History of genetics

What is genetics? Genetics is the science of heredity Basics of Biology founded by genetics: Matter is composed of atoms Cells are fundamental units of living organisms Nuclei somehow serve as the “life force” of cells Chromosomes housed within nuclei somehow plan an important role in heredity

Eugenics Applying the knowledge of genetics for the improvement of human existence

Gregor Mendel demonstrated clear quantitative patterns underlying inheritance and developed a theory involving heredity factors that explained these patterns

Mendel’s research was ignored until 1900 when two other scientists partially duplicated and then cited him Carl Correns Hugo de Vries William Batesman

How Genetics Began 10.2 Mendelian Genetics Sexual Reproduction and Genetics  Mendel performed cross- pollination in pea plants.  Mendel followed various traits in the pea plants he bred. Chapter 10

 The parent generation is also known as the P generation. Sexual Reproduction and Genetics 10.2 Mendelian Genetics Chapter 10

Sexual Reproduction and Genetics  The second filial (F 2 ) generation is the offspring from the F 1 cross Mendelian Genetics Chapter 10  The offspring of this P cross are called the first filial (F 1 ) generation.

 Mendel studied seven different traits. Sexual Reproduction and Genetics  Seed or pea color  Flower color  Seed pod color  Seed shape or texture  Seed pod shape  Stem length  Flower position 10.2 Mendelian Genetics Chapter 10

Gene: the unit that determines a specific trait

Allele: the different forms of a gene for a particular trait Organisms receive one allele from each parent

We use letters to represent the different forms (alleles) of a trait Example: B is an allele of b T is allele of t

Sexual Reproduction and Genetics  Homozygous: An organism with two of the same alleles for a particular trait  Ex. TT = tall tt = short RR = round rr = wrinkled 10.2 Mendelian Genetics Chapter 10

 Heterozygous: An organism with two different alleles for a particular trait  Ex. Tt = tall Rr = round This is also called a hybrid organism

Genotype and Phenotype Sexual Reproduction and Genetics  Genotype: An organism’s allele pairs Genetic make up of an organism TT → genotype Tt → genotype tt → genotype 10.2 Mendelian Genetics Chapter 10

 Phenotype: The observable characteristic or outward expression of an allele pair  TT → phenotype is tall  Tt → phenotype is tall  tt → phenotype is short

Mendel’s Law of Segregation Sexual Reproduction and Genetics  Two alleles for each trait separate during meiosis.  During fertilization, two alleles for that trait unite Mendelian Genetics Chapter 10

Dominant vs. Recessive One trait dominates or hides the other trait in a heterozygous organism Use a capital letter to represent the dominant trait and a lower case letter to represent the recessive (hidden) trait

Ex. T = tall and t = short T is dominant so it will be expressed if it is present

Other examples: R = round, r = wrinkled B = brown, b = blue

So…Eye Color? BB = ? bb = ? Bb = ?

Monohybrid Cross Sexual Reproduction and Genetics  A cross that involves hybrids for a single trait is called a monohybrid cross Mendelian Genetics Chapter 10

Sexual Reproduction and Genetics Law of Independent Assortm ent  Random distribution of alleles occurs during gamete formation  Genes on separate chromosomes sort independently during meiosis.  Each allele combination is equally likely to occur Mendelian Genetics Chapter 10

Exception: Some genes are considered “linked” and almost always travel together during meiosis

Sexual Reproduction and Genetics Punnett Square— Dihybrid Cross  Four types of alleles from the male gametes and four types of alleles from the female gametes can be produced.  The resulting phenotypic ratio is 9:3:3: Mendelian Genetics—Extra Info Chapter 10

Sexual Reproduction and Genetics Punnett Squares  Predict the possible offspring of a cross between two known genotypes 10.2 Mendelian Genetics Chapter 10

Genetic Recombination:  The new combination of genes produced by crossing over and independent assortment 10.3 Gene Linkage and Polyploidy Sexual Reproduction and Genetics Chapter 10

Polyploidy: cells having one or more extra sets of all chromosomes in an organism Ex. Oats have 6n, sugar cane have 8n— instead of 2n If it occurs in human cells, it is lethal

Often produces an increase in size of vegetation

Dominant and Recessive Which of the resulting offspring are: –Homozygous Dominant? –Heterozygous? –Homozygous Recessive?

Genotype and Phenotype Genotype – An organisms allele pairs. Phenotype – the observable outward characteristics of an organism.

Monohybrid Crosses Shows a cross of a single trait In this case, we are crossing two peas. Since we are only focusing on one trait (color), this is a monohybrid cross.

Dihybrid Cross A cross that shows inheritance patterns of two or more traits. In this case, we are looking at a cross between two peas and observing two characteristics (color and shape)

Sex-Linked Traits Genes that are carried by either sex chromosome are said to be sex linked. Men normally have an X and a Y combination of sex chromosomes, while women have two X's. Since only men inherit Y chromosomes, they are the only ones to inherit Y-linked traits. Men and women can get the X-linked ones since both inherit X chromosomes

Sex-Linked Trait Examples Two human X linked traits: –Red color blindness –Hemophelia (inability for blood to clot) Two human Y linked trait examples: –Male pattern baldness –Muscular dystrophy

BASIC PATTERNS OF HUMAN INHERITANCE Recessive Genetic Disorders: a recessive trait is expressed when the individual is homozygous recessive for the trait. This is true for other species not just humans

Carriers: Individuals with at least one dominant allele who do NOT express the disorder Ex. If rr represents a genetic disorder, a person with the genotype Rr is a carrier for the disorder, but does not express it him/herself

