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Biology 1 > Beyond mendel > Flashcards

Beyond mendel Flashcards

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1
Q

Beyond Mendel

A
  • Mendel’s principles of genetics are rather simplistic.
  • Most characters do not follow simple Mendelian rules and have more complicated patterns of inheritance.
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2
Q

Sex linked Inheritance

A
  • Characters governed by genes on autosomes show autosomal inheritance.
  • Characters governed by genes on sex chromosomes show sex- linked inheritance.
  • Sex-linked characters are inherited differently in males and females.
  • This type of inheritance was first discovered in fruit flies.
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3
Q

Fruit flies

A
  • Drosophila melanogaster
  • Are a common model organism for genetic research
    1mm
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4
Q

Several mutant traits exist for

A

characters that allow inheritance patterns to be studied as well as other genetic studies.

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5
Q

Wild-Type Trait

A

The most common phenotype for each character.

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6
Q

Mutant Trait

A

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

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7
Q

Gene names after

A

The Mutant phenotype (eg. W for white eyes)

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8
Q

Uppercase vs lower case letter

A

Uppercase letter W refers to the dominant wild-type allele and lowercase letter w for the recessive mutant allele.

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9
Q

What led to the discovery of sex-linked inheritance?

A
  • Reciprocal crosses produced different phenotype results in the sexes.
  • Sex / Trait combo of the parent was important in the inheritance pattern.
  • The discovery of sex-linked inheritance also convinced biologists that the chromosome hypothesis of inheritance was correct.
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10
Q

Sex chromosomes

A

Determine sex in animals

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11
Q

Sex determination

A
  • X/Y chromosomes system is used in mammals
  • other systems exist
  • Sex determination can also be controlled by environnement in some animals. e.g., sex determined by nest temperature in alligators.
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12
Q

Sex chromosome Structure

A

X and Y chromosomes differ in size and number of genes (1000’s genes on X, 100’s on Y in humans).

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13
Q

X chromosome genes

A

are essential for normal development of females and males

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14
Q

Many Y chromosome genes

A

Are necessary for male development (e.g., SRY gene) and male fertility.

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15
Q

PARs

A
  • Short segments of homology at ends of the X and Y chromosomes called pseudoautosomal regions (PARs) allow these chromosomes to behave as homologues during meiosis (including crossing over in regions of homology).
  • PARs contain genes for development of males and females.
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16
Q

Sex-linked chromosomes can be either

A

A. X-linked: character governed by a gene on the X chromosome.
B. Y-linked: character governed by a gene on the Y chromosome.

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17
Q

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

A

The Y chromosome is very small and carries only a few functional genes on it. Thus, X-chromosome must carry the gene for eye colour in the fruit fly.

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18
Q

Some X-linked recessive disorders in humans:

A

Red-green colour blindness
Hemophilia A and B

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19
Q

X-linked inheritance

A

Different from autosomal inheritance because males only have one X and most genes present on the X have no counterpart on the Y.

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20
Q

Things to think about concerning x linked- inheritance

A

A. Males are hemizygous; homozygous and heterozygous lack meaning to describe alleles.
B. Far more males have sex-linked recessive disorders.
C. Mothers can pass alleles to sons and daughters while fathers can only pass on alleles to daughters only.
D. Mothers can be carriers for X-linked recessive disorders.

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21
Q

Most Characters are Polymorphic

A
  • Polymorphic characters: have more than 2 phenotypes in a population.
    A. Qualitative Characters: various trait categories exist.
    B. Quantitative Characters: display a continuum of traits.
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22
Q

Increasing Phenotypes

A

More than two phenotypes exist in a population because of:
1. Spectrum of dominance
2. Multiple alleles
3. Interactions between genes
These 3 increases genotypes and, consequently, phenotypes

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23
Q
  1. Spectrum of Dominance
A

Complete dominance: only dominant phenotype expressed in heterozygotes
Incomplete dominance: phenotype is a mixture in heterozygotes
Codominance: both phenotypes expressed in heterozygotes

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24
Q

Incomplete dominance and codominance

A

increase the number of possible phenotypes in a population

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25
Q

Flower colour in impatiens

A
  • incomplete dominance
  • New phenotype is an intermediate phenotype when both alleles are present (heterozygous).
  • Results in 3 possible phenotypes from 2 allele.
26
Q

Colour in Andalusian chickens

A
  • codominance
  • New phenotype is both phenotypes being expressed at once when both alleles are present (heterozygous).
  • Also results in 3 possible phenotypes from 2 allele.
27
Q
  1. Multiple Alleles for a gene
A

• When three or more alleles of a given gene exist across the individuals in the population.
• Any one person can only have two of these alleles.
• Several genotypes are possible giving rise to several phenotypes.

28
Q

ABO Blood Group

A
  • Example of multiple alleles and codominance
  • There are three alleles for the gene that governs our ABO blood group: IA, IB, and i.
  • IA and IB alleles are codominant. While IA and IB are completely dominant over the i allele.
29
Q

Combination of multiple alleles and codominance leads to (blood example)

A

4 phenotypes

30
Q

ABO blood group alleles

A

ABO blood group alleles: IA, IB, and I reflect various types of cell membrane glycoproteins found on red blood cells in the human population

31
Q

ABO blood groups are important to

A

Match when transfusing blood to another individual to prevent a reaction by the immune system.

