Heredity( · • Heredity is the passing of traits from parent to offspring. • Generally, genes...
Transcript of Heredity( · • Heredity is the passing of traits from parent to offspring. • Generally, genes...
Heredity
8th Grade
What do you think?
• What do you think the Father looked like? • Orange with 8ger stripes • How do you Know? • The baby ki>en has orange and 8ger stripes
DNA
• A cell uses a code in its hereditary material. The code is a chemical called deoxyribonucleic acid, or DNA
• It contains information for an organism’s growth and function.
• DNA is stored in cells that have a nucleus. • When a cell divides, the DNA code is copied
and passed to the new cells.
• In this way, new cells receive the same coded information that was in the original cell.
• .
• In a DNA model, each side of the ladder is made up of sugar-phosphate molecules
• The rungs of the ladder are made up of other molecules called nitrogen bases.
• Most of your characteristics, such as the color of your hair, your height, and even how things taste to you, depend on the kinds of proteins your cells make.
• DNA in your cells stores the instructions for making these proteins.
• Proteins build cells and tissues or work as enzymes.
• Proteins are made of chains of hundreds or thousands of amino acids.
• Changing the order of the amino acids makes a different protein.
• The instructions for making a specific protein are found in a gene which is a section of DNA on a chromosome.
• Each chromosome contains hundreds of genes.
• Each chromosome pair has the same genes.
• The genes are lined up in the same order on both chromosomes.
• In many-celled organisms like you, each cell uses only some of the thousands of genes that it has to make proteins.
• Each cell uses only the genes that direct the making of proteins that it needs.
• For example, muscle proteins are made in muscle cells but not in nerve cells.
• If DNA is not copied exactly, the proteins made from the instructions might not be made correctly.
• These mistakes, called mutations, are any permanent change in the DNA sequence of a gene or chromosome of a cell
• Outside factors such as X rays, sunlight, and some chemicals have been known to cause mutations.
3 types of Muta8ons
• Not all mutations are harmful. They might be helpful or have no effect on an organism.
• A muta8on is harmful if it reduces an organism’s chance for survival and reproduc,on.
• Whether or not a muta8on is harmful depends partly on the organism’s environment. • For example, a white lemur may not survive in the wild, but the muta8on has no effect on its ability to survive in a zoo.
• Helpful muta8ons, on the other hand, improve an organism’s chances for survival and reproduc8on.
• An8bio8c resistance in bacteria is an example.
• An8bio8cs are chemicals that kill bacteria. Gene muta8ons have enabled some kinds of bacteria to become resistant to certain an8bio8cs—that is, the an8bio8cs do not kill the bacteria that have the muta8ons.
• The muta8ons have improved the bacteria’s ability to survive and reproduce.
• If the mutation occurs in a body cell, it might or might not be life threatening to the organism.
• If a mutation occurs in a sex cell, then all the cells that are formed from that sex cell will have that mutation.
• Mutations add variety to a species when the organism reproduces
• Genes control the traits you inherit
• Without correctly coded proteins, an organism can’t grow, repair, or maintain itself.
• A change in a gene or chromosome can change the traits of an organism.
• If three copies of chromosome 21 are produced in the fertilized human egg, Down’s syndrome results. • Individuals with Down’s syndrome can be short,
exhibit learning disabilities, and have heart problems.
• Eye color, nose shape, and many other physical features are some of the traits that are inherited from parents.
• An organism is a collection of traits, all inherited from its parents
• Heredity is the passing of traits from parent to offspring.
• Generally, genes on chromosomes control an organism’s form and function.
• The different forms of a trait that a gene may have are called alleles
• When a pair of chromosomes separates during meiosis, alleles for each trait also separate into different sex cells.
• Every sex cell has one allele for each trait.
• The study of how traits are inherited through the interactions of alleles is the science of genetics
Mendel Ponders (not in notes lets just think about it)
• A scien8st by the name of Mendel no8ced differences about pea plants.
• What differences do you think pea plants could have?
• He no8ced some were tall, some short, some produced yellow seeds, some produced green seeds.
• These are call traits or characteris8cs.
Mendel
• Gregor Mendel began experimenting with garden peas in 1856.
• Mendel made careful use of scientific methods, which resulted in the first recorded study of how traits pass from one generation to the next
• Mendel was the first to trace one trait through several generations.
• He was also the first to use the mathematics of probability to explain heredity.
• Each time Mendel studied a trait, he crossed two plants with different expressions of the trait and found that the new plants all looked like one of the two parents
• He called these new plants hybrids because they received different genetic information, or different alleles, for a trait from each parent
• An organism that always produces the same traits generation after generation is called a purebred.
• Tall plants that always produce seeds that produce tall plants are purebred for the trait of tall height.
•
First the Basics
• The flower’s petals surround the pis8l and the stamens.
• The pis,l produces female sex cells, or eggs. • The stamens produce pollen, which contains the male sex cells, or sperm.
• A new organism begins to form when egg and sperm join in the process called fer,liza,on.
• Before fer8liza8on can happen in pea plants, pollen must reach the pis8l of a pea flower through pollina,on.
• Pea plants are usually self-‐pollina,ng, meaning pollen from a flower lands on the pis8l of the same flower
• Mendel developed a method by which he cross-‐pollinated, or “crossed,” pea plants.
• To cross two plants, he removed pollen from a flower on one Plant. He then brushed the pollen onto a flower on a second plant.
