How are genes inherited? Mendelian Genetics Genetics – The Study of Heredity Heredity – Passing traits from parents to offspring How are genes inherited?

Each Chromosome Is Made of Millions of Base Pairs that Compose 100’s to 1000’s of Different Genes. Chromosome Maps Link

Chromosomes / Genes / Proteins / Traits ATGC sequence Proteins folded amino acid sequence Traits blue eyes contain produce determine But what are the rules that allow us to predict the likelihood of inheriting certain traits over others?

Important Vocabulary Allele = A gene, but in a specific form. Each characteristic (trait) is always determined by two alleles. Hair color is either brown (B) or blonde (b)

Dominant Allele = A gene that, if present, always produces a Dominant Allele = A gene that, if present, always produces a protein (and therefore a trait). Brown hair is dominant = BB or Bb

Recessive Allele = A gene that produces a protein (and therefore a trait) ONLY if present with another recessive allele. Blond hair is recessive = bb

Important Vocabulary Genotype = symbols (capital and lower case letters) that represent genes on homologous chromosomes. BB, Bb and bb are all genotypes.

Blond hair and brown hair are both phenotypes. Phenotype = the organism’s characteristic as a result of its genes. Blond hair and brown hair are both phenotypes.

Homozygous = a genotype showing two of the same allele. BB is homozygous dominant; bb is recessive.

Heterozygous = a genotype showing two different alleles. Bb is heterozygous.

Laws of Heredity Law of Unit Characters Law of Dominance Genes were discovered by Gregor Mendel. Mendel developed four laws that govern how traits are passed down Law of Unit Characters Law of Dominance Law of Segregation Law of Independent Assortment

Law of Unit Characters Example: Height can either be TT, Tt, or tt Law of Unit Characters – Characteristics of an individual are controlled by hereditary factors (genes) that occur in pairs (on homologous chromosomes) Example: Height can either be TT, Tt, or tt

Law of Dominance Law of Dominance – the dominant allele is expressed and the recessive allele can be hidden. This is why offspring don’t look like a complete blend of each of the parents.

Law of segregation Law of Segregation – a pair of genes are separated during the formation of gametes. You can inherit either allele with equal probability. Ex. T or t but not both.

The dominant allele is not passed on more often than the recessive allele. Parent has a dominant allele and recessive allele for hair color. Which allele will he pass on to his offspring? Answer: 50% chance for either allele

Law of Independent Assortment Law of Independent Assortment – inheritance of most traits does not depend on other traits. The fact that you have brown hair has no effect on the color of eyes that you have. There are exceptions to this law, and these will be discussed later.

Inheritance Patterns How can you determine what traits are being passed on? How can you predict what certain offspring will look like? Reginald Punnett, an English Biologist, developed an easy way to solve these problems.

Punnett Squares Suppose a woman with blue eyes marries a man with brown eyes, what color eyes will their children most likely have?

Punnett Squares Determine the genotypes of the parents Father has brown eyes. His genotype is either BB or Bb. For the sake of this problem, we’ll say his genotype is BB. Mother has blue eyes. Her genotype is bb. P1: BB x bb

Punnett Squares Create the grid. The father’s alleles go on the top, and the mother’s alleles go on the side: B B b b

B B b B b B b B b B b b Punnett Squares Fill in the grid. Combine the parent alleles inside the boxes. The letters show the genotypes of the offspring. B B b B b B b B b B b b

Punnett Squares B b Bb Determine the phenotypes. Use the law of dominance to determine the phenotype and phenotype ratio of the offspring. (brown) (brown) (brown) (brown) F1 Generation

B b Bb (brown) 4 : 0 0 : 4 : 0 F1 Phenotypic Ratio: Brown : blue 4 : 0 F1 Genotypic Ratio: Homozygous Brown: Heterozygous Brown: Homozygous blue BB Bb bb 0 : 4 : 0

Question: If one of these children were to have a child with a heterozygous brown-eyed spouse, what color eyes would their children have?

B b BB Bb bb Bb (brown) (brown) (brown) (blue) 3 : 1 1 : 2 : 1 To find the F2 generation: F1 (x) F1 (brown) (brown) bb Bb F2 generation (brown) (blue) 3 : 1 F2 Phenotypic Ratio: Brown : blue 1 : 2 : 1 F2 Genotypic Ratio: Homozygous Brown: Heterozygous Brown: Homozygous blue BB Bb bb

Genotypes of offspring: B- Brown White In mice, brown color is dominant over white. Two brown mice are mated several times. They have a total of 20 offspring, 14 brown, and 6 white. Determine the genotypes of the parents and all the offspring. B b B= brown b = white B b B b brown (x) brown B BB Bb 14 brown and 6 white Bb bb b B bb Genotypes of parents: Bb (x) Bb bb Genotypes of offspring: B- Brown White

T t tt Tt Tt t Tt tt Tt T- tt t Tt tt tt In humans, tongue-rolling is controlled by a dominant allele. A non-tongue roller man (whose parents are both tongue rollers) marries a woman who can role her tongue. The woman’s father was a tongue roller but her mother was not. The couple have one child who is a non-tongue roller. Determine the genotypes of all the people in the problem (7 total). T= tongue roller t = non tongue roller tt T t T t T - non tongue roller (x) tongue roller t t T t Genotypes : man= _____ His dad ______ His mom _____ woman = _____ Her dad ______ Her mom _____ Child = ________ T t tt Tt Tt t Tt tt Tt T- tt t Tt tt tt

Skipping a Generation When a trait disappears (not seen in parents) and then reappears in offspring generation Proof that trait is controlled by a recessive gene. Ex. Two white sheep produce a black sheep. Determine the genotypes of the parents and offspring.

