MBG 2040 First Half of Semester

genes come in multiple forms called _______ and are located on __________

alleles (same gene w small differences in sequences of DNA bases)
chromosomes

gene

genetic factor (region of DNA) that helps determine a characteristic

locus

the specific site of an allele on its chromosome

genotype VS phenotype

set of alleles possessed by individual organism
manifestation of alleles

heterozygote

possessing 2 different alleles at a locus

Mendel's Monohybrid cross

RR (dominant round) and rr (recessive wrinkled) produced: F1 generation of all Rr
-self fertilized F1 to produce F2 with (1/4 RR, 1/2 Rr, 1/4 rr) aka 3:1 ration of round to wrinkled

dihybrid cross produces what ratio of F2 generation

9:3:3:1

if trait is rare and autosomal recessive, then ppl who marry in are _________-

homozygous for normal allele

mitosis

meoisis 1

meiosis 2

null/amorphic alleles

-nonfunctional protein is produced OR
-no protein is produced

hypomorphic allele

- poorly functioning protein is produced OR
- reduced amounts of a normally functioning protein is produced

multiplication rule

aa AND AA
multiply probs

addition rule

aa OR/ EITHER AA
add probs

dominant hypermorphic alleles

negative phenotypic consequences due to:
- *over-production* of a normal protein
- production of protein w/ *increased activity* levels

neomorphic alleles

negative phenotypic consequences due to:
- presence of an altered protein that has a new function
- altered protein interferes w/ the wildtype protein

For traits to be rare and dominant.. affected individuals are most likely _______________, why?

heterozygous.
BB is very rare bc even Bb x Bb crosses are rare bc Bb die very young therefore infrequent mating

complete dominance and complete recessiveness are extremes of a range

BB = Bb same
bb = different

incomplete dominance

BB, Bb, bb all differ phenotypically
therefore, Bb is in between BB and bb (pink flower, in between white and red)

codominance

BB, Bb, bb are all different
Bb exhibit phenotypes of both homozygotes
white and red splotched flower

individual (diploid)

only 2 alleles coexist in each cell

I^A encodes a transferase which adds ______________

acetylgalactosamine

I^B encodes a transferase which adds ______________

galactose

i encodes a ______________ transferase

non-functional
**no antigen

blood types

A: IAIA, IA,i

B: IBIB, IBi

O: ii

AB: IAIB

Type AB blood has ____________ alleles, so both galactose and acetylgalactosamine

codominant
both alleles are expressed

wildtype allele

functional enzyme or other protein is produced
most common in nature

loss of function allele

enzyme or other protein is no longer being produced, is produced at lower levels, or is nonfunctional

haplosufficiency

often the wildtype allele is dominant over the loss of function allele
**half as much protein is synthesized yet this is often sufficient to achieve the wildtype phenotype

haploinsufficient

in heterozygote, half as much protein is synthesized and this is not sufficient for a normal phenotype
*dominant allele can be loss of function allele

dominant alleles can be gain of function mutations, in which the mutant allele produces a protein that has increased (detrimental) function

eg. Huntington's disease

recessive lethal alleles

essential genes, when mutated, lead to a lethal phenotype

**death in homozygotes****

1/4 die.. therefore its 2/3 to 1/3 colour ratios

dominant lethal genes can be expressed in both _________________ and the _______________-

heterozygote
homozygote
Bb and BB lethal
bb= not lethal

genes function to produce ________________-

polypeptides

wildtype allele produces a functional polypeptide ..... which then produces a _____________ phenotype

wild-type

recessive amorphic loss of function allele does not produce a functional polypeptide ....which then produces a _____________ phenotype... But since it is recessive, when paired w a wildtype allele, the phenotype is wildtype

severe mutant

recessive hypomorphic loss of function allele produces a partially functional polypeptide ....which then produces a _____________ phenotype...But since it is recessive, when paired w a wildtype allele, the phenotype is wildtype

