Genetics “The real key to explaining Inheritance”

Objectives To understand the experiments and conclusions of Gregor Mendel To understand the experiments and conclusions of Gregor Mendel To compare Monohybrid and Dihybrid crosses To compare Monohybrid and Dihybrid crosses To compare Complete, Incomplete and Co-dominance To compare Complete, Incomplete and Co-dominance To understand how Multiple Alleles work To understand how Multiple Alleles work

Gregor Mendel Austrian Monk in the 1800’s Austrian Monk in the 1800’s Experimented with pea plants Experimented with pea plants Kept detailed records of several characteristics for generations Kept detailed records of several characteristics for generations –Height –Flower color –Pod color –Shape of peas and pods –Position of flowers on the plant

Mendel’s Observations If he had tall plants in one section of the garden, they always produced tall offspring If he had tall plants in one section of the garden, they always produced tall offspring Similarly if he had short plants in another section the same would occur (short offspring) Similarly if he had short plants in another section the same would occur (short offspring) He called these plants Pure Lines He called these plants Pure Lines –Tall x Tall = Tall –Short x Short = Short –Mendel's Experiment Mendel's ExperimentMendel's Experiment

Mendel’s Experiment He decided to cross (breed) these pure lines He decided to cross (breed) these pure lines Pure Line Tall x Pure Line Short Pure Line Tall x Pure Line Short The result was ALL tall plants The result was ALL tall plants He decided to cross these plants with each other He decided to cross these plants with each other To his surprise, this resulted in both tall and short plants To his surprise, this resulted in both tall and short plants The ratio was exactly 3 to 1 (tall to short) The ratio was exactly 3 to 1 (tall to short) Parents Tall (Pure Line) x Short (Pure Line) First Generation (F1) All Tall Plants Second Generation (F2) Tall & Short Plants 3 to 1 ratio (75% Tall & 25% Short)

Mendel’s Conclusions(4) All characteristics are controlled by factors inherited from your parents All characteristics are controlled by factors inherited from your parents There are two factors for every trait (characteristic) There are two factors for every trait (characteristic) –These traits can be hair color, length of nose, skin tone, height, etc. One factor can dominate another One factor can dominate another –‘Mask’ the other These factors separate from each other during sex cell formation (meiosis) These factors separate from each other during sex cell formation (meiosis)

Modernizing Mendel’s Conclusions We now call these ‘factors’ Alleles We now call these ‘factors’ Alleles Alleles can be Dominant or Recessive Alleles can be Dominant or Recessive We represent Alleles with letters: We represent Alleles with letters: –Capitals = Dominant Allele –Lowercase = Recessive Allele –*Dominant Alleles always go first Genotype is the combination of alleles you have Genotype is the combination of alleles you have Phenotype is the expressed trait Phenotype is the expressed trait Homozygous – 2 alleles that are the same. Homozygous – 2 alleles that are the same. Heterozygous – 2 alleles that are different Heterozygous – 2 alleles that are different GenotypePhenotype TT Tall Plant Tt tt Short Plant BB Brown Eyes Bb bb Blue Eyes

Types of Genotypes Genotype in Letters Genotype in Words Phenotype TT Homozygous Dominant Tall Plant TtHeterozygous tt Homozygous Recessive Short Plant Genotypes can also be expressed in words Genotypes can also be expressed in words ‘Homo’ – Latin prefix for ‘the same’ ‘Homo’ – Latin prefix for ‘the same’

The Punnett Square Mendel started his experiments crossing a pure line of tall plants (TT) with a pure line of short plants (tt) Mendel started his experiments crossing a pure line of tall plants (TT) with a pure line of short plants (tt) Parents (Tt x Tt) Cross (Tt x Tt) CrossTt T tParents (TT x tt) Cross (TT x tt) CrossTTt t He then took those hybrids (Tt) and crossed them with one another

