Exam 2

Question 1

polypoid

Answer 1

having multiple complete sets of chromosomes

Question 2

aneuploid

Answer 2

having abnormal chromosome number that is less than a complete set

Question 3

monosomy

Answer 3

having only 1 of a certain chromosome

Question 4

trisomy

Answer 4

having 3 of a certain chromosome

Question 5

uniparental disomy

Answer 5

having 2 of a certain chromosome that both came from the same parent

Question 6

fragile chromosome

Answer 6

can disrupt a gene due to multiple repeats on a chromosome

Question 7

Robertsonian translocation

Answer 7

fusion of parts of different chromosomes

Question 8

Turner syndrome

Answer 8

45,X
Females; short stature; wide chest; abnormal ovaries; puffiness of hands and feet at birth; infertility.
Abnormalities of the aorta (~75%).

Question 9

Trisomy

Answer 9

47+(13/18/21)
13-Patau syndrome
Lethal; mean survival time is 6 months. Facial malformations, eye defects, extra fingers or toes etc. Severe malformations of brain, nervous system, and heart. Parental age is only known risk factor.

18-Edwards syndrome
Small at birth and slow growing. Severe developmental abnormalities of many organs and systems including:
brain, head, face, heart, hands, feet. For unknown reasons 80% of all trisomy 18 are female. Advanced maternal age is a risk factor.

21- Down syndrome
A leading cause of intellectual disability and heart defects in US. Wide flat skulls, skin folds in the corner of the eyelids, spots on the irises, and thick, furrowed tongues. Congenital heart defects. Higher risk of leukemia (~3%), respiratory infection

Question 10

Klinefelter syndrome

Answer 10

47,XXY
Mild symptoms, often unaware. Many have language and learning difficulties. Some features develop after puberty. Male with low fertility, low testosterone level, small testicles, low sperm count, may develop breast (~30%). More X chromosomes (like XXXY) also cause the same conditions; Increased severity.

Question 11

XYY syndrome

Answer 11

47, XYY
96% of XYY males look normal. Above average in height (by 2-3”). Antisocial violent behavior was once claimed.
Overrepresented in male criminals in prison:
4.5% violent male criminals had XYY,
0.1% overall
“Congenital criminals?”
Later studies can’t find any link. Vast majority of XYY are socially normal and unaware of their karyotype. They are fertile, normally do NOT transmit condition.

Question 12

Triple X syndrome

Answer 12

47,XXX
Symptoms vary but 90% exhibit no or few symptoms.

They are fertile.

Typical symptoms include:
Taller than average height
Delayed speech and language development
Learning disability (average IQ = 85 -90)
Weak muscle tone
Problems with motor skills
Behavior and emotional problems

Question 13

• Screening for chromosomal abnormalities

Answer 13

o Amniocentesis
 Withdraw fluid from sac surrounding fetus.
 Most common way to do this.

o Chorionic villus sampling
 Sample cells from placenta.
 Highest risk of miscarriage, but it can be done sooner.

o Sampling fetal DNA from mother’s blood
 Low risk, but technically very difficult

Question 14

what are the risks from older parents unto their offspring

Answer 14

o Older mother (maternal age)
 Non-disjunction more common due to long arrest of oocytes in metaphase of meiosis 1
 Causes aneuploidy.

o Older father (paternal age)
 De novo mutation more common due to continuous division of sperm precursors
 Causes mutation that could lead to various diseases, but not visible on karyotype.

Question 15

Understand how important experiments showed that DNA is genetic material.

Answer 15

o Transformation of bacteria
 Dead virulent cells made live non-virulent cells into live virulent cells.
 Something transferred to live cells – it was the DNA.

o Bacteriophage
 Viruses that infect bacteria were labeled with:
* 32P – labels DNA
* 35S – labels proteins
 When they infect bacteria only 32P goes into bacteria, so DNA must be the genes.

Question 16

Know the scientists who discovered the structure of DNA.

Answer 16

o Watson, Crick, Wilkins and Franklin
 Watson, Crick and Wilkins received Nobel prize

Question 17

Understand the structure of DNA.

Answer 17

o Double helix made of 2 strands of nucleotides.

o Nucleotides consist of phosphate, deoxyribose and base (A, C, T or G)

o Nucleotides are connected by phosphate (on 5’ end) connected to 3’ -OH of next nucleotide.

o Strands held together by hydrogen bonds between base pairs.
 A with T
 C with G

o Strands are anti-parallel.