32
Q

Mismatched Blood

A

will illicit a transfusion reaction since the immune system of the recipient judges the red blood cells as foreign (non-self) and the tissue will be attacked

33
Q

Crosses between chickens with different comb phenotypes give…
What is the pattern?
What explains this pattern?

A
  • odd results
  • New distinct traits appearing in each generation.
  • 4 phenotypes for one character.
  • 2 genes interact to control one character
34
Q
  1. Interactions between genes
A

b) A genetic model based on gene-by-gene interactions can explain the results.
Blanks in a genotype mean that either allele can be present
Two genes (R and P) interact to produce comb phenotype

35
Q

Epistasis

A

A special case of gene interaction where a gene at one locus masks the effects of a gene at another locus.

36
Q

Coat coloration in Mice

A

In mice, two genes determine coat (fur) color: Gene B and Gene C.

37
Q

Gene B

A

produces either black pigment or brown pigment for the coat. The black allele ( B) is dominant.

38
Q

Gene C

A
  • at another locus
  • determines whether the pigment produced (black or brown) is deposited in the hair.
39
Q

In order for the fur to take on the pigment

A

It must be deposited in the hair (or else no pigment is deposited and the coat is white).

40
Q

Deposition is

A

A dominant phenotype governed by the dominant C allele:
- The CC and Cc genotypes will allow for pigment to be deposited while the cc genotype does not.

41
Q

What is said to be epistatic

A

The pigment deposition gene C is said to be epistatic to the pigment colour gene B because is can mask (hide) the effect of the other.

42
Q

Polygenic inheritance produces

A

Quantitative characters
- Many genes interact to affect the expression of one character
- Additive effects of alleles for each gene.
- Quantitative characters have a continuum of phenotypes

43
Q

What can explain the pattern of new traits appearing in each generation

A
  • 2 genes interact to control 1 character and a spectrum of dominance is at play with additive effects!
44
Q

A. Wheat kernel color is a quantitative trait
B. Hypothesis to explain inheritance in kernel colour
How can you explain this?

A

A. 3 different genes contribute.
B. Two alleles exist for each.
C. In each case, one allele is incompletely dominant.
D. Color allele effects are additive.

An increase in the number of genes involved and the combination of incomplete dominance has increased the number of phenotypes to 7 for one character.

45
Q

Quantitative Characters

A
  • More complicated
  • Genes have various different effects on a phenotype when they interact (not necessarily equal and additive)
46
Q

Qualitative characters example

A

height in plants and animals is determined by several different genes that encode different proteins involved in very different aspects of growth in these organisms:
A. Growth hormone signaling
B. Cell division
C. Uptake of nutrients
D. Metabolism
E. Many other cellular activities that influence height!

47
Q

Other factors can influence Phenotype

A

It s not just about genes! Genotype to phenotype is often a complicated process and can be influenced by:
A. Environnemental Effect
B. Epigenetic Effects
- can potentially lead to different phenotypes for the same genotype

48
Q

A. Environnemental Effects

A
  • Phenotype = genotype(s) + environmental factors.
  • The expression of a phenotype for a particular genotype is not solely determined by genes.
  • Environmental effects can cause phenotypes to vary within individuals with the same genotype(s).
  • Helps create a continuum of phenotypes in quantitative characters.
49
Q

B. Epigenetic Effects

A
  • Our collection of phenotypes are governed by our genome but can be influenced by epigenetic changes.
50
Q

Epigenetic means

A

Above genetics

51
Q

Epigenetic effect are the result of changing

A

the way genes are used (i.e., change gene expression) in our cells.

52
Q

Epigenetic Changes

A

Chemical modification to DNA and packaging proteins influence the state of chromatin and expression of genes.

53
Q

Epigenetic effect might explain

A

Differences in monozygotic (identical) twins

54
Q

Epigenetic effect in inheritance ex

A
  • Tortoiseshell cat coloration
  • In heritance pattern is due to an epigenetic effect caused by X chromosome inactivation (epigenetic change)
  • female heterozygous for full colour gene has tortoiseshell coloration
55
Q

X inactivation in Female Mammals

A
  • Random inactivation of one X chromosome during development (embryo 10 days old in humans).
  • Inactivation occurs through changes to chromosome structure and alleles on this chromosome are not expressed.
56
Q

Which X is inactivated is

A

a permanent choice for that cell and passed on to
daughter cells.

57
Q

Somatic cells in an adult female mammals

A

Are a mixture:
≃ ½ the cells will express the alleles of the maternal X.
≃ ½ the cells will express the alleles of the paternal X.

58
Q

Barr Body

A

A highly condensed structure in the cells of female that is not found in the cells of males.

59
Q

Pleiotropy

A

One gene affects 2 or more characters (inverse of polygenic)
Pleiotropy is one of the genetic limitations in evolution

60
Q

Example of pleiotropy

A

The gene that determines flower color in pea plants also affects the color of the coating on the outer surface of the seed.

61
Q

Pleiotropy is evident in many

A

Human mono genetic diseases

Biology 1 (5 decks)

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