mild mutant

dominant-negative allele produces a polypeptide that interferes w/ the wild-type polypeptide ....which then produces a _____________ phenotype...since it is dominant, when paired w a wildtype allele, the phenotype is mutant

severe mutant phenotype

penetrance

proportion of individual organisms having a particular genotype that expresses the expected phenotype-variation in the **population**
ex. how many ppl have brown hair in a city

degree to which a phenotype is expressed (mild to severe); variation in the **individual**

expressivity
ex. the degree of brownness in the hair of the ppl in the city

complete penetrance

100% expected phenotype (every hedgehog is brown)

incomplete penetrance

< 100% expected phenotype (some hedgehogs brown, some white(lack of brown entirely))

constant expressivity

every hedgehog is the exact same shade of brown

variable expressivity

range of phenotypes
all diff shades of brown

all shades of brown, and also white hedgehogs

incomplete penetrance and variable expressivity

split hand foot syndrome

rare autosomal dominant disorder that shows variable expressivity
-missing one or more central digits in hand or foot

piebaldism

rare autosomal dominant disorder that shows variable expressivity
-absence of melanocytes in skin and hair

huntington disease

rare autosomal dominant disorder that shows variable expressivity in the time onset of the disease
-neuro degenerative - causes loss of muscle coordination, cognitive decline and dementia

what causes incomplete penetrance and expressivity

-effects of other genes
-environmental factors that can alter or completely suppress the effect of a particular gene (age, sex, temperature, chemicals)

norm of reaction

range of phenotypes expressed by a single genotype under different environmental conditions

example of environmental effects on phenotype -
himalayan allele in rabbits produces dark fur at extremes of body bc it can only develop at low temps

ex. siamese cat

a change in phenotype arising from environmental factors that mimic the effects of a mutation in a gene

ex. chemical can cause a limb to not develop in the womb like a rare dominant trait would

phenocopy

mendel's 2nd principle: law of independent assortment

inheritance pattern of one trait will not affect the inheritance pattern of another trait
ex: round by yellow seeds

when there is two genes contributing to a single trait, and complete dominance occurs

use multiplication rule
9:3:3:1 ratio..... ex: recessiveness dilutes fur colour from black to brown to grey

complementation

2 strains of an organism w/ different homozygous recessive mutations that produce the SAME phenotype, produce offspring of the wild-type phenotype when mated or crossed

-the other genome supplies the wild-type allele to "complement" the mutated allele

complementation will only occur is the mutations are in ________________

different genes

will not occur if the mutations are in the same gene!

heterogenous trait

mutation in any one of a number of genes can give rise to the same phenotype

in yellow

epistasis

masking of the expression of one gene by another, no new phenotypes are produced

**epistatic gene does the masking

T or F: the hypostatic gene is masked

true

recessive epistasis
ratio and purpose

F2 phenotypic ratio 9:3:4 recessive epistasis
-homozygous recessive at one gene pair mask expression from the other gene

**b/b does the masking

dominant epistasis
ratio and purpose

one dominant allele at one gene masks expression from the other gene

summary of F2 ratios!! really important

pleiotropy and examples

single gene affects two or more phenotypic traits
ex: sickle cell disease, cystic fibrosis

when 2 inbred lines are crossed, it leads to heterosis... whats this

hybrids are heterozygous for many genes... which have a ton more traits than the parents

Inbreeding increases the frequency of______________ and decreases the frequency of
heterozygotes

homozygotes

answer this

1/180... get 1/30 from hardy weinberg
pg. 78 of chapter 5 notes

what is the expected frequency of heterozygotes in a population with the allelic frequency x and y is in Hardy-Weinberg equation?

2xy

dosage compensation

way of equalizing gene expression in the face of different gene dosage

dosage compensation for X-linked genes is achieved by inactivating one of the two X chromosomes in females.

