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# Math of Genetics - PowerPoint PPT Presentation

Math of Genetics. Mary Simpson MATH 150. Objectives . Understanding how to find the probability of genetic outcomes for situations involving: Multiple Traits Linkage Incomplete Dominance Codominance Multiple Allelism

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### Math of Genetics

Mary Simpson

MATH 150

• Understanding how to find the probability of genetic outcomes for situations involving:

• Multiple Traits

• Incomplete Dominance

• Codominance

• Multiple Allelism

• Understanding Hardy Weinberg Equations in relation to population genetics

• Genetics: the study of the inheritance of traits

• Gene: a section of DNA that influences the heredity of a trait

• Genetics: the study of the inheritance of traits

• Gene: a section of DNA that influences the heredity of a trait

• Chromosome: dense coils of DNA that contain multiple genes

• Allele: denotes different versions of the same gene

• Genetics: the study of the inheritance of traits

• Gene: a section of DNA that influences the heredity of a trait

• Chromosome: dense coils of DNA that contain multiple genes

• Allele: denotes different versions of the same gene

• Gregor Mendel was a pioneer in genetics

• Gregor Mendel (1822-1884)

• Studied the inheritance of traits in pea plants

• Gregor Mendel (1822-1884)

• Studied the inheritance of traits in pea plants

• Mendel looked for patterns in the inheritance traits from parents with specified traits

• The average human had 46 chromosomes (2 sets of 23)

• The average human had 46 chromosomes (2 sets of 23)

• Half of these chromosomes come from the mother and half from the father (1 set from each parent)

• The average human had 46 chromosomes (2 sets of 23)

• Half of these chromosomes come from the mother and half from the father (1 set from each parent)

• Because there are two sets of chromosomes, a person inherits two copies of each gene

• The average human had 46 chromosomes (2 sets of 23)

• Half of these chromosomes come from the mother and half from the father (1 set from each parent)

• Because there are two sets of chromosomes, a person inherits two copies of each gene

• A person has two alleles for each trait that interact, resulting in the expressed trait

• Dominant Trait: if a gene for the dominant trait (called a dominant allele) is present, it will be expressed

• Usually expressed with an uppercase letter (ex. A)

• Recessive Trait: this trait will only be expressed in the absence of a dominant allele

• Usually expressed with a lowercase letter (ex. a)

• Dominant Trait: if a gene for the dominant trait (called a dominant allele) is present, it will be expressed

• Usually expressed with an uppercase letter (ex. A)

• Recessive Trait: this trait will only be expressed in the absence of a dominant allele

• Usually expressed with a lowercase letter (ex. a)

• Genotype: the combination of two alleles (ex. Aa)

• Phenotype: the trait expression that results from a genotype

• Dominant Trait: if a gene for the dominant trait (called a dominant allele) is present, it will be expressed

• Usually expressed with an uppercase letter (ex. A)

• Recessive Trait: this trait will only be expressed in the absence of a dominant allele

• Usually expressed with a lowercase letter (ex. a)

• Genotype: the combination of two alleles (ex. Aa)

• Phenotype: the trait expression that results from a genotype

• Homozygous: genotype with two copies of the same allele (ex. AA, aa)

• Heterozygous: genotype with one dominant allele and one recessive allele (ex. Aa)

• To form a punnett square, form a grid with the paternal genotype on the top and the maternal genotype down the left side

• To form a punnett square, form a grid with the paternal genotype on the top and the maternal genotype down the left side

• In the center sections of the table, combine the paternal and maternal alleles to create all possible genotypes for the offspring

• If we have a mother with genotype aa and a father with genotype Aa

• The punnett square would look as follows:

• If we have a mother with genotype aa and a father with genotype Aa

• The punnett square would look as follows:

• If we have a mother with genotype aa and a father with genotype Aa

• The punnett square would look as follows:

• If we have a mother with genotype aa and a father with genotype Aa

• The punnett square would look as follows:

Genotypic Ratio: a ratio of the number of possible outcomes of each genotype (in this example 1:1)

Phenotypic Ratio: ratio of the number of outcomes that will result in different phenotypes (in this example 1:1)

• The allele for dark hair (B) is dominant and the allele for light hair (b) is recessive

• If a female with genotype Bb and a male with genotype Bb mate, what are the chances that they will have a light haired offspring?

