EXAM 5 - Chapter 15, Simple Patterns of Inheritance Flashcards
The laws of inheritance were first described by
Gregor Mendel
Gregor Mendel was a
Roman Catholic Monk in Austria-Hungry (1800s)
Lots of experiments…
had been performed and reported prior to Mendel
Mendel, after failing a test…
for a teaching certificate, was sent to the Univ. of Vienna to study math and science
He learned a _______ approach
quantitative
Mendel used…
the ratio of the different types of offspring to predict how genes were inherited
This was before…
a good understanding of Mitosis and Meiosis
didnt know what genes were, Mendel actually discovered Meiosis for the first time
Gene
a section of DNA that codes for a particular trait
Allele
variable form of a gene
for example, white and purple colored, same type but different allele
Homozygous
2 copies of a gene (alleles) in a diploid organism are the SAME
Heterozygous
2 copies of a gene (alleles) in a diploid organism are DIFFERENT
Gentotype
genetic makeup of an individual
Phenotype
physical expression of that genotype
dominant
one allele expressed in a heterozygote
capital letter
recessive
allele not expressed in a heterozygote, only expressed when trait is two copies of recessive
lowercase letter
Mendels Monohybrid cross ..
Tall plants (TT) x Dwarf plants (tt)
(Monohybrid Cross) Parental Genotypes
TT x tt
(Monohybrid Cross) gamete types of each parents
T t
(Monohybrid Cross) means
dealing with one trait at a time
Tall is…short is…
dominant, recessive
The plants are…
diploid, each has TT and tt
(Monohybrid Cross) genotypic ratio…
all heterozygous (Tt)
not rly ratio, would be 1:0 since 100% hetero and 0% anything else
(Monohybrid Cross) phenotypic ratio
all tall
For the punnett sqaure…
outside square = meiosis
inside square = fertilization
After monohybrid cross…
crossed the two heterozygotes (still monohybrid cross)
allowed F1’s to self pollinate
(Heterozygous Cross, still monohybrid) parental genotypes…
Tt x Tt
(Heterozygous Cross, still monohybrid) Gamete Type..
T,t T,t
can have T and t sperm
and T and t egg
can make two types of gametes
Punnett square for heterozygotes
put down gamete types (meiosis) on outside of square, female on left, male on top
Then fill in punnett square (fertilization)
For heterozygous cross, genotypic ratio…
1:2:1
genotypic ratio ALWAYS written in order…
homo dominance, hetero, hetero/homo recessive
for heterozygous cross, phenotypic ratio..
3:1
Mendels first law ________ was…
(of segregation)…
-adults are diploid (have 2 copies/alleles of each gene
- the 2 copies of each gene segregate one to each gamete
- fertilization restores the diploid number
Individuals with dominant phenotype can..
have either of the 2 genotypes which are TT, or Tt
To determine the genotype of an individual with dominant phenotype…
cross with a homo recessive
if test individual is homo dominant (TT)…
All offspring will be dominant meaning tall after crossing with homo recessive (tt)
If test individual is hetero (Tt)…
phenotypic ratio would be 1:1 with two being tall (Tt) and then two being small (tt)
This testing is just…
an application of what Mendels is already saying
Mendels Dihybrid cross means…
tracking two genes at once, to see how genes are related, are tall plants always white? can tall be white or purple?
**have 4 alleles because each have 2 alleles, diploid, 2 from each
(Dihybrid) parental genotypes
YYRR x yyrr
the dominant genes are…and the recessive are…
dominant = yellow and round
recessive = green and wrinkled
(Dihybrid) gamete types
Y,R and y,r
(Dihybrid) if put in punnet sqaure…
100% will be YyRr, heterozygous for shape and color
(Dihybrid)All offspring…
are heterozygous yellow and heterozygous round seeded
Next experiment is…
two of these double hetero are crossed (dihybrid hetero)
(dihybrid hetero) parental genotypes
YyRr x YyRr
(dihybrid hetero) all possible gamete types
TY, Yr, yR, yr , 4 kinds of eggs, 4 kinds of sperm
(dihybrid hetero) After punnet sqaure is made…
9:3:3:1
9 Yellow round
3 Yellow wrinkled
3 Green round
1 Green wrinkled
again, the order you must list phenotypic ratio in is…
both dominant : dominant, recessive: recessive, dominant: recessive, recessive
Dont usually include…
the genotypic ratio when crossing a lot of things, just look at phenotypic ratio
Mendels second law…
(Independent Assortment)
- alleles of different genes will assort into gametes independently of one another
- so that all possible combinations of alleles can occur in gametes
so you can have tall and white, or tall and purple, each gene assorting independent of each other
Biochemical pathways…
involve enzymes which determine phenotypes
A gene codes…
for an enzyme which will convert a chemical precursor into a purple pigment
Homo dominant…
has two alleles, both produce a functional enzyme and pigment
PP both convert to purple pigment
Hetero…
has one copy of gene producing functional enzyme, but that one functional enzyme if enough to convert all of the precursor to purple pigment
Pp, even if has broken enzyme, but one enzyme is enough to make whole thing purple
Homo recessive…
- has both copies of gene producing defective enzyme
- without the functioning enzyme, presurcor is not converted to enzyme
- flower remains colorless (white)
both pp, gene cant make enzyme to produce purple
If cross is made between Rr and rr, what is the expected phenotypic ratio
draw punnett sqaure 1:1
If cross between Ssyy and ssYy, what is exprected phenotypic ratio
draw square, Sy and sy on top, sY and sy on left
1:1:1:1 phenotypic ratio, all a bit different
In complete/simple dominance…
only one allele is expressed in a heterozygote
Incomplete dominance…
both alleles are expressed in a heterozygote (b/c dominant allele does not completely mask recessive) so an intermediate phenotype of produced
blending of two alleles
(Four O’clock flower) parental genotypes..
