Observable Patterns of InheritanceChapter 11

Earlobe VariationWhether a person has attached or detached earlobes depends on a single gene Attached earlobes: two copies of the recessive allele for this gene Detached earlobes: either one or two copies of the dominant allele

Early Ideas about HeredityPeople knew that sperm and eggs transmitted information about traits Blending theory Problem:Would expect variation to disappear Variation in traits persists

Gregor MendelStrong background in plant breeding and mathematics Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring

Comments: GeneMendel never used the term, gene, gene, although he clearly made a distinction between, genotypes and phenotypes. The term, gene, was coined by Wilhelm Johannsen (1909) based on the term, Pangenisis which Hugo de Vries (1889) used to describe Mendels concept of inherited units that determine phenotypes.

Genes(Stopped here)Units of information about specific traits Passed from parents to offspring Each has a specific location (locus) on a chromosome

AllelesDifferent molecular forms of a gene Arise by mutation Dominant allele masks a recessive allele that is paired with it

Allele CombinationsHomozygoushaving two identical alleles at a locus AA or aa

Heterozygoushaving two different alleles at a locus Aa

Genetic TermsA pair of homologous chromosomes

Figure 11.4 Page 179A gene locus

A pair of alleles

Three pairs of genes

Figure 11.4 Page 179

Question 11. An early idea about inheritance was theblending theory. What was it and why was it deficient?

Answer 11. An early idea about inheritance was theblending theory. What was it and why was it deficient? Traits from the male and female were blended in the offspring. If this were truth, then eventually, all individuality would disappear.

Question 22. What does the term locus mean?

Answer 22. What does the term locus mean? This is the location of a gene (which chromosome and where on the chromosome). Its address.

Question 33. What are alleles?

Answer 33. What are alleles? These different molecular forms of the same gene.

Question 44. If two genes are homologous, what does that mean?

Answer 44. If two genes are homologous, what does that mean? Homologous means the same. They are identical.

Question 55. What does heterozygous mean?

Answer 55. What does heterozygous mean? Heterozygous means" different. Heterozygous for attached earlobes would mean that the individual carries a normal gene and a mutant gene.

Question 66. If Sally is homozygous dominate for gene A, how would you write that in standard symbolic form? If she were heterozygous for A? If she were homozygous for the recessive form of A?

Answer 66. If Sally were (a) homozygous dominate for gene A, how would you write that in standard symbolic form? (b) If she were heterozygous for A? (c) If she were homozygous for the recessive form of A? AA, Aa, aa

Genotype & PhenotypeGenotype refers to particular genes an individual carries Phenotype refers to an individuals observable traits Cannot always determine genotype by observing phenotype

Parental generation P mates to produce First-generation offspring F1 mate to produce Second-generation offspring F2

Monohybrid CrossesExperimental intercross between two F1 heterozygotes AA X aa Aa X Aa Aa (F1 monohybrids) ?

Question 77. Define phenotype.

Answer 77. Define phenotype. Phenotype refers to an individuals observable traits

Question 88. Define genotype.

Answer 88. Define genotype. Genotype refers to particular genes an individual carries

Question 99. How do you represent the first generation of a cross?

Answer 99. How do you represent the first generation of a cross? Parental cross? Second generation? F1; P; F2

Question 1010. What is monohybrid cross (how many traits are being investigated)?

Answer 1010. What is monohybrid cross (how many traits are being investigated)? It is a cross where two true breeding individuals are mated (AA x aa). Usually (AA aa). they are homozygous dominant and homozygous recessive. One trait (two alleles).