• The allele for dark hair (B) is dominant and the allele for light hair (b) is recessive

• If a female with genotype Bb and a male with genotype Bb mate, what are the chances that they will have a light haired offspring?

• The allele for dark hair (B) is dominant and the allele for light hair (b) is recessive

• If a female with genotype Bb and a male with genotype Bb mate, what are the chances that they will have a light haired offspring?

• The allele for dark hair (B) is dominant and the allele for light hair (b) is recessive

• If a female with genotype Bb and a male with genotype Bb mate, what are the chances that they will have a light haired offspring?

• The allele for dark hair (B) is dominant and the allele for light hair (b) is recessive

• If a female with genotype Bb and a male with genotype Bb mate, what are the chances that they will have a light haired offspring?

To have light hair the genotype must be bb

There is only a 1/4 chance of that, therefore the chance is 25%

• Looking at the inheritance of two traits is called a dihybrid cross

• Looking at the inheritance of two traits is called a dihybrid cross

• To set up the punnett square you have to look at all possible combinations of maternal and paternal DNA

• Looking at the inheritance of two traits is called a dihybrid cross

• To set up the punnett square you have to look at all possible combinations of maternal and paternal DNA

• You use those 4 combinations from each parent to set up the punnett square

• We will look at the inheritance of brown and black fur and coarse and soft fur in hamsters

• Brown fur (B) and soft fur (S) are dominant

• We will look at the inheritance of brown and black fur and coarse and soft fur in hamsters

• Brown fur (B) and soft fur (S) are dominant

• We will look at the inheritance of brown and black fur and coarse and soft fur in hamsters

• Brown fur (B) and soft fur (S) are dominant

• If the mother has genotype BBssand the father has genotype BbSs, what is the chance that an offspring will have brown coarse fur?

• If the mother has genotype Bbss and the father has genotype BbSs, what is the chance that an offspring will have brown coarse fur?

• If the mother has genotype Bbss and the father has genotype BbSs, what is the chance that an offspring will have brown coarse fur?

• If the mother has genotype Bbss and the father has genotype BbSs, what is the chance that an offspring will have brown coarse fur?

• If the mother has genotype Bbss and the father has genotype BbSs, what is the chance that an offspring will have brown coarse fur?

Phenotypic Ratio 6:6:2:2

• If the mother has genotype Bbss and the father has genotype BbSs, what is the chance that an offspring will have brown coarse fur?

Phenotypic Ratio 6:6:2:2

• If the mother has genotype Bbss and the father has genotype BbSs, what is the chance that an offspring will have brown coarse fur?

Phenotypic Ratio 6:6:2:2

Out of the sixteen possible genetic combinations, 6 result in brown, coarse fur

6/16= .375 = 37.5%

• Linked genes are those found on the same chromosome

• Linked genes are those found on the same chromosome

• This means that these traits should not follow the same pattern of inheritance because the traits cannot be independently assorted into gametes

• Linked genes are those found on the same chromosome

• This means that these traits should not follow the same pattern of inheritance because the traits cannot be independently assorted into gametes

• In terms of a punnett square, having two linked traits would be treated like having a single trait

• Linked genes are those found on the same chromosome

• This means that these traits should not follow the same pattern of inheritance because the traits cannot be independently assorted into gametes

• In terms of a punnett square, having two linked traits would be treated like having a single trait

• Mendel was lucky that each of the traits he studied had genes that were not linked

• Incomplete dominance means that the dominant allele will not completely dominant the recessive allele

• Incomplete dominance means that the dominant allele will not completely dominant the recessive allele

• In many cases this means that heterozygous individuals will have intermediate phenotypes

• Incomplete dominance means that the dominant allele will not completely dominant the recessive allele

• In many cases this means that heterozygous individuals will have intermediate phenotypes

• This will not alter genotypic ratios, but it will alter phenotypic ratios

• The allele for white flowers (R) is dominant, but it’s dominance incomplete

• The allele for red flowers (r) is recessive

• The allele for white flowers (R) is dominant, but it’s dominance incomplete

• The allele for red flowers (r) is recessive

• What are the possible phenotypes of the offspring of two plants with genotypes Rr and Rr?

