3.1-3.5 Genes, inheritance, meiosis

Question 1

Karyotype and karyogram definition

Answer 1

Appearance, number, arrangement of chromosomes in a cell

Diagram showing the systematic arrangement of chromosomes present in order of appearance, number and arrangement

Question 2

Allele definition

Answer 2

Alternative forms of the same gene, at same locus on same type of chromosome that differ from each other by a few bases

Question 3

Mutations definition

Answer 3

Spontaneous, random changes in the genetic code

Question 4

Genome definition

Answer 4

All genetic information of an organism, including DNA in organelles

Question 5

Human genome project aims (6)

Answer 5

1. Identification of all human genes, the proteins they code for ant ehir function
2. Evidence for evolutionary relationships
3. Mutations, genes which cause diseases
4. Drug development based on gene sequences
5. Tailor medicine to individual gene sequences
6. International cooperation

Question 6

Why more genes does not mean more complex - give example

Answer 6

Human - 20 000 genes
Rice - 41500
Fruit fly - 14000
Ecoli - 4300

Question 7

Gene mutation vs chromosome mutation

Answer 7

Gene - small scale alteration of genetic material, change in nucleotide sequence of a particular gene.
Chromosome - large scale alteration of chromosome, number or structure of chromosome is changed

Gene - two types - point mutation and frameshift mutation
Chromosome - three types - duplication, inversion, deletion

Question 8

Explain frameshift and point mutations

Answer 8

Frameshift - insertion or deletion of base, resulting in change in reading frame as mRNA is read in triplets during translation

Point - base pair substitution, replacement of nucleotide and its cbp with another pair of nucleotides

Question 9

Sickle cell anemia condition and inheritance - explain
Symptoms + treatment

Also explain resistance to malaria

Answer 9

• Autosomal codominant
• Gene on sense (coding) strand for beta globin of Hb
• GAG –> GUG
• Glutamic acid (glu) become Valine (Val)
• formation of abnormal beta chains in haemoglobin > abnormal haemoglobin
• in low oxygen content > Hb aggregate into long rods, normal circular biconcave RBC deforms into sickle shape
• sickle shape can clog and clump small vessels
• sickle cells die after 10-20 days, marrow cannot produce new ones fast enough to replace dying ones

Symptoms
- Chronic anemia, stroke, acute chest syndrome, splenic and renal dysfunction, organ damage
Treatment
- Regular blood transfusions in kids, drugs to manage symptoms

Hbs Hbs have severe sickle cell disease, do not survive well
HbA HbA are not resistant to malaria, susceptible to infection
HbA HbS are resistant to malaria, HbS allele makes it hard for malaria parasite to survive well in RBC. Carriers survive malaria infection.
- High HbS allele frequency in areas where malaria is prevalent, confer selective advantage in malaria areas.
- Mild anemia that is only symptomatic during vigorous exercise or low ox levels.

Question 10

Prokaryote vs eukaryote dna

Answer 10

ATGC
- no histones vs histones
- one copy of genome, multiple copies
- nucleoid vs nucleus/chloroplast/mitochondria
- circular vs linear
- no organelles, found in organelles
- no introns, introns
- smaller number of genes vs larger number of genes

Question 11

Bacterial chromosomes explain

Answer 11

• 1 circular chromosome containing all info for basic life processes
• nucleoid
• Single copy of each gene present

Question 12

Plasmids explain (5)

Answer 12

Double stranded, naked, circular
Useful genes, but may not be needed for basic life processes
Replicate independently from chromosomal DNA
Can cross species barrier
Absent in eukaryotes

Question 13

Eukaryote chromosomes explain

Answer 13

Long, linear DNA molecules with histone proteins
Histone proteins: globular, wider than DNA molecule, numerous, DNA molecule wound around
Sister chromatids connected at centromere
Telomeres at ends of chromosome
Gene occupies a specific locus
Alternative alleles on homologous chromosomes
DNA exists as chromatin in interphase, supercoils to form chromosome during mitosis.

Question 14

Hybrid vigor?

Answer 14

Organisms are more vigorous if they have 2 different alleles in stead of just one, which explains why F1 crops grow so quick

Question 15

John Cairns?

