The Inheritance of Physical Traits and Gregor Mendel The Inheritance of Physical Traits and Gregor Mendel. “Father of Genetics” 1822 - 1884

Who was Gregor Mendel? Once upon a time (1860's), in an Austrian monastery, there lived a monk named Gregor Mendel. Monks had a lot of time on there hands and Mendel spent his time cross pollinating pea plants. As he did this over & over & over & over again, he noticed some patterns to the inheritance of traits from one set of pea plants to the next. By carefully analyzing his pea plant numbers (he was really good at mathematics), he discovered three laws of inheritance.

Mendel studied the patterns of how physical traits passed from one generation to the next using peas

Mendel Studied The Inheritance Patterns of These Following Physical Traits in Peas Seed (pea) shape Round/Wrinkled Seed Color Yellow / Green Seed Coat Color Gray / White Pod Shape Smooth/Constricted Pod Color Green / Yellow Flower Position Axial / Terminal Plant Height Short / Tall Flower Color Purple / White

Wrinkled Peas Round Peas

An Example of How Traits Passed from Parent to first offspring generation

All of the peas of the next (hybrid) generation were smooth All of the peas of the next (hybrid) generation were smooth. Why weren’t there any wrinkled peas? Why weren’t there any sort – of wrinkled/sort of smooth peas?

But when he allowed that first new (hybrid) generation of pea plants to self pollinate………….

9 Round Peas & 3 Wrinkled Peas What Happened ???????????

When Mendel Cross pollinated Pea plant with different traits, only one trait seemed to be “expressed” in that firs generation of offspring. This trait “dominated” the other. Yet, when that first generation of plants were self pollinated, on average, three of every four plants had the dominant trait, and one of every three had the weaker or recessive trait.

After he analyzed his results: Mendel concluded that individual factors (genes) that do not blend with one another control each trait in living things. Each of the traits that Mendel studied was controlled by one gene that occurred in two contrasting forms. These different forms are now referred to as alleles.

Mendel also concluded that some of these factors (genes) are dominant, (smooth peas/purple flowers) whereas others (wrinkled peas/white flowers) are recessive.

Answer me this… Which of the following pairs is not correct? A. kk = hybrid  B. hybrid = heterozygous  C. heterozygous = Hh  D. homozygous = RR

Genetics vocabulary DOMINANT In genetics, a trait that will appear in the offspring if one of the parents contributes it. RECESSIVE -traits that can be carried in genes without appearing in that organism HOMOZYGOUS ("homo" means "the same“) TT, tt HETEROZYGOUS ("hetero" means "other") Tt This is also a HYBRID. GENOTYPE = the genes present in the DNA of an organism.  We will use a pair of letters (ex: Tt or YY or ss, etc.) to represent genotypes for one particular trait. PHENOTYPE = how the trait physically shows-up in the organism. ALLELES = (WARNING - THIS WORD CONFUSES PEOPLE; READ SLOW) alternative forms of the same gene.  Alleles for a trait are located at corresponding positions on homologous chromosomes.

The Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. Offspring that are hybrid for a trait will have only the dominant trait in the phenotype. ANY TIME TWO PARENT ORGANISMS LOOK DIFFERENT FOR A TRAIT, AND ALL THEIR OFFSPRING RESEMBLE ONLY ONE OF THE PARENTS, YOU ARE DEALING WITH MENDEL'S LAW OF DOMINANCE.

The Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.  Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

The Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another

Punnett Square- TT x TT

Breaking the Rules What happens when the rules of dominance and recessiveness are blurred? What happens when there aren’t just two possible alleles for a trait but three? How about four, five, six or 100? http://www.gatorland.com/images/thinking-gator.gif

Incomplete Dominance + = R¹ and R² instead of R and r. Incomplete Dominance: The heterozygote is an intermediate form of both alleles for a trait. Blending is observed. R¹ and R² instead of R and r. R¹R¹ is Red, R¹R² is pink, R²R² is white. + = http://www.allensfarmandfloral.com/Images/132002.jpg http://www.weddingsolutions.com/articles/snapdragon.jpg http://www.naturalabstraction.com/a11_09_2001Neg09CuriosityFarmMed.jpg

Codominance Codominance: Both alleles are expressed equally. Notation is B and W instead of B and b. B for black, W for white BB-black, BW-white and black, WW-white. Ex. Chickens. BW BB WW http://images.google.com/imgres?imgurl=www.bbc.co.uk/insideout/east/series2/images/chicken_rare_breed_150.jpg&imgrefurl=http://www.bbc.co.uk/insideout/east/series2/ http://www.curlytailz.co.uk/black_chicken2.jpg http://www.americanmountedgamebirds.com/Chicken2002/smSpeckledSussex.jpg

