Genetics Flashcards
who was the father of genetics
Mendel, an 1800s monk who studied plant breeding and statistics
19th century theories of inheritance
blending
Mendel’s studies showed
Particulate inheritance..
Inheritance of discrete units (genes)
allele
version of a gene
true breeding
both alleles are the same
hybrid
produced by crossing 2 true breeding parents (have one of each allele
p generation
parent generation
F1 generation
offspring of P
F2 generation
offspring of 2 F1 individuals (brother sister)
phenotype
physical appearance
genotype
describe genes
In mendelian genetics how what is required for dominant and recessive genes to be expressed
Dominant genes require 1 copy to be expressed
recessive genes are only expressed if an individual gets 2 copies of the recessive gene
What letters express dominant and recessive genes
CAPITAL for dominant
lower for recessive
what are the three genotypes
homozygous dominant (AA) homozygous recessive (aa) heterozygous (Aa)
what genotypes are true breeding and which are hybrid
homozygous dominant and homozygous recessive are true breeding. Heterozygous are hybrid
Flower parts;
stigma
stamen
stigma-female part
stamen- male part
mendels experiment
Plants self-pollinate
so To make crosses Mendel cut off stamens and cross-pollinated artificially
Each pea seed contains
an embryo:
An offspring
Mendel found
No blending, flowers one color or the other.
2) All F1 looked same : called that trait dominant
3) the other trait was hidden in some of the F1s but was passed on to F2: called that trait recessive
Law of segregation
each parent only gives one of their genes to the offspring hence..
the 2 parental genes must be separated from each other (segregated from each other)
F2 crosses led Mendel to formulate
the Law of Independent Assortment
Punnett squares
Analytical tool for determining probabilities of inheritance
what goes on the sides of the Punnett square
ALL possible Gametes go on top and sides of square …gametes are (1n) so only one letter
Boxes inside square represent
possible offspring
So each must get 2 copies of gene (2n) so 2 letters
Ratio of possible offspring in box is
The probability that that type of offspring will be produced
purpose of test crosses
done to determine genotype
how to do test crosses
Cross unknown individual with homo recessive
if any recessive phenotype offspring then ..Unknown is heterozygous
monohybrid cross
only looks at one gene
dihybrid cross
looks at probability of inheriting certain alleles of 2 different genes
Dihybrid Punnett squares
All possible gametes on top
Heterozygous for both traits makes ..4 different gametes
Each box is a zygote so needs
2 copies of each gene
multiplication rule
To determine the chances of 2 different events happening together…
Multiply the probabilities of each event
P to get A & B = Probability A x Probability B
addition rule
If more than one way to get a desired outcome….
Add the probabilities of each way together.
non mendelian genetics
Any genes that are not straight forward dominant or recessive allele
6 different non mendelian genetics
1) Incomplete dominance
2) Co-dominance
3) Multiple alleles
4) Polygenic traits
5) Linked genes
6) Sex linked genes
incomplete dominance
Neither allele completely dominates the other NO recessive (hidden) allele Both traits are partially expressed (blending)
letter symbols for incomplete dominance
must be same letter…same gene
must both be capital letters ……….not recessive
use superscripts to differentiate alleles
co dominance
2 alleles both fully expressed (NO blending)
spotted instead of blended
Multiple alleles and Co-Dominance
Human ABO blood types
3 alleles ….. 2 dominant and one recessive
Gene designated as letter I for
inherited antigenic substance
polygenic traits
traits controlled by more than one gene
Multiple genes determine the phenotype
Example skin color in humans.
Phenotypes show a range of many different each only slightly different from the next
linked genes
genes with loci on the same chromosome
more likely to be inherited together than alleles on different chromosomes
The only way liked alleles do NOT end up in the same gamete is if
crossing over takes place
sex linked genes
Genes on X or y chromosome Most often on X y very small mostly codes for male trait Writing sex linked genotypes : XX and Xy Use superscripts to designate alleles
who produced the first solid evidence for Chromosome Theory of Inheritance
morgan
what experiment for Chromosome Theory of Inheritance
Used fruit flies…
Found mutant male w/ white eyes
Crossed mutant male with normal female
w+ x w
all F1 had red eyes so Trait is recessive
F2 generation…. Some white but only males
so differences between sex
why were fruit flied a good choice
good choice because…
produce hundreds of offspring
mature quickly
small /cheap
only 4 chromosomes (3 autosomes, Xy)
mutations created new phenotypesNatural phenotypes are called
wild type (+)
morgan tried a reciprocal cross
Change which parent has the mutation
all males got white eyes
Supports Chromosomal Theory of Inheritance
Chromosomal Theory of Inheritance
individual genes are carried by specific chromosomes
New alleles created by mutation
May be helpful, harmful, lethal, or silent
May be dominant or recessive
Some cause genetic disorders
New alleles created by mutation: ones to know
cystic fibrosis sickle-cell disease/trait achondroplasia Huntington’s disease Hemophilia
Cystic Fibrosis
Most common lethal disorder in U.S.A. 4% of European Americans carriers Recessive mutant gene for cell membrane protein Chloride channels fail = thick mucus Problems with lungs & pancreas Chronic illness shortened life span With treatment 50% survival to 30s Research into gene therapy promising
Sickle Cell Anemia
Most common disorder of African Americans
0.1 % African Americans have sickle cell trait
Co-Dominant mutation to Hemoglobin gene
One single nucleotide is substituted
Changes one amino acid
Mutated hemoglobin causes RBC to sickle and block capillaries if anaerobic
Sickle Cell Genes are
co dominant
sickle cell genes
Hn = normal hemoglobin Hs = mutated hemoglobin HnHn = normal HnHs = sickle cell trait HsHs = sickle cell disease….organ/brain damage
malaria
Protist parasite that lives in RBC
heterozyote advantage
HnHs = reduced parasite densities in blood…
better survival rates
Linked to improved malaria survival
Achondroplasia
(w/o cartilage formation)
Dominant mutation in gene that forms cartilage into bone
Heterozygotes = short appendages
Homozygous dominant = still born
80% new mutations, 20% inherited from parent
Huntington’s disease
Lethal dominant allele
Late onset so gene is passed on before onset
Mutated Huntington protein causes brain damage and is fatal
Genetic test available
Hemophilia
X-linked recessive mutation
Mutant clotting factor
No treatment = 11 year life expectancy
Now nearly normal with treatment
Environmental & Genetic disorders
Different alleles predispose to a disorder
Environmental factors determine if disorder is expressed
Multifactorial disorders
Most are polygenic
Cardiovascular health, cancer, alcoholism, bipolar disorder
Genetic counseling
Use pedigrees to determine genotypes
Pre-conception genetic testing
fertility drugs cause multiple eggs to complete meiosis I and emerge from ovary
eggs collected by surgery
polar body tested for known genetic defect
if mom is heterozygous and defect is in polar body, then egg is healthy
Genetic Testing Embryo
Embryos created by invitro fertilization
At 8 cell stage one cell is removed and tested (day 3)
Only healthy embryos implanted into mom
Genetic Testing of Fetus
Chorionic Villi Amniocentesis
Chorionic Villi
sampling removes fetal cells from placenta (10-12 weeks) use suction tube
Amniocentesis
samples fetal cells from amniotic fluid (15-18 weeks) long needle
by 15 weeks
4 inches long 1.7 ounces
