Genetics is the study of theMapping Between

Phenotype and Genotype

Genotype: Genetic state of an individual.

Phenotype: Physical state of an individual, i.e.,size, shape, behavior, physiology.

YY

Yy

yy

Our Goal: To understand the “population consequences”Of Mendel’s Laws.

Question 1: How do we describe a Mendelian populationin evolutionary terms?

Question 2: How is a population with Mendelian inheritancedifferent from a population with Blending Inheritance?

Question 3: What effect does reproduction have on the heritable variation in a Mendelian population?

Question 1: How do we describe a Mendelian population?

TWO Possibilities for the description:1. List all the different genetic kinds of individuals.2. List all the different kinds of genes.

Three kinds of Individuals:

YY individuals

Yy individuals

yy individuals

Two kinds of Genes:

Y and y

Genetic Terms

Allele: a type of gene. For example, for seed color, thereare two types of genes, Y and y. Y and y are alleles of the seed color gene.

Dominant Allele: Y is the dominant allele.Recessive Allele: y is the recessive allele.

Genotype: Genetic state of an individual.

Phenotype: Physical state of an individual.

YY Yy yy

YY Yy

Genetic Terms for Genes

Allele: a type of gene. For example, for seed color, thereare two types of genes, Y and y. Y and y are alleles of the seed color gene.

How Many Alleles can one gene have?

More than 285 alleles for cattle coat color gene!More than 480 alleles for human blood group gene!

Polymorphism: A polymorphic gene has > 1 allele.

Genetic Terms for Individuals

Genotype: the genetic state of an individual. YY, Yy, and yy are seed color genotypes.

Haploid individuals have one allele of each gene.

Diploid individuals have two alleles for each gene.

A a

AA aa

Genetic Terms for Individuals

Species with Haploid individuals (one allele of each gene):

1. Bacteria and viruses2. Males in the bees, ants, and wasps. 3. Male mammals are haploid for all genes on the

X-chromosome: Males Xy but Females XX

Species with Diploid individuals:1. Insects2. Mammals3. Birds4. Plants.

Genetic Terms for IndividualsHaplo-diploid female individuals have two alleles for each gene, but males have only one allele. These include Hymenoptera: the bees, ants, wasps.

Females Males

Triploid individuals have three alleles for each gene. These include some parthenogenic frogs, lizards, and weevils.

Tetraploid individuals have four alleles for each gene. These include many varieties of ornamental and agricultural plants, like sunflowers, mums.

AAA

AAAA

AAA

Haploid individuals have ONE allele of each gene

Cyanobacteria

Staphylococcus aureus

More than 100,000 species. Oldest known fossils 3.5 billion years ago. Aquatic, photosynthetic, engineers of the atmosphere, and oil. A relative is the chloroplast in plants, one of the oldest symbioses.

Vibrio cholerae

A

Diploid individuals have TWO alleles of each gene AA

Haplo-Diploid species: Males are Haploid Females are Diploid

Hymenoptera the bees, ants, and

wasps. More than 100,000 species.Why so many Social Species?

Queen andworkers are

Diploid

Male dronesare Haploid

A

AA

Triploid individuals have THREE alleles of each gene

Hemidactylus garnotti

Rana esculenta

Poecilia formosa

Why are all vertebrate parthenogens triploid?

AAA

Tetraploid individuals have FOUR alleles of each gene

Magnolia

Coffea arabicaArachis hypogaea

AAAA

More Genetic Terms for Individuals

Diploid Individuals: Mendel’s peas and humans for the autosomal genes!

Homozygous Genotype: YY and yy individuals. These individuals have two copies of the same allele.

Heterozygous Genotype: Yy individuals. These individuals have two different alleles, Y and y.

How many Genotypes are there?

Answer depends upon how many alleles there are at each gene and upon how many genes you are describing.

Genetic Terms for Diploid Individuals

How many one-gene diploid Genotypes are there?

Alleles Genotypes 1 allele, Y1 1 genotype: Y1Y1

2 alleles, Y1 and Y2 3 genotypes: Y1Y1, Y1Y2, Y2Y2

Question: If there were a gene with 3 alleles, Y1, Y2, Y3, How Many Diploid Genotypes could exist?

Genetic Terms for Diploid Individuals

How many one-gene diploid Genotypes are there?

Alleles Genotypes 3 alleles, Y1, Y2, Y3 6 genotypes: Y1Y1, Y1Y2, Y1Y3

Y2Y2, Y2Y3,

Y3Y3

Genetic Terms for Diploid Individuals

How many one-gene diploid Genotypes are there?

