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MED-109 Biology II > topic 1: mendelian inheritance > Flashcards

topic 1: mendelian inheritance Flashcards

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1
Q

children do not inherit particular physical traits, but rather

A

genes

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2
Q

what is heredity?

A

the transmission of traits from one generation to the next

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3
Q

what is variation?

A

the differences in appearance between offsprings and their parents

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4
Q

what are the 2 laws of inheritance discovered by Gregor Mendel?

A
  • law of segregation
  • law of independent assortment
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5
Q

what are some advantages of using pea plants for genetic study?

A
  • many different characteristics and traits
  • mating of plants can be controlled
  • each pea plant has sperm and egg producing organs
  • cross pollination
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6
Q

what are sperm-producing organs and egg-producing organs known as?

A

stamens - (sperm-producing)
carpels - (egg-producing)

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7
Q

what is the difference between characteristics and traits?

A

characteristics - distinct heritable features (ex: flower color)

traits - characteristic variants (ex: purple or white flower)

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8
Q

what is cross-pollination?

A

fertilization between different plants
(can be achieved by dusting one plant with pollen from another)

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9
Q

what are true-breeding varieties?

A
  • homozygotes
  • plants that produce offspring of the same variants only when they self-pollinate
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10
Q

what is hybridization?

A

mating 2 CONTRASTING true-breeding plant varieties
(ex: white and purple flowered pea plants)

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11
Q

if all F1 plants had purple flowers after mating true-breeding white and purple flowered plants, what conclusion does that give?

A

purple flowers are dominant, while white flowers are recessive

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12
Q

if all F1 plants had purple flowers after mating true-breeding white and purple flowered plants, what is the ratio of purple to white flowers in the F2 generation?

A

3:1

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13
Q

what is meant by homozygous?

A

an organism with 2 identical alleles for a character for a gene controlling that character
(ex: AA or aa; true-breeding)

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14
Q

what is meant by heterozygous?

A

an organism with 2 different alleles for a character for a gene controlling that character
(ex: Aa; hybrid)

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15
Q

what is the difference between phenotype and genotype?

A

phenotype - the physical appearance of an organism
genotype - the genetic make up of an organism

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16
Q

what are dominant and recessive alleles?

A

dominant alleles - the ones expressed in the phenotype

recessive alleles - not expressed in the phenotype when combined with a dominant allele

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17
Q

what are the 4 related concepts explaining the 3:1 inheritance pattern Mendel observed in F2 offspring?

A

1 - alternative versions of genes (alleles) account for variation in inherited characteristics
2 - an organism inherits 2 alleles for each characteristic
3 - if the 2 alleles differ at a locus, then the dominant allele determines the phenotype of an organism while the recessive allele has no noticeable feature
4 - the law of segregation

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18
Q

what does the law of segregation state?

A

segregation of alleles corresponds to the separation of homologous chromosomes to different gametes during meiosis

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19
Q

what is a Punnett square used for?

A

a diagram that predicts the results of a genetic cross between individuals of known genetic makeup

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20
Q

how can we tell the genotype of an individual with the dominant phenotype?

A

by carrying out a testcross

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21
Q

how is a testcross carried?

A

by breeding the unknown genotype individual with a homozygous recessive individual

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22
Q

if the offspring displays the recessive phenotype in a testcross, then the unknown parent must be?

A

heterozygous

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23
Q

what are monohybrids?

A

organisms that are heterozygous for ONE character

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24
Q

Mendel derived the law of segregation through the inheritance pattern of?

A

monohybrids

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25
Q

Mendel derived the law of independent assortment using a?

A

dihybrid cross

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26
Q

what is a dihybrid cross?

A

crossing 2 true-breeding parents differing in 2 characteristics, produces dihybrids in F1 heterozygous for both charateristics

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27
Q

what is the one requirement for the law of independent assortment to be applied?

A

2 genes must be located on DIFFERENT chromosomes
(non-homologous chromosomes)

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28
Q

what does a dihybrid cross determine?

