LB#144:#Organismal#Biology#

Class#8#02/04/2016#

Learning#objec<ves##

1.  Explain# Mendel’s# laws# with# rela<on# to# gamete#forma<on#and#inheritance#of#traits.#

2.  Model# and# diagram# how# meiosis# accounts# for#Mendel’s#observa<ons.#

3.  Apply# the# principles# of# simple# Mendelian#inheritance#to#predict#paLerns#of#inheritance.#

2#

1. Principle of Segregation -  Diploid organisms have pairs of alleles -  Individual alleles in the pair separate during meiosis -  Meiosis I- separation of homologous chromosomes

2. Principle of Independent Assortment -  Different pairs of alleles on different chromosomes

separate independently of each other during meiosis. -  Meiosis I- alignment of chromosomes

Mendel’s(Laws(

Parental(Genotype:((

Male((((((((((((((((((((((((((((Female(

RrTt((((((((((((((x(((((((((((((((RrTt(

Carbonless: Mendel 2. Name (Last, First) Group Number, name

Q1. You are a researcher in a plant lab, performing a series of mating experiments with peas. You are studying 2 monogenic traits: plant height and seed shape. Genes for the two traits are on different chromosomes. Gene for height has 2 alleles: T = tall plants t = short plants. T is dominant, t is recessive Gene for seed shape has 2 alleles: R = round seeds r = wrinkled seeds. R is dominant, r is recessive You set up a cross between parents that are heterozygous for both traits.

Q1. What are the parental genotypes and phenotypes? Male: Female:

Q2. List all possible genotypes for male and female gametes. Male: RT Rt rT rt Female: RT Rt rT rt

How does alignment for chromosomes affect gamete formation?

- In meiosis 1, the arrangement of homologous chromosomes on either side of the equatorial plane is random. -  Alleles on different chromosomes separate independently - Principle of Independent Assortment

OR

Parental(Genotype:(( RrTt((((((((((((((x(((((((((((((((RrTt(

Carbonless: Mendel 2. Name (Last, First) Group Number, name

Q1. You are a researcher in a plant lab, performing a series of mating experiments with peas. You are studying 2 monogenic traits: plant height and seed shape. Gene for height has 2 alleles: T = tall plants t = short plants. T is dominant, t is recessive Gene for seed shape has 2 alleles: R = round seeds r = wrinkles seeds. R is dominant, r is recessive You set up a cross between parents that are heterozygous for both traits.

On your whiteboard: draw a punnet square to predict genotype and phenotype of progeny. Q3 Write down the phenotypic ratio for progeny

Phenotypic Ratio:

1. Principle of Segregation -  Diploid organisms have pairs of alleles -  Individual alleles in the pair separate during meiosis -  Meiosis I- separation of homologous chromosomes

2. Principle of Independent Assortment -  Different pairs of alleles on different chromosomes

separate independently of each other during meiosis. -  Meiosis I- alignment of chromosomes

Mendel’s(Laws(

•  genes that occur on the same chromosome

•  In the figure to the right, the SCA1, IDDM1, and EPM2A genes are linked because they all occur on Chromosome 6

Viola;on(of(Independent(

Assortment:(Linked(Genes(

f F F f

QQq q Linked(Genes(

Genes#that#occur#on#the#same#chromosome#will#not#assort#independently#

Independent#assortment#applies#to#whole(chromosomes(

R R R R

T T t t

f F F f

QQq q

CQ1:#How#many#unique(

genotypes(of(

gametes(will#form?#

A. 2#B. 4#

C. 8#D. 16#

R R R R

T T t t

Prophase(I(of(meiosis(

Nonsister(chroma;ds(

held(together(

during(synapsis(

Pair(of(homologs(

Does(this(mean(genes(on(the(same(

chromosome(can(never(be(separated?(

Prophase(I(of(meiosis(

Nonsister(chroma;ds(

held(together(

during(synapsis(

Pair(of(homologs(

Chiasma(

Centromere(

TEM(

Anaphase(I(

Anaphase(II(

Daughter(

cells(

Recombinant(chromosomes(

t

f F

TTt

F f

QQq q CQ2.(Which#crossingSover#event(s)#will#

change#the#possible#genotypes#of#the#resul<ng#gametes?#

R R R R

A A a a

D dd D

A)(

B)(

C)(

Gene 1 Gene 2 Gene 2

Gene 3

Crossing over occurs frequently between genes that are far apart

Crossing over is rare between genes that are close together

Larger the distance between genes, more likely to have cross-over Linkage mapping

Four#mechanisms#contribute#to#gene<c#varia<on#among#offspring:#

– #Muta<on#(origin#of#all#new#alleles,#and#thus#varia<on,#segrega<on#of#alleles#makes#sure#you#get#one#from#each#parent)#

– #Independent#Assortment#

– #Recombina<on#

– #Random#fer<liza<on#

Q4. In 1-2 sentences explain

a) Mendel’s law of segregation

b) Mendel’s law of independent assortment

?

