chapter 2-3 genetics

Question 1

What gives nucleus a granular appearance?

Answer 1

chromatin

Question 2

chromosomes

Answer 2

chromatins condense to form these organelles just before cell divides. Contains genes which contain DNA sequences

Question 3

3 components of DNA

Answer 3

5 carbons monosaccharide deoxyribose; a phosphate; 4 types of nitrogenous bases.

Question 4

4 types of nitrogenous bases

Answer 4

Cytosine and Thymine (pyrimidines—single carbon nitrogen rings) adenine and guanine (purines–double carbon nitrogen rings). ACTG

Question 5

Double helix

Answer 5

2 sides with deoxyribose and phosphate united by phosphodiester bonds and each nitrogenous base projecting from each side. Bases are bound by weak H+ bond (rungs of the ladder)

Question 6

nitrogenous base pairing

Answer 6

Adenine pairs with thymine, guanine with cytosine.

Question 7

nucleotide

Answer 7

1 DNA subunit (1 deoxyribose and 1 phosphate

Question 8

codon

Answer 8

triplet of bases determines protein

Question 9

DNA polymerase

Answer 9

important protein for DNA replication—travels along DNA and adds correct nucleotide to free end of new strand, proofreads.

Question 10

base pair substitution

Answer 10

one base pair replaces another. CAN results in change in amino acid sequence. Often has no consequence because the rest of the strand will be correct (called a silent mutation)

Question 11

2 types of base pair substitutions

Answer 11

missense (change in 1 amino acid) and nonsense (change in 3 stop codons-UAA, UAG, UGA in the mRNA)

Question 12

frameshift mutation

Answer 12

insertion or deletion of 1+ base pair in the DNA molecule. Changes the entire reading frame because it’s not a multiple of 3 base pairs. Alters amino acid sequence

Question 13

mutagens

Answer 13

increase frequency of mutation (radiation, chemical, mustard gas, formaldehyde, etc)

Question 14

DNA is formed in the

Answer 14

nucleus

Question 15

Protein synthesis occurs in the

Answer 15

cytoplasm

Question 16

transcription and translation are both mediated by

Answer 16

RNA

Question 17

how does RNA differ from DNA

Answer 17

Sugar molecule is RIBOSE, not DEOXYRUBOSE and URACIL not THYAMINE

Question 18

DNA transcription

Answer 18

i) RNA polymerase binds to promoter site (specifies beginning of gene), separates a portion of DNA and then leaves, leaving a DNA strand to provide the template for mRNA.
ii) RNA Stops at termination sequence—group of codons that act as signals to stop protein synthesis. Then RNA detaches from DNA and transcribed mRNA moves out of the nucleus into cytoplasm

Question 19

DNA translation

Answer 19

RNA directs synthesis of a polypeptide interacts with transfer RNA

i) tRNA—amino acid attaches. Has 3 nucleotide sequence at opposide side of cloverleaf called antiocodon. Undergoes complementary base pairing with appropriate codon in mRNA which specifies the sequence of amino acid through tRNA
(1) Ribosome—site of protein synthesis
(2) Ribosome binds to start site on mRNA and pairs tRNA and mRNA bases. Moves alon mRNA reading codon and translating an amino acid.
(a) Ribosome has enzyme that catalyzes form. Of covalent bonds between adjacent amino acidsgrowing polypeptide. @ termination signal on mRNA it stops, mRNA, ribosome and polypeptide separate and polypeptide is released into cytoplasm.

Question 20

somatic cell

Answer 20

46 chromosomes (all cells besides gametes) diploids (1/2 mom, ½ dad). Formed through mitosis and cytokinesis

Question 21

gamete cell

Answer 21

23 chromosomes—no pairs. Haploid formed by meiosis. 22 of 23 chromosome pair are homologous (autosome) last pair is the sex chromosome can be homologous or nonhomologous (XY)

Question 22

karyotype or kryogram

Answer 22

ordered display of chromosomes. Varies from person to person

Question 23

polyploidy

Answer 23

cell that has more than the diploid # of chomosomes (46). Some cells are normally polyploid—liver, bronchial, epithelial (1+ SET of chromosomes gained, i.e. 3+ full sets)
3 are compatable with life: down syndrome, edwards (trisomy 18), patau syndrome (trisomy 13)

Question 24

trisomy vs quadrosomy

Answer 24

types of polyloidy

(1) Triploidy—3 copies of each chromosome—most are spontaneously aborted or are stillborn
(2) Tetraploidy—92 chromosomes—mostly in aborted fetuses.