Alleles Genotypes

3 alleles, Y1, Y2, Y3 6 genotypes: Y1Y1, Y1Y2, Y1Y3 Y2Y2, Y2Y3, Y3Y3

M alleles, Y1, Y2, …YM (M)(M + 1)/2 genotypes

285 coat color alleles 40,755 possible cattle genotypes480 blood group alleles 115,440 human blood genotypes

Genetic Terms for Individuals

How many two gene diploid Genotypes are there? Y-gene 1 allele, Y1 1 genotype: Y1Y1 X1X1

X-gene 1 allele, X1

Y-gene 2 alleles, Y1,Y2 9 genotypes:X-gene 2 alleles, X1,X2 Y1Y1 X1X1 , Y1Y1 X1X2

Y1Y1 X2X2 , Y1Y2 X1X1

Y1Y2 X1X2 , Y1Y2 X2X2

Y2Y2 X1X1 , Y2Y2 X1X2, Y2Y2 X2X2

(3 Y genotypes)(3 X genotypes) = 9 genotypes

Alleles Genotypes

Genetic Terms for Individuals

How many two gene Genotypes are there?

Alleles Genotypes

N genes each with M alleles, Y1, Y2, …YM (M)(M + 1)/2 genotypes/gene

Total Possible Genotypes {(M)(M + 1)/2}N

Number of Alleles and Number of Genotypes

Haploid Species: The number of possible genotypes at one gene with M alleles equals M.

…..

Diploid Species: The number of possible genotypes at one gene with M alleles, equals (M)(M + 1)/2 .

…..

A1 A2 A3AM

A1A1 A1A2 A1A3A1AM

A2A2 A2A3 A2A4 A2AM

AMAM

Total Possible Diploid Genotypes {(M)(M + 1)/2}N

How many Human Genotypes are there?

Estimated 26,000 genes in the human genome.

Each gene has a minimum of 10 alleles or (10)(10 + 1)/ 2 = 55 genotypes per gene.

5526,000 >>>>>>>>> 6 x 109 people now on Earth

Each human genotype is unique, never occurred beforeand will never occur again in human history.(Not even with cloning!)

Describing a Mendelian Population with N diploid individuals, where N = an integer number.

There are TWO Possible Descriptions:1. List all the different genetic kinds of individuals,

i.e., list all genotypes.

2. List all the different kinds of genes, i.e., list all the alleles at all the genes.

Population of Genes is described in terms of Gene Frequencies. If there are two seed color genes, Y and y, the frequency of the

Y allele is represented as

pY = (Number of Y genes)/(Total Size 2N)

py = (Number of y genes)/(Total Size 2N)

pY + py = 1.0

Question: Why is the denominator 2N?

Populations of Genotypes: Described in terms of Genotype Frequencies. If there are three seed color genotypes, YY, Yy, and yy, the genotype frequency

of YY is represented GYY = (Number of YY genotypes)/(Total Size, N)

GYy = (Number of Yy genotypes)/(Total Size, N)

Gyy = (Number of yy genotypes)/(Total Size, N)

GYY + GYy + Gyy = 1.0

Question: Why is the denominator N?

Populations of Genes from Populations of Genotypes pY = {(2)(Number of YY) + (1)(Number of Yy)}/(2N)

pY = (2)(Number of YY)/(2N) + (Number of Yy)/(2N)

pY = GYY + (1/2) GYy

py = {(2)(Number of yy) + (1)(Number of Yy)}/(2N)

pY = (2)(Number of yy)/(2N) + (Number of Yy)/(2N)

pY = Gyy + (1/2) GYy

AAGametes: 1 A

Frequency: GAA

AaGametes: ½ A, ½ a

Frequency: GAa

aaGametes: 1 a

Frequency: Gaa

AAGametes: 1 A

Frequency: GAA

AaGametes: ½ A, ½ a

Frequency: GAa

aaGametes: 1 a

Frequency: Gaa

Female Parents in Population

Males

The Mating System determines how frequent each of the different Mendelian families is relative to the other families. The Mating System describes howindividuals find their mates and provides a rule fordetermining the frequencies of the Mendelian Families.

Many different Mating Systems are possible: Monogamy = “one mate per individual”Polygyny = “several females per male”Polyandry = “several males per female”Positive Assortative Mating = “like mates with like”Negative Assortative Mating = “opposites attract”Random Mating