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7- Genetics, populations, evolution, and ecosystems > Genetic crosses > Flashcards

Genetic crosses Flashcards

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1
Q

Define genotype

A

Genotype is the genetic constitution of an organism. It describes all the alleles that an organism has and determines the limits within which the characteristics of an individual may vary.

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2
Q

Define phenotype

A

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

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3
Q

Define gene

A

A section of DNA that contains the coded information for making polypeptides and functional RNA. A gene is located at a particular position called a locus on a DNA molecule.

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4
Q

What is an allele

A

An allele is one of the different forms of a gene.

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5
Q

What are homologous chromosomes

A

A chromosome pair, one paternal and one maternal, with the same gene loci.

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6
Q

When is a recessive allele present in the phenotype of an organism

A

The effect of a recessive allele is apparent in the phenotype of a diploid organism only when it is in the homozygous state.

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7
Q

Define locus

A

The specific linear position of a particular gene on a certain chromosome

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8
Q

What is meant by alleles being homozygous

A

Situation or organism in which paired alleles are the same

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9
Q

What is meant by alleles being heterozygous

A

Situation or organisms in which paired alleles are different

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10
Q

What is meant by a dominant allele

A

An allele that expresses itself in the phenotype in heterozygous organisms

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11
Q

What is meant by a recessive allele

A

An allele that does not express itself in the phenotype of heterozygous organisms

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12
Q

What is means by co-dominant alleles

A

Alleles which both contribute to the phenotype in the heterozygous condition

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13
Q

What is meant by multiple alleles

A

Multiple alleles refers to the situation where there are more than two alleles for each gene in the gene pool. There are only two chromosomes in a homologous pair so only two of the three or more alleles can be present in a single organism.

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14
Q

What is monohybrid inheritance

A

Monohybrid inheritance is the inheritance of a single gene- that has a single pair of alleles.

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15
Q

What is pure breeding/a pure breeding strain

A

A pure breeding strain is a group of organisms on which a certain characteristic is unaltered for generations, indicating that organisms are homozygous for that feature.

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16
Q

What is the law of segregation (a basic 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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17
Q

What observation led to the formation of the law of segregation

A
  • Gregor Mendel crossing two heterozygous peas and noticing that the phenotypic ratio was 3:1
18
Q

What is dihybrid inheritance

A

The inheritance of two genes together- with two pairs of alleles

19
Q

What did Mendel use to investigate dihybrid inheritance

A
  • He investigated the inheritance of two characters of a pea plant at the same time. These were:
    1) Seed shape
    2) Seed colour
20
Q

What do each of the gametes contain during dihybrid inheritance

A

One allele for the first characteristic and one allele for the second characteristic

21
Q

What is Mendelssohn’s law of independent assortment

A

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

22
Q

Explain what type of alleles the I(A) I(B) and I(O) for blood grouping are

A

The I(A) and I(B) alleles are codominant whereas the I(O) allele is recessive to both.

23
Q

What is an important example of codominance

A

The ABO blood grouping in humans

24
Q

How many pairs of chromosomes do diploid human cells contain

A

23 pairs (46 chromosomes in total)

25
Q

What is a sex-linked gene

A

Any gene that is carried on either the X or Y chromosome

26
Q

Define autosome

A

A chromosome that is not a sex chromosome

27
Q

What is autosomal linkage

A

The situation where two or more genes are carried on the same autosome

28
Q

Why do sex-linked genes/diseases sometimes occur more frequently in males

A
  • The X chromosome is much longer than the Y chromosome.
  • This means that, for most of the length of the X chromosome, there is no equivalent homologous portion of the Y chromosome.
  • Those characteristics that are controlled by recessive alleles on this non-homologous portion of the X chromosome will appear more frequently in the male.
  • This is because there is no homologous portion of the Y chromosome that might have the dominant allele, in the presence of which the recessive allele does not express itself.
29
Q

What is an X-linked genetic disorder

A

A disorder caused by a defective gene on the X chromosome.

30
Q

What is an example of an X-linked genetic disorder in humans

A

Haemophilia

31
Q

What is haemophilia

A
  • An X-linked genetic disorder that causes blood clots to form too slowly and causing slow and persistent bleeding, especially in joints.
  • One of a number of causes of haemophilia is a recessive allele with an altered sequence of DNA nucleotide bases that therefore codes for a faulty protein which does not function.
  • This results in an individual being unable to produce a functional protein that is required in the clotting process.
  • The production of this functional protein by genetically modified organisms means that it can now be given to haemophiliacs, allowing them to lead near normal lives.
32
Q

Why is haemophilia almost entirely confined to males

A
  • It is a recessive, sex linked gene which is found on the X chromosome
  • Females that do have haemophilia often die with the onset of menstruation at puberty.
33
Q

How are key factors represented on a pedigree chart

A
  • A male is represented by a square
  • A female is represented by a circle.
  • Shading within either shape indicates the presence of a character in the phenotype.
34
Q

What is autosomal linkage

A

The situation where two or more genes are carried on the same autosome

35
Q

What is epistasis

A

Epistasis arises when the allele of one gene affects or masks the expression of another in the phenotype

36
Q

What is the null hypothesis for the chi squared test

A

The null hypothesis is used to examine the results of scientific investigations and is based on the assumption that there will be no statistically significant difference between sets of observations, any difference being due to chance alone.

37
Q

What does the chi squared test investigate

A

Wether any deviation between the observed and the expected numbers in an investigation is significant or not

38
Q

What criteria must be met in order to carry out the chi squared test

A
  • The sample size must be relatively large (at least over 20)
  • the data must fall into discrete categories
  • only raw counts and now percentages/rates can be used.
  • it is used to compare experimental results with theoretical ones
39
Q

What is the equation for chi squared

A

X^2 = the sun of (observed numbers(O)-expected numbers(E))^2/ expected numbers E

40
Q

Describe the steps in carrying out the chi squared test

A

1) Caluclate the degree of freedom
2) Look up the critical value for this degree if freedom
3) calculate chi squared and see if it is higher or lower than the critical value:
- if chi squared is less than the critical value, the null hypothesis can be accepted.
- If chi squared is greater than the critical value, the null hypothesis can be rejected.

41
Q

What is the most common null hypothesis you will use when implementing chi squared for genetic crosses

A

There is no difference between the observed and expected ratios

42
Q

How do you work out the degree of freedom for chi squared

A

Work out how many options of outcomes there are and subtract one

7- Genetics, populations, evolution, and ecosystems (4 decks)

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