Gregor Mendel How did Mendel come up with his four laws? 1822-1884 The Laws of Heredity were discovered using PEA PLANTS, but they are the same laws for ALL living things!!! Law of Unit Characters Law of Dominance Law of Segregation Law of Independent Assortment How did Mendel come up with his four laws?

Why Peas? Easy to care for Characteristics are easy to identify. Short life span, so you can get several generations in a short amount of time.

Large number of offspring at one time, providing lots of data. Easily control the mating of pea plants in a green house. Pea offspring can be mated with their parents and with one another.

Mendel’s Experiments (mated with) Purebred tall plants were crossed with purebred short P1 Generation (original parents) X All F1 offspring are tall. Short trait disappeared! F1 Generation X Short trait reappears in a consistent ratio of 3 tall : 1 short F2 Generation

Mendel’s Experimental Results Purebred or Homozygous P1 Generation: Tall (x) Short TT (x) tt F1 Generation: All Tall F2 Generation: 3 Tall and 1 Short T t Tt Tt Tt Tt F1 T t TT Tt Tt tt F2

Mendel’s Results

Incomplete Dominance When there is no dominant allele for a trait and blending occurs in the heterozygous condition

Example: Flower in Four- O’Clocks and Snapdragons Red (RR), Pink (Rr), White (rr) Pink Flower (x) Pink Flower Rr (x) Rr R r RR Rr Rr rr 1 : 2 : 1 Phenotypic Ratio: Red : Pink : White Genotypic Ratio: 1 : 2 : 1 Homozygous RR : Heterozygous Rr : Homozygous rr Phenotypic & Genotypic Ratios are the same!

Pedigree Chart Show relationships in a family (family tree) Shaded individuals have different phenotype from unshaded Circles – females Squares - males

WRONG! - B = Brown eyes b = blue eyes - - bb B b B bb bb B b B b B b B

DIHYBRID CROSSES – Two factor inheritance Crosses involving two traits Demonstrates Law of Independent Assortment

First, Outside, Inside, Last TtRr – Tall and Round outside first ( T x t ) ( R x r ) inside last F O I L First, Outside, Inside, Last

Key 1 Tall = TT or Tt, thus T- Short = tt Round= RR or Rr, thus R- Wrinkled= rr Key 2 Tall, Round = T-R- Tall, Wrinkled= T-rr Short, Round = ttR- Short, wrinkled = ttrr P1 Pure Tall, Pure Round (x) Pure Short, Pure Wrinkled P1 TTRR (x) ttrr Possible Gametes: TR, TR, TR, TR (x) tr, tr, tr, tr TR (x) tr

Possible Gametes: TR (x) tr TtRr F1 1 : 0 : 0 : 0 Phenotypic Ratio: Tall, Round : Tall, Wrinkled : Short, Round : Short, Wrinkled We will not be doing genotypic ratios for dihybird problems.

Find the F2 phenotype ratio: F1 (x) F1 Heterozygous Tall, Heterozygous Tall, Heterozygous Round (x) Heterozygous Round TtRr (x) TtRr Possible Gametes: TR, Tr, tR, tr (x) TR, Tr, tR, tr

Possible Gametes: TR, Tr, tR, tr (x) TR, Tr, tR, tr TTRR TTRr TtRR TtRr Tr TTRr TTrr TtRr Ttrr tR TtRR TtRr ttRR ttRr tr TtRr Ttrr ttRr ttrr Phenotypic Ratio: Tall, Round : Tall, Wrinkled : Short, Round : Short, Wrinkled

Possible Gametes: TR, Tr, tR, tr (x) TR, Tr, tR, tr TTRR TTRr TtRR TtRr Tr TTRr TTrr TtRr Ttrr tR TtRR TtRr ttRR ttRr tr TtRr Ttrr ttRr ttrr 9 : 3 : 3 : 1 Phenotypic Ratio: Tall, Round : Tall, Wrinkled : Short, Round : Short, Wrinkled

Heterozygous Tall, Homozygous Tall, Heterozygous Round (x) Homozygous Round TtRr (x) TTRR Possible Gametes: TR, Tr, tR, tr (x) TR

Possible Gametes: TR, Tr, tR, tr (x) TR TTRR TTRr TtRR TtRr 4 : 0 : 0 : 0 Phenotypic Ratio: Tall, Round : Tall, Wrinkled : Short, Round : Short, Wrinkled

Practice Law of Unit Characters Law of Dominance Law of Segregation Law of Independent Assortment A. Characteristics of an individual are controlled by hereditary factors (genes) that occur in pairs B. States that a pair of genes are separated during the formation of gametes. You can inherit either allele with the same probability. C. The dominant allele is expressed and the recessive allele can be hidden. D. Most traits do not depend on other traits.