Heredity 2012-2013

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)

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 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: 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

Other Types of Inheritance Insert chart here

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

Pedigree A pedigree is a map of a family genetic history

Selective Breeding Genetic Engineering 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 Disadvantages 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 Disadvantage 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