Genetics Exam 2 Material

for final

Genes on different chromosomes

Independent

Same chromosomes

depends on distance

close = assort together/linked

far = recombinant/crossing over can occur

Linked genes

close together

passed down as unit

do not assort independently

MUST BE ON SAME CHROMOSOME

Mendel’s law of independent assortment

genetic linkage violates this because the law states that no genes have affect on others

Linkage groups

n-sex chromosomes

Humans: 22 autosomal linkage groups, 1 x linkage, 1 y linkage

and mitochondrial linkage groups

Max distance to be considered a linkage group

5mu/cM

Bateson and Punnet

Flower color and pollen shape inherited togetherBa

Bateson and Punnett expected and observed

Expected 9331

However, got 16:1:1:5

Linked genes produce

more parental (nonrecombinant) offspring

fewer recombinant offspring

Incomplete linkage

crossing over

complete linkage

no crossing over = parental only

Recombination frequency

recombinants/total x 100 = % or muCo

Coupling

cis

wild type with wildtype

mutant with mutant

A—B

a—h

Repulsion

trans

wild type with mutant

A—b

a—B

Testcross: of AaBb and aabb yields

91 AaBb

409 aaBb

395 Aabb

105 aabb

Is this repulsion or coupling?

Repulsion because recombinants most common

Why use gene mapping

organization

reproduction predictions

evolutionary relationships

basd on recombinant rates: shows distance and order

Genes close vs Genes far

Genes close: few recombinants (inherited together)

Genes far: many recombinants (crossing over)

Max % of recombinant offspring

anything above 50% or 50 map units are assorted independently

Crossing over occurs between what

non-sister chromatids of homologous chromosomes

Three point cross

Determines gene order, detects double crossovers, construct accurate maps

Interference

measures how one crossover affects another In

Interference equation

I=1-coefficient of coincidence

Coefficient of coincidence calculation

observed double crossover/expected double crossoevers P

Positive interference

fewer double crossovers than expectedE

what does i=0.6 mean

60% of expected crossover did not occur

Quantitative traits

traits showing continuous variation

influenced by multiple genes and environmental effects'

numerical, overlapping phenotypes

bell shaped curve

Quantitative traits examples

Height, skin color, weight, litter size, autism spectrum, multiple sclerosis

Qualitative traits

only a few phenotypes

presence or absence q

qualitative traits examples

cystic fibrosis

Achondroplasia

huntington’s disease

Types of quantitative traits

truly continuous, meristic, thresholdT

Truly continuous

No discrete, spectrum

height weight autism

Meristic

whole numbers only, genetic and environmental

litter size, number of bristles

Thershold

presence or absence (but not qualitative)

susceptibility to disease, big range until threshold

Polygenic

each gene contributes a small additive effect

more contributing alleles = stronger expression

Additive effect example

each allele adds 1 inch to overall plant height

just add + from minimum to find genotype

Nilsson Ehle experiment

intensity of red pigmentation in wheat

F2 generation: # phenotypic classes increase became number of loci affecting character increases'nu

nilsson ehle ratio

F1 all intermediate (light red)

F2 1:4:6:4:1

Chromosomal Abnormalities purpose

medical relevance, agriculture importance

Aneuploidy

changes to individual chromosomes

2n+1 or 2n-1

add or delete ONE chromosome

Polyploidy

changes to sets of chromosomes

2n+n, 2n, 2n+2n

adding an entire set

common in plants

2 types of alterations

change in number of genetic material: duplications and deletions

rearrange, but no change to amount: inversions and translocations

Deletions

chromosome breaks fragment lost c

cru de chat is an example of what

deletion on chromosome 5

Consequence of deletion depends on what

size of delotion, the matieral lost

effects of deletion

imbalances in gene product, expression of normally recessive gene, haploinsufficiency (nonfunctional)

Duplications

Abnormal events during recombination

Duplication consequences

if crossing over: unequal crossing over = nonallelic homologous recombination

Duplication effects depend on what

size

but OVERALL LESS HARMFUL THAN DELETION

gene family

can be caused by duplication, additional material for new genes within a species.