Sample Problem # 1 Widow’s peak is dominant to straight hairline Widow’s peak is dominant to straight hairline A homozygous woman with widow’s peak reproduces with a man with a homozygous man with straight hairline A homozygous woman with widow’s peak reproduces with a man with a homozygous man with straight hairline What hairline will their children (F1) have? What hairline will their children (F1) have? Hairline Cross WW w w What genotype (in words) can we expect from a homozygous dominant, homozygous recessive cross? ALL offspring will be heterozygous

Sample # 1 Continued Now if an offspring of that cross reproduces with another of the same genotype, what hairlines can we expect for their children? Now if an offspring of that cross reproduces with another of the same genotype, what hairlines can we expect for their children? What genotype(s) (in words) can we expect from a cross such as this? What genotype(s) (in words) can we expect from a cross such as this? What ratio of phenotype? What ratio of phenotype?

Our Findings Homozygous dominant crossed with homozygous recessive yields heterozygous offspring (100%) Homozygous dominant crossed with homozygous recessive yields heterozygous offspring (100%) A heterozygous crossed with heterozygous yields three options: A heterozygous crossed with heterozygous yields three options: –Homozygous Dominant –Heterozygous –Homozygous Recessive The ratio of those options are: The ratio of those options are: –A genotype Ratio of 1:2:1 (HD:H:HR) –A phenotype Ratio of 3:1 (Dominant Trait : Recessive)

Sample Problem # 2 Attached earlobes are recessive to un-attached (hanging) lobes Attached earlobes are recessive to un-attached (hanging) lobes A homozygous dominant man (for the trait) mates with a heterozygous woman (for same trait) A homozygous dominant man (for the trait) mates with a heterozygous woman (for same trait) What are the chances of their offspring having attached earlobes? What are the chances of their offspring having attached earlobes? The chances of their child having a child with attached earlobes is 0%, 0 in 4, 0/4 The chances of their child having a child with attached earlobes is 0%, 0 in 4, 0/4

Let’s follow Mendel’s Experiment P1 – P1 – F1 – F1 – F2 – F2 –

Let’s try some problems 1. Genetics Practice Problems 1. Genetics Practice Problems 2. Bikini Bottom Genetics 2. Bikini Bottom Genetics

Variations in Dominance All of the eight traits Mendel looked at had two alleles (dominant & recessive) All of the eight traits Mendel looked at had two alleles (dominant & recessive) This ‘all-or-nothing’ expression is known as complete dominance This ‘all-or-nothing’ expression is known as complete dominance Another form is incomplete dominance Another form is incomplete dominance This is where neither of the alleles can be considered dominant or recessive This is where neither of the alleles can be considered dominant or recessive The phenotype is a mixing of the two different alleles The phenotype is a mixing of the two different alleles The classic case is with flowers The classic case is with flowers Red flowers crossed with white flowers gives us pink flowers Red flowers crossed with white flowers gives us pink flowers

Incomplete Dominance In order to represent these alleles we need to make a change In order to represent these alleles we need to make a change Since we’re talking about color we’ll use the letter C Since we’re talking about color we’ll use the letter C For each color we add the capital superscript to the allele For each color we add the capital superscript to the allele Capital designation always indicates Incomplete Dominance Capital designation always indicates Incomplete Dominance Therefore: Therefore: –C R = Red Allele –C W = White Allele What the genotypes mean: What the genotypes mean: –C R C R = Red –C W C W = White –C R C W = Pink –C W C R = Pink

Codominance with Flowers With codominance neither allele is dominant, they both show through With codominance neither allele is dominant, they both show through Lets look at flower color Lets look at flower color In codominance a plant with red flowers mating with one having white flowers produces a plant with what? In codominance a plant with red flowers mating with one having white flowers produces a plant with what? Both red & white flowers Both red & white flowers So again we write the alleles differently So again we write the alleles differently Lower case designation indicates Codominance Lower case designation indicates Codominance For flower color: For flower color: –C r C r Red Flowers –C w C w = White Flowers –C r C w = Red & White Flowers Lets cross a homozygous red plant with a heterozygous one Lets cross a homozygous red plant with a heterozygous one What are the chances of our baby plant having red & white flowers? What are the chances of our baby plant having red & white flowers?