• The allele for white flowers (R) is dominant, but it’s dominance incomplete

• The allele for red flowers (r) is recessive

• What are the possible phenotypes of the offspring of two plants with genotypes Rr and Rr?

• The allele for white flowers (R) is dominant, but it’s dominance incomplete

• The allele for red flowers (r) is recessive

• What are the possible phenotypes of the offspring of two plants with genotypes Rr and Rr?

• The allele for white flowers (R) is dominant, but it’s dominance incomplete

• The allele for red flowers (r) is recessive

• What are the possible phenotypes of the offspring of two plants with genotypes Rr and Rr?

RR will have white flowers

rr will have red flowers

Rr will have pink flowers (intermediate between white and red)

• If we mated two of that same type of flowers with the genotypes, RR and Rr, what is the probability that the offspring will have pink flowers?

• If we mated two of that same type of flowers with the genotypes, RR and Rr, what is the probability that the offspring will have pink flowers?

• If we mated two of that same type of flowers with the genotypes, RR and Rr, what is the probability that the offspring will have pink flowers?

• If we mated two of that same type of flowers with the genotypes, RR and Rr, what is the probability that the offspring will have pink flowers?

2/4 or 50% chance

• Codominance: when heterozygotes have the phenotypes associated with each allele (because both alleles are dominant)

• Codominance: when heterozygotes have the phenotypes associated with each allele (because both alleles are dominant)

• The best example is blood type

• There are three alleles for blood type (IA, IB, i)

• Codominance: when heterozygotes have the phenotypes associated with each allele (because both alleles are dominant)

• The best example is blood type

• There are three alleles for blood type (IA, IB, i)

• IA and IB are codominant, so if a person has genotype IAIB, they will have type AB blood

• IAi, results in type A, IBi in type B and ii in type O

• What are the possible blood types of offspring of parents with genotypes IAi and IBIB

• What are the possible blood types of offspring of parents with genotypes IAi and IBIB

• What are the possible blood types of offspring of parents with genotypes IAi and IBIB

• What are the possible blood types of offspring of parents with genotypes IAi and IBIB

IAIB will result in type AB

IBi will result in type B

• What is the chance that a mother with genotype IBi and a father with genotype IAi will have a child with type O blood?

• What is the chance that a mother with genotype IBi and a father with genotype IAi will have a child with type O blood?

• What is the chance that a mother with genotype IBi and a father with genotype IAi will have a child with type O blood?

• What is the chance that a mother with genotype IBi and a father with genotype IAi will have a child with type O blood?

1/4 or 25%

• Multiple Gene Inheritance: there is more than one gene that controls the expression of a trait

• Multiple Gene Inheritance: there is more than one gene that controls the expression of a trait

• Example: Pepper Color

• Pepper color is controlled by two different genes

• The first gene controls the expression of red pigment

• The dominant allele (R) indicates the presence of red pigment

• The recessive allele (r) indicates the absence of red pigment

• Multiple Gene Inheritance: there is more than one gene that controls the expression of a trait

• Example: Pepper Color

• Pepper color is controlled by two different genes

• The first gene controls the expression of red pigment

• The dominant allele (R) indicates the presence of red pigment

• The recessive allele (r) indicates the absence of red pigment

• The second gene controls the expression of either green (G) or yellow (g) pigment

• If red pigment is expressed, the pepper will be red, regardless of the second gene.

• If red pigment is expressed, the pepper will be read, regardless of the second gene.

