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BIO 102 > Quiz 5 > Flashcards

Quiz 5 Flashcards

1
Q

differences between law of segregation and law of independent assortment

A

law of segregation: for monohybrids; dependent assortment

law of independent assortment: for dihybrids; independent assortment

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2
Q

law of segregation

A

2 alleles for each gene segregate during gamete formation (like a coin flip)

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3
Q

law of independent assortment

A

each pair of alleles segregates independently of other pairs of alleles during gamete formation (when on different, nonhomologous chromosomes)

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4
Q

complications with Mendelian genetics

A
  • inheritance patterns are more complex
  • many characters are not just one gene with 2 allele types
  • BUT principles of segregation and independent assortment still apply
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5
Q

situations when inheritance may deviate from Mendelian patterns

A
  • alleles not completely dominant/recessive (incomplete dominance, co-dominance)
  • gene has >2 alleles
  • gene produces multiple phenotypes (pleitropy)
  • multiple genes affect a single phenotype (polygenic inheritance)???
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6
Q

3 degrees of dominance

A

complete dominance: phenotypes of a heterozygote and dominant homozygote are identical

incomplete dominance: phenotype of F1 hybrids is somewhere between phenotypes of the 2 parental varieties

co-dominance: 2 dominant alleles affect the phenotype in separate, distinguishable ways

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7
Q

subjectiveness of phenotypes

A
  • alleles are simply variations in a gene’s nucleotide sequences that change the way it’s expressed
  • for any character, dominance/recessiveness relationships of alleles depend on the level at which we examine the phenotype
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8
Q

what is Tay-Sachs disease

A
  • accumulation of lipids in the brain and spinal cord due to deficiency of an enzyme that is required to break down fatty substances
  • fatal; destroys brain and spinal cord
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9
Q

different types of dominance for Tay-Sachs disease

A
  • organismal level: recessive allele
  • biochemical level: phenotype (i.e. enzyme activity) is incompletely dominant (may be in-between level)
  • molecular level: alleles are codominant
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10
Q

example of recessive alleles being more common

A

polydactyly (extra fingers/toes) is dominant, but only seen in 1/400 babies born in the US - recessive allele far more prevalent!

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11
Q

example of gene with more than 2 allelic forms

A
  • 4 human blood phenotypes are determined by 3 alleles for enzyme I that attaches either A or B carbs to red blood cells

Type A: Ia Ia, Ia i
Type B: Ib Ib, Ib i
Type AB: Ia Ib
Type O: i i

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12
Q

pleiotropy

A

genes have multiple phenotypic effects

- e.g. multiple symptoms of hereditary conditions (CF, sickle cell anemia)

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13
Q

epistasis

A

gene at one locus alters phenotypic expression of gene at 2nd locus

  • e.g. lab (and other mammals) coat color depends on 2 genes; one determining pigment color (black B or brown b) and one determining if pigment will be deposited in hair (color C or no color c)
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14
Q

quantitive characters

A

characters that vary in a population along a continuum (e.g. skin color, height)
***usually indicates polygenic inheritance

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15
Q

polygenic inheritance

A

additive effect of 2 or more genes on a single phenotype

  • phenotype is usually a quantitive character
  • e.g. human skin color
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16
Q

example of environmental impact on phenotype

A

hydrangea flowers of the same genotype vary from blue to pink depending on soil acidity–varies from Mendelian genetic patterns

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17
Q

norm of reaction

A

range of phenotypes for a genotype (e.g. hydrangea color) influenced by the environment (also called multifactorial)

***norm of reaction is broadest for polygenic characters

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18
Q

multifactorial inheritance

A

phenotypes are influenced by both genetic and environmental factors

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19
Q

what makes up an organism’s phenotype, and what does it reflect?

A
  • phenotype includes physical appearance, internal anatomy, physiology, and behavior
  • phenotype reflects genotype and unique environmental history
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20
Q

why are humans bad subjects for genetic research?