Pedigree(=(family(tree(with(relatedness,(sex(and(phenotype(

Many(human(gene;c(disorders(are(known(to(be(inherited(

as(dominant(or(recessive(traits(controlled(by(1(gene(locus(

Autosomal Recessive Inheritance

•  Males and females are equally likely

to be affected

•  Affected offspring often have

unaffected parents

•  Trait often skips generations

•  Unaffected parents of affected

offspring are heterozygous (carriers)

•  Affected offspring are homozygous

Unaffected male Unaffected female Affected male Affected female

Homework 1

Q1. Assume that cystic fibrosis is a single gene disorder. Draw a pedigree showing the family history of cystic fibrosis in Sarah and Michael’s families. Predict all possible genotypes for each person in the pedigree. [Hint: For some individuals, there might be more than one possible genotype. Write all possible genotypes.] 2.5 pts - 1.5 pts for correct pedigree chart and genotypes , 1pt for key

?

Ff Ff Ff Ff

ff Ff FF

Ff FF

ff

Unaffected male Unaffected female Affected male Affected female

F dominant allele (WT) f recessive allele (Cys.fibrosis/ mut CFTR)

Sarah Mike

Autosomal Recessive Inheritance

•  Males and females are equally

likely to be affected

•  Affected offspring often have

unaffected parents

•  Trait often skips generations

•  Unaffected parents of affected

offspring are heterozygous

(carriers)

•  Affected offspring are homozygous

?

Ff Ff Ff Ff

ff Ff FF

Ff FF

ff

Unaffected male Unaffected female Affected male Affected female

F dominant allele (WT) f recessive allele (Cys.fibrosis/ mut CFTR)

Q2. Based on the pedigree predict the mode of inheritance (recessive/dominant) for cystic fibrosis. Write a scientific argument to support your claim. [Note: Scientific explanations consist of Claim, Evidence, Reasons/Warrants.] 1.5 pts, 0.5 for each

?

Ff Ff Ff Ff

ff Ff FF

Ff FF

ff

Unaffected male Unaffected female Affected male Affected female

F dominant allele (WT) f recessive allele (Cys.fibrosis/ mut CFTR)

Claim: Cystic fibrosis has a recessive mode of inheritance

Evidence: Parents are unaffected with affected child.

Warrants: Unaffected parents are carriers (Ff) and can each pass on recessive (f) allele to offspring, resulting in homozygous (ff) offspring with recessive phenotype (cystic fibrosis). (If the mode of inheritance were dominant at least one parent MUST be affected.)

Q3. Use a box and arrow model to explain how certain genotype(s) result in cystic fibrosis. [Note: box and arrow models must have; 1. A legend/title 2. A purpose, or objective. Structures, or components in boxes 4. Relationships, or mechanisms (how the elements interact – write this on the arrow!) 5. It can have branches] 2pts

bb genotype includes

2 b alleles that code for

Defective/No CFTR protein

Chloride and water efflux from cells

that does not result in

Sticky mucus

resulting in Blocked airways and bacterial infections

that results in

Cystic Fibrosis resulting in

Title: ‘bb’ genotype results in individuals with cystic fibrosis. b is a recessive allele that codes for defective or no CFTR protein

Bb genotype

WT mucus

resulting in No blocked airways and bacterial infections that results in

NO Cystic Fibrosis/ Unaffected individual resulting in

Title: ‘Bb’ genotype results in individuals with no cystic fibrosis (unaffected). b is a recessive allele that codes for defective or no CFTR protein, B is a dominant allele and codes for WT CFTR protein

that codes for Defective/No CFTR protein

that codes for WT CFTR protein

Chloride and water efflux from cells

includes 1 b allele

1 B allele

Q4. Once sequencing of the CFTR gene is complete, you would have the genotypes of Sarah and Michael. a) From the sequencing results, what would Sarah and Michael’s genotypes have to be for it to be possible for them to have a child with cystic fibrosis. 1pt

?

Ff Ff Ff Ff

ff Ff FF

Ff FF

ff

Unaffected male Unaffected female Affected male Affected female

F dominant allele (WT) f recessive allele (Cys.fibrosis/ mut CFTR)

Ff and Ff

b) From the sequencing results, what would Sarah and Michael’s genotypes have to be so that they do not need to worry about having a child with cystic fibrosis. 1pt Both FF OR One FF and one Ff

Research proposal 1. The study of a ‘DNA repeat structure’ found in Haloferax mediterranei, a microorganism that can survive in extremely high salt conditions.

Summary: H. mediterranei is a microbe that can survive in extremely high salt conditions. The presence of similar repeat structures in multiple salt tolerant microbes may indicate its importance in establishing salt tolerance. Other repeats with similar structure have also been potentially identified in other microbial species, indicating that the repeats likely play an important role in bacteria. Based on preliminary evidence, here are some hypotheses for the role of these repeats in bacteria: Bacterial gene regulation, bacterial DNA repair…

Research proposal 2. Using gene Therapy as a cure for single gene disorder cystic fibrosis.

Summary: Cystic fibrosis is a single gene disorder that is caused by a mutation in the CFTR gene. Recent medical progress has resulted in multiple treatments for patients with CF that treat the symptoms. However, there is no cure for this disorder and CF patients today are still likely to die in their thirties. With gene therapy, we could replace the mutant CFTR allele in patients with a normal copy, thus resulting in a permanent cure. The normal copy could potentially be targeted specifically to affected organs such as lungs, thus alleviating symptoms permanently.

Q5. Make a decision and give a SHORT explanation [NO more than one paragraph] as to why you came to this decision. Keep in mind that you might be asked to defend your decision before Congress and the general public. (2pt)