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Biology A2 UNIT 4 > Inheritance and Selection > Flashcards

Inheritance and Selection Flashcards

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1
Q

What is genotype?

A

The genetic make up of an organism. It describes all the alleles that an organism contains. The genotype sets the limits within which the characteristics of an individual may vary.

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2
Q

What is a change in a genotype as a result to a change in DNA called?

A

A mutation.

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3
Q

What is phenotype?

A

The observable characteristics of an organism. It is the result of the interaction between the expression of the genotype and the environment

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4
Q

What is a modification?

A

A change to the phenotype that does not affect the genotype.

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5
Q

What is a gene?

A

A section of DNA that usually determines a single characteristic of an organism. It does this by coding for a particular polypeptide.

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6
Q

What are alleles?

A

Different forms of a gene.

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7
Q

What is the locus?

A

The position of a gene on a chromosome.

Only one allele of a gene can occur at the locus of any one chromosome.

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8
Q

What are homologous chromosomes?

A

A pair of chromosomes that have the same gene loci and therefore determine the same features. They are not necessarily identical as the individual alleles of the same genes may vary. Homologous chromosomes are capable of pairing during meiosis.

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9
Q

HOMOZYGOUS

A

If the allele on each of the homologous chromosomes are the same

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10
Q

HETEROZYGOUS

A

If the allele on each of the homologous chromosomes are different.

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11
Q

Dominant allele

A

The allele of the heterozygote that expresses itself in the phenotype is said to be dominant.

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12
Q

Recessive allele

A

The allele that does not express itself in phenotype.

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13
Q

Homozygous dominant

A

A homozygous organism with two dominant alleles

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14
Q

Homozygous recessive

A

A homozygous organisms with two recessive alleles?

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15
Q

When does a recessive allele show in the phenotype?

A

When it is homozygous recessive (two of same).

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16
Q

Co-dominance

A

When two alleles both contribute to the phenotype.

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17
Q

Multiple alleles

A

A gene with more than two allelic forms.

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18
Q

How do you make a genetic cross?

A
  1. Choose first letter (one for each characteristic)
  2. Higher case letter dominant, lower case recessive.
  3. Label parents and phenotypes
  4. State gametes produced by each parent. Encircled.
  5. State phenotypes of each gamete genotype, state number of each type.
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19
Q

Monohybrid inheritance

A

The inheritance of a single gene

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20
Q

Law of genetics

A

In diploid organisms, characteristics are determined by alleles that occur in pairs. Only one of each pair of alleles can be present in a single gamete.

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21
Q

How many pairs of chromosomes do humans have?

A

23 pairs.

22
Q

What are the sex chromosomes?

A

22 of a humans pairs of chromosomes have partners that are identical in appearance, whether in male or female. Remaining pair are sex chromosomes.
IN FEMALES: XX
IN MALES: XY

23
Q

What gametes are produced by females/males?

A

Females: gamete with two X chromosomes
Males: some gametes with X some with Y

24
Q

Sex linked gene

A

Any gene that is carried on X or Y chromosome.

25
Q

Why do characteristics that are controlled by recessive alleles on non-homozygous portion of X chromosome appear more frequently in males?

A

X chromosome much longer than the Y, this means that, for most of the length of the X chromosome, there are no homologous portion of the Y. Characteristics that are controlled by recessive alleles on this non-homologous portion of the X-chromosome will appear more frequently in males. This is because there is no homologous portion of Y chromosome that might have dominant allele.

26
Q

What is haemophilia?

A

When blood clots only slowly and there may slow and persistent internal bleeding. Almost entirely restricted to males.

27
Q

What causes haemophilia?

A

Recessive allele with altered DNA nucleotides that therefore do not code for the required protein. Results in an individual being unable to produce a protein required in clotting process.

28
Q

What is a carrier?

A

An organism which carries an allele without showing any signs of the character in their phenotype.

29
Q

Describe features of pedigree charts.

A
  • Males represented as square
  • Females represented as a circle
  • Shading within either shape indicates the presence of a character, such as haemophilia, in the phenotype.
  • A dot within the circle signifies a woman with a normal phenotype but who carries the defective allele.
30
Q

What is an example of a gene with multiple alleles?

A

The inheritance of the human ABO blood groups.
There are three alleles associated with the gene I (immunoglobulin) which lead to the production of different antigens on the surface membrane of red blood cells.
Only two alleles present at one time.

31
Q

What are the different alleles for Blood group?

A 
I^A- lead to production of antigen A
I^B- leads to production of antigen B
I^O- does not lead to the production of either antigen. 
I^A and I^B are co-dominant
I^O is recessive to both.
32
Q

What are the possible genotypes for blood group A?

A

I^A I^A or I^A I^O

33
Q

What are the possible genotypes for blood group B?

A

I^B I^B or I^B I^O

34
Q

What are the possible genotypes for blood group AB?