RR homo red x WW homo white
(Four O’clock flower) Gamete types
R x W
Since both contribute to the offspring…
we put them both as capital letter, no lowercase
(Four O’clock flower) after combination…
all offspring heterozygous
(Four O’clock flower) phenotypic ratio
all pink (RW)
(Four O’clock flower) monohybrid cross parental genotype…
RW x RW
(Four O’clock flower) monohybrid cross gamete types
R,W x R,W
(Four O’clock flower) monohybrid cross genotypic and phenotypic ratio…
1:2:1 (draw square) RR (red), RW (pink) x2, WW (white x1)
Ratios are same for both because…
each genotype has its own phenotype
If a pink flower is crossed to a white one, what is the expected phenotypic ratio..
Parental genotypes: RW x WW
Gamete types: R,W x W
Phenotypic ratio:
half pink, half white, 1:1
DRAW SQAURE)
Human males can have…
XY, XXY, XYY, XXYY
Human females can have
XX, X, XXX, XXXX
Human sex determination
presence of a Y-chromosome determines males
DAX1 gene activation on X chromosome determines females
Sex-chromosomes..
those that contain the gene(s) which determine the sex of an individual (only one pair)
Autosomes
non-sec chromosomes
Eyecolor in Drosophila (fruit flies) was
pattern of inheritance found by Morgan when studying fruit flies
Morgans observations
found white-eyed male fly
Cross #1
crossed white eyed male with red eyed female
all offspring red eyed
Cross #2
did brother sister cross of red-eyed flies and got 3 red:1 white
but all white eyed were males
Morgans Hypothesis was…
Eye color is sex-linked (ie gene located on X chromosome
Sex linked genes are found
on the X chromosome
Y chromosome…
does not carry most of genes, there are way less genes
(Fly Cross #1) Parental Genotypes
XRXR , XwY
Female has two X with red eyes, male has one X with white, Y does not carry color gene
(Fly Cross #1) Gamete types
XR Xw, Y
Hemizygous means
genotype of individual with only one copy of sex-linked gene (for example, male) can be wither hemizygous dominant or hemizygous recessive
(Fly Cross #1) phenotypic ratio
all red-eyed females
all red-eyed males
(Brother Sister Cross #2) Parental Genotypes
XRXw , XRY
(Brother Sister Cross #2) Gamete Types
XR,Xw XR,Y
(Brother Sister Cross #2) phenotypic ratio
3 red:1 white
but ALL white eyed flies were male
half of males had white eyes
If a white eyed female is crossed to a red eyed male, what is the expected phenotypic ratio
Half red eyed female, half white eyed males
Homo recessive female, meaning XwXw
Hemi dominant male, meaning XRY
so offspring XwXR and XwY, since red is dominant female is red and then white is male
Gene Dosage Compensation
A process that equalizes expression of X-linked genes in male and female mammals
First proposed mechanism in gene dosage compensation…
is X inactivation
X inactivation is
- 1 X chromosome inactivated in each female cell
- reduces number of expressed copies of X-linked genes from 2 to 1 in females
- so expression roughly equal in males and females
Barr Bodies are
small dark staining bodies in the interphase nucleus in females but not males
Lyon Hypothesis is…
Barr bodies are heterochromatic (highly condensed and inactivated X-chromosomes)
You must have…
at least one activated X per cell
males…
do not have barr bodies because have only 1 X chromosome so cant be inactivated
Typical females have…
1 Barr body (XX)
Typical males have…
0 Barr Bodies (XY)
Klinefelter males have…
1 Barr Body (XXY)
Turner females have…
0 bar bodies (XO)
Triple X females have…
2 barr bodies (XXX)
Evidence in favor of Lyon Hypothesis …
calico cats are always female
they are heterozygous for color (orange and black parts)
Example of one X inactivated in calico cats…
1 - initially both X’s have active orange and black (early embryo)
2 - randomly, one of two inactivated, this becomes Barr body
3 - Pattern of diff. remain because duplicate, then results in patchiness
But for many X-linked traits in humans…
heterozygous females usually show dominant trait
Expression of dominant allele in 50% of cells is…
sufficient to produce dominant phenotype
With recessive X-linked form of hemophilia (blood disorder)
hetero females usually have healthy phenotype
normal blood clotting protein produced in approx. 50% of liber cells enough to prevent hemophilia
50% make good gene, 50% make bad gene, 50% is enough to be okay
Pedigree symbol for female
circle
Pedigree symbol for male
square
Pedigree symbol for affected
dark circle or sqauer
Pedigree symbol for unaffected
light circle or square
Generation shown as
roman numerals
Individuals shown with
arabic(normal) numbers
Pedigree usually used
for diseases, or specific inheritance of traits
Tell tale sign of recessively inherited trait
affected child has two unaffected parents
anywhere in pedigree means the trait is recessive
If the trait was dominant..
the child would have inherited one dominant allele from at least one of parents, so parents would have disease
for autosomal…
the gender does not matter so just follow rules
in sex linked…
have to remember that male only has one X that it passes on
sex linked affected male
always hemizygous recessive
sex linked unaffected male
always hemizygous dominant
sex linked affected female
always homo recessive
go through practice on powerpoint
