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DNA  Deoxyribonucleic acid  Hereditary material passed from parent to child  In the nucleus in one of two forms:  Chromatin – loose molecule with DNA and proteins.  Chromosomes – compact, X-shaped 2

DNA Structure Made of two long chains that are arranged into a ladder-like structure called a Double Helix. A molecule of DNA is made up of millions of tiny subunits called Nucleotides. Each nucleotide consists of: 1. Phosphate group 2. Pentose sugar 3. Nitrogenous base 3

Nucleotide Structure Phosphate Pentose Sugar Nitrogenous Base 4

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Arrangement of sugar-phosphate backbone  The phosphate and sugar form the backbone  The bases form the “rungs”  There are four types of nitrogenous bases. 6

Arrangement of the bases Each base will only bond with one other specific base. Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Form a base pair. 7

Complementary base pairing and DNA Replication  Because of complementary (matching) base pairing  the order of the bases in one strand determine the order of the bases in the other strand.  DNA is able to make accurate copies of itself 8 If D.N.A. could not copy itself, how could new cells ever be made?

A C T G C A T 9

Genes A gene is a section of DNA that codes for a protein Each gene has a unique sequence of bases. In each cell, only specific genes are “read” to produce certain proteins 10

Chromosomes  Compact and X-shaped (formed when chromatin compacts)  Formed when chromatin coils into compact X-shaped structures  Different organisms have different number of chromosomes  Ex: Humans 46, butterflies 80, cows 60 11

Human Chromosomes  Humans have 46 chromosomes  Chromosomes occur in pairs  Each parent contributes 23 chromosomes  The 23 rd pair is the sex chromosomes:  XX: female  XY: male 12

13 Homologous Chromosomes  Chromosomes of the same type are said to be homologous chromosomes  They have the same length  They have genes controlling the same trait at the same position  One came from the father & the other from the mother  When stained, they show similar banding patterns

14 Homologous Pairs of Chromosomes  The precise location where the gene is found on the chromosome is referred to as the locus  Many genes exist in several variant forms (alleles), but only 2 forms are present in an organism  2 identical alleles for a specific gene on both homologs (homozygous for the trait)  2 different alleles for a specific gene on both homologs (heterozygous for the trait)  A dominant allele is expressed phenotypically in the heterozygote and the homozygote  A recessive allele is only expressed phenotypically in the homozygote

Dominant vs Recessive Alleles 15  Lack of pigment deposition in the human body is an abnormal recessive trait called ''albinism.''  Using A to represent the dominant (pigment- producing) allele and a to represent the recessive (albino) allele, we can describe the three genotypes and two phenotypes that are possible:

16 Punnett Square Table listing all possible genotypes resulting from a cross  All possible sperm genotypes are lined up on one side  All possible egg genotypes are lined up on the other side  Every possible zygote genotypes are placed within the squares

17 Punnett Square Showing Earlobe Inheritance Patterns

Sickle cell frequency  High frequency of heterozygotes  1 in 5 in Central Africans = H b H s  unusual for allele with severe detrimental effects in homozygotes 1 in 100 = H s H s usually die before reproductive age Why is the H s allele maintained at such high levels in African populations? Suggests some selective advantage of being heterozygous…

Malaria Single-celled eukaryote parasite (Plasmodium) spends part of its life cycle in red blood cells 1 2 3

Heterozygote Advantage  In tropical Africa, where malaria is common:  homozygous dominant (normal) die of malaria: H b H b  homozygous recessive die of sickle cell anemia: H s H s  heterozygote carriers are relatively free of both: H b H s survive more, more common in population Hypothesis: In malaria-infected cells, the O 2 level is lowered enough to cause sickling which kills the cell & destroys the parasite. Hypothesis: In malaria-infected cells, the O 2 level is lowered enough to cause sickling which kills the cell & destroys the parasite. Frequency of sickle cell allele & distribution of malaria

21 Human Genetic Disorders Autosome - Any chromosome other than a sex chromosome Genetic disorders caused by genes on autosomes are called autosomal disorders  Some genetic disorders are autosomal dominant 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 An individual with AA does NOT have disorder An individual with Aa does NOT have disorder, but is a carrier An individual with aa DOES have the disorder

22 Autosomal Recessive Pedigree Chart Look for:  Skips in generation  Unaffected parents can have affected children  Affected person must be homozygous  Males and females affected equally

23 Autosomal Dominant Pedigree Chart Look for:  Trait in every generation  Once leaves the pedigree does not return  Every person with the trait must have a parent with the trait  Males and females equally affected

Sex linked recessive

Incomplete dominance

27 Co-dominance 2 alleles are present in the genotype and both are fully observed in the phenotype ABO blood types The alleles:  I A = A antigen on red cells, anti-B antibody in plasma  I B = B antigen on red cells, anti-A antibody in plasma  I = Neither A nor B antigens, both anti-A & anti-B antibodies Phenotype (Blood Type) Genotype A (actually AA or AO) I A I A or I A i B (actually BB or BO) I B I B or I B i AB IAIBIAIB O (actually OO) ii

28 Inheritance of Blood Type

29 Polygenic Inheritance Occurs when a trait is governed by two or more genes having different alleles Each dominant allele has a quantitative effect on the phenotype These effects are additive Result in continuous variation of phenotypes

30 Height in Human Beings

31 Frequency Distributions in Polygenic Inheritance