GN 301 Exam 2 Review

Galactosemia

inability to metabolize glucose

What happens if there is no precursor in a biochemical pathway?

there are no intermediates produced and no end product

What happens if genotype AABBcc

Enzymes A and B are produced but no enzyme c, and no end product

Alkaptonura

build up of homogentistic acid

* results in dark urine, joint paint, etc.

PKU/ Phenylketonuria

inability to metabolize phenylaline

* intellectual disabilities
* behaviorial probelms
* low phenylaline diet

Albinism

lack of melanin production

* vision problems, skin cancer risk

What do enzymes produced by genes control?

biochemical reactions

Mutation

a change in a DNA sequence

Mutagen

an agent that causes the mutation rate to go above normal (UV light, radiation, etc)

What is the incidence of spontaneous mutation?

1 in 100,000 per gene/ per cell (1 in 5 genes are averagely mutated)

Point mutation

change of one nucleotide

Transition point mutation

change from a purine to a purine or a pyramidine to a pyramidine

Transversion point mutation

change from a purine to a pyrimidine or vice versa

Missense mutation

a point mutation where an amino acid is changed into a different amino acid, but the end point is the same

Silent mutation

a nucleotide changes but the same amino acid gets produced

Nonsense mutation

a nucleotide is changed that leads to an early stop in the chain of amino acids

Readthrough mutation

a nucleotide is changed that leads to a delayed stop in the chain of amino acids

Sickle cell anemia is caused by a…

point mutation in hemoglobin

Sick cell anemia is beneficial for fighting

malaria

Frameshift mutation

one or more nucleotides are inserted or deleted from a chain of amino acids

Insertion

amino acid inserted

deletion

amino acid deleted

Suppressor mutation

if the original mutation was an insertion, a deletion could suppress the mutation

What community is Cystic Fibrosis most common in?

Jewish population

* frameshift mutation

What mutation causes Tay-Sachs?

a frameshift mutation

* autosomal recessive
* prevalent in Jewish populations > testing used to avoid intermarrying of people with the allele

Trinucleotide repeat

a group of disorders that result from expansion of a 3-nucleotide DNA sequence

* Huntington’s Disease
* Fragile X Syndrome

Huntingson’s Disease

trinucleotide repeat expansion of CAG trinucleotide repeat with huntingtin gene

* dominant
* anticipation

Fragile X Syndrome

trinucleotide repeat, expansion of CGG repeat on X chromosome.

* leads to mental retardation
* more common in males because they only have one X

Which 2 disorders come from trinucleotide repeats?

Huntingson’s Disease and Fragile X syndrome

Anticipation

the severity of a disease increases with each generation

Ames Test

chemicals are mixed with liver enzymes to observe the number of mutations that occur from the chemicals

* used to see if harmful chemicals present
* liver enzymes used to mimic human body

What does UV light cause?

pyrimidine dimers

Xeroderma Pigmentosa

autosomal recessive

* sensitivity to UV light
* missing DNA repair mechanism that repairs pyrimidine dimers

What is the normal total amount of exposure to radiation we get a year?

6\.2 mSV

* 3.1 from natural causes
* 3.1 from manmade causes

Fukushima

a nuclear disaster in 2011

* employees were allowed to work with 250 msV

“safe” level of radiation in the workplace

50 mSv

LD50/60

lethal dose where 50% of people die in 60 days

* happens at 320-450 rad

Examples of good and bad mutations

Bad: mutation of p54 gene, causes cancer

Good: mutation of lactase, allowing adults to drink milk

Hereditary

traits are transmissible from parent to child through cells

Congenital defect

traits present at birth due to genes/environment

Phenocopy

a condition resulting from environmental factors that mimics a genetic disorder

Carcinogen

a mutagen that causes cancer (tobacco, radiation, etc)

Teratogen

an agent that causes birth defects or congenital malformation

* EX: birth defects due to use of alcohol during pregnancy

Fetal Alcohol Syndrome

condition due to mother drinking alcohol during pregnancy

* baby has small head and eyes, behavioral issues, etc

Thalidomide

a drug prescribed for morning sickness to moms that ended up causing teratogenic effects like limb stunted growth

DES

synthetic hormone estrogen made to prevent miscarriages, but caused reproductive problems in children later

Accutane

medicine used to treat acne that causes teratogenic effects, among other side effects (due to excessive Vitamin A)

Aneuploidy

fewer chromosomes than normal (not a multiple of the haploid number)

Monosomy

missing one chromosome

Trisomy

extra chromosome

Tetrasomy

two extra copies of a chromosome

Double monosomy

two different pairs of chromosome missing a match, so 2 less chromosomes (44)

Double trisomy

individual has 3 copies of 2 diff chromosomes, so 6 extra chromosomes (52)

Nullisomy

both copies of the same chromosome are missing

How many births have a chromosome disorder?

1 in 150

What % of pregnancies spontaneously miscarry?

