Unit 4 Review

Question 1

Process of meiosis

Answer 1

MEIOSIS I (genetic recombination and reduction division)
Prophase I
homologous chromosomes line up next to each other
Crossing over: non-identical sister chromatids exchange DNA – cross over at places called chiasmata, chromosomes break in identical locations, pieces exchanged – creates NEW combinations of genes
Metaphase I
Random orientation: homologous chromosomes line up randomly along middle of cell (2n possible orientations)
Anaphase I
Spindle fibers pull homologous chromosomes to opposite ends of the cell (independent assortment – genes on different chromosomes separate independently of each other)
Telophase I
Reduction division (cytoplasm divides – each new cell now haploid)

MEIOSIS II (resembles mitosis – separates sister chromatids)
Prophase II
New meiotic spindle forms (eggs in females arrested in this stage)
Metaphase II
Chromosomes (made of sister chromatids) line up along middle of cell
Anaphase II
Centromeres break, sister chromatids separate, one copy of each pulled to opposite ends of cell
Telophase II
Cytoplasm divides: 4 haploid cells that are genetically UNIQUE

Question 2

Infinite genetic variation

Answer 2

Crossing over in prophase I and random orientation in metaphase I
random fertilization with another individual too – takes into account THEIR crossing over and random orientation

Question 3

Non-mendelian inheritance

Answer 3

Linked genes
Genes on the same chromosome
Linked genes do NOT follow law of independent assortment: inherited together because on SAME chromosome
Only way for recombination to occur in linked genes is during crossing over in prophase I
Most offspring will show parental phenotypes because genes inherited together on same chromosome

Polygenic inheritance Genes that have multiple alleles Phenotypes do NOT fit into distinct categories Phenotypes are continuous because SO many alleles influence the expression of the gene

Mitochondrial DNA is always inherited from the mother for males

Sex-linked traits
Traits that are on the X or Y chromosomes (sex chromosomes)
Sex linked traits are more commonly seen in males because they only have one X chromosome
Only females can be carriers of sex-linked traits
Hemophilia and red-green color blindness are sex linked traits

Codominant alleles both show if they are present (A B for blood type)

Question 4

How karyograms are made and used to diagnose non-disjunction and determine biological sex

Answer 4

Fetal cells obtained from amniotic fluid or chorionic villus
Chromosomes arranged in pairs according to size/ structure
23rd pair used to diagnose gender (XX = female, XY = male)

Nondisjunction:
Failure of sister chromatids to separate
Cells produced missing a chromosome (monosomy – ONE copy ONLY when fertilized) or have an extra chromosome (trisomy – three copies when fertilized)

Question 5

Outcomes of non-disjunction

Answer 5

Nondisjunction results in gametes that are either n+1 or n-1 chromosomes
Patau’s Syndrome (trisomy 13)
Edwards Syndrome (trisomy 18)
Down Syndrome (trisomy 21)
Klinefelter Syndrome (XXY)
Turner’s Syndrome (monosomy X)

Question 6

Polygenic inheritance

Answer 6

The inheritance of traits that are determined by more than one gene
Continuous variation (bell shaped)
Skin color (amount of melanin)

Question 7

Chi-square analysis

Answer 7

Df = n - 1
If your chi-square calculated value is greater than the chi-square critical value, then you reject your null hypothesis
Chi-square calculated > critical value, reject null hypothesis

Question 8

PCR

Answer 8

artificial method of replicating DNA under laboratory conditions
used to amplify large quantities of a specific sequence of DNA from an initial minute sample
uses a thermocycler

Question 9

Gel electrophoresis

Answer 9

DNA sample amplified using PCR
Cut DNA with restriction enzymes then run through gel using electric current (separates based on SIZE and charge – fragment lengths UNIQUE to each individual due to unique sequences of DNA)
Produces banding pattern in gel (bands represent sizes of fragments – smaller fragments travel faster/ farther)
Used in DNA Profiling (typically use highly repetitive/ satellite DNA because unique to every individual):
1. Forensic Investigations
2. Paternity testing (half of baby’s bands from mom, other half MUST come from dad)

Question 10

Pros and cons of GMO

Answer 10

PROS
Added nutrients (vitamin A/ beta carotene in rice)
Higher yields, longer shelf life
Resistance to herbicides, drought, cold etc.; Reduced need for pesticides (harmful to humans etc.)

CONS
Introduced genes cause allergies
Introduced genes mutate (outcompete wild populations and/ or spread/ cross species) and reduce genetic variation/ biodiversity (Potato blight/ Bt corn)
Monopolies on food production (small farms out of business?)

Question 11

Process of producing genetically modified organisms

Answer 11

PCR conducted
Gene cloning (clone = genetically identical copy) using recombinant DNA
Produce recombinant DNA
Cut vector (plasmid) and gene of interest with restriction enzyme (endonuclease)
Combine DNA fragments (will base pair at sticky ends)
Add DNA ligase (to seal fragments together)
Insert recombinant DNA back into host (bacteria, yeast, sheep etc)
Able to do because DNA/ genetic code is universal
Allow cells to reproduce gene (and make protein)
Ex: Insulin for diabetics , Factor IX for hemophiliacs

Gene transfer
Recombinant DNA made (donor + host) and placed into host organism
Host organism now transgenic (GMO = genetically modified organism): has had an artificial genetic change to its genome
Genes transferred to treat disease (gene therapy), for medical treatments
(insulin), and for commercial use (crops/ livestock)

Question 12

Sickle cell anemia

Answer 12

GAG changed to GTG coding for valine instead of glutamic acid
hemoglobin misshapen and cannot carry oxygen as well
provides some protection against malaria