Question 18

DNA replication

Answer 18

o Strands separate and DNA polymerase adds new nucleotides base paired with each strand to make copy.

Question 19

Replication fork

Answer 19

where DNA strands come apart

Question 20

Replication bubble

Answer 20

separated area of DNA with a replication fork at both ends

Question 21

DNA synthesis always goes 5’ to 3’

Answer 21

direction new strand grows in

Question 22

Leading strand

Answer 22

synthesized continuously toward replication fork

Question 23

Lagging strand

Answer 23

synthesized in pieces, because it must proceed away from replication fork

Question 24

Genome

Answer 24

o Is very large – DNA must be condensed.
o DNA is wrapped around proteins called histones (make a nucleosome like beads on a string)
o This is coiled up and then super-coiled to make chromosome.

Question 25

Chromosome also has:

Answer 25

o Centromere -constricted region where sister chromatids attach.
o Kinetochore – on side of centromere where microtubules attach during mitosis.
o Telomere – repeats of DNA at ends that prevent damage to chromosome.

Question 26

Proteins

Answer 26

chains of amino acids
o 20 different amino acids based on different R group.
o Has different ends – N-terminus (made first) and C-terminus (made last)
o Fold into different shapes – to do different jobs.

Question 27

RNA – similar to DNA but…

Answer 27

o Uses ribose instead of deoxyribose.
o Uses uracil instead of thymine.
o Single stranded.

Question 28

Prions

Answer 28

o Proteins that are infectious (can cause disease)
o Causes normal proteins to mis-fold damaging tissue.

Question 29

Translation

Answer 29

uses information in mRNA to make a protein.
 Genetic code – 3 bases in a row form a “codon”. This is like words that tells the cell which amino acids to use in the protein.
 Don’t memorize code – except that you should know the start codon is AUG.
 mRNA binds to ribosome.
 tRNA base pairs with codon and acts as an adaptor, bringing in the correct amino acid.
 Ribosome moves along the mRNA adding one amino acid for every codon until STOP codon is reached.

Question 30

Transcription

Answer 30

copy gene as a piece of RNA – called mRNA.
 Strands of DNA separate and RNA polymerase adds new RNA nucleotides that base pair with one of the strands (called the template strand)
 Pre-RNA is then processed into mRNA.
* Parts called introns, that don’t code for protein, are removed.
* Exons, that do code for protein, are joined together.
* Structure called 5’-cap is added at 5’ end.
* Poly A tail is added at 3’ end.
 Transcription is highly regulated.
* Controlled by binding of proteins called transcription factors to part of the gene called the promoter.
* Very complicated (don’t need to know details), but ultimately controls binding of RNA polymerase to DNA, which starts transcription.

Question 31

Polygenic traits

Answer 31

controlled by more than one gene

Question 32

Multifactorial traits

Answer 32

controlled by more than one gene and environmental factors

Question 33

Understand why polygenic traits give multiple phenotypic classes.

Answer 33

o Due to number of dominant alleles.
o Number of phenotypic classes = number of genes controlling trait X 2 +1
 So for 3 genes = 7 classes

Question 34

What does heritability mean?

Answer 34

o Correlation of offspring phenotype with parents phenotype.
o Better correlation = higher heritability

Question 35

Role of leptin in obesity

Answer 35

leptin signals brain to decrease hunger and burn fat, so mutation in leptin or leptin resistance lead to weight gain

Question 36

Trifty gene hypothesis

Answer 36

 May partially explain high obesity rates in Pacific island nations.
 People who stored more energy as fat better survived long ocean voyages to colonize islands

Question 37

Role of melanin in skin color and importance in conditions of different sunlight

Answer 37

 Melanin blocks UV-induced skin cancer
 Melanin prevents UV-induced degradation of folate.
 But too little UV can decrease production of vitamin D.

Question 38

What does a Manhattan plot show?

Answer 38

o Results of Genome-wide association study
o Can identify genes that may be involved in inheritance of a trait.

Question 39

De novo mutation

Answer 39

o Mutation that does not exist in either parent (new mutation)
o Higher risk with increasing father’s (paternal) age, due to continuous division of sperm precursor cells.