Question 25

aneuploidy

Answer 25

cell doesn’t contain multiple of 23 chromosomes

trisomy or monosomy (1+ chromosome lost or gained, polyploidys are aneuploidys, but not all aneuploidys are polyploidys)

Question 26

trisomy vs monosomy

Answer 26

types of aneuploidy

trisomy: 3 copies of 1 chromosome (trisomic)—trisome 13, 18, 21 or X can survive
ii) Monosomy—presence of only 1 copy of chromosome in a diploid cell—lethal
iii) Loss of chromosome material has more serious consequences than duplication of chromosome material***

Question 27

nondisjunction

Answer 27

sister chromatids fail to separate normally during meiosis or mitosis.

Question 28

partial trisomy

Answer 28

extra portion of chromosome in each cell. NOT as severe as complete trisomies.

Question 29

chromosomal mosaic

Answer 29

common in down syndrome (2% of cases)
body has 2+ cell lines, each cell line has a different karyotype
(a) Most often formed by early MITOTIC nondisjunction in 1 embronic cell AFTER FERTILIZATION but not the others.

Question 30

down syndrome

Answer 30

1/800 to 1/1000 live births.
(i) Increases with maternal age, due to old embryos
polysomy

Question 31

sex chromosome aneuploidy

Answer 31

1/500 males and 1/900 females. Less severe than autosomal. All forms except absence of ANY X allows for survival.
Trisomy X, turner and klinefelter

Question 32

Trisomy X

Answer 32

(a) 1/1000 females. Instead of 2 x, have 3 X in each cell.
(i) No overt physical abnormalities. sterility, menstrual irregularity, intellectual disability. 4 x’s=severe intellectual disability. More X’s =more severe

Question 33

Turner Syndrome

Answer 33

1 X chromosome, no X or Y (45 chromosomes)aka 45,X
(a) Only in females, not intellectually disabled, but dumb. Short stature, thick neck, wide nipples, coarctation of aorta, sterile. Usually d/t meiotic error in the father

extra skin on the neck (webbed neck), puffiness or swelling (lymphedema) of the hands and feet, skeletal abnormalities, heart defects and kidney problems.

do not start their periods or develop breasts without hormone treatment at the age of puberty

Question 34

Klinefelter

Answer 34

(3) Klinefelter syndrome—2X1Y, 47,XXY
(a) STERILE. Male appearance, female like breasts. Mod. Mental impairment high pitched voice, small testes. Mosaicism common

Question 35

deletion errors

Answer 35

gamete with lost DNA+normal DNA=some normal genes and some missing (cri du chat)

Question 36

cri Du chat

Answer 36

low birth weight, severe intellectual disability, microcephaly and heart defects. DELETION OF SHORT ARM OF CHROMOSOME 5

Question 37

Fragile X syndrome

Answer 37

intellectual disability, second most common genetic cause of intellectual disability. Males always exhibit symptoms, females not always
(2) Caused by duplication in CGG multiple times (200), number of repeats increases from generation to generation. Huntington and myotonic dystrophy are also caused by this mechanism

Question 38

locus

Answer 38

the position on the chromosome for a particular gene.

Question 39

allele

Answer 39

genes with different nucleotide sequence @ 1 allele (different forms of a gene). Each allele has 1 representation from father and 1 from mother
i) Homozygous or heterozygous

Question 40

polymorphic

Answer 40

locus with 2+ alleles that each occur frequently in a population

Question 41

genotype

Answer 41

composition of genes @ a locus

Question 42

phenotype

Answer 42

outward appearance (presentation of those genes)
i)	Example: PKU—is genotype.  Phenotype if untreatedintellectual disability Phenotype if treated with dietary restrictionsnormal

Question 43

autosomal dominant

Answer 43

ii) Autosomal dominant male=female transmission. No generation skipped. Affected heterozygous ind. Transmit disease to 50% of their children
iii) If child born with auto. Dom disease and no hx in family child is prob. Prod. Of new mutation.