A

whether 2 characteristics are transmitted to offspring as a package (together) or separately

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29
Q

what does the law of independent assortment state?

A

each pair of alleles segregates independently of one another during gamete formation

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30
Q

what is the difference between the phenotypic ratio produced by an independent assortment and a dependent assortment?

A

law of independent assortment - produces a 9:3:3:1 ratio (genes are located on different chromosomes)

law of dependent assortment - produces a 3:1 ratio (genes are located on the same chromosomes or are LINKED)

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31
Q

when may inheritance deviate from simple Mendelian patterns?

A
  • when alleles are not completely dominant or recessive
  • when a gene has more than 2 alleles
  • when a gene produces multiple phenotypes
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32
Q

what are the different types of dominance?

A
  • complete dominance
  • incomplete dominance
  • codominance
33
Q

what is complete dominance?

A

when phenotypes of the heterozygote and dominant homozygote are identical
(expression of dominant allele phenotype)

34
Q

what is incomplete dominance?

A

when the phenotype of heterozygotes (F1 hybrids) is somewhere between the phenotypes of the 2 parental phenotypes
(neither allele is expressed; intermediate phenotype)

35
Q

what is codominance?

A

2 dominant alleles affect the phenotype in separate distinguishable ways
(both alleles are expressed)

36
Q

what are examples of incomplete dominance?

A
  • palomino horses
  • pink flowers (from crossing of white and red flowers)
37
Q

what is an example of codominance?

A

human blood group types

38
Q

describe the 3 alleles in human blood group types

A

A and B = codominant alleles
O = recessive allele

AA or AO - blood group A
BB or BO - blood group B
AB - blood group AB
OO - blood group O

39
Q

what is an example of multiple allelism?

A

human blood group types

40
Q

what do the 4 phenotypes of the ABO blood group (A, B, AB, O) depend on?

A
  • RBC membrane carbohydrates
  • 3 alleles for the enzyme (I) that attaches A or B carbohydrates to RBCs: IA, IB, i
41
Q

what does each allele of the (I) enzyme add?

A

IA allele - codes for enzyme that adds A carbohydrate

IB allele - codes for enzyme that adds B carbohydrate

i allele - codes for enzyme that adds neither

42
Q

what is an example of a recessive allele being more prevalent than a dominant allele

A

having 6 fingers is caused by a dominant allele, which is way less common in a population than having 5 fingers, caused by a recessive allele

43
Q

what is pleiotropy?

A

a property of most genes to have multiple phenotypic effects

44
Q

what are examples of hereditary diseases that have multiple symptoms caused by pleiotropic alleles?

A
  • sickle-cell disease
  • cystic fibrosis
45
Q

what are some ways traits can be determined/controlled by 2 or more genes?

A
  • epistasis: when the effects of 1 gene are modified by other genes
  • polygenic inheritance: when 2 or more genes control the expression of a single phenotype
46
Q

what is epistasis? give an example

A
  • a gene at one locus alters the phenotypic expression of a gene at a 2nd locus and results in 2 different gene sets affecting the same phenotypic characteristic
  • example: coat color of mice depends on 2 genes
  • one gene determines pigment color
    (B for black, b for brown)
  • the other gene determines where the pigment will be deposited in the hair
    (C for color, c for no color)
47
Q

what is an example of a human epistatic disease?

A

albinism

48
Q

describe albinism

A

a congenital autosomal recessive disorder characterized by the complete or partial absence of pigment in the skin, hair, eyes

49
Q

how is albinism caused?

A

it is caused due to the absence of tyrosinase, the enzyme responsible for the production of melanin

50
Q

what is polygenic inheritance? what is it characterized by?

A
  • when 2 or more genes control the expression of a single phenotype
  • usually characterized by quantitative variation
51
Q

what are quantitative characteristics? what are examples of polygenic inheritance?

A
  • characters that vary in the population along a continuum (continuous variation)
  • height and skin color in humans are examples of polygenic inheritance
52
Q

what are some environmental conditions (internal/external) that affect some phenotypes?

A
  • temperature
  • chemicals
  • nutritional habits
53
Q

what are multifactorial characteristics?

