Review #4 presentation Flashcards
What are the problems in meiosis
Non-disjunction
- failure of sister chromatids to separate (anaphase II)
- cells produced missing a chromosome (monosomy: one copy only when fertilized)
or they have an extra chromosome (trisomy: three copies when fertilized)
how is nondisjunction diagnosed
Karyograms
- fetal cells obtained from amniotic fluid (amniocentesis) or chorionic villus (placenta)
- chromosomes are arranged in paris according to size and structure
- 23rd pair used to diagnose gender (XX female XY male)
what is genetics
science of heredity (pass on of genetic material from parent to offspring)
prokaryotes genetics
circular, naked (no proteins) chromosomes
pass directly to offspring (asexual reproduction)
eukaryotes genetics
linear with proteins (histones)
many pairs
passed to offspring through sexual reproduction
genes are carried on …
chromosomes
what are genes
heritable factors (DNA) that determine specific traits (code for proteins)
what is a genome
the complete set of all DNA base sequences of an organism
what is unique to different species
number of genes, chromosomes, and size of genome
more DNA does not always mean…
that an organism is more complex/advanced than another
What is a genes location on specific places of chromosomes
locus
what are the different forms of genes
alleles
two things that an allele can be
dominant or recessive
what is the difference between dominant and recessive
dominant: stronger - written with a capital letter
recessive: weaker - written with lowercase letter
what is the physical expression of a trait (what you see)
phenotype (ie Green eyes)
what is a genotype
combination of alleles an organism has for a trait (ie: bb)
What can genotypes be
heterozygous: different alleles - Aa
homozygous: same alleles
homozygous dominant: AA
homozygous recessive: aa
what is a carrier
a heterozygous individual (Nn)
they carry recessive alleles but do not show them in their phenotype due to the presence of a dominant allele
this is important in sex-linked traits and genetic diseases
what are codominant alleles
equal in strength alleles - both will show if this is present
what is an example of codominant alleles
blood groups
what alleles are equally dominant and what is recessive
A (I^A) and B (I^B) are dominant
O (i) is recessive
what are genes carried on
sex-chromosomes (sex-linked)
what do males additionally inherit from an egg (mothers)
mitochondrial DNA
X and Y are not ______ chromosomes
homologous
some genes on larger X chromosome are absent from shorter Y chromosome
What are more commonly seen in males
sex-linked traits
only one x chromosome so whatever they inherit will show because there is no other chromosome to overpower it
Examples of sex linked traits
hemophilia and red-green color blindness
- on the x chromosome
- males inherit x from mother
- IF the recessive allele is on the X, the man WILL have the condition (XY)
Who is a carrier of sex-linked traits
females - two X chromosomes so they can be heterozygous -> dominant allele on one X and a recessive allele on the other
polygenic
genes that have multiple alleles
what do polygenic traits show
continuous (bell-shaped curve) varition
non-discrete variation
Do phenotypes fit into distinct categories
no
phenotypes are continuous because so many alleles influence the expression of the gene
(ie: SKIN COLOR (melanin), height, hair color, etc)
What is something that could influence the expression of skin color, height, hair color, etc
environment: UV liet, diet/nutrition
if a dominant phenotype is showing:
conduct a TEST CROSS
mate with homozygous recessive
if any offspring show the recessive phenotype - parent is heterozygous
if all offspring show dominant phenotype - parent is homozygous dominant
what is a mutation
changes in genetic material (DNA)
rare
what is base substitution
one base in DNA is changed
- causes wrong codon in mRNA
- causes wrong amino acid in translation
what is an example of a mutation
sickle cell anemia
- DNA: GAG is changed to GTG
- mRNA: wrong codon codes for valine instead of glutamic acid in the polypeptide chain
results in the hemoglobin being misshapen (sickle shaped) and can’t carry oxygen as well
why does sickle cell anemia and other disease causing alleles persist in populations
they can provide some advantages
- resist to maleria if you have sick cell anemia
- beneficial if you live an environment where maleria is present
what determines if an allele is good or bad
ENVIRONMENT
dihybrid
two trait cross in unlinked genes
dihybrid heterozygous cross shows what ratio
9:3:3:1
numbers in ratios are out of 16
how do you set up a dihybrid heterozygous punnet square
4x4
number alleles 1,2,3,4
foil them and place the combinations over the boxes for each parent
1,3 1,4 2,3 2,4
dihybrid crosses are ____ genes
linked
who discovered that dihybrid crosses are linked genes