Inversions 2 types

paracentric, pericentric

Paracentric

does not include centromereP

Pericentric

includes centromere

Inversions affects

Break point and PositionP

Break point effect

gene disrupted by breaking within gene = 2 nonfunctional parts

Position effect

gene order is important, when repositioned there is an effect on expression

Translocations

occur between tnonhomologous chromosomes

Types of translocations

1. simple/nonreciprocal

2. reciprocal

3. Robertsonian

Simple/non-reciprocal translocations

chromosome attaches to another chromosome

Reciprocal translocation

2 chromosomes exchange info

• chromosomal breakage and dna repair

  • abnormal crossovers

Robertsonian translocation

familial down syndromed

unbalanced translocation

Robertsonian translocation outcome

6 total

• 3 lethal

• 3 viable

  • 2 with normal phenotype

    • one normal chromosome number: 46

    • one carrier: 45 total chromosomes

  • 1 with FDS

    • 46 chromosomes total

Euploidy

overall variation of number or sets of chromosome

nullisomy

o copies of chromosome

2n-2tr

trisomy

3 copies of chromosome

2n+1mon

monosomy

1 copy of chromosome

2n-1

tetrasomy

4 copies of chromosome

2n+2

Aneuploidy effect

depends on size, less genes = less effect

more effect with autosomal than sex linked due to barr body

triploid

3n

tetraploid

4n

pentaploid

5n

Polyploidy effects in plants

benefits because cell size yields larger plants and can create new species

Odd number of sets yields

autopolyploidy

usually sterile

forms aneuploid gametes

seedless fruit and flowers

Autopolyploidy

1 species

self ferta

allopolyploidy

2 species

Nondisjunction

cell division error

cells with abnormal number of chromosomesM

Nondisjunction Meiosis 1

homologus chromosomes fail to separate

trisomic or monosomic

no normal gametes

Nondisjucntion meiosis 2

half normal, half abnormal gametes

complete nondisjunction

one empty one full gametes

Nondisjunction disorders

down syndrome, turner syndrome, klinefelter syndrome

4 criteria for genetic matieral

Information: stores biological instructions

replication: copied accurately

transmission: passed to daughter cells/offspring

variation: allows mutations for evolution

Classic Experiments

Griffith

avery macleod mccarty

hershey chase

Griffith experiments

Transformation

S smooth strain kills mice

R rough strain does not kill mice

Live s injected into mouse, mouse dies

Avery macleod and mccarty

DNA as the transforming agent

DNase, RNase, Protease

Transformation

horizontal gene transfer, genetic info transferred without reproduction

Hershey and Chase

conclusion: dna not protein is genetic material

bacteriophages labeled with 32P, 35S

phosphorus for dna, was found in cell

sulfur for protein

4 level of dna complexity

1. nucleotide

2. single polynucleotide strand

3. double stranded dna

4. chromsome (dna and proteins)

Nucleotides, what are they made of

phosphate group, sugar, nitrogenous base

DNA made up of

deoxyribose

ATGC

double stranded

NucloeSide

sugar and base, no phosphate

DNA strand structure

sugar phosphate backbone

phosphodiester bond 5-3

Antiparallel strands

complementary base pairing

H-bonds

Chargaff

A=T, G=C

Franklin

x-ray diffractionW

Watson and Crick

model of double helix

A DNA

right helix

11bp per turn

dna/rna hybrids

B DNA

right helix

10 bp per turn

occurs in cells

Z DNA

left helix

12 bp per turn

gc-rich dna

RNA structure

single stranded

ribose sugar

uracil instead of thymine

can fold

Gel Electrophoresis

DNA loaded into gel, electric current applied

DNA moves NEGATIVE TO POSITIVE DIRECTION

smaller fragments move faster

due to negatively charged phosphate backbone

FISH

fluorescence in situ hybridization

fluorescent ssDNA probe binds target DNA

DNA denatured to single strands

binding via complementary base pairingp

purpose of FISH

detect and find out location of specific dna sequences on chromosomes

Where is the dna sequence located in the genome/