Mendels Monohybrid Cross ResultsF2 plants showed dominant-torecessive ratio that averaged 3:1

5,474 round

1,850 wrinkled 2,001 green

6,022 yellow

882 inflated 428 green

299 wrinkled 152 yellow

705 purple

224 white

651 long stem

207 at tip

Figure 11.5 Page 180

787 tall

277 dwarf

ProbabilityThe chance that each outcome of a given event will occur is proportional to the number of ways that event can be reached

Monohybrid Cross Illustrated

True-breeding homozygous recessive parent plant

F1 PHENOTYPES

aaTrue-breeding homozygous dominant a parent plant

Aa a Aa Aa Aa

Aa

A AA A

Aa Aa

Aa

An F1 plant self-fertilizes and produces gametes:

F2 PHENOTYPES

Aa AA A a Aa

A AA Aa

Figure 11.7 Page 181

a

Aa

aa

Aa

aa

Monohybrid Cross #1Long hair is dominant to short hair in guinea pigs. Show the results of a cross between a homozygous short haired male and a pure long haired female.

Monohybrid Cross #1What do we know? Both parents are homologous. Short haired male hh Long haired female HH (H gene is dominant) hh x HH Draw the Punnett Square

#1 Punnett Squarehh x HHH HMeiosis 2n -> n Ova

h

Hh

Hh zygotes

h sperm

Hh

Hh

All of the F1s are hybrids, or heterogenous and they are long haired.

Monohybrid #2What is the probability that a cross between two guinea pigs both heterogeneous for long would produce a short haired guinea pig?

Monohybrid #2Hh x Hh Draw the Punnett squareH H h h

Complete the problem (p = or 25%)

Monohybrid #3In Holstein cattle the spotting of the coat is due to a recessive allele while the solid colored coat is controlled by a dominant allele. What types of offspring might be produced by a cross between two spotted animals?

Monohybrid #3Cross: spotted cow x spotted cow Cross: ss x ss(where S = solid and s = spotted)

Is it possible to have a solid calf?

Monohybrid #4In lemurs brown eyes are dominant over blue eyes. If a heterozygous brown eyed female mates with a blue eyed male, what would be the expected genotypic and phenotypic ratios of their offspring?

Monohybrid #4Cross: Brown eyed heterozygous female and a blue eyed male (homozygous) B = brown and b = blue Bb x bb = 2 Bb and 2 bb Genotypic ratio Bb:bb 1:1 Phenotypic ratio Brown: blue 1:1

Monohybrid Problem SetForm cooperative groups of 2 to 4 and Solve the problems in the Monohybrid Problem Set. Well check the answers in class.

Mendels Theory of SegregationAn individual inherits a unit of information (allele) about a trait from each parent During gamete formation, the alleles segregate from each other

Test CrossIndividual that shows dominant phenotype is crossed with individual with recessive phenotype Examining offspring allows you to determine the genotype of the dominant individualBB or Bb ? Both brown phenotypes

Punnett Squares of Test CrossesHomozygous recessive a a A a Aa aa Aa aa A A Homozygous recessive a a Aa Aa Aa Aa

Two phenotypes 1:1

All dominant phenotype

Dihybrid Cross

Experimental cross between individuals that are homozygous for different versions of two traits

Dihybrid Cross: F1 ResultsTRUEBREEDING PARENTS: purple flowers, tall AABB x aabb white flowers, dwarf

GAMETES:

AB

AB AaBb

ab

ab

F1 HYBRID OFFSPRING:

All purple-flowered, tall

Figure 11.9 (1) Page 183

Dihybrid Cross: F2 ResultsAaBb X AaBb 1/4 AB 1/4 Ab 1/4 aB 1/4 AB 1/16 AABB 1/16 AABb 1/16 AaBB 1/16 AaBb 1/16 AABb 1/16 AAbb 1/16 AaBb 1/16 Aabb 1/16 AaBB 1/16 AaBb 1/16 aaBB 1/16 aaBb 1/4 ab 1/16 AaBb 1/16 Aabb 1/16 aaBb 1/16 aabb 9/16 purple-flowered, tall 3/16 purple-flowered, dwarf 3/16 white-flowered, tall 1/16 white-flowered, dwarf

