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BIOL 1101 > Lecture 9: Mendel, Genes, and Inheritance > Flashcards

Lecture 9: Mendel, Genes, and Inheritance Flashcards

final focus

1
Q
  • rbc in sickle-cell disease
A

SICKLE CELL ANEMIA
- non flexible shape making it hard to move through capillaries
- mutated gene that codes for hemoglobin so it doesn’t form O2 properly, making it difficult to deliver to cells
important bc we need o2 as final e acceptor for atp

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2
Q

What is blending theory of inheritance

A
  • hereditary traits blend evenly in offspring through mixing of parents blood
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3
Q

what does blending theory of inheritance NOT explain

A
  • extremes do not gradually disappear
    (sometimes offspring has traits that’s EXACTLY like 1 parent, brown eyes for ex even if the other parent has blue eyes)
  • offspring sometimes have traits that differ from both parents (or its not a blend, where blue+brown eyes=brown eyes NOT A BLEND OF COLOURS)

= proven false

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4
Q

who is Gregor Mendel

A

founder of genetics
-first to use scientific method to study inheritance

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5
Q

Mendel’s hypotheses

A
  • 4 total, and he used experimental results to support 2 principles

1) principle of segregation
2) principle of independent assortment

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6
Q

Why did Mendel choose the garden pea

A
  • easy to grow (reproduce fast)
  • clearly defined characteristics (colour)
  • variation in chatacter-TRAITS
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7
Q

characters are passed onto offspring as

A

genes (discrete hereditary factors)
-determine the traits for characteristics you have

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8
Q

true breeding garden peas

A

true breeding varieties
-self fertilized plants, same trait in each generation (purple flower produces all purple flowers through self-pollination)

cross-pollination
- between different parent plants
(same and different traits in each generation); i.e. white + purple flower

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9
Q

P vs F1 vs F2

A

P- parents
- plants used in the initial cross
- each pea produced contains an embryo

F1-filal (offspring)
- first generation

F2
- second generation

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10
Q

cross pollination proves what

A
  • that blending theory isn’t true because even with a purple flower and a white flower that produces a purple offspring, its not a blend of the colours
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11
Q

FLOWER COLOUR CROSS (purple and white)

A

P- purple crossed w/ white

F1- all F1 seeds formed purple
- purple flower offspring crossed

F2- purple flowers: 75%
- white flowers: 25% (reintroduction of trait seen in P generation not in F1, but F2)
= 3:1 RATIO

  • NO BLENDING !!!!!
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12
Q

What was Mendels First hypothesis

A

1) genes for genetic characteristics occur in pairs
- one gene inherited from each parents
- alleles are different versions of a gene

  • diploid= two copies of a gene
  • non-applicable to bacteria
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13
Q

What was Mendel’s Second hypothesis

A

2) If two alleles of a gene are different, one allele is dominant over the other
- dominant allele is expressed
- recessive allele is masked

  • recessive is only expressed when two copies are present (rr)
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14
Q

What was Mendel’s Third Hypothesis

A

3) 2 alleles of a gene segregate and enter gametes singly (when they need to form gametes)

  • half of the gametes carry 1 allele, half carry the other (haploid)
  • PRINCIPLE OF SEGREGATION
  • two gametes will fuse=zygote, containing 2 alleles (diploid)
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15
Q

What is a monohybrid cross

A

crossing individuals to look at 1 characteristic
- done through Punnett squares
- 3:1 ratio
- results support mendels 3 hypothesis, leading to PRINCIPLE OF SEGREGATION

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16
Q

Homozygous vs Heterozygous

A

homo: both alleles are the same
- PP (dominant)
- pp (recessive)

hetero: two different alleles
- Pp

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17
Q

Genotype vs Phenotype

A

geno:
- genetic constitution
- PP, Pp, pp (3 options therefore 3:1)

pheno:
- appearance
- purple vs white flowers (2 options)

18
Q

Mendel’s Predictions (what could he predict)