Question 44

huntington disease

Answer 44

autosomal dominant Delayed age onset—HUNTINGTON DISEASE

(1) Progressive dementia, inc. uncontrolled limb movement, no symptoms until 40 years or later.
(2) Due to trinucleotide repeats

Question 45

proband

Answer 45

first person in the family dx or seen in clinic

Question 46

penetrance

Answer 46

% of people with a genotype that exhibit a particular phenotype

Question 47

expressivity

Answer 47

extent of variation in phenotype associate with genotype (neurofibromatosis type 1 can cause café au lait spots to learning disorders)

Question 48

Cystic Fibrosis

Answer 48

autosomal recessive
gene responsible encodes a chloride ion channel in some epithelial cells. Dec. chloride transport NaCL imbalance very thick mucous, dehydrated, clogging f dig. Organce and pancrease. Death from lung disease or HF before age 40 in 50% of those affected.
(1) Males=females. Common in consanguinity. Common in siblings but not parents. ¼ of offspring of carrier parents will be affected, ½ will be carriers.

Question 49

X link recessive

Answer 49

males hemizygous, females homozygous. Males will be more affected since they only have 1 X chromosome.
i) X inactivation happens after fertilization. ½ x chromosomes inactivated, not the same in each cell.

Question 50

epigenetics

Answer 50

chemical changes that cause dramatically different phenotypes. Methylation on DNA can cause certain pieces not to be able to be transcribed by mRNA. This affects the expression of genes

Question 51

Trisomy 21

Answer 51

trisomy 21 (3 copies of 1 chromosome). small, low set ears, broad short ears, short eyelashes, protruding tongue. 20-25% survive until birth. increased risk of heart disease d/t high cholesterol levels.

having heart defects, digestive problems such as gastroesophageal reflux or celiac disease, and hearing loss. Some people who have Down syndrome have low activity of the thyroid gland (hypothyroidism) -

Question 52

Fragile X (per genetics website)

Answer 52

A boy who has the full FMR1 mutation has fragile X syndrome and will have moderate intellectual disability. They have a particular facial appearance, characterized by a large head size, a long face, prominent forehead and chin and protruding ears. In addition males who have fragile X syndrome have loose joints (joint laxity), and large testes (after puberty).

Affected boys may have behavioral problems such as hyperactivity, hand flapping, hand biting, temper tantrums and autism. Other behaviors in boys after they have reached puberty include poor eye contact, perseverative speech, problems in impulse control and distractibility. Physical problems that have been seen include eye, orthopedic, heart and skin problems.

Girls who have the full FMR1 mutation have mild intellectual disability.

Question 53

Cri du chat (per genome website)

Answer 53

rare genetic condition that is caused by the deletion (a missing piece) of genetic material on the small arm (the p arm) of chromosome 5. Not hereditary.

The symptoms of cri du chat syndrome vary among individuals. The variability of the clinical symptoms and developmental delays may be related to the size of the deletion of the 5p arm.

The clinical symptoms of cri du chat syndrome usually include a high-pitched cat-like cry, mental retardation, delayed development, distinctive facial features, small head size (microcephaly), widely-spaced eyes (hypertelorism), low birth weight and weak muscle tone (hypotonia) in infancy. The cat-like cry typically becomes less apparent with time.

Most individuals who have cri du chat syndrome have difficulty with language. Half of children learn sufficient verbal skills to communicate. Some individuals learn to use short sentences, while others express themselves with a few basic words, gestures, or sign language.

Other characteristics may include feeding difficulties, delays in walking, hyperactivity, scoliosis, and significant retardation. A small number of children are born with serious organ defects and other life-threatening medical conditions, although most individuals with cri du chat syndrome have a normal life expectancy.

Question 54

Duchenne Muscular dystrophy

Answer 54

DMD is a rapidly progressive form of muscular dystrophy that occurs primarily in boys. It is caused by an alteration (mutation) in a gene, called the DMD gene that can be inherited in families in an X-linked recessive fashion, but it often occurs in people from families without a known family history of the condition. Individuals who have DMD have progressive loss of muscle function and weakness, which begins in the lower limbs. The DMD gene is the second largest gene to date, which encodes the muscle protein, dystrophin. Boys with Duchenne muscular dystrophy do not make the dystrophin protein in their muscles.

Duchenne muscular dystrophy affects approximately 1 in 3500 male births worldwide. Because this is an inherited disorder, risks include a family history of Duchenne muscular dystrophy.

The symptoms usually appear before age 6 and may appear as early as infancy. Typically, the first noticeable symptom is delay of motor milestones, including sitting and standing independently. The mean age for walking in boys with Duchenne muscular dystrophy is 18 months. There is progressive muscle weakness of the legs and pelvic muscles, which is associated with a loss of muscle mass (wasting). This muscle weakness causes a waddling gait and difficulty climbing stairs. Muscle weakness also occurs in the arms, neck, and other areas, but not as severely or as early as in the lower half of the body.

breathing complications and cardiomyopathy are most common causes of death