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z - A Level Biology > 6.1.2: Patterns of inheritance > Flashcards

6.1.2: Patterns of inheritance Flashcards

1
Q

Types of variation

A
  • Discontinuous

* Continuous

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2
Q

Discontinuous variation

A
  • Qualitative differences between phenotypes
  • Clear phenotypic categories (blood group, sex)
  • Generally monogenic; if polygenic, genes interact in an epistatic way
  • Different alleles at single locus have large effects on phenotype
  • Unaffected by environment
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3
Q

Continuous variation

A
  • Quantitative differences between phenotypes
  • No distinct categories (height, weight)
  • Usually polygenic; each gene provides an additive effect to the phenotype
  • Strongly influenced by the environment
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4
Q

Polygenic (of a characteristic)

A

A characteristic is controlled by two or more genes

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5
Q

Both _______ and ________ contribute to phenotype

A

Both genotype and environment contribute to phenotype

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6
Q

Example of how genotype and environment contribute to phenotype

A

Height
⟶ Have genetic potential for certain height
⟶ Malnutrition can mean this potential is not reached

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7
Q

Variation

A

differences between members of the same species, arising as a result of mutations and essential in natural selection and therefore evolution.

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8
Q

Allele

A

version of a gene

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9
Q

Dominant allele

A

version of a gene that will always be expressed if present

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10
Q

Recessive allele

A

version of a gene that will only be expressed if two copies of the allele are present

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11
Q

Genotype

A

The genetic information of an organism

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12
Q

Phenotype

A

The observable characteristics of an organism

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13
Q

Homozygous

A

Two identical alleles for a characteristic

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14
Q

Heterozygous

A

Two different alleles for a characteristic

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15
Q

How variation plays a role in selection

A
  • When environment changes, organisms well adapted will survive and reproduce
  • They pass on ALLELES to offspring
  • This forms the basis of evolution by natural selection
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16
Q

How is genetic variation produced?

A
  • Prophase 1: crossing over of non-sister chromatids –> formation of recombinants
  • Metaphase 1: independent assortment –> it is random which chromosomes end up at each pole of the cell
  • Metaphase 2: Random orientation –> centromere splits, different alleles to each pole of cells –> large number of possible allele combinations for gametes
  • Mutations (random) in DNA replication in Interphase
  • Fusion of gametes in fertilisation is random
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17
Q

What is an example of codominant alleles in context of disease

A
  • Sickle cell anaemia
  • Missense mutation
  • When haemoglobin is deoxygenated, becomes crystalline and deforms RBC, eventually impeding blood flow and leading to tissue damage
  • Codominant heterozygotes: typically phenotypically symptomless ∵ presence of normal Hb in RBC prevents sickling
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18
Q

What is sex linkage?

A

When genes are carried on (either sex chromosome)

⟶ Tend to be carried on the X chromosome because Y chromosome v. short

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19
Q

In a classic Mendelian dihybrid cross

A
  • The 2 genes don’t affect each other
  • The 2 genes are not linked on the same chromosome
  • Independently assorted at M1 of meiosis
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20
Q

Why do actual ratios differ from expected ratios?

A

• Random fertilisation
• Genes may be linked
⟶ Larger sample = closer

21
Q

Recessive epistasis

A

A homozygous recessive genotype at 1 locus overrides the genotype at the other locus, even if there is a dominant allele present there.

22
Q

Difference between epistasis and dominance?

A

Epistasis occurs between 2 genes coding for different characteristics
Dominance occurs between 2 alleles of the same gene

23
Q

Epistasis

A

Interaction between gene loci; occurs between two genes coding for different characteristics.

24
Q

Dominant epistasis

A

A single dominant allele at 1 locus overrides all alleles at the other locus.

25
Q

The alleles that are masking the effect are called the…

A

epistatic alleles

26
Q

The alleles whose effect is being masked is called the…

A

hypostatic alleles

27
Q

Ratio that suggests dihybrid inheritance of 2 unlinked genes

A

9:3:3:1

28
Q

Ratio that suggests recessive epistasis

A

9:3:4

29
Q

Ratio that suggests dominant epistasis

A

12:3:1 or 13:3

30
Q

Ratio that suggests epistasis by complementary action

A

9:7

31
Q

9:7 suggests

A

Epistasis by complementary action

32
Q

12:3:1 or 13:3 suggests

A

Dominant epistasis

33
Q

9:3:4 suggests

A

Recessive episasis

34
Q

9:3:3:1 suggests

A

Dihybrid inheritance of 2 unlinked genes

35
Q

Hardy Weinberg equation describes populations that

A

are not evolving

36
Q

Genotype frequencies stay the same if what conditions are met:

A

1) Very large population: no genetic drift
2) No gene flow: no emigration or immigrant
3) No mutations: no new alleles added to the gene pool
4) Random mating: no sexual selection
5) No natural selection: all traits aid equally in survival

37
Q

Hardy Weinberg equilibrium: equations

A

p + q = 1.00

p² + 2pq + q² = 1.00

38
Q

In the Hardy-Weinberg equilibrium equations, what does p represent?

A

Frequency of the dominant allele

39
Q

In the Hardy-Weinberg equilibrium equations, what does q represent?

A

Frequency of the recessive allele

40
Q

In the Hardy-Weinberg equilibrium equations, what does p² represent?

A

Frequency of homozygous dominant genotype

41
Q

In the Hardy-Weinberg equilibrium equations, what does q² represent?

A

Frequency of homozygous recessive genotype

42
Q

In the Hardy-Weinberg equilibrium equations, what does 2pq represent?

A

Frequency of the heterozygous genotype

43
Q

Factors affecting evolution

A
  • Mutation
  • Sexual selection
  • Gene flow
  • Genetic drift
  • Natural selection
44
Q

How do mutations affect evolution?

A

Mutations lead to new alleles

45
Q

How does sexual selection affect evolution?

A

Sexual selection leads to alleles coding for mating success.

46
Q

Epistasis by complementary action

A

At least 1 dominant allele at each different loci needed to produce an effect

47
Q

Why is genetic drift more of a concern in small populations?

A
  • 1 individual or allele has a higher effect proportionally in a smaller population
  • Less variation so more vulnerable to environmental change e.g. disease
48
Q

Why is maintaining genetic diversity good?

A
  • Useful in changing climate
  • Prevention of inbreeding depression
  • Promotion of hybrid vigour
  • Prevent dwindling gene pool

z - A Level Biology (25 decks)

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