A
  • several human traits follow Mendelian patterns but
    * generation time is long
    * parents produce too few offspring
    * breeding experiments unacceptable (eugenics)
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21
Q

pedigree and their uses

A

family trees (called pedigree charts) that describes interrelationships or people across generations

  • can be used to trace inheritance patterns of particular traits
  • we can use these to predict the probability of specific phenotypes
22
Q

general info and example of recessively inherited conditions/diseases

A
  • condition only shows up in homozygous recessive
  • heterozygotes called carriers (recessive allele but phenotypically normal)
  • if recessive allele is rare, the chance of 2 carries mating is generally low

example: albanism–lack of pigmentation in skin and hair

23
Q

impact of consanguineous matings on recessive diseases

A
  • consanguineous matings increase chance of mating between 2 carries of the recessive allele
  • therefore many societies/cultures have laws or taboos against marriage between close relatives
24
Q

cystic fibrosis prevalence, impact, and symptoms

A
  • most common lethal genetic disease in the US; strikes 1/2500 of European descent
  • CF allele results in defective/absent chloride transport channels in plasma membrane, leading to chloride buildup outside of cell
  • symptoms include mucus buildup in internal organs and abnormal absorption of nutrients in the small intestine
25
Q

sickle-cell disease prevalence, impact, symptoms

A
  • found in 1/400 African Americans, caused by substitution of a single amino acid that causes deformed hemoglobin proteins in RBCs
  • symptoms include physical weakness, pain, organ damage, paralysis
  • 1/10 African Americans are carriers, prevalence is so high for a detrimental allele because heterozygotes are less susceptible to malaria parasite (but may have some symptoms)
26
Q

dominantly-inherited disorders and examples

A

dominant alleles that cause these disorders are generally rare, they arise by mutation

  • Achondroplasia: form of dwarfism caused by rare dominant allele
  • Huntington’s disease: degenerative disease of the nervous system
27
Q

Huntington’s disease

A
  • causes deterioration of the nervous system–fatal
  • autosomal dominant genetic disease; person needs only 1 defective allele
  • parent with a dominant allele had 50% chance of passing it to child, it’s often passed on because there’s no phenotypic effect until age 35-40
28
Q

multifactorial disorders

A

many diseases have genetic and environmental components (although little understood about genetics of most)

i.e. heart disease, diabetes, cancer, alcoholism, mental illness

29
Q

role of genetic testing and counseling

A
  • genetic counselors can use Mendelian genetics, probability, and even tests to help people concerned with family history of a specific disease
  • use known family information to predict probabilities for certain conditions, although these probabilities always are changing as we learn more
30
Q

types of genetic testing

A

fetal testing - more invasive

  • aminocentesis: liquid that bathes the fetus tested
  • chorionic villus samping (CVS): placenta sample
  • also types of imaging, ultrasound or fetascopy

newborn screening
- simple tests routinely done in US hospitals for genetic info

31
Q

discoveries after Mendel

A
  • Mendel’s “hereditary factors” were chromosomes
  • mitosis and meiosis first described in late 1800s
  • chromosomal theory of inheritance followed; Morgan’s work proved it (flies)
  • then Griffith’s DNA discovery (pathogenic/harmless bacteria)
  • finally double helix discovered
32
Q

chromosome theory of inheritance

A
  • genes have specific loci on chromosomes

- chromosomes undergo segregation and independent assortment

33
Q

Morgan’s first experiment

A
  • bred mutant male flies with white eyes with wild type females with red eyes
  • F1 gen had all red eyes, F2 had 3:1 ratio of red/white but only males had white
  • concluded that white allele must be on x chromosome, supporting the chromosomal theory of inheritance
34
Q

wild type vs mutant alleles

A

wild type are normal phenotypes in fly populations, mutant are alternatives

35
Q

why were fruit flies ideal for Morgan’s experiments

A
  • breed at high rate (new generation every 2 weeks)

- only 4 pairs of chromosomes

36
Q

info on human sex chromosomes

A
  • larger X and smaller Y (only ends of Y chromosome have regions homologous with X)
  • each ovum contains X, sperm may contain X or Y
  • SRY gene on Y codes for development of testes

*however, some animals have different methods for sex determination (XX or X, different chromosomes entirely)

37
Q

sex-linked genes and recessive conditions more common in males

A

genes located on either sex chromosome

  • sex chromosomes have many genes for characters unrelated to sex
  • usually genes found on X chromosome
  • recessive X-linked traits need only 1 copy to be expressed in males, causing certain recessive disorders to be more common in males (color blindness, muscular dystrophy, hemophelia)
38
Q

