6 3 Mendel and Heredity The student is

6. 3 Mendel and Heredity The student is expected to: 3 F research and describe the history of biology and contributions of scientists and 6 F predict possible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses and non. Mendelian inheritance TEKS 3 F, 6 F

History of Genetics • Gregor Mendel was an Austrian monk and scientist who was in charge of the monastery garden. Mendel studied garden peas.

6. 3 Mendel and Heredity TEKS 3 F, 6 F KEY CONCEPT Mendel’s research showed that traits are inherited as discrete units.

6. 3 Mendel and Heredity Mendel laid the groundwork for genetics. • Traits are distinguishing characteristics that are inherited. • Genetics is the study of biological inheritance patterns and variation. • Gregor Mendel showed that traits are inherited as discrete units. • Many in Mendel’s day thought traits were blended. TEKS 3 F, 6 F

6. 3 Mendel and Heredity TEKS 3 F, 6 F Mendel’s data revealed patterns of inheritance. • Mendel made three key decisions in his experiments. – use of purebred plants – control over breeding – observation of seven “either-or” traits

Pea plants happened to be a good choice to study because: – They are self-pollinating. – He had different pea plants that were truebreeding. – True-breeding - means that they are homozygous for that trait. – EX. if the plants self-pollinate they produce offspring identical to each other and the parents.

When discussing generations’ traits, we label them as following: • The true-breeding parental generation is called the “P generation”. • The offspring of the two parental plants is called the “F 1 generation”. • A cross between F 1 generation would be called “F 2 generation. ”

6. 3 Mendel and Heredity TEKS 3 F, 6 F • Mendel used pollen to fertilize selected pea plants. – P generation crossed to produce F 1 generation – interrupted the self-pollination process by removing male flower parts Mendel controlled the fertilization of his pea plants by removing the male parts, or stamens. He then fertilized the female part, or pistil, with pollen from a different pea plant.

6. 3 Mendel and Heredity TEKS 3 F, 6 F • Mendel allowed the resulting plants to self-pollinate. – Among the F 1 generation, all plants had purple flowers – F 1 plants are all heterozygous – Among the F 2 generation, some plants had purple flowers and some had white

Original cross (P) Parental Generation (true breeding) F 1 Generation (offspring) Cross pollination F 2 Generation (Cross of F 1 Generations)

Mendel’s Investigations • Mendel saw that when he crossed plants with different versions of the same trait (P generation), the F 1 offspring were NOT blended versions of the parents. • The F 1 plants resembled only one of the parents. Tall x short all tall…

6. 3 Mendel and Heredity • Mendel observed patterns in the first and second generations of his crosses. TEKS 3 F, 6 F

6. 3 Mendel and Heredity TEKS 3 F, 6 F • Mendel drew three important conclusions. – Traits are inherited as discrete units. – Organisms inherit two copies of each gene, one from each parent. – The two copies segregate during gamete formation. – The last two conclusions are called the law of segregation. purple white

Mendel concluded: • 1. Biological inheritance is determined by “factors” that are passed from one generation to the next. • Factors were later defined as “genes”– Mendel discovered all of this without the knowledge of DNA!

Mendel concluded: • In Mendel’s plants, there was one gene for each trait. For example, there was one gene for plant height. – But, there were two versions of this gene: one for a tall plant and one for a short plant.

Mendel concluded: – Alleles: Different versions of the same gene • Remember, genes are used to make proteins. • Each allele contains the DNA that codes for a slightly different version of the same protein • This gives us the different characteristics for each trait

2. Principal of dominance: • Some alleles are dominant and some alleles are recessive. – Recessive alleles are able to be masked – Dominant alleles mask recessive alleles • The trait that was represented in the F 1 generation was the dominant trait.

2. Principal of dominance: • How many alleles do you have for each gene? Two • Where do they come from? One comes from mother and one comes from father.

3. Segregation: • • Observation: After seeing that his F 1 plants looked like only one generation of the P generation plants, Mendel wanted to know what happened to the recessive alleles. Question: Did they disappear?

3. Segregation: • Experiment: Mendel self-pollinated the F 1 plants, or crossed the F 1 plants with each other, to produce the F 2 generation. From his F 1 crosses, Mendel observed: – The versions of the traits coded for by recessive alleles reappeared in the F 2 plants. – The recessive trait was still there!

3. Segregation: – About 25% (or ¼) of the F 2 plants exhibited the recessive version of the trait. In this case the recessive phenotype is short. The dominant phenotype, tall, was found in 75% (or ¾) of the F 2 plants. P generation F 1 generation F 2 generation

Segregation of alleles during meiosis: • When the F 1 plants produce gametes (sex cells) and self-pollinate, the two alleles for the same gene separate from each other so that each gamete carries only one copy of each gene. • Remember, gametes are haploid. In the example, we use “T” to represent the dominant, tall allele and “t” to represent the recessive, short allele.

6. 4 Traits, Genes, and Alleles The student is expected to: 6 A identify components of DNA, and describe how information for specifying the traits of an organism is carried in the DNA and 6 F predict possible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses and non-Mendelian inheritance TEKS 6 A, 6 F

6. 4 Traits, Genes, and Alleles TEKS 6 A, 6 F KEY CONCEPT Genes encode proteins that produce a diverse range of traits.

