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Biology A2 > Inheritance > Flashcards

Inheritance Flashcards

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1
Q

What is monohybrid inheritance?

A

Inheritance of a single gene

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2
Q

What does pure-breeding mean and how does it come about?

A

Pure-breeding = homozygous for a particular characteristic.
Organisms with the same phenotype are consistently bred together so all offspring have this phenotype and they are homozygous for the gene.

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3
Q

Monohybrid inheritance: F1 generation when 2 pure breeding organisms are crossed - genotypes and phenotypes

A

Phenotype: all dominant
Genotype: all heterozygous

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4
Q

Monohybrid inheritance: F2 generation when F1 heterozygous offspring breeding are crossed - genotypes and phenotypes

A

Phenotype: 3:1 dominant to recessive
Genotype: 1 homozygous dominant: 2 heterozygous: 1 homozygous recessive

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5
Q

Why are the actual outcomes of genetic crosses different to the predicted?

A

due to statistical error: chance determines which gametes fuse with which.

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6
Q

How can you make sure the actual results are close to the theoretical ones when carrying out an crossing experiment?

A

By using a large sample size

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7
Q

What is dihybrid inheritance?

A

how two characteristics, determined by two different genes located on different chromosomes are inherited.

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8
Q

General dihybrid cross F1
Parents: XXYY and xxyy
Offspring: ?

A

all XxYy

all have phenotype of dominant for both genes

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9
Q

Why is the allele for one gene independent of the other in dihybrid inheritance?

A

As the genes are found on different chromosomes, and chromosomes arrange themselves at random during meiosis and independent segregation occurs.
Fertilisation is also random, so any of the 4 types of gametes can combine.

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10
Q

Types of gamete for an organism with genotype XxYy

A

XY, Xy, xY, xy

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11
Q

Dihybrid inheritance: theoretical ratio of phenotypes for the F2 generation - cross between 2 XxYy individuals.

A

9:3:3:1

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12
Q

Mendel’s law of independent assortment

A

each member of a pair of alleles may combine randomly with either of another pair.

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13
Q

Codominance

A

where 2 different alleles of a single gene trait are expressed in the phenotype - instead of one allele being dominant and the other recessive.

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14
Q

Xx

which letter represents the dominant allele and which the recessive

A 
X = dominant
x = recessive
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15
Q

How are codominant alleles represented?

A

Different letters are used to represent the alleles, as superscripts to a letter which represents the gene.

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16
Q

Why can’t upper and lowercase letters be used to represent codominant genes?

A

As this would imply that one gene is dominant.

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17
Q

Linked genes

A

genes that are inherited together, i.e. on the same chromosome, so if one gene is inherited, the linked one is too.

18
Q

Unlinked genes

A

genes that are inherited separately - e.g. on different chromosomes, due to independent segregation.

19
Q

Why can 4 different combinations of alleles in gametes arise with dihybrid inheritance?

A

Meiosis separates homologous chromosomes and alleles.

Independent segregation means you can get any combination of the 2 alleles an a gamete.

20
Q

Multiple alleles

A

A gene may have more than 2 alleles, so more different combinations and phenotypes can arise.
Only 2 alleles can be present at one time as there are only 2 homologous chromosomes.

21
Q

Example of multiple alleles

A

the human ABO blood system

22
Q

Sex-linkage

A

inheritance of a gene located on one of the sex chromosomes

23
Q

Autosome

A

any one of the 22 pairs of chromosomes which are not sex chromosomes.

24
Q

Gene

A

A sequence of bases on a DNA molecule that codes for a protein which results in a characteristic.

25
Q

Allele

A

A different version of the same gene. Most organisms have 2 alleles of each gene, one on each homologous chromosome.

26
Q

Genotype

A

The genetic constitution of an organism - all the alleles it has

27
Q

Phenotype

A

The expression of an organism’s genetic constitution and its interaction with the environment, an organism’s observable or biochemical characteristics.

28
Q

Dominant

A

An allele which is expressed in the phenotype even when only one copy is present.
Represented with a capital letter.

29
Q

Recessive

A

An allele which is only expressed in the phenotype if 2 copies are present.

30
Q

Homozygote

A

An organism that carries 2 copies of the same allele, e.g. BB or bb

31
Q

Heterozygote

A

An organism that carries 2 different alleles of the same gene, e.g. Bb

32
Q

Carrier

A

An organism carrying an allele which is not expressed in the phenotype but can be passed on to offspring.

33
Q

Why are males more likely to express recessive phenotypes?

A

as the X chromosome is much longer than the Y and carries more genes, so most of the X chromosome doesn’t have an equivalent homologous portion of the Y chromosome.
Males only have 1 X chromosome so often only have 1 allele for sex-linked genes. This allele is always expressed, even if it is recessive.

34
Q

Autosomal linkage

A

Inheritance of 2+ genes which are carried on the same autosome.

35
Q

Why are females less likely to be colour-blind than males?

A

As the condition is X-linked/ gene is found on the X chromosome, so females need 2 recessive alleles but males only need 1.

36
Q

Epistasis

A

Where different genes control the same characteristic, and the expression of 1 gene affects the expression of another.

37
Q

Examples of epistasis

A

Metabolic pathways - stages controlled by enzymes

Fur colour and fur length

38
Q

What is the chi squared test used to test?

A

whether deviation between theoretical and experimental ratios/ outcomes for genetic crosses are significant or not.

39
Q

Why are the ratios different to dihybrid inheritance when genes are linked? e.g. cross between 2 GgNn individuals,

A

Genes on same chromosome so GgNn individual produces mainly GN and gn gametes. Crossing over produces a few Gn and gN gametes, so there are fewer Ggnn and ggNn individuals.

40
Q

What type of data is the chi squared test used for?

A

categorical

41
Q

What type of epistatic allele would give these ratios in a dihybrid cross?

9: 3:4
12: 3:1

A

recessive

dominant

Biology A2 (12 decks)

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