Polygenic Traits /Inheritance Polygenic Inheritance: The inheritance pattern of a trait that is controlled by more than one gene. Genes may be on the same chromosome or different chromosomes. Ex. Skin color Very often, the more dominant alleles that are involved, the more the trait is expressed. Ex. 1 dominant allele: light skin, 2: darker, 4: very dark, etc. http://www.patrick.fm/starpics/britney%20spears.jpg http://www.cabrinihigh.com/faculty/gcano/webproject1/kim/j.%20lo%205.jpg http://www.georgwa.demon.co.uk/aretha_franklin.htm

Multiple Alleles Multiple Alleles: more than two alleles exist for any one gene or trait. Only two alleles are found in an individual, but there can be many different alleles that exist for that particular trait. Ex. Blood type. A, B, or O are all alleles.

Blood Type & Antigens The A and B antigens will cause an immune response if mixed incorrectly (blood type compatibility) O is the universal blood type because it has no antigens!

Understanding Multiple Alleles: The ABO Blood Group Blood Group Genes: ABO:3 alleles: IA, IB, i IA, IB Show co-dominance (both alleles expressed equally) i is recessive Rh: single gene, 2 alleles: Rh- & Rh+ Rh+ /Rh+ and Rh+/ Rh- is positive Rh-/ Rh- is negative (“I” is for immunoglobin…a protein extract in blood)

The + or – is determined by the Rh factor Ex. A person who is AB-…..has IA and IB from the ABO gene and Rh- and Rh- from the Rh gene

Compare and contrast incomplete dominance and co-dominance Compare and contrast incomplete dominance and co-dominance. Give an example of each. What are 2 examples of traits that follow the polygenic mode of inheritance? What are the 4 blood group genes? What would the phenotype be for someone with the genotype IAIB?

DID YOU KNOW???? In addition to the genes you receive from your parents, the environment can also play a role in an organism’s development!

Environmental Factors External: Temp., light, nutrition, chemicals, etc. Internal: Hormones or age. Baldness in males, horn production in sheep, and vibrant feather coloring in birds are all hormone related.

SO HOW DO GENES ACTUALLY GET PASSED ON TO OFFSPRING? REMEMBER…DNA is in genes, genes are on chromosomes, chromosomes are in the nuclei of cells. Let’s now focus on CHROMOSOMES…

Types of Chromosomes: Males: XY Females: XX Sex Chromosomes: 2 chromosomes that determine sex (male or female) Males: XY Females: XX Autosomes: the “rest” of your chromosomes We have 46 Chromosomes! Karyotype = chart of chromosome pairs used to pinpoint unusual chromosome #’s in cells

The Human Karyotype

Sex-Linked Genes: genes carried on the X or Y chromosome Males: XY a disorder on the X or Y will be expressed…even if it’s recessive because males only have one X!

Sex-Linked Inheritance Patterns (Disorders carried on sex chromosomes) Colorblindness Hemophilia Muscular Dystrophy

Autosomal Genes: genes carried on the autosomes These follow the rules of dominance, recessiveness, and codominance

Autosomal Inheritance Patterns (Disorders carried on autosomes) Genetic disorders caused by recessive alleles: Albinism Cystic Fibrosis PKU

Genetic disorders caused by dominant alleles Achondroplasia (dwarfism) Huntington’s disease  Kenadie Jourdin-Bromley, 7 pounds at age 2 with father Court / Primordial Dwarfism

Genetic disorders caused by Codominant alleles: Sickle cell disease

FYI…Characteristics of some autosomal inheritance patterns…… Sickle cell anemia Sickle-shaped red blood cells damage tissue and blood vessels Cystic fibrosis Excess mucus in lungs, digestive tract, and liver Susceptible to infections Huntington’s disease Mental deterioration & uncontrollable movements Usually occurs in middle-age

PKU- Phenylketonuria Inability to break down phenylalanine All newborns are tested for this Untreated PKU can lead to mental retardation and other serious medical problems

Tracking Inheritance Patterns & Disorders… The Human Pedigree A way of showing a family tree that helps us understand diseases and where the dangerous alleles exist within a family.

The Human Pedigree A circle is a female A square is a male Dark color is an affected individual or ½ dark and ½ light is a carrier, or an individual that does not show the phenotype but carries the dangerous allele. Slash is death.