The X and Y chromosomes pair during meiosis, even
though they are not homologous (the genes located
on each are different). how does this happen

X and Y chromosomes are homologous only at pseudoautosomal regions, which are essential for the XY pairing

If a cell contains more than 2 X chromosomes, all but one of them are inactive
• X0 females have no Barr Bodies, XXY males have 1 Barr Body, XXX
females have 2 Barr Bodies
• Therefore, females are functionally hemizygous for X-linked genes at the cellular level
– Approximately 50% cells express one allele, and 50% cells will express the other allele

females that are heterozygous for X linked traits are __________

genetic mosaics

X inactivation

Explain calico cats

chromosome

sister chromatid

homologue

mitosis

meiosis

how do chromosomal nondisjunction events cause aneuploidy

how is polyploidy common in plants and rare in animals

30-35% of flowering plants are polyploids
animals: rare

monoploidy, what is it and what types of animals/insects are this

one set of chromosomes (Sterile)
1N

ants, bees, wasps MALES

diploid

2 sets of chromosomes
2N

polyploidy

more than 2 sets of chromosomes (2 is normal)
ex: triploid banana 3N, tetraploid 4N

~usually sterile but can sometimes reproduce, like how 4N could theoretically reproduce if everything split up the exact same way (very small chance)

autopolyploids
-are chromosomes identical?
-sterility?

chromosome sets are identical (Ex: 4N= AAAA homologous groups are identical) (not getting alleles from diff parents to diversify aka... spontaneous doubling)
all chromosomes derived from same species (no crossing between ex: two plant species)
-MORE GROWTH (larger cells, larger plant)
-less seeds/STERILE

UNIVALENTS HAS TO EQUAL BIVALENTS

two types of 3N distribution.. what happens

Meiosis 1: (1 cell)

1) 1 bivalent and 1 univalent
2) 1 trivalent

Demonstrate the paths of 3N in meiosis 1 and meiosis 2

Allopolyploids

-cross between TWO species (related)

spontaneous doubling

restores fertility to sterile allopolyploids
A B ------> AA BB
2N--------> 4N

aneuploidy

diploid genome which lacts a chromosome or has an extra chromosome
2N + 1 = trisomies
2N - 1 = monosomies

Turner syndrome and how it happens

X__
how it happens:

female but just one X chromosome, there is no other x chromosome to inactive like w normal females
-therefore there is no genetic leakage coming from the other inactivated X.. this leakage is important and is what makes normal females normal!
-only 45 chromosomes in total

Klinefelter syndrome and how it happens

XXY
-nondisjunction in *meiosis 1* in the mother, put both chromosomes into the same gamete. meiosis 2 splits them up normally into 2 sister chromatids in each cell , leaving finished zygote cell with 2 X chromatids and 1 Y chromatid

-one of the Xs is inactivated, but not completely, there's some leakage, which affects male displaying traits
47 chromosomes in total

XYY male

how do you get TWO Ys
-in meiosis 1 when the X and Y separate, the chromosome is made up of 2 Y sister chromatids
**Non -disjunction in meiosis 2** both Y sister chromatids go into same gamete, therefore YY in one gamete instead of one Y in each

not much damage done by having 2 Ys

Triple X syndrome and how it happens

XXX
-in meiosis 1 when the X and Y separate, the chromosome is made up of 2 X sister chromatids
**Non -disjunction in meiosis 2** both X sister chromatids go into same gamete, therefore XX in one gamete instead of one X in each ***** CHECK THIS IDK IF ITS RIGHT***

two of the X's are inactivated, but not completely so there's too much X

Down Syndrome

2N + 1
extra chromosome for the 21st chromosome
trisomy

Patau Syndrome

2N + 1
extra chromosome on 13th chromosome
die before 2

Edward Syndrome

2N + 1
extra chromosome on 18th chromosome
die before 2

deletion/deficiency

missign chromosome segment

duplication

extra chromosome segment

hypoploidy

less genetic material such as a deletion of a chromosome segment or the loss of an entire chromosome