Heredity

Your Physical Appearance Heredity is the passing of traits from parents to an offspring. Gregor Mendel was the first scientist to successfully study inheritance He is the “Father of Genetics”

Why Pea Plants? Mendel use Garden Pea Plants for his research because: –They grow quickly –They naturally self-pollinate

Mendel’s Success Mendel was successful with his pea plant research because: – he studied one trait at a time! (independent variable) –He had studied statistics *A trait is a distinct phenotypic characteristic that may be inherited

Pea Plant Traits Flower Color Flower Position Seed Color Seed Shape Pod Shape Pod Color Plant Height

The Experiment Mendel began by taking pure trait plants and cross-pollinating them He did this by hand, not with bees!

The Experiment Part I (Example 1) Plant height Mendel crossed a Tall parent plant with a short parent plant: Tall x short = All Tall TT x tt = Tt parent 1 x parent 1 = First Filial (F1) Both parent plants were true-breeding: They always produced the same type of offspring.

The Experiment Part I (Example 2) Flower Color Mendel crossed a Purple parent plant with a white parent plant: Purple x white = All Purple PP x pp = Pp parent 1 x parent 1 = First Filial (F1)

The Experiment Part II He wondered why one trait disappeared when he crossed the two pure (true- breeding) plants He decided to allow the new F1 plants to naturally self-pollinate and here is what he found……..

Example 1- Plant Height F1 Tall plants self-pollinate and produce: 75% Tall Plants 25% short plants

Example 2 - Flower Color F1 Purple Flower color plants self-pollinate and produce: 75% Purple flowers 25% white flowers

Mendel’s Conclusion The Principle of Dominance and Recessiveness states that one trait is more likely to occur than the other. –Dominant is a trait that is most likely to occur –Recessive is a trait that is usually hidden in the first generation, but may reappear later

Probability The chance or possibility that a certain outcome will occur. Usually written as: –Fractions –Decimals

Let’s Learn a New Language.. Genotype- the genetic make-up of an organism (TT, Tt, tt) Phenotype- the physical appearance of an organim (Tall, short, Purple, white) Dominant- more likely to occur (The tall plants or the purple flowers) Recessive- less likely to occur (The short plants or the white flowers)

Let’s Learn a New Language.. Homozygous- when both alleles are the SAME –Homozygous Dominant: TT, PP, WW –Homozygous Recessive: tt, pp, ww Heterozygous- when each allele is DIFFERENT –Tt, Pp, Ww

Let’s Learn a New Language.. An Allele is an alternate form of a gene; one part of a pair A Gene is composed of two alleles, one from each parent Allele + Allele = Gene T (mom) + t (dad) = Tt (child)

Punnett Squares Developed by Rudolph Punnett to make genetics easier for us to understand

Genetics Example 1 In garden pea plants, tall plants are dominant (T) and short plants are recessive (t). A pea plant that is homozygous dominant for height is crossed with one that is homozygous recessive for plant height. Draw a Punnett square to represent the problem. What are the possible genotypes? What are the possible phenotypes? What is the probability of each genotype? What is the probability of each phenotype?

Genotypes Phenotypes Probability of genotypes Probability of phenotypes

Genetics Example 2 In garden pea plants, purple flower color (P) is dominant over white flower color (p). A pea plant that is homozygous recesive for flower color is crossed with one that is heterozygous for flower color. Draw a Punnett square to represent the problem. What are the possible genotypes? What are the possible phenotypes? What is the probability of each genotype? What is the probability of each phenotype?

Genotypes Phenotypes Probability of genotypes Probability of phenotypes

Genetics Examples In garden pea plants, yellow seeds (Y) are dominant and green seeds (y) are recessive. What offspring would result if two heterozygous plants were crossed? Draw a Punnett square to represent the problem. What are the possible genotypes? What are the possible phenotypes? What is the probability of each genotype? What is the probability of each phenotype?

