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General Biology I > lecture 14: beyond mendel > Flashcards

lecture 14: beyond mendel Flashcards

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1
Q

Do most characters follow Mendelian rules?

A

No, most have more complicated patterns of inheritance as Mendel’s principles of genetics are rather simplistic

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2
Q

What are examples of characters that follows a more complicated pattern than Mendelian rules?

A

Height, skin colour…

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3
Q

What is autosomal inheritance?

A

Inheritance of characters governed by genes on autosomes

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4
Q

What is sex-linked inheritance?

A

Inheritance of characters governed by genes on sex chromosomes (X or Y)
- Sex-linked characters are inherited differently in males and in females

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5
Q

Where was sex-linked inheritance first discovered?

A

in fruit flies

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6
Q

What is a wild-type trait?

A

The most common phenotype for each character

- uppercase W = dominant wild-type allele

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7
Q

What is a mutant trait?

A

Less common phenotype attributable to a mutation in a gene (recessive mutant allele)

  • Lowercase w
  • The gene is named after the mutant phenotype
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8
Q

What is the mutant eye colour of fruit flies?

A

White = ww

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9
Q

What is the wild-type eye colour of fruit flies?

A

Red = WW or Ww (dominant allele)

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10
Q

How was sex-linked inheritance discovered in fruit flies?

A

Reciprocal crosses produce DIFFERENT phenotype results in males and females —> so the sex/trait combo (mother with red eyes with father with white eyes, mother with white eyes with father with red eyes, etc) MATTERED in the inheritance pattern

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11
Q

How is sex defined in animals?

A
  • with sex chromosomes
  • X/Y chromosome system in mammals, but other sex determination systems exist too
  • sex determination can also be controlled by the environment (ex: sex determined by nest temperature in alligators)
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12
Q

What are the difference between X and the Y sex chromosome and their roles?

A
  • X = bigger and Y = smaller —> only two small homologous parts at top and bottom called pseudoautosomal regions (PARs) —> these parts allo these chromosomes to behave as homologues during meiosis —> PARs contain genes for development of males and females
  • X chromosome genes = essential for development of females and males
  • Y = only necessary for male development and male fertility
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13
Q

What are the two types of sex-linked inheritance?

A
  1. X-linked: character governed by a gene on the X chromosome
  2. Y-linked: character governed by a gene on Y chromosome
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14
Q

Is eye colour in fruit flies X or Y-linked?

A

X-linked —> only exist on X chromosomes

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15
Q

What were the 3 possible genotypes for eye colour in female fruit flies vs the 2 possible genotypes for male fruit flies?

A

FEMALE:

  1. X(W)X(W) = red
  2. X(W)X(w) = red
  3. X(w)X(w) = white

MALE:

  1. X(W)Y = red
  2. X(w)Y = white

—> so mutant eye colour (white) is more common in males (50% chance)

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16
Q

What are some examples of X-linked recessive disorders in humans?

A
  • Red-green colour blindness

- Hemophilia A and B

17
Q

Difference (1) between autosomal inheritance vs sex-linked inheritance and the 4 consequences of this difference?

A

Because males only have one X and most genes present on the X have no counterpart on the Y

  1. Males (XY) are therefore HEMIZYGOUS dominant or recessive —> cannot be homozygous/heterozygous
  2. Far more males have sex-linked recessive disorders (bc of 50/50 chance to have the disorder) —>females are more protected from X-linked recessive disorders
  3. Mothers (XX) can pass alleles to sons & daughters while fathers (XY) can ONLY pass on alleles to daughters
  4. Mothers can be carriers for X-linked recessive disorders (X(W)X(w)) —> males cannot bc they have the disorder OR they don’t (50% chance)
18
Q

What is a polymorphic character and the two types?

A

Character that has more than 2 phenotypes in a population

  1. Qualitative characters: various trait CATEGORIES
  2. Quantitative characters: display CONTINUUM of traits (human height)

—> Eye colour = both qualitative and quantitative

19
Q

Which 3 factors increase the number of phenotypes for a character in a population?

A
  1. Spectrum of dominance: not only complete dominance
  2. Multiple alleles: not only two alleles for 1 character
  3. Interactions between genes: one trait is usually governed by many different genes, not only two

—> Increase number of genotypes, and consequently phenotypes

20
Q

What are the 3 categories on the spectrum of dominance?

A
  1. Complete dominance: only the dominant phenotype is expressed in HETEROzygotes
  2. Incomplete dominance: phenotype is a MIXTURE of both in heterozygotes (“blending” hypothesis)
  3. Codominance: both phenotypes are expressed in heterozygotes (ex: splash of white and purple colours on the petals)
21
Q

How do incomplete dominance/codominance differ with Mendelian genetics?

A

Mendel: only 2 phenotypes as homozygous dom. and heterozygous give the SAME phenotype

On spectrum of dominance: 3 phenotypes —> heterozygous gives a NEW phenotype, different from the one given by homozygous dom. —> an INTERMEDIATE phenotype

22
Q

How many phenotypes does codominance give?