Answer 15

Autoradiography to measure length of DNA
- Incubate cultures of ecoli with radioactive thymine, 2 generations later DNA is radioactive
- release DNA by digesting cell wall with lysozymes
- Apply film of photographic emulsion to sample, hold it in place, in the dark for a few weeks
- Microscope to observe where photographic negative has gone dark due to radioactive decay of atoms
- Length and shape observed

Question 16

Meiosis importance

Answer 16

1. Formation of gametes - fertilization involves fusion of 2 haploid to form diploid zygote.
2. If not halved by meiosis, fertilization would cause doubling of chromosome number

Question 17

Meiosis - essay + know how to draw

Answer 17

1. DNA replication - each chromosome has 2 sister chromatids
2. Meiosis - reductive division of diploid cell into 4 haploid cells - meiosis I and II

Prophase I: pair up, cross over between non-sister chromatids, nu envelope, nucleolus break down
Met 1: Pairs line up at equator, spindle fiber attached to centromere
Ana 1: Spindle fibers shorten, homochrom separate and move to opposite poles of cell
Telo 1: Chromosome reach poles, unwind, nu envelope forms

Pro 2: Chromatin threads condense into chromosomes, spindles are formed, nuc envelope breaks down
Met 2: Chromosomes line up at equator of spindle
Ana 2: Sister chromatids seperate
Telo 2: Sister chromatids reach poles, unwind, nu envelope, nucleolus reforms
Subsequent division of cytoplasm to form 4 haploid non-genetically identical daughter cells.

Question 18

Sources of genetic variation - explain

Answer 18

Crossing over: Reshuffling of linked genes resulting in recombinant chromosomes to increase number of allele combinations which occurs during prophase I

Independent assortment: Random orientation of homologous chromosomes during met I and II results in genetic variation. Number of possible chromosome combinations on a cell produced doubles for each additional bivalent. For haploid no n, combinations = 2^n

Random fertilization:
- fusion of gametes is random, resulting combination of alleles is unlikely to have previously existed, promoting genetic variation.

Question 19

Downs syndrome

Answer 19

non-dysjunction during meiosis
hc pairs fail to separate during met I, or chromatids during met II
Results in some gametes to have extra chromosome, individual have extra chromosome
trisomy 21
higher probability with increased age

Question 20

Exception to Mendels law of assortment, Thomas hunt

Answer 20

Anomalous data could not be described by law of indep assortment
Thomas hunt proposed idea of linked genes to account

Question 21

Process of recombination

Answer 21

Def: Recombination - exchange of alleles between non-sister chromatids, occurs during crossing over, resulting formation of new genotype of gamete

Offspring with diff combination known as recombinants

Question 22

Dominant allele, recessive allele definition, codominant allele

Phenotype def

Answer 22

Allele exerts same effect on the phenotype whether it is present in homozygous or heterozygous condition

Allele only exerts effect when present in homozygous state

Alleles which affect phenotype equally when present in heterozygous

Phenotype: observable physical and physiological traits of an organism determined by their genetic makeup

Question 23

Recall how to draw punnet square

Answer 23

Let B = allele for x, let b be allele for Y
F0 phenotype
F0 genotype
Possible gametes
Punnet square for F1

F1 Genotypic ratio
F1 phenotypic ratio

Question 24

Autosomal recessive disease

Autosomal dominant disease

Answer 24

Cystic fibrosis
- CFTR gene on chromosome 7
- CFTR protein is a channel protein controlling movement of Cl ions
- Dysfunctional CFTR - sweat contains exccessive Cl-, mucus and digestive juices not secreted with sufficient Cl, not enough water in secretions, thick mucus build up in lungs, pancreatic duct blocked

Autosomal dominant - huntingtons
- HHT gene on chromosome 4, produces huntingtin
- Degenerative changes on brain

Codominant - sickle cell

Sex-linked - colour blindless/hemophilia

Question 25

Hemophilia

Answer 25

Bleeding disorder, blood does not clot properly - Sex linked, recessive - Allele is on the X chromosome - Sex chromosomes in female: XX, male: XY Hemophiliac males: - XhY, only have one copy of X chromosome so as Y chromosome does not have the allele, so trait is not masked. - inherit Xh from mother, do not pass to sons, carrier daughters Hemophiliac female - XhXh: two copies of hemophilia allele, one from each parent, homozygous Carrier female - XhXH, normal blood clotting as recessive allele is masked. - Heterozygous - Obtained the allele from either parent - 50% chance of affected son

Question 26

Mutation, effects?