1/4 Ab

1/4 aB

1/4 ab

Figure 11.9(2) Page 183

Dihybrid Problem #1A person is heterozygous for tonguetonguerolling and homozygous recessive for freckles. This person marries an individual who is heterozygous for both tonguetonguerolling and freckles. Show all the possible genotypes for their children. Tongue roller Dominant and Non-tongue Nonroller Recessive FrecklesFreckles- Dominant and No Freckles Recessive

Dihybrid Problem #1(Tongue roller no-freckles) x (Tongue norollerroller- freckles) T = tongue rolling dominant tt = non-tongue rolling nonF = freckles dominant ff = no freckles Ttff x TtFf (the cross) Ttff produces Tf and tf gametes TtFf produces TF, Tf, tF, and tf gametes TF, Tf, tF,

Dihybrid Problem #1Ttff x TtFf (symbolizes the cross)TF Tf tF TtfF ttFf tf Ttff ttffzygotes Ova

Tf

TTFf TTff TtFf Ttff

tfsperm

Dihybrid Problem #1Ttff x TtFf (symbolizes the cross)TF Tf tF TtfF ttFf tf Ttff ttffzygotes Ova

Tf

TTFf TTff TtFf Ttff

tfsperm Rollerfrecked Rollerno freckles Nonroller freckles Nonroller No freckles

Phenotypic ratios: 3:3:1:1

Question 1111. Describe or define: dihybrid cross.

11. Describe or define: dihybrid cross.

Experimental cross between individuals that are homozygous for different versions of two traits Example: AABB x aabb

Independent AssortmentMendel concluded that the two units for the first trait were to be assorted into gametes independently of the two units for the other trait Members of each pair of homologous chromosomes are sorted into gametes at random during meiosis

Independent Assortment

Metaphase I:A B A a B b a b

ORa b a b A b A b

A b

A a b B

a B

Metaphase II:A B A B a B a B

Gametes:

B A A 1/4 AB

B a

b a 1/4 ab

b A

b A 1/4 Ab

b a

B a 1/4 aB

B

Dihybrid Problem SetForm cooperative groups of 2 to 4 and Solve the problems in the Dihybrid Problem Set. Well check the answers in class.

Tremendous VariationNumber of genotypes possible in offspring as a result of independent assortment and hybrid crossing is 2n (n is the number of gene loci at which the parents differ)

Impact of Mendels WorkMendel presented his results in 1865 Paper received little notice Mendel discontinued his experiments in 1871 Paper rediscovered in 1900

Dominance RelationsComplete dominance Incomplete dominance Codominance

Incomplete Dominance

X Incomplete Homozygous Homozygous parent parent Dominance All F1 are heterozygous

X

Figure 11.10 Page 184 F2 shows three phenotypes in 1:2:1 ratio

Codominance: ABO Blood TypesGene that controls ABO type codes for enzyme that dictates structure of a glycolipid on blood cells Two alleles (IA and IB) are codominant (I when paired Third allele (i) is recessive to others (i

ABO Blood Type: Allele CombinationsRange of genotypes: IA IA or IA i IA IB IB IB or IB i ii

Blood types:

A

AB

B

O

Figure 11.11 Page 184

ABO and TransfusionsRecipients immune system will attack blood cells that have an unfamiliar glycolipid on surface Type O is universal donor because it has neither type A nor type B glycolipid

Question 12.12. What three types of dominance?

Question 12. What three types of dominance?12. What three types of dominance?

Complete dominance Incomplete dominance Codominance

PleiotropyAlleles at a single locus may have effects on two or more traits Marfan syndrome - Mutation in gene for fibrillin affects skeleton, cardiovascular system, lungs, eyes, and skin

Marfan Syndrome

EpistasisInteraction between the products of gene pairs Common among genes for hair color in mammals

Coat Color in Retrievers

BBEE

X

bbee

F1 puppies are all BbEe

F2 puppies BE BE Be bE Figure 11.13 Page 186 be BBEE BBEe BbEE BbEe Be BBEe BBee BbEe Bbee bE BbEE BbEe bbEE bbEe be BbEe Bbee bbEe bbee yellow black brown