Genotypes Phenotypes Probability of genotypes Probability of phenotypes

More Genetics

Incomplete Dominance Sometimes one trait is not completely dominant over the other –The same letter allele is used –Red x White = Pink RR x R’R’ = RR’ This results with a combined genotype –Snap dragons

Codominance Sometimes both traits are equally dominant –Different letter alleles are used –Black x White = Checkered BB x WW = BW This results in both traits being expressed –Checkered Chickens

Alternate forms of Genetics Gregor Mendel studied simple genetic inheritance: –Offspring were either dominant or recessive But not all traits are simple!!

Thomas Hunt Morgan Studied Fruit Flies Discovered –Gender inheritance –Other traits associated with gender

Gender Gender is always determined by the male

Sex-linked Traits Some traits are only located on the “X” chromosome Since Males only have one “x” chromosome, they are more likely to show the trait than a female with two “x” chromosomes

Sex-linked Traits Colorblindness Hemophilia Muscular dystrophy

Colorblindness Charts

Other Types of Inheritance Name:Description:Examples: Multiple Allele Traits Traits can be determined by 3 or more alleles Fur Color in Rabbits, Blood Type in Humans Polygenetic Traits Traits are determined by more than one GENE Human height, Human eye color **Most Traits that can have a “range”

Meiosis Meiosis is the formation of gametes in sexually reproducing organisms –Sperm (male) –Egg (female)

Benefits of Meiosis Forms gametes (sex cells) Allows for genetic variation Reduces the number of chromosomes by half –Human body cells 46 chromosome –Human sex cells 23 chromosome Allows the chromosome number of any organism to remain consistent

Haploid vs Diploid Haploid cells contain 1 set of chromosomes (23 total in humans) –Sperm –Egg Diploid cells contain 2 sets of chromosomes (46 total in humans) –One set from mom –One set from dad

Meiosis

Male vs Female Meiosis

Karyotype A karyotype is a picture of someone’s chromosomes

Male Karyotype

Female Karyotype

What do you think?

Genetic Disorders Genetic disorders are caused by mutations in DNA –Mutations that occur spontaneously –Congenital ( people are born with them) –Unable to cure –Can occur in children even when parents do not have them (recessive traits)

Genetic Counselors Genetic counselors are available for people who fear passing genetic disorders to their offspring –Cystic fibrosis –Sickle-cell anemia –Huntington’s disease –Down’s syndrome –Many others They begin with making a pedigree to observe the family history of traits

NameDescriptionChromosomeIncidence Among Newborns Autosomal Recessive Disorders Cystic fibrosis Mucus in the lungs & digestive tract is thick, making breathing & digestion difficult 7One in 2,500 Caucasians Tay-Sachs disease Neurological & psychomotor difficulties develop early, followed by blindness, seizures and death 15 One in 3,600 eastern European Jews Autosomal Dominant Disorders Huntington disease Minor problems with balance & coordination in middle age that progress toward severe neurological problems, then death 4One in 20,000 Acondroplasia Form of dwarfism where cartilage does not form normally 4One in 15,000-40,000 Incomplete Dominance Sickle-cell disease Poor circulation, anemia, internal bleeding, due to sickle-shaped blood cells 11One in 500 African Americans X-Linked Recessive Hemophilia A Likely to bleed freely, often internally, due to the lack of a blood clotting factor XOne in 15,000 live male births Duchenne muscular dystrophyMuscle weakness develops early & progresses until death XOne in 5,000 live male births

Pedigree A pedigree is a map of a family genetic history

Genetics in Action Selective Breeding Genetic Engineering

Genetics Terminology Purebred organisms result from crossing two organims with similar traits Hybrids are produced when two organisms with different traits are combined

Purebred Advantages –Predictable outcome Example: Dog breeds Lab x Lab = Lab LL x LL = LL Disadvantages –Undesirable traits are possible –A lack of genetic variation will result

Hybrids Advantages –Variety of traits may appear –Can encourage desirable traits to occur Example: kiwi x strawberry = kiwiberry Disadvantage –Unpredictable outcomes are likely

Selective Breeding Selective breeding involves the crossing of organisms with desired traits to maximize their potential –Fruits –Vegetables –Flowers –Livestock –Insulin

Genetic Engineering A faster form of selective breeding Genetic engineering is when genetic information is changed within the DNA of an organism