A

3 phenotypes: 1 new phenotype = a blend between the 2 parental phenotypes

23
Q

Explain how having multiples alleles for one gene increases the number of phenotypes in a population.

A
  • Three or more alleles can exist for one single gene, not only two
  • One person can only have two of all these alleles
    —> So many possible genotypes giving rise to many different phenotypes
24
Q

How does the concept of multiple alleles for one gene differ with Mendelian genetics?

A

Mendel = only two alleles giving rise to two phenotypes possible (1 dominant and 1 recessive)

25
Q

How are ABO blood groups inherited?

A
  • Multiple alleles: 3 alleles for the gene that governs our ABO blood group (I(A), I(B), and i)
  • Codominance: I(A) and I(B) are codominant
  • Complete dominance I(A) and I(B) and completely dominant over the i allele
    I(A)I(A) and I(A)i = Type A
    I(B)I(B) and I(B)i = Type B
    I(A)I(B) = Type AB
    ii = Type O
    —> Combination of multiple alleles and codominance leads to 4 phenotypes
26
Q

How does ABO blood groups differ and why is it important to identity one’s blood type?

A

I(A), I(B), and i reflect various types of cell membrane glycoproteins found on red blood cells

  • Type A has a certain type of glycoproteins (antigens)
  • Type B has another type of glycoproteins (antigens)
  • Type O does not have any antigens

Matching blood types for blood transfusion: to prevent a reaction of in the immune system —> mismatched blood causes a transfusion reaction —> immune system judges the red blood cells as foreign (different glycoproteins) and the tissue will be attacked

27
Q

Which blood type is the universal donor and the universal acceptor and why?

A 
Donor = Type O, because type O does not have any antigens so everyone can accept O blood and not recognize it as foreign
Acceptor = Type AB, because has both types of antigens and O does not have any
28
Q

What do interactions between two genes for one character give in terms of phenotypes?

A
  • 4 different phenotypes for 1 character: 2 parental and 1 appearing at each generation (F1 and F2)
  • Qualitative
29
Q

How does the concept of interactions between genes differ with Mendelian genetics?

A
  • Mendel = only 1 gene (2 alleles) defining 1 character —> MONOGENIC characters
  • With interactions between two genes = 4 alleles in total = 4 possible genotypes (as one persons only inherits 2 alleles of the 4) = 4 possible phenotypes
    —> POLYGENIC characters
30
Q

What is epistasis?

A

Special case of gene interaction where a gene at one locus MASKS the effect of a gene at another locus
—> Two genes involved: the one masking the other = the EPISTATIC gene, the MODIFIER/MASKING gene
- The epistatic gene can act in a dominant or recessive fashion (masks the other gene when the epistatic one is inherited as homozygous dominant OR as homozygous recessive)

31
Q

How does epistasis work in coat coloration in mice?

A
  • TWO genes: Gene B and C
  • Gene B = black (B) or brown pigment (b) where black allele (B) is DOMINANT
  • Gene C (at another locus) determines whether the pigment produced (black or brown) is DEPOSITED in the hair —> if no pigment is deposited, the coat is WHITE
  • Dominant allele = C, Recessive = c
  • CC and Cc genotypes ALLOW the pigment to be deposited while cc genotype does NOT
    —> Gene C = EPISTATIC to the pigment colour gene B because it can MASK THE EFFECT of gene B, but in a RECESSIVE (cc) manner
    —> So if cc in the genotype, it does not matter if there is dominant BB or Bb —> the coat will be white
32
Q

How can polygenic inheritance produce quantitative characters?

A
  • Many genes interact to affect the character of one character + Incomplete dominance between the alleles
  • But there are ADDITIVE effects of alleles for each gene
    —> Give quantitative characters with a CONTINUUM of phenotypes (ex: human height)
    —> Distribution of phenotypes gives bell-shaped curve on a graph
    —> Increase in the number of genes involved and combination of incomplete dominance will INCREASE THE NUMBER OF PHENOTYPES
33
Q

Explain how the effects of alleles can be additive.

A
  • Incomplete dominance —> gives phenotypes that are mix of the 2 parental phenotypes, where one of the phenotype is the DOMINANT one
  • The more number of dominant alleles you have, the more your phenotype is close to the dominant phenotype

EX: Kernel Colour:
PARENTS: aabbcc (pure-line white) + AABBCC (pure-line red)
—> So 3 different genes with 2 alleles each contribute to 1 genotype/1 phenotype/to the colour of the kernel
F1: AaBbCc = medium red (equal mix of red and white) with 3 dominant red alleles and 3 recessive white ones
SELF-FERTILIZED F2: gives SEVEN possible phenotypes ranging from pure white to pure red —> in the middle = shades of mixtures of white+red
—> The more there are red (ABC) alleles in one genotype, the more the colour will be close to the parent’s pure red

34
Q

Most characters are polymorphic. What does polymorphic mean?

A

Multiple phenotypes

General Biology I (19 decks)

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