Thomas Hunt Morgan using fruit flies
What law do linked genes not follow
the law of independent assortment:
they are inherited together because they are on the same chromosome
Linked genes do not…
show typical ratios (9:3:3:1 or 1:2:1)
vaary significantly
chi-squared test performed: compare observed and expected
this shows the significant difference btw observed and expected phenotype ratios in offspring
how are genotypes written for dihybrid crosses
vertical pairs with two horizontal lines between them
what is the only way for recombination in linked genes
crossing over (phrophase I) unlinked genes follow independent assortment to create new combinations of chromosomes
why will most offspring show parental phenotypes
because genes are inherited together on the same chromosome (only a small percentage of recombinants)
what are recombinants
New phenotypes, not present in parents from crossing over
what are some genetic disorders caused by
dominant alleles
ie: huntington’s disease
how do you make multiple copies of a gene
PCR (polymerase chain reaction)
Gene cloning
what is PCR
makes many copies of a small amount of DNA (amplifies it) using a thermocycler
what is gene cloning
clone = genetically identical copy
uses recombinant DNA
- produce recombinant DNA (DNA from two or more different sources/organisms)
- cut vector (plasmid) and gene of interest with a restriction enzyme (endonuclease)
- combine DNA fragments (will base pair at sticky ends)
- add DNA ligase to seal fragments back together - insert recombinant DNA back into host (bacteria, yeast, sheep, etc)
- able to do this because the DNA code is universal - allow cells to reproduce gene and make proteins
- insulin for diabetics
- facter IX for hemophiliacs
Gene transfer
- recombinant DNA made (donor + host) and placed into host organism
- host organism is now transgenic (GMO) has had an artificial change to its genome
- genes transferred to treat disease (gene therapy) for medical treatments (insulin), and commercial use (crops)
pros to GMO crops
- added nutrients (vitamin A in rice)
- higher yields
- longer shelf life
- resistance to herbicides, drought, cold, etc
- reduced need for pesticides
cons of gmo crops
- introduced genes cause allergies
- long term effects on human health unknown
- introduced genes mutate (outcompete wild populations and or cross species)
- reduce genetic variation (potato blight)
- monopolies on food production
what is reproductive cloning
exact genetic copy of entire organism using adult, differentiated cells
- remove an egg’s nucleus
- take nucleus of differentiated cell and place in egg (somatic nuclear transfer)
- zap with electricity to trick it into thinking it’s fertilized
- mitotic divisions in embryo
- place embryo in surrogate mother and all to develop into baby
what is theraputic cloning
- use embryonic stem cells (undifferentiated) to produce new tissues for transplantation
arguments that support theraputic cloning
- can be screen for genetic abnormalities
- natural process (identical twins)
- increased change of offspring for infertile couples
- help burn victims, paralysis, and leukemia patients
- reduce risk of rejection because they genetically identical
arguments that are against therapuetic cloning
- destroys embryo (when does life begin)
- higher rates of miscarriage and developmental disorders
- long term health effects are unknown
- suppression of patient’s immune system is risky
- human clones?
human genome project
All base sequences including mutations are sequenced for humans as a species
- mapping outcome: number and location and base sequence for all human genes
- medical outcome: specific genes targeted to produce specific proteins for those who can’t
- ancestry outcome: improved insight into human origins/evolution
- screening outcome: specific gene probes to detect genetic disorders and carriers
gel electrophoresis
- DNA sample amplified using PCR (from crime scene, father/baby, bones)
- Cut DNA with restriction enzymes then run through gel using electric current
- separate based on size and charge: fragment lengths are unique to each individual due to unique sequences of DNA - produces banding pattern in gel
- band represent sizes of fragments, smaller fragments travel faster)
what is gel electrophoresis used in
DNA profiling (typically use highly repetive DNA because it is unique to every individual
- Forensic investigations (identify victims and suspects
- paternity testing (half of babys bands from mom and half from dad)
DNA profiling and gel electrophoresis
- amplify DNA samples using PCR then cut with restriction enzymes (endonucleases)
- run samples through gel electrophoresis and analyze banding patterns (show fragments lengths and sizes)
- can also add probes (fluorescently labeled specific, complementary DNA sequences) to gels to identify genes of interest and can cause disease (sickle cell)
