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Biology A2 > Inheritance > Flashcards

Inheritance Flashcards

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1
Q

Zygote

A

Fertilised egg cell

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2
Q

Allele

A

Alternative form of a gene

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3
Q

Dominant gene

A

Always expressed in phenotype

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4
Q

Recessive gene

A

Only expressed in phenotype when homozygous

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5
Q

Homozygous

A

Pair of chromosomes that have two of the same alleles of a gene

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6
Q

Heterozygous

A

Pair of chromosomes that have two different alleles of a gene

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7
Q

Genotype

A

Combination of alleles for a particular gene

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8
Q

Phenotype

A

Expression of characteristic due to genotype AND environment

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9
Q

Monohybrid inheritance

A

Inheritance of a single phenotype affected by one gene

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10
Q

Acronym for Genetic Diagram

A

First
Inside
Outside
Last

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11
Q

Genetic Diagram Points (5)

A 
(Parent phenotype)
Parent genotype 
Gametes
Offspring genotype (in table) 
Offspring phenotype with proportions (for monohybrid match genotype to phenotypes but with dihybrid give phenotypes in ratio)
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12
Q

Test cross

A
  • Determine if individual with dominant characteristic is homozygous or heterozygous
  • Crossbred with homozygous recessive individual (give genotype)
  • All offspring dominant = homozygous
  • Some offspring recessive = heterozygous
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13
Q

How to prove gene is dominant

A

Affected parents produce unaffected offspring

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14
Q

How to prove gene is recessive

A

Unaffected parents produce affected offspring

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15
Q

Codominant gene

A

Both alleles are equally dominant so both are expressed in phenotype

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16
Q

Multiple Alleles

A

More than two alternative forms of a gene (alleles) that can occupy the same locus, of which only two can be present in a single organism’s homologous chromosomes

E.g. ABO system of blood groups is controlled by three alleles, only two of which are present in an individual

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17
Q

Sex-linked gene

A

A gene found only on sex chromosomes, i.e. X chromosomes in humans

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18
Q

Differences between X and Y chromosomes

A
  • X larger compared to Y

- X contains more genes

19
Q

Suggest why sex-linked diseases are more common in men compared to women

A
  • men only have one X chromosome
  • Y chromosome does not have an equivalent non homologous portion as X
  • recessive alleles on non homologous portion of X are more frequently expressed
20
Q

Dihybrid Inheritance

A

Inheritance of two phenotypes determined by different genes located on different chromosomes

21
Q

Dihybrid Cross

A

Mating experiment between two organisms both heterozygous for different traits

Gives theoretical ratio 9:3:3:1

22
Q

What does dihybird cross prove

A
  • 9:3:3:1 ratio
  • pairs of alleles for a trait are sorted independently from one another from generation to generation
  • independent assortment
23
Q

Suggest why there are four possible gametes in a dihybrid cross

A
  • genes for both traits on separate chromosomes

- independent segregation occurs during meiosis where chromosomes arrange themselves randomly along equator

24
Q

Autosomal Linkage

A

Two or more genes carried on the same autosome (non-sex chromosome) so are linked

25
Q

What impact does cross over have on autosomal linkage

A

Cross over creates new combinations of alleles so there are four possible gametes as oppose to two

26
Q

What determines if two genes are likely to be separated during cross over

A

Two alleles are less likely to be separated during cross over if they are closer together on chromosome

27
Q

Epistasis

A

When one gene prevents the expression of another gene

28
Q

Dominant Epistasis

A

Epistatic gene requires at least one dominant allele to prevent expression of other gene

29
Q

Recessive Epistasis

A

Epistatic gene must be homozygous recessive to prevent expression of other gene

30
Q

Phenotypic ratios when breeding parents that are both heterozygous for two genes

A

9: 3:3:1 (independent genes/no epistasis)
9: 3:4 (recessive epistasis)
12: 3:1 or 13:3 (dominant epistasis)

31
Q

Explain why observed ratios are often not the same as expected ratios in a population

A
  • small sample size
  • random fusion of gametes
  • lethal alleles / selective disadvantage
32
Q

How do multiple alleles of a gene arise

A

mutations

33
Q

Suggest what dashes represent in a genotype

A

Either dominant or recessive allele

34
Q

Suggest what assumptions are made when using Hardy-Weinberg equation

A
  • no selection
  • random mating
  • large population / gene pool
  • no mutations
  • population is isolated
  • (generations do not overlap)
  • (no immigration or emigration)
35
Q

Suggest why there might be a high incidence of a genetic disease in a population

A
  • common ancestor
  • genetic isolation / small gene pool
  • in breeding
  • high probability of mating with individual carrying disease causing allele
36
Q

Suggest how results of a genetic cross demonstrate independent assortment is involved in production of gametes

A
  • new combinations of alleles

- in offspring but not parents

37
Q

Explain how evidence from a pedigree diagram shows a condition is recessive

A
  • unaffected parents have a child with condition

- both parents must be carriers

38
Q

Suggest why sex linked genes are found only on the X chromosome

A
  • X chromosome is larger

- Y lacks equivalent non homologous section where sex-linked genes are found

39
Q

Suggest why number of people with a fatal genetic disease may actually be lower than predicted by the Hardy-Weinberg equation

A

Some of those with condition die

40
Q

Suggest what the Hardy-Weinberg principle predicts

A

The proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next

41
Q

Describe how to determine if a trait in an organism is genetic or environmental

A
  • breed in a lab
  • observe / measure trait
  • if trait is present then must be genetic and not environmental
42
Q

Explain how you can tell genes are linked

A
  • certain phenotypes are more common when you would expect equal numbers
  • alleles controlling more common phenotype are linked
  • gametes mainly produce linked combination of alleles
  • cross over rarely produces other combinations of alleles
43
Q

Suggest reasons why ratio of offspring might not be the same as predicted

A 
- epistasis 
OR 
- autosomal linkage 
- no independent segregation 
- linked alleles inherited in same gamete UNLESS cross over occurs

Biology A2 (15 decks)

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