Multiple Alleles Multiple Alleles Some traits are controlled by multiple alleles Some traits are controlled by multiple alleles It still only takes two alleles to make a gene It still only takes two alleles to make a gene However there are more than two options for alleles However there are more than two options for alleles For example, the eye color of fruit flies have four options for alleles For example, the eye color of fruit flies have four options for alleles –E 1 = Red –E 2 = Apricot –E 3 = Honey –E 4 = White Each allele is dominant to the remaining Each allele is dominant to the remaining –E 1 is dominant to E 2, E 3, & E 4 –E 2 is dominant to E 3 & E 4 –E 3 is dominant to E 4 –E 4 is the recessive allele Options for genes would be: Options for genes would be: –E 1 E 4 = Red Eyes –E 2 E 3 = Apricot –E 4 E 4 = White Examples of Multiple Alleles: Examples of Multiple Alleles: –Blood Types –Types of Corn –Feather Color (in some cases)

Let’s try a Multiple Allele Cross

Monohybrids & Dihybrids Everything we talked about so far have been examples of monhybrid crosses Everything we talked about so far have been examples of monhybrid crosses Monohybrids – crosses that are looking at one set of alleles Monohybrids – crosses that are looking at one set of alleles We can also do dihybrid crosses We can also do dihybrid crosses Dihybrids – crosses that are looking at two sets of alleles Dihybrids – crosses that are looking at two sets of alleles The following are two examples The following are two examples –A monohybrid cross –A dihybrid cross The color is just coding for different phenotypes The color is just coding for different phenotypes

Independent Assortment

Dihybrid Example In peas plants tall is dominant to short and purple flowers are dominant to white In peas plants tall is dominant to short and purple flowers are dominant to white So if a pea plant is heterozygous for height and heterozygous for flower color what is their genotype? So if a pea plant is heterozygous for height and heterozygous for flower color what is their genotype? –TtPp During the creation of sex cells (meiosis) there are four combinations of alleles the gamete (sex cell) could hold: During the creation of sex cells (meiosis) there are four combinations of alleles the gamete (sex cell) could hold: –TP (Dominant & Dominant alleles) –Tp (Dominant & Recessive alleles) –tP (Recessive & Dominant alleles) –tp (Two recessive alleles) If a plant that is heterozygous for both traits reproduced with a plant having the same genotype, what might the phenotype of their offspring be? If a plant that is heterozygous for both traits reproduced with a plant having the same genotype, what might the phenotype of their offspring be?

Dihybrid Cross Summary If we look at the combinations of phenotypes possible from a dihybrid cross between two heterozygous organisms for two traits we find a ratio of = 9:3:3:1 If we look at the combinations of phenotypes possible from a dihybrid cross between two heterozygous organisms for two traits we find a ratio of = 9:3:3:1 9 = Tall plants with purple flowers 9 = Tall plants with purple flowers 3 = Tall Plants with white flowers 3 = Tall Plants with white flowers 3 = Short Plants with purple flowers 3 = Short Plants with purple flowers 1 = Short Plant with white flowers 1 = Short Plant with white flowers

Test Cross

Dihybrid Cross Practice Dihybrid Cross Problems Dihybrid Cross Problems Dihybrid Cross Problems Dihybrid Cross Problems Guinea Pig Activity Guinea Pig Activity Guinea Pig Activity Guinea Pig Activity Mendel's Peas and the Pedigree Chart Mendel's Peas and the Pedigree Chart Mendel's Peas and the Pedigree Chart Mendel's Peas and the Pedigree Chart