6. 4 Traits, Genes, and Alleles TEKS 6 A, 6 F The same gene can have many versions. • A gene is a piece of DNA that directs a cell to make a certain protein. • Each gene has a locus, a specific position on a pair of homologous chromosomes.

6. 4 Traits, Genes, and Alleles TEKS 6 A, 6 F • An allele is any alternative form of a gene occurring at a specific locus on a chromosome. – Each parent donates one allele for every gene. – Homozygous describes two alleles that are the same at a specific locus. – Heterozygous describes two alleles that are different at a specific locus.

6. 4 Traits, Genes, and Alleles • Alleles can be represented using letters. – A dominant allele is expressed as a phenotype when at least one allele is dominant. – A recessive allele is expressed as a phenotype only when two copies are present. – Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters. TEKS 6 A, 6 F

6. 4 Traits, Genes, and Alleles TEKS 6 A, 6 F • All of an organisms genetic material is called the Genome • A Genotype refers to the makeup of a specific set of alleles • A Phenotype is the physical expression of a trait

Key Terms in Mendelian Genetics: • Dominant- allele that can mask; represented by capital letters (B, D, F, etc. ) • Recessive- alleles that can be masked; represented by lower case letters (b, d, f, etc. )

Key Terms in Mendelian Genetics: • Phenotype- observable traits (brown eyes, yellow seed pods) • Genotype- actual alleles; describes the genetic characteristics (BB, dd, Ff) Phenotype: brown eyes Genotype: could be BB, or Bb

Key Terms in Mendelian Genetics: • Homozygous (True-Breeding)- having two identical alleles for the same trait (TT, tt); “homo” means same • Heterozygous- having two different alleles from the same trait (Tt); “hetero” means different

6. 4 Traits, Genes, and Alleles TEKS 6 A, 6 F • Both homozygous dominant and heterozygous genotypes yield a dominant phenotype. • Most traits occur in a range and do not follow simple dominant-recessive patterns.

6. 5 Traits and Probability The student is expected to: 3 F research and describe the history of biology and contributions of scientists; 6 F predict possible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses and non-Mendelian inheritance; 6 G recognize the significance of meiosis to sexual reproduction TEKS 3 F, 6 G

6. 5 Traits and Probability TEKS 3 F, 6 G KEY CONCEPT The inheritance of traits follows the rules of probability.

6. 5 Traits and Probability TEKS 3 F, 6 G Punnett squares illustrate genetic crosses. • The Punnett square is a grid system for predicting all possible genotypes resulting from a cross. – The axes represent the possible gametes of each parent. – The boxes show the possible genotypes of the offspring. • The Punnett square yields the ratio of possible genotypes and phenotypes.

6. 5 Traits and Probability TEKS 3 F, 6 G A monohybrid cross involves one trait. • Monohybrid crosses examine the inheritance of only one specific trait. – homozygous dominant-homozygous recessive: all heterozygous

6. 5 Traits and Probability TEKS 3 F, 6 G – heterozygous-heterozygous— 1: 2: 1 homozygous dominant: heterozygous: homozygous recessive; 3: 1 dominant: recessive

6. 5 Traits and Probability TEKS 3 F, 6 G • heterozygous-homozygous recessive— 1: 1 heterozygous: homozygous recessive; 1: 1 dominant: recessive • A testcross is a cross between an organism with an unknown genotype and an organism with the recessive phenotype.

6. 5 Traits and Probability TEKS 3 F, 6 G A dihybrid cross involves two traits. • Mendel’s dihybrid crosses with heterozygous plants yielded a 9: 3: 3: 1 phenotypic ratio. • Mendel’s dihybrid crosses led to his second law, the law of independent assortment. • The law of independent assortment states that allele pairs separate independently of each other during meiosis.

6. 5 Traits and Probability TEKS 3 F, 6 G Heredity patterns can be calculated with probability. • Probability is the likelihood that something will happen. • Probability predicts an average number of occurrences, not an exact number of occurrences. number of ways a specific event can occur • Probability = number of total possible outcomes • Probability applies to random events such as meiosis and fertilization.

6. 6 Meiosis and Genetic Variation TEKS 6 F, 6 G The student is expected to: 6 F predict possible outcomes of various genetic combinations such as monhybrid crosses, dihybrid crosses and non. Mendelian inheritance and 8 G recognize the significance of meiosis to sexual reproduction

6. 6 Meiosis and Genetic Variation TEKS 6 F, 6 G KEY CONCEPT Independent assortment and crossing over during meiosis result in genetic diversity.

6. 6 Meiosis and Genetic Variation TEKS 6 F, 6 G Sexual reproduction creates unique combinations of genes. • Sexual reproduction creates unique combination of genes. – independent assortment of chromosomes in meiosis – random fertilization of gametes • Unique phenotypes may give a reproductive advantage to some organisms.

6. 6 Meiosis and Genetic Variation TEKS 6 F, 6 G Crossing over during meiosis increases genetic diversity. • Crossing over is the exchange of chromosome segments between homologous chromosomes. – occurs during prophase I of meiosis I – results in new combinations of genes

6. 6 Meiosis and Genetic Variation TEKS 6 F, 6 G • Chromosomes contain many genes. – The farther apart two genes are located on a chromosome, the more likely they are to be separated by crossing over. – Genes located close together on a chromosome tend to be inherited together, which is called genetic linkage. • Genetic linkage allows the distance between two genes to be calculated.