A

I^A I^B

35
Q

What are the possible genotypes for blood group O?

A

I^O I^O

36
Q

Dominance hierarchy

A

Sometimes more than 3 alleles so arranged in a dominance hierarchy- each allele being dominant to the one below it and recessive to that above it.

37
Q

Gene pool

A

All the alleles of all the genes of all the individuals in a population at any one time.

38
Q

Allelic frequency

A

The number of times an allele occurs within the gene pool is referred to as the allelic frequency.

39
Q

What is the total number of alleles in a population taken to be?

A

1.0

40
Q

What is the Hardy-Weinberg equation used for?

A

Provides a mathematical equation that can be used to calculate the frequencies of the alleles of a particular gene in a population.

41
Q

What does the Hardy Weinberg equation predict?

A

That the proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next provided that 5 conditions are met:

  1. No mutations arise
  2. The population is isolated, that is, there is no flow of alleles into or out of the population.
  3. There is no selection, that is, all alleles are equally likely to be passed to next generation.
  4. The population is large.
  5. Mating within the population is random.
42
Q

What is the Hardy Weinberg equation?

A

Let freq. of allele A = p
freq of allele a = q

First equation:
p+q= 1.0

Only two alleles so freq. of on plus other must be 1.0 (100%)

Only four possible arrangements of the two alleles, all four added together must equal 1.0.

Second equation:
AA+Aa+aA+aa = 1.0

or

p^2+2pq+q^2 = 1.0

43
Q

Describe selection.

A
  • All organisms produce more offspring than can be supported by food supply.
  • Despite overproduction, most populations remain relatively constant in size.
  • This means there is competition between members of a species to be the ones who survive.
  • Within any pop. there will be a gene pool containing a wide variety of alleles.
  • Some individuals will possess combinations of alleles that make them better able (fitter) to survive in their competition with others.
  • These individuals are more likely to obtain the available resources and so grow more rapidly and live longer. As a result, they will have a better chance of successfully breeding and producing more offspring.
  • Only those individuals that successfully reproduce will pass alleles to next gen.
  • Alleles that gave parents advantage that are more likely to be passed on.
  • New individuals are more likely to survive and reproduce . -Over many gen. the number of individuals with the “advantageous” alleles will increase at expense of individuals with “less advantageous”.
  • Over time, freq. of advantageous increases

Advantageous depends on environment.

44
Q

What are the two types of selection?

A
  • Selection may favour individuals that vary in one direction from the mean of the population. Called directional selection and changes characteristics of pop.
  • Selection may favour average individuals. Called stabilising selection and preserves characteristics of pop.
45
Q

Describe directional selection.

A

If the environmental conditions change, so will the phenotypes needed for survival. Some individuals who fall either to the left or the right of the mean, will possess a phenotype more suited to the new conditions. These individuals will be more likely to survive and reproduce. They will therefore contribute more offspring (and the alleles these offspring posses) to the next gen. than other individuals.

Directional selection results in phenotypes at one extreme of the population being selected for and those at the other extreme being selected against.

46
Q

Describe stabilising selection.

A

If the environmental conditions remain stable, it is the individuals with phenotypes closest to the mean that are favoured. These individuals are more likely to pass their alleles to the next generation. Those individuals with phenotypes at the extremes are less likely to survive and pass on alleles. Stabilising selection therefore rends to eliminate phenotypes at the extremes.

47
Q

What is speciation?

A

The evolution of a new species from existing species.

48
Q

What is a species?

A

A group of individuals that share similar genes and are capable of breeding with one another to produce fertile offspring. Same gene pool.

49
Q

Describe speciation.

A

If two populations become separated in some way, the flow of alleles between them may cease. The environmental factors that each group encounters may differ. Selection will affects the two populations in different ways and so the type and frequency of alleles change. Each population will evolve along different lines. In time, the gene pools of two populations will become so different that, even if reunited, they would be incapable of successfully breeding. They would have become separate species, each with its own gene pool.

50
Q

Describe geographical isolation.

A

Geographical isolation occurs when a physical barrier prevents two populations from breeding with one another. Such barriers include, oceans, rivers, mountain ranges and deserts. What proves a barrier for one species may be no problem for another.

  • Individuals of species X form a single gene pool and freely interbreed.
  • Climate change over the centuries lead to drier conditions which reduce the area of forest and separate it into two regions that are many hundred of km apart.
  • Further climate change cause one forest region (A) to become much colder and wetter and other forest region (B) to become much warmer and drier.
  • In A, phenotypes are selected- ones better able to survive in colder wetter conditions.
  • In B, phenotypes selected that are better able to survive warmer drier conditions.
  • The type and frequency of the alleles in the gene pools of each group of species X become increasingly different.
  • In time, the differences are so great between the two gene pools that they are, in effect, different species.
  • Further climate change and regrowth of forest may lead to the species being reunited. However, they will not be able to interbreed.

Biology A2 UNIT 4 (8 decks)

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