X inactivation in female mammals

A
  • in some mammalian females one of the X chromosomes in each cell is inactivated during cell development, condensing into a Barr body
  • if females are heterozygous for an X gene, the phenotype will be a mosaic for that character (i.e. calico cat)
  • very rare for males, usually sterile
39
Q

Morgan’s 2nd experiment

A
  • crossed flies differing in body color and wing size
  • traits usually inherited together in specific combinations that parent phenotype had
  • showed genes must be on the same chromosome if they don’t assort independently
  • some nonparental phenotypes that showed up could be explained by genetic recombination (crossing over)
40
Q

types of offspring observed in Morgan’s 2nd experiment

A
  • parental types: phenotype matching parent phenotype

- recombinant types: new combinations of traits, nonparental from crossing over

41
Q

frequency of recombination for genes on same/different chromosome

A
  • 50% frequency of recombination for any 2 genes on different chromosomes
  • genes far apart on same chromosome can have a frequency near 50% (genetically unlinked despite physical linkage)
42
Q

chromosome alterations

A
  • large-scale alterations often result in miscarriage or a variety of developmental challenges
  • some caused by nondisjunction–pairs of homologous chromosomes don’t separate in meiosis (one gamete receives 2 of same chromosome and one gamete receives none)
  • some are structural changes–caused by breakages
43
Q

problems caused by nondisjunction

A

aneuploidy: fertilization of gametes with nondisjunction; offspring have variation in chromosome #
- monosomic zygote: only 1 copy of a chromosome
- trisomic zygote: 3 copies of a chromosome

polyplody: organism has > 2 full sets of chromosomes (common in plants but not animals, more “normal” in appearance than aneuploids

44
Q

4 types of alterations of chromosome structure from breakage

A

deletion - removes segment
duplication - repeats segment
inversion - reverses segment
translocation - moves segment from one chromosome to another

45
Q

human conditions due to aneuploidy

A

autosomal
- Down Syndrome: trisomy 21

sex chromosomes

  • Hinefelter syndrome: extra chromosome in men, XXY
  • Turner syndrome: monosome X, only viable monosomy in humans but females sterile
46
Q

examples of human conditions due to chromosomal alterations

A
  • cri du chat syndrome: deletion in chromosome 5; child has diminished mental development and catlike cry, death in infancy or early childhood
  • some cancers (i.e. chronic mylogenous leukemia) caused by chromosomal translocations between chromosome 9 and 22 (called a Philadelphia chromosome!)
47
Q

how does inheritance of organelle genes cause conditions

A
  • cytoplasmic/extranuclear genes with circular DNA are found in organelles (mitochondria, chloroplasts, plastids)
  • these genes are inherited maternally (cytoplasm comes from egg)

examples

  • some defects in mitochondrial genes prevent cells from making ATP, resulting in diseases affecting muscular and nervous systems
    • mitochondrial myopathy and Lever’s hereditary optic neuropathy
48
Q

experiment that discovered DNA as the genetic material

A
  • Frederick Griffith (1928) used 2 strains of bacteria, one pathogenic and one harmless
  • mixed heat-killed remains of pathogenic bacteria with harmless living cells and some cells became pathogenic
  • showed transformation: a change in genotype/phenotype due to assimilation of foreign DNA
  • identification of molecules of inheritance had previously been a major challenge, this led to discovery of DNA as genetic material
49
Q

discovery of DNA structure and its role

A
  • Watson and Crick stole images from Maurice Wilkins and Rosalind Franklin (x-ray crystallography) to introduce the double-helical model of DNA present in all body cells
  • hereditary info in DNA present in all cells of the body
  • DNA directs biochemical, anatomical, physiological, and sometimes behavioral traits
50
Q

more evidence for DNA as the genetic material (Chargaff)

A
  • 1950 Erwin Chargaff hypothesized DNA composition varied among species
  • evidence of diversity made DNA more credible as genetic material (different bases)
51
Q

Chargaff’s rules

A
  • base composition of DNA varies among species
  • in any species, the number of A/T bases are equal and the number of G/C bases are equal
  • the basis for these rules was not understood until the discovery of the double helix!!

BIO 102 (14 decks)

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