Answer 26

Spontaneous, random change to base sequence of gene - Radiation - Chemical mutagens Cause changes in DNA, cell divide uncontrollably, cancer Mutations in germ cells may result in mutations passed on to gametes and then to offspring

Question 27

Mendels Laws

Answer 27

Law of segregation - 2 alleles for a gene separate during meiosis Law of independent assortment - Alleles on homologous chromosomes separate independently and are randomly oriented during meiosis. Transmission of traits to offspring are independent to one another.

Question 28

Linkage group definition

Answer 28

Genes carried on the same chromosome, inherited together, do not assort independently Sex linkages - genes carried on sex chromosome

Question 29

Crossing over process

Answer 29

Synapsis - homologous chromosomes associate Chiasma formation: neighbouring non-sister chromatids cross over each other, point of crossing over is known as chaisma Holliday jn: Chromatids are cut at the chiasma, Holliday junction forms, DNA of cut section attaches to open end of opposite non-sister chromatid Recombination - alleles swapped, increase in genetic variation, recombination of linked alleles.

Question 30

Discrete vs continuous variation

Answer 30

Discrete - one gene - distinct categories - qualitative - unaffacted by environment Continuous - multiple genes: Polygenic inheritance, a result of many genes which may be on different chromosomes interacting together. - no distinct categories - quantitative - affected by environment

Question 31

Explain skin colour inheritance

Answer 31

- Polygenic inheritance - Many genes contribute to skin colour - amount of melanin - Combination of alleles determines phenoype - Phenotype not follow Mendelian ratios - Is affected by environmental conditions - exposure to sunlight stimulates production of melanin in skin

Question 32

AGE purpose

Answer 32

- Separate charged molecules based on size, electrical charge, other physical properties - Nucleic acids are -ve charge, move to positive electrodes - Splice DNA with restriction enzymes into fragments - Pipette fragments into wells, apply electric field - DNA move across the gel fragments, larger fragments > heavier > slower - Based on size, DNA fragments from pattern of bands on the gel - Stain to produce unique pattern - DNA profile

Question 33

DNA profile process and uses

Answer 33

- Get DNA sample - PCR to amplify copies - Cut with restriction endonuclease enzymes at specific places - AGE to sort fragments by size - Staining of bands to produce DNA profile - Compare profiles of different individuals Forensic evidence Determination of paternity Diagnosis of inherit disorders Develop cure for inherited disorders - locate location of genetic disorder on chromosome based on info from DNA fingerprint

Question 34

Genetic modification - plasmid as a vector essay

Answer 34

1. mRNA for required gene identified, extracted 2. DNA copies made with reverse transcriptase 3. PCR to amplify copies 4. Restriction endonuclease enzyme, sticky ends 5. Obtain plasmid, cut with same restriction enzyme to produce sticky ends 6. mix DNA copy with plasmid, join together by cbp at sticky ends. 7. Add ligase to link nucleotides of DNA fragment with that of plasmid 8. Recombinant plasmid 9. Introduce recombinant plasmid into suitable bacteria to form recombinant bacteria

Question 35

Pros and cons for GM crops

Answer 35

Pros - Higher crop yield - Increased tolerance to harsh conditions - Pest resistance - Shelf life - Nutritious - Lack toxins or allergens - Natural vaccines that confer natural disease resistance Cons - Crops may spread to sites where they cause harm - Transferred gene spread to other species: superweeds - GM crops producing pesticide kills non-pest insects - Reduce diversity, encourage monoculture - Encourage overuse of herbicides - Proteins from transferred genes - allergic reaction - Antibiotic genes used as markers during gene transfer could spread to pathogenic bacteria - Health effects of exposure unclear

Question 36

Cloning process

Answer 36

1. Obtain diploid cells from donor animal 2. Obtain egg cells from second donor 3. Remove haploid nucleus from egg cell 4. Extract first donor cells diploid nucleus, insert into egg to form zygote/fuse two cells with electric shock 5. Implant embryo in surrogate mother 6. Completion of normal pregnancy results in clone.