A
  • classes of offspring (traits)
  • proportions of those offspring
  • done through sum rule in probability
19
Q

sum rule and product rule

A

sum: DIFF EVENTS, =OUTCOME
- probability of 2 different events producing 1 outcome
- individual probabilities added

product: INDEPENDENT EVENTS
- probability of 2 independent events occurring in succession
- individual probabilities multiplied

20
Q

Results if we validate mendels hypothesis with a test cross

A
  • cross an unknown genotype with a homozygous recessive individual
  • determines if the unknown is a heterozygote or homozygote
  • can validate that F2 is more heterozygous, can tell us if a purple flower is Pp (1:1 ratio, 1 white, 1 purple..see below)

crossing Pp with pp
1) Pp-purple
2) pp-white

crossing PP with pp
- all purple
1:0 ratio

21
Q

What was Mendel’s fourth hypothesis

A

4) alleles of genes that govern 2 different characters (during meiosis) segregate independently during gametes)=PRINCIPLE OF INDEPENDENT ASSORTMENT

  • occurs to independent assortment during meiosis
22
Q

Dihybrid Cross results

A

P generation: RRYY x rryy
- RR YY produces RY gametes
- rr yy produces ry gametes

F1:
- all offspring are Rr Yy (all dominant)

Crossing F1
F1: Rr Yy x Rr Yy
- produce 4 gametes:
1/4 R Y
1/4 R y
1/4 r Y
1/4 r y

F2: offspring have 4 phenotypes
- 9/16=both dominant
- 3/16= 1 dominant one recessive
- 3/16= 1 dominant one recessive (just opposite traits as above)
- 1/16= both recessive

9:3:3:1 ratio (using sum and product rules)

23
Q

Independent assortment In a cross refers to

A

the combinations of gametes produced by each generation

24
Q

F1 x Homozygous recessive dihybrid testcross

A
  • testcross: crossing with homozygous recessive
  • 1/4=both dominant
  • 1/4= 1 dominant one recessive
  • 1/4= 1 dominant one recessive (just opposite traits as above)
  • 1/4= both recessive
  • 1:1:1:1 RATIO
    supports that f1 are heterozygous
25
Q

Chromosome theory of inheritance

A
  • Walter sutton: theorized that parallels between genes and chromosomes in meiosis and fertilization
  • applies only to diploids (bc they separate and enter gametes)

1) chromosomes occur in pairs in diploid organisms
2) chromosomes of each pair are separated and delivered singly to gametes
3) independent assortment of chromosomes
4) each chromosome of each pair id derived from each parents
- paired back in zygote 1 per parents

26
Q

where are discrete hereditary factors found (said by Walter sutton)

A
  • on chromosomes

we now call these genes, he was essentially saying that the behaviour of chromosomes during meiosis matched segregation and independent assortment patterns of mendels hereditary factors

27
Q

Homologs Chromosomes have what that is occupied by a gene

A

LOCUS
- site occupied by a gene on a chromosome

  • alleles on different homologs chromosomes have the same loci
  • can be = (homo) or diff (hetero)
28
Q

What human traits follow mendelian principles

A
  • albinism (autosomal recessive, follows principles segregation)
  • webbed fingers (autosomal dominant, follows dominance and segregation)
  • short limbed dwarfism (autosomal recessive/co-dominant, follows segregation and dominance)
29
Q

What were some modifications to Mendel’s Hypothesis

A

1) Incomplete dominance- dominant alleles don’t fully mask recessive alleles
2) Codominance- effects of different alleles are equally detectable in heterozygotes
3) Multiple Alleles- 2+ alleles are present in a populations

4) Epistasis- genes interact, activity of 1 influencing the other
5) Polygenic Inheritance- character is controlled by common effects of several genes
6) Pleiotropy- 2+ characters are affected by a single gene

30
Q

Incomplete Dominance

A
  • dominant alleles IS NOT FULLY DOMINANT over recessive (not always strong enough)
  • heterozygote phenotype : different from either homozygote phenotype

P: Red flower (CRCR) x White flower (CWCW)
F1: all offspring: CRCW
- all pink flowers (incomplete dom=mix, 100% heterozygous offspring)

