GeneticsGenetics Gregor MendelGregor Mendel Genotypes: Homozygous and Heterozygous, Genotypes: Homozygous and Heterozygous,

Dominant, RecessiveDominant, Recessive Phenotypes: Traits you seePhenotypes: Traits you see Law of HeredityLaw of Heredity

- law of segregation- law of segregation- law of independent assortment- law of independent assortment

Probability: punnett squaresProbability: punnett squares Pedigree charts: genes are sex-linked or Pedigree charts: genes are sex-linked or

autosomalautosomal

Polygenetic traits, incomplete dominance, Polygenetic traits, incomplete dominance, codominance, multiple alleles.codominance, multiple alleles.

Gregor Mendel: Father of GeneticsGregor Mendel: Father of Genetics Found the following using Pea plantFound the following using Pea plant

- Inheritance: passing of traits- Inheritance: passing of traits

- Heredity: transmission of traits from parents to - Heredity: transmission of traits from parents to offspringoffspring

Used pea plants for his experiments. WHY??Used pea plants for his experiments. WHY??

- Either the flower is either purple or white, no - Either the flower is either purple or white, no intermediate intermediate

colors such as pinkcolors such as pink

- You can control pollination. (able to control the - You can control pollination. (able to control the mating)mating)

- small, easily grown, matures quickly, produces many - small, easily grown, matures quickly, produces many offspringoffspring

Mendel’s ExperimentsMendel’s Experiments He did the experiment by both self-pollinating (pollen is not He did the experiment by both self-pollinating (pollen is not

transferred to another plant, the plant uses its pollen) and transferred to another plant, the plant uses its pollen) and cross-pollinating (cross-fertilization: transferring pollen from cross-pollinating (cross-fertilization: transferring pollen from one plant to the other)one plant to the other)

His experimentHis experiment 1. He crossed a purple flower with a purple flower producing 1. He crossed a purple flower with a purple flower producing

plants with purple flowers and a white flower with a white plants with purple flowers and a white flower with a white flower flower

producing plants with only white flowers. He referred to producing plants with only white flowers. He referred to this as this as

“ “True-breeding” (display 1 particular trait). These plants True-breeding” (display 1 particular trait). These plants served as his parental generation or “P” generationserved as his parental generation or “P” generation EX: White X White = All WhiteEX: White X White = All White

Purple X Purple = All PurplePurple X Purple = All Purple

Mendel’s Experiment Con’tMendel’s Experiment Con’t

2. He then crossed a white P generation flower with a purple 2. He then crossed a white P generation flower with a purple

P generation flower. He called the offspring of the P P generation flower. He called the offspring of the P generation generation

the Fthe F11 Generation. All offspring were purple Generation. All offspring were purple

EX: White X Purple == All PurpleEX: White X Purple == All Purple

3. He then enabled the F3. He then enabled the F11 generation to self-pollinate. This generation to self-pollinate. This produced the Fproduced the F22 generation. 705 were purple and 224 generation. 705 were purple and 224 flowers were white . A ratio of 3:1 flowers were white . A ratio of 3:1

EX: Purple X purple == 3 Purple, 1 WhiteEX: Purple X purple == 3 Purple, 1 White

See the following website:See the following website:http://www2.edc.org/weblabs/Mendel/mendel.html

Mendel’s ConclusionsMendel’s Conclusions

1. He concluded that purple was the dominant 1. He concluded that purple was the dominant colorcolor

2. He concluded that purple was masking the white 2. He concluded that purple was masking the white color.color.

3. He concluded that white was recessive because 3. He concluded that white was recessive because it returned in the Fit returned in the F22 generation generation

Mendel’s HypothesesMendel’s Hypotheses

1. For each inherited trait, an individual has 2 copies of 1. For each inherited trait, an individual has 2 copies of the gene- one from the father one from the motherthe gene- one from the father one from the mother

Through the process of meiosis, parents Through the process of meiosis, parents can only contribute one allele for an can only contribute one allele for an inherited trait.inherited trait.