15%

* about 50% of these had a chromosome disorder
* 6% of intellectually disabled hospitalized patients have a chromosome disorder

Polyploidy

extra copies of a chromosome

triploid

4 copies of each chromosome (69 chromosomes total)

How is polyploidy beneficial to plants?

Some of the most important consequences of polyploidy for plant breeding are the increment in plant organs ("gigas" effect), buffering of deleterious mutations, increased heterozygosity, and heterosis (hybrid vigor).

Autopolyploidy

polyploids with multiple copies of the SAME chromosome (think auto = same)

Alloplyploidy

having two or more complete sets of chromosomes derived from different species. (think allo = set)

Triticale

a man-made cereal grain made from hybrid wheat

Down Syndrome

trisomy 21 (47 chrom)

Patau Syndrome

trisomy 13 (47 chrom)

Edward Syndrome

trisomy 18 (47 chrom)

Turner Syndrome

X0

* females lack an X chrom, so they don’t go through puberty

Klinefelter Syndrome

XXY

* men have an extra X chromosome so they become feminized

Deletions

* terminal deletion: segment at the end of a chromosome end is separated from the rest
* Cri-du-chat (cat’s cry)
* think (terminal = cat)
* interstitial deletion: segment of chrome. deleted that isn’t at the end
* William’s Syndrome (25-27 genes are missing)
* think (interstitial = William)

Duplication

more than one copy of a region of a chromosome

* crossing over happens incorrectly
* CMT disease
* duplication = CMT

inversions

a segment of a chromosome is removed, turned 180 degrees, and reinserted

* paracentric inversion: does not include centromere
* pericentric: includes centromere

Translocations

* Reciprocal translocation: 2 nonhomologues overlap, break, and rejoin so their arms are swapped
* Burkitt’s Lymphoma
* Robersonian translocation: 2 smaller telocentric homologues break apart near the centromere; smaller pieces are lost, larger pieces fuse into metacentric chromosomes
* Familial Down Syndrome
* the carrier has 45 chromosomes. Kid has 47

Mendel’s Law of Random Segregation

alleles randomly segregate into gametes. when gametes are formed, each allele of one parent segregates randomly into the gametes, such that half of the parents gametes carry each allele

Mendel’s Law of Independent Assortment

the alleles of 2+ genes get sorted into gametes independently of one another; the allele a gamete receives for one gene doesn’t influence the allele received for another gene

* violated by crossing over

loci

physical location of a specific gene on a chromosome

Autosomal

if 2 parents of the same genotype have a different child

* dominant: if there is an unshaded child from 2 shaded parents
* recessive: if there is a shaded child from 2 unshaded parents

Primary Sex Ratio

ratio of males to females at Conception (1.2 to 1)

Secondary Sex Ratio

ratio of males to females at BIRTH (105 to 100)

Tertiary Sex Ratio

ratio of males to females after birth (100:100 around 20)

SRY gene

activates the ovotestes on the Y chromosome, directing male testis development

* if lack of SRY gene, female development
* this develops 6-8 weeks after conception

Male versus female sex organs

Females: Clitoris. Males: Penis.

Females: Fallopian tubes. Males: vas deferens

Females: ovaries. Males: testes

Methods of determining child sex at birth

* physical traits like testes

Barr body

inactivated X chromosome

* if a Barr body is present, we can assume gender is female

Why are females mosaic for traits on the X chromosome?

Because they have 2 X chromosomes, one is usually deactivated so cells are mixed

Androgen Insensitivity

* testicular feminization
* XY
* looks like female but sterile
* dysfunctional androgen receptor, testes formed, retracted

Adrinal Villysum

* XX
* Girl with masculine characteristics (elevated androgen levels)

Congenital adrenal hyperplasia

* XX or XY
* mixed traits, ambigous genitals

Guevedoces

* XY
* appear as females at birth, but transition to males at puberty

Turner Syndrome

* X0
* Female characteristics, delayed at puberty

Klinefelter Syndrome

* XXY
* Feminized but tall, have testicles. Few sperm and learning disabilities.

hemizygous

only one member of a chromosome pair or segment is present

* usually X linked
* in males always present, since XY, only one X

holandric

genes on a Y chromosome are passed from father to son

Rett Syndrome

X linked dominant disorder

* Boys die soon after birth but girls can survive since they have 2 X’s (regressing over time)

Congenital Generalized Hypertriochosis

Werewolf syndrome

* X linked dominant disorder
* hair all over body
* very very rare

Fragile X Syndrome

* X linked dominant disorder
* extra copies of trinucleotide on X chromosome
* long face
* anticipation

Amelogenesis Imperfecta

* can be X linked, autosomal dominant, or autosomal recessive
* defects in enamel production

colorblindness

* X linked recessive
* unable to see color

Hemophilia

* X linked recessive blood disorder
* blood can’t clot at all

Sex-linked inheritance

traits inherited through sex chromosomes X and Y

Sex limited inheritance

a trait only expressed in one sex

* only male chickens have long tail feathers, but not always have them
* female chickens never have them even if they have the trait

Sex influenced inheritance

a trait expressed differently in different genders even if they both carry the trait