From F1 generation:
CRCW x CRCW (both pink)
F2 generation:
- 1/4 red
- 1/4 white
- 1/2 pink
= 1:2:1 ratio (NOT BLENDING ANYMORE, because they come back)

31
Q

Incomplete dominance in human traits

A

SICKLE CELL:
- homozygous recessive is a carrier, heterzygote has a milder trait

FAMILAL HYPERCHOLESTEROLEMIA:
- homozygous recessive has severe form of disease
- heterozygote has mild form of disease

TAY-SACHS DISEASE
- homozygous recessive has serious symptoms
- heterozygote has 0 symptoms but detectable biochemical effects

32
Q

Co-Dominance

A

different allés of gene have equal effects in heterozygotes
- both alleles are expressed

I.E. blood types
Human M,MN,N blood types (glycoproteins on RBC)

1) LMLM= M glycoprotein present: blood type M

2) LNLN= N glycoprotein present: blood type N

3) LMLN= both glycoproteins present: blood type MN

  • similar inheritance to incomplete dominance
    1:2:1 RATIO
33
Q

what cant the 1:2:1 ratio tell you

A

if its codom or incomplete Dom for f2

34
Q

Multiple Alleles

A

More than 2 types alleles for a gene
- found among all individuals in a population
- diploid individuals only have 2 of the alleles

Phenotype depends on relationship between different pairs of alleles
- still follows mendels principles

  • Small differences in DNA sequences result in multiple alleles *
    = 1 change results in new allele, changes phenotype in F1/F2
35
Q

Example for all 3 (incomplete, codom, and multiple alleles)

A

HUMAN ABO BLOOD GROUP

1) ANTIGENS
- glycoprotein on surface of RBC (triggers immune response)
* IA allele produces A antigen (dominant)
* IB allele produces B antigen (dominant)
* i allele produces neither A/B (recessive)= blood type O
(A antigen doesn’t make B and vice versa)

2) BLOOD TYPES (phenotypes) *based on above
-IAIA or IAi= type A
- IBIB or IBi= type B
- ii= type O
- IAIB= type AB

not rlly incomplete bc no allele is partly expressed

36
Q

Human ABO Blood group
- purpose and phenotype

A
  • immune system produces antibodies against antigens not found on its own RBC
    because you don’t make 3 naturally, the body recognizes it as a foreign substance, produces an immune system if you got blood B instead of A for instance

UNIVERSAL ACCEPTOR: AB
UNIVERSAL DONOR: O

37
Q

Epistasis

A

genes interact:
- allele of one locus inhibits or masks effects of allele at a different locus
- some expected phenotype don’t appear among offspring

Example: Labrador retrievers

MELANIN
- B allele= black
- b allele= brown
(dependent on …(below))
PIGMENT DEPOSITION
- E allele= normal amount of pigment (black/brown)
- e allele= blocked pigment (yellow fur)

PHENOTYPE
- BLACK FUR: BB EE, BB Ee, Bb EE, Bb Ee
- BROWN FUR: bb EE, bb Ee
- YELLOW FUR: BB ee, Bb ee, bb ee

38
Q

What can be said about the epistasis genes in labradors

A

e- E gene is EPISTATIC to B gene
- 9:3:4 ratio (follows independent assortment because genotype ratio matches, not the phenotype since the genes affect each others expression)

39
Q

Polygenic Inheritance

A
  • several genes at different loci interact to control 1 character
  • produces variation
    Phenotypic Distribution: Bell-shaped curve
    Often modified by environmental effects
    = Quantitative Traits

Example
- height, weight, skin colour, hair colour
(based on nutrition, hormones, environment)
- perfect bell curve indicated continuous variation in population, larger sample the closer it is to perfect shape

40
Q

Pleiotropy

A
  • 1 gene affects more than 1 character
    sickle cell disease (mutation to B globin gene which makes hemoglobin)
  • recessive allele affects hemoglobin function and structure
  • leads to blood vessel, tissue, and organ damage
  • different symptoms result

OPPOSITE OF POLYGENIC INHERITANCE

41
Q
A

BIOL 1101 (16 decks)

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