When two different alleles occur together, When two different alleles occur together, only 1 may be completely expressed. The only 1 may be completely expressed. The other may not have an observable effect other may not have an observable effect on the organism’s appearance. on the organism’s appearance.

Other Important Info.Other Important Info. Dominant:Dominant: The gene (trait) that is expressed in the physical The gene (trait) that is expressed in the physical

appearance. Represented by a capitol letter (T, S, H)appearance. Represented by a capitol letter (T, S, H) Recessive:Recessive: the gene (trait) that is not expressed, but you still have the gene (trait) that is not expressed, but you still have

the gene for the trait. It is masked by the dominant trait. the gene for the trait. It is masked by the dominant trait. Represented by a lower case letter. (t, s, h)Represented by a lower case letter. (t, s, h)

Genotype:Genotype: set of alleles or genes that an individual has set of alleles or genes that an individual has PhenotypePhenotype:: The physical appearance of an individual. (determined The physical appearance of an individual. (determined

by your alleles)by your alleles) Alleles can be homozygous or heterozygous Alleles can be homozygous or heterozygous

-- -- homozygous:homozygous: alleles are the same for a particular trait alleles are the same for a particular trait

ex: TT, SS, HH=== Homozygous dominantex: TT, SS, HH=== Homozygous dominant

tt, ss, hh=== Homozygous recessivett, ss, hh=== Homozygous recessive

--- --- heterozygous:heterozygous: alleles are different for a particular trait alleles are different for a particular trait

ex: Tt, Ss, Hhex: Tt, Ss, Hh

Laws of HeredityLaws of Heredity Mendel’s findings led to the laws of Mendel’s findings led to the laws of

heredityheredity 2 laws2 laws

1. Law of segregation: two alleles for the same 1. Law of segregation: two alleles for the same trait separate when gametes are formed. trait separate when gametes are formed. (remember when chromosomes separate during (remember when chromosomes separate during meiosis)meiosis)

2. Law of independent assortment: alleles of 2. Law of independent assortment: alleles of different genes (ex hair and eye color), separate different genes (ex hair and eye color), separate independently of one another during gamete independently of one another during gamete formation. One gene does not influence the formation. One gene does not influence the inheritance of the other. inheritance of the other.

Studying Heredity

Punnett Square: Finding the probability that a trait will be passed from one generation to the next.

-- monohybrid: 1 trait

-- dihybrid: 2 traits Pedigree charts: family history chart that shows

how a trait has been inherited over several generations.

Punnett Squares

Monohybrid crosses A man homozygous dominant for blonde hair marries a women

who in homozygous recessive for black hair. What is the likelihood that their children will have black hair??

b bB Bb Bb Genotypes: 4 or 100% Heterozygous Phenotypes: 100% BlondeB Bb Bb

No chance of having a child with black hair

Punnett Squares Continued Dihybrid crosses -- Look at 2 traits. Two heterozygous black haired and blue eyed

people marry. Look at probability of having a child with black

hair and blue eyes. B- black, b-blonde, E-blue, e-brown

-- Genotypes Father: Bb, Ee Mother: Bb, Ee

1. find all possible genotypes: Father BE, Be, bE, be

Mother: BE, Be, bE,be

Dihybrid cross BE Be bE be

BE BBEE BBEe BbEE BbEe

Be BBEe BBee BbEe Bbee

bE BbEE BbEe bbEE bbEe

be BbEe Bbee bbEe bbee

Phenotypes Genotypes

9 or 56.25% black haired and blue eyed 4 Homo dominant

3 or 18.75% blonde haired and blue eyed 8 Heter

1 or 6.25% blonde haired and brown eyed 4 Homo Recessive

3 or 18.75% black haired and brown eyed Ratio: 1:2:1

Pedigree Charts

A family history that shows how a trait has been inherited over many generations.

