6.3 Mendel and Heredity

13.1 Ecologists Study Relationships Fundamentals of Genetics Genetics – field of biology devoted to understanding how characteristics are transmitted from parents to offspring

6.3 Mendel and Heredity Father of Genetics Gregor Mendel Austrian Monk Heredity – transmission of characteristics from parents to offspring Garden Peas

6.3 Mendel and Heredity CharacteristicTraits 1.Plant HeightTallShort 2.Flower position AxialTerminal 3.Pod appearance Inflated Constricted 4.Seed TextureSmoothWrinkled 5.Seed ColorYellowGreen 6.Flower ColorPurpleWhite 7.Pod ColorGreen Yellow

6.3 Mendel and Heredity

Mendel’s Methods Pollination – pollen grains produced in the male reproductive parts of the flower (anther) are transferred to the female reproductive part of a flower (stigma) Self-pollination – pollen is transferred from the anthers of a flower to the stigma on a flower on the same plant Cross-pollination – involves flowers of two separate plants

6.3 Mendel and Heredity Mendel’s Experiments Grew plants PURE for a trait (always produce offspring with that trait) STRAIN - plants that are pure for a specific trait He allowed plants to self-pollinate for several generations to obtain 14 strains: Parental Generation (P1) Cross-pollinated these strains one pure for one trait with another pure for the contrasting trait P1 (tall) X P1 (short)  First Filial Generation(F1) Then allowed F1 to self pollinate  second filial generation (F2)

6.3 Mendel and Heredity 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. interrupted the self-pollination process by removing male flower parts

6.3 Mendel and Heredity Mendel’s Results Only one of the two traits in P1 appeared in the offspring F1 The trait then reappeared in F2 in a ratio of 3:1

6.3 Mendel and Heredity Mendel’s Conclusions Factor – something controlling the traits (allele) Pair of factors controls each trait (gene) Recessive & Dominant Traits - Dominant factor – masked the other factor (appeared in F1) - Recessive – is masked by the presence of another (reappeared in F2)

6.3 Mendel and Heredity Chromosomes and Genes Molecular genetics – study of the structure and function of chromosomes and genes Gene – segment of DNA on a chromosome that controls a particular hereditary trait Letters are used to represent alleles - capital letters refer to dominant alleles T = tall - lowercase letters refer to recessive alleles t = short Genome - All of an organism’s genetic material

6.3 Mendel and Heredity Genetic Crosses Genotype – genetic makeup of an organism TTTttt Phenotype – appearance of an organism as a result of its genotype TT  Talltt  short Homozygous – both alleles of a pair are alike TT or tt Heterozygous – two alleles in the pair are different Tt

6.3 Mendel and Heredity Genotypic ratio – ratio of the genotypes that appear in offspring 1TT:2Tt:1tt Phenotypic ratio – ratio of the offspring's phenotypes 3 Tall:1 short

6.3 Mendel and Heredity 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

6.3 Mendel and Heredity A monohybrid cross involves one trait. (12 points) 6.5 Traits and Probability Homozygous Dominant XHomozygous Recessive

6.3 Mendel and Heredity 6.5 Traits and Probability Heterozygous XHeterozygous

6.3 Mendel and Heredity Testcross Individual of unknown genotype is crossed with a homozygous recessive individual Determine the genotype of an individual whose phenotype is dominant

6.3 Mendel and Heredity Testcross (10 points): Offspring 100% Dom 6.5 Traits and Probability

6.3 Mendel and Heredity Complete Dominance – one allele completely dominant over the other Incomplete dominance – two or more alleles influence the phenotype resulting in a phenotype intermediate between the dominant and recessive traits R=red W=white RW  pink

6.3 Mendel and Heredity Codominance – both alleles for a gene are expressed in a heterozygous offspring – neither is dominant or recessive RW  red & white polka dots

6.3 Mendel and Heredity Multiple Alleles – 3 or more alleles of the same gene Blood Types I A I B i I A I Aor I A i=Blood type A I B I Bor I B i=Blood type B I A I B =Blood type AB ii=Blood type O The ABO blood types result from codominant multiple alleles.

6.3 Mendel and Heredity Sex-linked Inheritance Traits controlled by genes located on the sex chromosomes X-linked gene Y-linked gene X-linked traits more common in males Sex-Influenced Inheritance – traits affected by how much sex hormones are present

6.3 Mendel and Heredity Punnett Square: Sex-Linked Traits Determine Sex of Offspring Difference in sex-linked traits. 7.1 Chromosomes and Phenotype

6.3 Mendel and Heredity Male mammals have an XY genotype. –All of a male’s sex- linked genes are expressed. –Males have no second copies of sex-linked genes. 7.1 Chromosomes and Phenotype

6.3 Mendel and Heredity Female mammals have an XX genotype. –X chromosome inactivation randomly “turns off” one X chromosome. 7.1 Chromosomes and Phenotype

6.3 Mendel and Heredity A dihybrid cross involves two traits. (12 points) Homozygous Dominant for bothX Homozygous Recessive for both 6.5 Traits and Probability

6.3 Mendel and Heredity 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. Probability = number of ways a specific event can occur number of total possible outcomes 6.5 Traits and Probability

6.3 Mendel and Heredity Laws Law of Segregation – a pair of factors is segregated, or separated, during the formation of gametes (1 trait: Tall from short) Law of Independent Assortment – factors for different characteristics are distributed to gametes independently (all characteristics being separated) i.e. Tall plant from yellow peas

6.3 Mendel and Heredity Mendel’s rules of inheritance apply to autosomal genetic disorders. –A heterozygote for a recessive disorder is a carrier. –Disorders caused by dominant alleles are uncommon. (dominant) 7.1 Chromosomes and Phenotype

6.3 Mendel and Heredity Polygenic Inheritance Traits controlled by many genes Multifactorial ~180 genes have been described to control human height  up to 700 Add the effect of all genes to get the manifestation of the trait ABC – each having their own set of alleles AaBbCc

6.3 Mendel and Heredity An epistatic gene can interfere with other genes. 7.2 Complex Patterns of Inheritance

6.3 Mendel and Heredity The environment interacts with genotype. Height is an example of a phenotype strongly affected by the environment. The sex of sea turtles depends on both genes and the environment Phenotype is a combination of genotype and environment. 7.2 Complex Patterns of Inheritance

6.3 Mendel and Heredity Many genes may interact to produce one trait. Order of dominance: brown > green > blue. 7.2 Complex Patterns of Inheritance