Comb Shape in PoultryP: RRpp (rose comb) X rrPP (pea comb)

F1: F2: 9/16 walnut RRPP RRPp RrPP RrPp 3/16 rose RRpp Rrpp

RrPp (all walnut comb)

3/16 pea rrPP rrPp

1/16 single rrpp

Figure 11.15 Page 187

Comb Shape in PoultryRose RRpp R_pp 3/16

Pea rrP_ 3/16

Single Rrpp 1/16

Walnut R_P_ 9/16

Is the ratio, 9:3:3:1 consistent with a dihybrid cross?

Walnut Comb

http://www.longtail-fowl.com/images/sketches/minohiki_

Campodactyly: Unexpected PhenotypesEffect of allele varies:Bent fingers on both hands Bent fingers on one hand No effect

Many factors affect gene expression

Continuous VariationA more or less continuous range of small differences in a given trait among individuals The greater the number of genes and environmental factors that affect a trait, the more continuous the variation in versions of that trait

Human VariationSome human traits occur as a few discrete typesAttached or detached earlobes Many genetic disorders

Other traits show continuous variationHeight Weight Eye color IQ

Polygenic InheritanceSuppose height in humans is controlled by three sets of genes each on a different chromosome (independently assorted). Assume that each dominant allele contributes 1 unit of height and a recessive allele produces only unit of height. Two average heigth parents have the genotypes: AaBbCc x AaBbCc

Polygenic InheritanceEach parent can produce 8 gametic gene combinations: ABC, ABc, AbC, aBC, Abc, aBc, abC, abc ABc, AbC, aBC, Abc, aBc, abC, What size Punnett Square would we need?

ABC

AB c

Ab C

aB C

ab C AaBb CC AaBb Cc AabbC C aaBb CC aabb CC aaBb Cc Aabb Cc aabb Cc

aB c AaBB Cc AaBB cc AaBb Cc aaBB Cc aaBb Cc aaBB cc AaBb cc aaBbc c

A bcAABb Cc AABb cc AAbb Cc AaBb Cc AaBb cc AaBb cc AAbb cc Aabb cc

ab c AaBb Cc AaBb cc Aabb Cc aaBb Cc aabb Cc aaBbc c Aabb ccaabbcc

ABC ABc

AAB BCCAABB Cc AABb CC AaBB CC AaBb CC AaBB Cc AABb Cc AaBb Cc

AABB Cc AABB cc AABb Cc AaBB Cc AaBb Cc

AABb CC AABb Cc AAbb CC AaBb CC Aabb CC

AaBB CCAaBB CcAaBbC C

AbC aBC abC aBc Abc `abc

aaBB CC

aaBb CC

AaBB cc AABb cc AaBb cc

AaBb Cc AAbb Cc Aabb Cc

aaBB Cc AaBb Cc aaBb Cc

6 units

5.5 units 5 units

4.5 units 4 units

Polygenic inheritance produces a more or less continuous distribution of phenotypes. The more genes involved, the smoother the distribution. Parents AaBbCc 4.5 units each

3.5 units 3 units

Roughly bell shaped

Describing Continuous Variation

Number of individuals with some value of the trait

(line of bell-shaped curve indicates continuous variation in population)

Range of values for the trait

Number of individuals with some value of the trait

Range of values for the trait

Question 13.13. Define pleiotrophy.

Question 1313. Define pleiotrophy. Alleles at a single locus may have effects on two or more traits Examples: Marfans syndrome and Sickle Cell Anemia

Temperature Effects on PhenotypeRabbit is homozygous for an allele that specifies a heatheat-sensitive version of an enzyme in melaninmelaninproducing pathway Melanin is produced in cooler areas of bodyFigure 11.18 Page 190

Environmental Effects on Plant PhenotypeHydrangea macrophylla Action of gene responsible for floral color is influenced by soil acidity Flower color ranges from pink to blue