Meet the Parents
• What are their characteris8cs? • One’s short; One’s tall
F1 -‐Genera8on
• What do you no8ce about the first genera8on compared to the P genera8on?
• They are all tall?
• When the plants in the F1 genera8on were full-‐grown, Mendel allowed them to self-‐pollinate.
• What do you no8ce?
• In all of Mendel’s crosses, only one form of the trait appeared in the F1 genera,on.
• However, in the F2 genera,on, the “lost” form of the trait always reappeared in about one fourth of the plants.
• In his experiments, Mendel used pollen from the flowers of purebred tall plants to pollinate by hand the flowers of purebred short plants.
• This process is called cross-pollination
• He found that tall plants crossed with short plants produced seed that produced all tall plants.
Dominant and Recessive Alleles
• Mendel reasoned that individual factors, or sets of gene8c "informa8on," must control the inheritance or traits in Peas.
• The factors that control each trait exist in pairs. The female parent contributes one factor, while the male parent contributes the other factor.
• One factor in a pair can mask, or hide, the other factor. The tallness factor, for example, masked the shortness factor.
• Mendel called the tall form the dominant factor because it dominated, or covered up, the short form.
• He called the form that seemed to disappear the recessive factor.
Genes and Alleles
• The word gene is used for the factors that control a trait.
• Alleles (uh LEELZ) are the different forms of a gene.
• The gene that controls stem height in peas, for example, has one allele for tall stems and one allele for short stems.
• Each pea plant inherits two alleles from its parents-‐one allele from the egg and the other from the sperm.
• A pea plant may inherit two alleles for tall stems, two alleles for short stems, or one of each.
• A dominant allele is one whose trait always shows up in the organism when the allele is present.
• A recessive allele is hidden whenever the dominant allele is present. A trait controlled by a recessive allele will only show up if the organism does not have the dominant allele.
• Many human genetic disorders, such as cystic fibrosis, are caused by recessive genes.
• Some recessive genes are the result of a mutation within the gene.
• Such genetic disorders occur when both parents have a recessive allele responsible for this disorder.
• Because the parents are heterozygous, they don’t show any symptoms.
Lets look at some allele’s
• Gene8cists use a capital le>er to represent a dominant allele and a lowercase version of the same le>er for the recessive allele.
• Probability is a branch of mathematics that helps you predict the chance that something will happen.
• Mendle studied almost 30,000 pea plants over a period of eight years.
• A handy tool used to predict results in Mendelian genetics is the Punnett square.
• In a Punnett square, letters represent dominant and recessive alleles
• An uppercase letter stands for a dominant allele
• A lowercase letter stands for a recessive allele
• They show the genotype, or genetic makeup, of an organism.
• The way an organism looks and behaves as a result of its genotype is its phenotype
Examples
• Most cells in your body have two alleles for every trait.
• These alleles are located on chromosomes within the nucleus of cells.
• An organism with two alleles that are the same is called homozygous – Ex= TT or >
• An organism that has two different alleles for a trait is called heterozygous – Ex= Tt
• Which is heterozygous? • Which is homozygous?
Which is Heterozy? Which is Homozy?
Mul8ple Alleles
• Many traits are controlled by more than two alleles.
• A trait that is controlled by more than two alleles is said to be controlled by multiple alleles.
• Traits controlled by multiple alleles produce more than three phenotypes of that trait.
• Blood type in humans is an example of multiple alleles that produce only four phenotypes
• The alleles for blood types are called A, B, and O.
Blood Type
• AB= AB • A= AA or AO • B=BB or BO • O= OO
• In addi8on to the A and B an8gens, there is a third an8gen called the Rh factor, which can be either present (+) or absent ( – ). In general, Rh nega8ve blood is given to Rh-‐nega8ve pa8ents, and Rh posi8ve blood or Rh nega8ve blood may be given to Rh posi8ve pa8ents.
• The universal red cell donor has Type O nega8ve blood type.
• The universal plasma donor has Type AB blood type.
WWW.redcrsossblood.org
• Blood Types and the Popula,on • O posi8ve is the most common blood type. Not all ethnic groups have the same mix of these blood types. Hispanic people, for example, have a rela8vely high number of O’s, while Asian people have a rela8vely high number of B’s.
WWW.redcrsossblood.org
The mix of the different blood types in the U.S. popula8on is:
WWW.redcrsossblood.org
• Polygenic inheritance occurs when a group of gene pairs acts together to produce a trait
• The effects of many alleles produces a wide variety of phenotypes.
• Your height and the color of your eyes and skin are just some of the many human traits controlled by polygenic inheritance.
• It is estimated that three to six gene pairs control your skin color.
• The environment also plays an important role in the expression of traits controlled by polygenic inheritance
Gender and Alleles
• Each egg produced by a female normally contains one X chromosome.
• Males produce sperm that normally have either an X or a Y chromosome.
• When a sperm with an X chromosome fertilizes an egg, the offspring is a female, XX.
• A male offspring, XY is the result of a Y-containing sperm fertilizing an egg.
• An allele inherited on a sex chromosome is called a sex-linked gene.
• Color blindness is a sex-linked disorder in which people cannot distinguish between certain colors, particularly red and green.
• This trait is a recessive allele on the X chromosome.
• Because males have only one X chromosome, a male with this allele on his X chromosome is color-blind.
• A color-blind female occurs only when both of her X chromosomes have the allele for this trait.