A

characteristics where both genetic and environmental factors influence phenotype

54
Q

what is meant by norm of reaction? give an example

A

the phenotypic range of a genotype influenced by the environment
(broadest for polygenic characteristics)

ex: hydrangea flowers of the same type range from blue-violet to pink, depending on soil acidity

55
Q

what does an organism’s phenotype include?

A
  • its physical appearance
  • internal anatomy
  • physiology
  • behavior
56
Q

why would humans not be good subjects for genetic research?

A
  • generation time is too long
  • parents produce relatively few offspring
  • breeding experiments are unacceptable
  • unethical
57
Q

what are the common features of homologous chromosomes?

A
  • have the same length and shape
  • carry genes controlling the same inherited characteristics
  • do not necessarily carry the same alleles
58
Q

what are pedigrees? what are they used for?

A
  • a family tree that describes the interrelationships of parents and children across generations
  • used to make predictions about future offspring and finding the probability of getting children
59
Q

how can you determine if a trait is dominant or recessive from a pedigree?

A

dominant - if 2 affected parents have an unaffected child

recessive - if 2 unaffected parents have an affected child

60
Q

what are two examples where pedigree diagrams were used to determine cause of conditions?

A
  • endogamy in kingdoms
  • Habsburg lip
61
Q

inherited human disorders can be of 3 types, which are?

A
  • autosomal dominant
  • autosomal recessive
  • sex-linked
62
Q

what are examples of autosomal recessive diseases?

A
  • cystic fibrosis
  • albinism
  • sickle cell anemia
  • α/β thalassemia
63
Q

describe autosomal recessive disorder

A
  • due to a mutation in an allele in one of the 22 autosomes
  • the mutant allele is recessive
  • AA or Aa = healthy individuals
  • aa = individuals with disease
64
Q

recessively inherited disorders show up only in what individuals?

A

in individuals homozygous for the allele

65
Q

what are carriers?

A

heterozygous individuals who carry the recessive allele but are phenotypically normal

66
Q

why are autosomal recessive disorders more common than autosomal dominant disorders?

A
  • because the disease alleles “hide” in the healthy heterozygous carriers that have a normal phenotype
  • in autosomal dominant, the disorder is always expressed phenotypically
67
Q

what are consanguineous matings?

A
  • mating between close relatives
    (taboo or illegal in most societies/cultures)
  • increase the chance of mating between 2 carriers of the same rare allele
68
Q

what causes sickle-cell anemia?

A

the substitution of a single amino acid (Glu -> Val) in the hemoglobin protein in RBCs

69
Q

what are the symptoms of sickle-cell anemia? how are heterozygotes affected?

A
  • physical weakness
  • organ damage
  • pain
  • paralysis
  • heterozygotes are usually healthy but may suffer some symptoms
  • less susceptible to malaria parasite
70
Q

describe how sickle-cell anemia arises

A
  1. substitution mutation of glutamic acid to valine (glu –> val) leads to exposed hydrophobic region
  2. hemoglobin molecules interact with one another, and crystallize into a fiber, greatly reducing the capacity to carry oxygen (meant to be separated so they can each carry oxygen)
  3. fibers of abnormal hemoglobin deform red blood cell into sickle shape
71
Q

what causes thalassemia?

A

a mutation in the hemoglobin gene (mutations in the α or β chains cause α or β thalassemia respectively)

72
Q

describe cystic fibrosis

A
  • the cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes
  • it is characterized by scarring (fibrosis) and cyst formation within the pancreas
  • symptoms include: mucus buildup in some internal organs and abnormal absorption of nutrients in small intestine
73
Q
A
74
Q
A
75
Q

what are examples of autosomal dominant diseases?

A
  • Huntington disease
  • Achondroplasia
  • Marfan syndrome
  • Polycystic kidney disease
76
Q

what are examples of X-linked diseases?

A
77
Q

what is the most common type of genetic disorders?

A

autosomal recessive disorders

78
Q
A

MED-109 Biology II (10 decks)

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