromosome.
Sex-Linked Genes●A common sex-linked gene is colorblindness.
Is anyone unable to see the image in this circle?If so, you have red-green colorblindness!This is a sex-linked recessive trait.
Sex-Linked Genes●This punnet square shows sex-linked genes for colorblindness.●Only the X chromosome carries the gene, so if a male getsa recessive Xc and a Y, he automatically has the disease.●Females, however, can be carriers of the disorder with onedominant XC and one recessive Xc, but only have the disorder ifshe has both recessive: Xc Xc●A carrier is a person who has one recessive and one dominantallele for the trait.
Environment●Environmental factors also determine how genes are expressed.●A person can have genes to be really tall, but if they do not haveproper nutrition, they will not reach their optimal height.●A person can even have genes which wire the brain to be good atmaking music, but if they never try to play an instrument, they willnever know.●This is why everyone should try everything at least once; you couldend up being really great at anything!
Genetic Disorders●A Genetic Disorder is an abnormal condition that a person inheritsthrough their genes.●Genetic disorders can be caused by either changes in the DNA,or an extra, or a missing chromosome.
Types of Genetic Disorders●Cystic Fibrosis is where the body produces abnormally thick mucusin the lungs.●It is caused by a recessive allele on one chromosome.●The recessive allele is a mutation where strands of DNA are deleted.
Types of Genetic Disorders●Sickle Cell Disease is where a persons blood cells are shapeddifferently.●The sickle shape of blood causes it to clot in vessels and causeblockage and carries less oxygen.●The allele for the disease is codominant with the normal allele.●A person with one recessive and one dominant allele will producehalf normal blood cells, half sickle.●A person with two recessive alleles will produce only sickle cells.Normal RBC Sickle-Cell RBC
Types of Genetic Disorders●Hemophilia prevents blood clotting.●It is a recessive sex-linked disorder, found on the X sex chromosome.●It is dangerous because even small wounds can cause unnecessarybleeding and even death through blood loss.
Types of Genetic Disorders●Down Syndrome is a form of mental retardation and physicalabnormalities.●It is caused by a duplicate 21st chromosome. Instead of two,they have three 21st chromosomes.●This occurs when the chromosomes fail to seperate during meiosis.
Pedigrees●A Pedigree is a chart or “family tree” which maps genetic disordersin a family.
Pedigrees●Below is a sample of a pedigree from a family which carrieshemophilia.
Karyotypes●A Karyotype is a picture of all the chromosomes in a cell.●Modern scientists can take a blood sample from an unborn child toan adult, create a karyotype by seperating chromosomes, and be ableto determine if any genetic disorders are present.●A couple who wishes to have children can receive genetic counsellingwhere a doctor looks at both parents karyotypes to see if anydisorders will pass to offspring.