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Biology: for a level year 2 > Inheritance > Flashcards

Inheritance Flashcards

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1
Q

what is a gene?

A

A sequence of DNA that codes for a polypeptide

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2
Q

Define allele

A

different sequences
A single gene may have one, two or many alleles.
Alleles always occupy the same locus because they are different versions of the same gene

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3
Q

diploid individuals

A

has one of each chromosome from each parent and, therefore, one copy of each gene from each parent

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4
Q

Define homozygous

A

If the alleles of a particular gene are the same from both parents, the individual is homozygous for that gene

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5
Q

Define heterozygous

A

If the alleles of a particular gene are different from both parents, the individual is heterozygous for that gene

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6
Q

Define genotype

A

All the alleles they contain

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7
Q

Define phenotype

A

their expression of the genotype in a specific environment

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8
Q

Define dominant

A

The allele that is always expressed when it is present

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9
Q

Define recessive

A

The allele that is only expressed when it is homozygous

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10
Q

Define monohybrid inheritance

A

The inheritance of a single gene

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11
Q

Peas were a useful choice for experiments because

A
  • They are easy to grow
  • Their flowers can self-fertilise and cross-fertilise
  • They make flowers and fruit in the same year
  • They make a large number of seeds from each cross. This means that when the phenotypes of the next generation are counted, their numbers make them statistically meaningful
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12
Q

Mendel chose characteristics that are:

A
  • Controlled by single genes
  • Controlled by genes on different chromosomes
  • Clear cut and easy to tell apart
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13
Q

Describe continuous variation

A

They have a range of values and are controlled by a number of genes, for instance height, in humans

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14
Q

A diagram of a genetic cross show

A
  • The generations, i.e. parents, first generation (F1), second generation (F2) and, sometimes further generations
  • The genotypes of parents and offspring
  • The alleles present in the gametes
  • The symbols for the alleles are defined
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15
Q

What is the F1 (first filial) generation

A

It is the offspring of the parents of the cross.
F2 stands for the second filial generation. It is the offspring of a self- fertilised F1 plant or a cross between members of the F1 generation. It is also the grandchildren of the original parents

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16
Q

Define fillial

A

Relating to a son or daughter

17
Q

Instructions for writing a diagram for a genetic cross

A
  1. Choose suitable symbols for the alleles
    - Use a single letter for each characteristic, for example, the first letter of one of the contrasting features
    - If possible, use a letter in which the upper and lower cases differ in shape and size
    - Use the upper case for the dominant characteristic and the lower case letter the recessive
  2. Write the parents’ genotypes with the appropriate pairs of letters. Label ‘Genotype of parents, and state their phenotypes
  3. Show the gametes produced by each parent. Circle and label them ‘Gametes’
  4. Use a matrix, called a punnet square, to show the results of the possible combinations that result from random crossing of all the gametes. Label ‘Genotype of F1’
  5. Show the phenotype of each F1 genotype in the Punnet square
  6. Indicate the ratio of the phenotypes
18
Q

How can you tell if a dominant characteristic is determined by one of two dominant alleles?

A

By carrying out a test cross

19
Q

How do you do test crosses work?

A

Cross the heterozygous alleles with the unknown

E.g. If the tall plant were TT, all of the F1 would be tall, but if it were Tt, 50% would be tall and 50% would be dwarf

20
Q

What is co-dominance?

A

Both alleles in a heterozygote are expressed individually

As a result, the heterozygote has a combination of both of the homozygotes’ characteristics

21
Q

What is incomplete dominance?

A

For some genes, the phenotype of the heterozygote is intermediate between the two parental phenotypes, rather than their both being expressed

22
Q

1st law of inheritance- the law of segregation

A

states that the characteristics of an organism are determined by factors (alleles) which occur in pairs
Only one pair is present in each gamete

23
Q

What are unlinked genes?

A

Genes that behave independently in relation to each other

24
Q

Define dihybrid inheritance

A

The simultaneous inheritance of two unlinked genes, i.e. genes on different cromosomes

25
Q

How would you carry out a dihybrid test cross?

A

Testing a genotype by crossing it with an individual which is homozygous recessive for both genes
The ratios of phenotypes in the progeny indicate the genotype of the parent

26
Q

Why are some genes described as linked?

A

The alleles of two genes that are on the same chromosome cannot segregate independently, i.e. they cannot move to opposite poles of the cell at meiosis
This is because they are on the same physical structure- the chromosome- so they must move together

27
Q

The further apart two genes are on a chromosome

what does this lead to?

A

the more opportunity there is for crossover to occur between them. This leads to more recombinant gametes and therefore more offspring with recombinant phenotypes

28
Q

Recognising linkage

A

If the numbers of progeny with different combinations of characteristics do not correspond with Mendelian ratios, it is likely that the genes are linked

29
Q

What is a common explanation for rejecting the null hypotheses?

A

If the numbers of progeny with different combinations of characteristics do not correspond with Mendelian ratios, it is likely that genes are linked

30
Q

What is the expected ratio of phenotypes in a dihybrid cross?

A

9:3:3:1

31
Q

What is the null hypothesis?

A

This states that there is no difference between the observed and expected frequencies

32
Q

The reason that this is a null hypothesis is that Mendelian inheritance is based on there being no difference in:

A
  • The number of the different types of gamete
  • The probability of each gamete type fusing with another type of gamete
  • The viability of the embryos, whatever their genotype
  • And that genes are not linked

Biology: for a level year 2 (11 decks)

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