• If the red pigment is absent, you must look to the second gene to determine color

• If red pigment is expressed, the pepper will be red, regardless of the second gene.

• If the red pigment is absent, you must look to the second gene to determine color

• What would the color of a pepper with the genotype Rrgg be?

• If red pigment is expressed, the pepper will be read, regardless of the second gene.

• If the red pigment is absent, you must look to the second gene to determine color

• What would the color of a pepper with the genotype Rrgg be?

• Red

• If red pigment is expressed, the pepper will be red, regardless of the second gene.

• If the red pigment is absent, you must look to the second gene to determine color

• What would the color of a pepper with the genotype Rrgg be?

• Red

• If red pigment is expressed, the pepper will be read, regardless of the second gene.

• If the red pigment is absent, you must look to the second gene to determine color

• What would the color of a pepper with the genotype Rrgg be?

• Red

• Green

• Looks at the frequency of alleles in a population

• The Principle makes several important assumptions:

• There is not natural selection regarding the gene in question

• There is no genetic drift

• There is no gene flow

• There is no mutation

• Random mating with respect to the gene in question is occurring

• Hardy Weinberg Equation:

• p2 + 2pq + q2 = 1

• p + q = 1

• Hardy Weinberg Equation:

• p2 + 2pq + q2 = 1

• p + q = 1

• p=allele frequency of the dominant allele

• q=allele frequency of the recessive allele

• Hardy Weinberg Equation:

• p2 + 2pq + q2 = 1

• p + q = 1

• p=allele frequency of the dominant allele

• q=decimal version of the recessive allele

• p2 is the frequency of the homozygous dominant genotype

• q2 is the frequency of the homozygous recessive genotype

• 2pq is the frequency of the heterozygous genotype

• Tongue Rolling (dominant)

• Tongue Rolling (dominant)

• Free (dominant) v. Attached (recessive) Earlobes

• Tongue Rolling (dominant)

• Free (dominant) v. Attached (recessive) Earlobes

• Hand Clasping

• Left thumb over right (dominant)

• Right thumb over left (recessive)

• Tongue Rolling (dominant)

• Free (dominant) v. Attached (recessive) Earlobes

• Hand Clasping

• Left thumb over right (dominant)

• Right thumb over left (recessive)

• Widow’s Peak (dominant)

• Tongue Rolling (dominant)

• Free (dominant) v. Attached (recessive) Earlobes

• Hand Clasping

• Left thumb over right (dominant)

• Right thumb over left (recessive)

• Widow’s Peak (dominant)

• Mid-Digital Hair (dominant)

• If the frequency of the recessive allele for sickle cell anemia is .4 in a population of 100,000

• The dominant allele has a frequency of .6

• Individuals that are heterozygous for this allele have a higher resistance to malaria

• How many members of the population would have the increased resistance to malaria?

• If the frequency of the recessive allele for sickle cell anemia is .4 in a population of 100,000 people

• The dominant allele has a frequency of .6

• How many members of the population would have the increased resistance to malaria?

• Heterozygous Frequency = 2pq

• If the frequency of the recessive allele for sickle cell anemia is .4 in a population of 100,000 people

• The dominant allele has a frequency of .6

• How many members of the population would have the increased resistance to malaria?

• Heterozygous Frequency = 2pq

• 2pq = 2 * 0.4 * 0.6 = .48

• If the frequency of the recessive allele for sickle cell anemia is .4 in a population of 100,000 people

• The dominant allele has a frequency of .6

• How many members of the population would have the increased resistance to malaria?

• Heterozygous Frequency = 2pq

• 2pq = 2 * 0.4 * 0.6 = .48

• 48,000 people would have increased malaria resistance

• What is the probability that a father with genotype Hhpp and a mother with genotype HHPp will have offspring that have the dominant phenotype for both traits?

• If the allele frequency for blue eyes in a population is 0.35 and that allele is recessive, what is the frequency of heterozygous individuals in the population?