Scientist can determine the following: Autosomal or sex-linked? If a trait is autosomal, traits will appear in

both sexes equally. If a trait is sex-linked, males will show the trait. A sex-linked trait is a recessive trait whose allele is located on the X chromosome. Because males only have one X chromosome, a male who carries this recessive allele on the x chromosome will show the trait. The only way a female will exhibit the trait if both of her X chromosomes carries the recessive trait.

Dominant or Recessive? If the trait is autosomal dominant, every offspring that has the trait will have a parent with the trait. If it is recessive, the individual will have 1, 2, or neither parent exhibit the trait (depending on their genotype)

Heterozygous or Homozygous? If the trait is dominant, they will have a genotype of homozygous dominant or heterozygous and their phenotype will show the trait. Two people heterozygous for a recessive trait will not show the trait but can pass it on to their children.

Pedigree charts

Horizontal lines: indicate matings Vertical lines: Offspring

Males Male affected Carrier females female affected

Complex HeredityComplex Heredity

There is more to the patterns of There is more to the patterns of heredity than the simple heredity than the simple dominant/recessive patterns.dominant/recessive patterns.

Polygenic traitsPolygenic traits Incomplete dominanceIncomplete dominance CodominanceCodominance Multiple allelesMultiple alleles Environmental influencesEnvironmental influences

Polygenic traitsPolygenic traits

Traits influenced by several genesTraits influenced by several genes Hard to determine effects because many different Hard to determine effects because many different

combinations occur due to independent combinations occur due to independent assortment and crossing-over.assortment and crossing-over.

Examples: eye color, height, weight, hair and skin Examples: eye color, height, weight, hair and skin color. color.

Incomplete DominanceIncomplete Dominance An individual displays a trait that is An individual displays a trait that is

intermediate between the two parents. intermediate between the two parents. Ex: Red flower is crossed with a White Ex: Red flower is crossed with a White

flower: Results in pink flowersflower: Results in pink flowers Pink flowers because they show less Pink flowers because they show less

pigment than red but more than white.pigment than red but more than white. Ex: One parent with curly hair and one Ex: One parent with curly hair and one

parent has straight hair and their child parent has straight hair and their child has wavy hair. has wavy hair.

CodominanceCodominance

Traits with two forms displayed at once. Traits with two forms displayed at once. 2 dominant alleles displayed at the 2 dominant alleles displayed at the

same time same time EX: A homozygous white horse and a EX: A homozygous white horse and a

homozygous red horse produces a homozygous red horse produces a heterozygous offspring. The offspring heterozygous offspring. The offspring will show both red and white hair and in will show both red and white hair and in equal numbers. (called a Roan horse) equal numbers. (called a Roan horse)

Multiple AllelesMultiple Alleles Genes with 3 or more alleles.Genes with 3 or more alleles. ABO blood system: IABO blood system: IA, IB, A, IB, ii A and B are carbohydrates located on red blood cellsA and B are carbohydrates located on red blood cells ii does not have this carbohydrates does not have this carbohydrates Nor A or B are dominate over each other: they are Nor A or B are dominate over each other: they are

codominantcodominant They are dominant over They are dominant over ii 3 alleles can produce 4 genotypes: A, B, AB, O3 alleles can produce 4 genotypes: A, B, AB, O

IAIA IBIB ii

IA IAIAIA IAIA IAIBIAIB IAiIAi

IBIB IBIA IBIA IBIBIBIB IBiIBi

i IAii IAi IBiIBi iiii

Environmental InfluencesEnvironmental Influences

EX: Hydrangea plants: color of flowers EX: Hydrangea plants: color of flowers depends on the acidity of the soildepends on the acidity of the soil

Hair Color of some animals: Artic fox; Hair Color of some animals: Artic fox; during summer months it turns reddish during summer months it turns reddish brown to blend in with its environment. In brown to blend in with its environment. In the winter it is whitethe winter it is white

Humans: skin color- exposure to the sun, Humans: skin color- exposure to the sun, behavior, height and weight controlled by behavior, height and weight controlled by nutrition. Identical twins are genetically nutrition. Identical twins are genetically the same but can be very differentthe same but can be very different