Complex Inheritance and Human Heredity Cystic Fibrosis  Affects the mucus-producing glands, digestive enzymes, and sweat glands  Chloride ions are not absorbed into the cells of a person with cystic fibrosis but are excreted in the sweat.  Without sufficient chloride ions in the cells, a thick mucus is secreted Basic Patterns of Human Inheritance Chapter 11

Complex Inheritance and Human Heredity Albinism  Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes  White hair  Very pale skin  Pink pupils 11.1 Basic Patterns of Human Inheritance Chapter 11

Complex Inheritance and Human Heredity Tay-Sachs Disease  Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides  Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration Basic Patterns of Human Inheritance Chapter 11

Complex Inheritance and Human Heredity Galactosemia  Recessive genetic disorder characterized by the inability of the body to digest galactose Basic Patterns of Human Inheritance Chapter 11

11.1 Basic Patterns of Human Inheritance Complex Inheritance and Human Heredity Chapter 11 Recessive Genetic Disorders

Dominant Gene Disorders: Organisms who have the disorder are homozygous dominant or heterozygous dominant for the genetic disorder

Complex Inheritance and Human Heredity Dominant Genetic Disorders  Huntington’s disease affects the nervous system Basic Patterns of Human Inheritance Chapter 11

 Achondroplasia is a genetic condition that causes small body size and limbs that are comparatively short.

Complex Inheritance and Human Heredity 11.1 Basic Patterns of Human Inheritance Chapter 11

Complex Inheritance and Human Heredity Pedigrees  A diagram that traces the inheritance of a particular trait through several generations 11.1 Basic Patterns of Human Inheritance Chapter 11

Complex Inheritance and Human Heredity Inferring Genotypes  Knowing physical traits can determine what genes an individual is most likely to have. Predicting Disorders  Record keeping helps scientists use pedigree analysis to study inheritance patterns, determine phenotypes, and genotypes Basic Patterns of Human Inheritance Chapter 11

11.2 Complex Patterns of Inheritance Complex Inheritance and Human Heredity Incomplete Dominance  The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes. Chapter 11

INCOMPLETE DOMINANCE

Complex Inheritance and Human Heredity Codominance  Both alleles are expressed in the heterozygous condition Complex Patterns of Inheritance Chapter 11

Complex Inheritance and Human Heredity Sickle-cell Disease  Changes in hemoglobin cause red blood cells to change to a sickle shape.  People who are heterozygous for the trait have both normal and sickle-shaped cells. Sickle cell Normal red blood cell 7766x 11.2 Complex Patterns of Inheritance Chapter 11

Multiple Alleles: genotype/phenotype that is determined by more than two alleles Ex. Blood type is determined by 3 alleles A, B, O 3 genes produce 4 blood types

I A = type A I B = type B i = type O I A and I B are codominant i is recessive to I A and I B

Complex Inheritance and Human Heredity Multiple Alleles  Blood groups in humans  ABO blood groups have three forms of alleles Complex Patterns of Inheritance Chapter 11

AB is a universal recipient OO is a universal donor

Complex Inheritance and Human Heredity Coat Color of Rabbits  Multiple alleles can demonstrate a hierarchy of dominance.  In rabbits, four alleles code for coat color: C, c ch, c h, and c Complex Patterns of Inheritance Chapter 11

Complex Inheritance and Human Heredity Coat Color of Rabbits Light gray Dark gray Himalayan Albino Chinchilla 11.2 Complex Patterns of Inheritance Chapter 11

Complex Inheritance and Human Heredity Epistasis  Variety of fur color is the result of one allele hiding the effects of another allele. No dark pigment present in fur Dark pigment present in fur eebb eeB_ E_bbE_B_ 11.2 Complex Patterns of Inheritance Chapter 11

Two sets of alleles control fur color E: dark pigment, B darkness of pigment EEBB: eebb:

Humans have 23 pairs of chromosomes 22 pairs of autosomes 1 pair of sex chromosomes

Complex Inheritance and Human Heredity Sex Determination  Sex chromosomes determine an individual’s gender Complex Patterns of Inheritance Chapter 11

XX = female genotype XY = male genotype It is the male that determines the gender of the offspring

Complex Inheritance and Human Heredity Dosage Compensation  The X chromosome carries a variety of genes that are necessary for the development of both females and males.  The Y chromosome mainly has genes that relate to the development of male characteristics Complex Patterns of Inheritance Chapter 11

The X chromosome carries some traits that are not carried on the Y chromosome Because males only have one X chromosome, they will inherit any X-chromosome trait; recessive or not

 Chromosome inactivation: because females have 2 X chromosomes, one of them stops working so the organism will not have too many X related chromosomes Barr bodies: stain darker than activated chromosomes

Complex Inheritance and Human Heredity Sex-Linked Traits  Genes located on the X chromosome  Red-green color blindness  Recessive trait on the X chromosome  10% of all males (only 1 out of 100 females) 11.2 Complex Patterns of Inheritance Chapter 11

PUNNETT SQUARE FOR SEX-LINKED GENE IN HUMANS

Always use X and Y for genotype and put the letter for the disorder as a superscript Female normal: X C X C or X C X c (carrier) Male colorblind: X c Y Male normal: X C Y

OTHER SEX LINKED GENE DISORDERS Hemophilia: Organisms cannot produce clotting protein in blood Recessive on the X chromosome Approximately 1 in 10,000 males (1 in 1,000,000 females)

Muscular Dystrophy: sudden deterioration of muscles Recessive on the X chromosome 1 in 3,000 males

Complex Inheritance and Human Heredity Polygenic Traits  Polygenic traits arise from the interaction of multiple pairs of genes Complex Patterns of Inheritance Chapter 11

Complex Inheritance and Human Heredity Environmental Influences  Environmental factors  Diet and exercise  Sunlight and water  Temperature 11.2 Complex Patterns of Inheritance Chapter 11