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Agricultural Science - Leaving Cert 2018 > Chapter 17 - Dihybrid and sex-linked crosses > Flashcards

Chapter 17 - Dihybrid and sex-linked crosses Flashcards

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1
Q

Define Dihybrid Cross.

A

A dihybrid cross involves the inheritance of two characteristics.

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2
Q

What is the Law of Independant Assortment?

A

The Law of independant assortment states that when gametes are formed, either of a pair of alleles is equally likely to combine with either or another pair of alleles.

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3
Q

Is the Law of Independant Assortment Gregor Mendal’s first or second law?

A

Second law.

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4
Q

What form of cell division causes the law of independant assortment?

A

Meiosis

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5
Q

What is Sex determined by?

A

Sex is determined by a pair of sex chromosomes (the X and Y chromosomes ). Females are XX and Males are XY.

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6
Q

What are linked genes

A

Linked genes are genes that are located on the same chromosome and tend to be transmitted together into the gamete.

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7
Q

How many pairs of chromosomes do humans have?

A

23 pairs.

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8
Q

What are 22 pairs of human chromosomes known as?

A

22 pairs of human chromosomes are known as autosomes

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9
Q

One pair of human chromosomes is known as what?

A

One pair of human chromosomes is known as sex chromosomes.

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10
Q

Name the sex chromosomes

A

X and Y

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11
Q

What do sex chromosomes determine?

A

The sex chromosomes determine the sex of the individual.

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12
Q

What 2 chromosomes do females have

A

Females have two X chromosomes.

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13
Q

What 2 chromosomes do males have

A

Males have an X and Y chromosome.

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14
Q

Define Sex chromosome

A

Sex chromosome is a chromosome that determines the sex of an organism

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15
Q

Which chromosome is smaller than the other?

A

The Y chromosome is much smaller than the X chromosme.

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16
Q

Does the Y chromosome have the same amount of information on it as the X chromosome?

A

The Y chromosome does not have the same amount of information on it as the X chromosome.

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17
Q

Why are males responsible for sex determination of their offspring?

A

Males are responsible for sex determination of their offspring as males contain two different chromosomes, X and Y.

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18
Q

When meiosis occurs, females produce gametes that all contain what chromosome?

A

When meiosis occurs, females produce gametes that all contain the X chromosome.

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19
Q

When meiosis occurs, half of the male’s gametes carry what?

A

When meiosis occurs, half of the males gametes contain the X chromosome and half carry the Y chromosome.

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20
Q

On fertilisation, the egg cell contributes what?

A

On fertilisation, the egg cell contributes an X chromosome.

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21
Q

What does the male sperm determine?

A

The male sperm determines the sex of the offspring.

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22
Q

If an X sperm cell fertilises the egg, what will the offspring be?

A

If an X sperm cell fertilises the egg, the offspring will be female (XX)

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23
Q

If a Y sperm cell fertilises the egg, what will the offsprig be?

A

If a Y sperm cell fertilises the egg, the offspring will be male. (XY)

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24
Q

Every time a male and female are mated, what are the chances that the offspring will be male or female?

A

Every time a male and female are mated, there is a 50% chance that the offspring will be female and a 50% chance that the offspring will be male.

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25
Q

In the dairy industry, why does the 50% probability of male or female have particular consequences?

A

In the dairy industry, the 50% probability of male or female has particular consequences as female calves are often preferred over male calves.

26
Q

Scientists involved in cattle breeding have done what for the reason of particular consequences of 50% male or female in dairy industry?

A

Scientists involved in cattle breeding have determined a way of separating sperm carrying X chromosomes from sperm carrying Y chromosomes in order to produce semen samples that have been sexed.

27
Q

In mammals, what sex determines the sex of the offspring?

A

In mammals, the male determines the sex of the offspring.

28
Q

In birds, what sex determines the sex of the offsprig?

A

In birds, the female determines the sex of the offspring.

29
Q

In birds, what are the 2 chromosomes called?

A

In birds, the 2 chromosomes are called Z and W.

30
Q

In birds, which chromosome is larger and has more genes?

A

In birds, the Z chromosome is larger and has more genes than the W chromosome.

31
Q

What are the 2 sex chromosomes for female birds?

A

The 2 sex chromosomes for female birds are ZW.

32
Q

In birds, what are the 2 sex chromosomes for males?

A

In birds, the 2 sex chromosomes for males are ZZ.

33
Q

Define Sex Linkage

A

Sex-Linkage or X-Linkage is a gene that is found on the X cheomosome but there is no copy on the Y chromosome.

34
Q

Name the fruit fly that Thomas Hunt Morgan conducted genetic crosses with.

A

Thomas Hunt Morgan conducted genetic crosses with the fruit fly Drosophila melanagaster.

35
Q

What did Morgan intend to use fruit flies for?

A

Thomas Hunt Morgan intended to use fruitflies to reproduce Mendel’s monohybrid crosses.

36
Q

What colour eyes do fruit flies usually have, and what did Thomas Hunt Morgan notice in one of his crosses?

A

Fruit flies usually have red eyes, however, Thomaa Hubt Morgan noticed a white-eyed male in one of his crosses.

37
Q

What did Thomas Hunt Morgan do with the white-eyed male fruit fly?

A

He crossed the white-eyed male fruitfly with a red-eyed female fruitfly and all the F1 produced had red eyes.

38
Q

What did Morgan naturally presume after this result ?

A

That red eyes were dominant in fruit flies and white eyes were recessive.

39
Q

Give 2 examples of sex linkage or x linkage

A

In fruit flies the gene for eye colour is located on the X chromosome, and in humans the gene for blood clotting and colour vision are carried on the X chromosome.

40
Q

Name three characteristics caused by recessive genes.

A

White eye, haemophilia and colour blindness are all caused by recessive genes.

41
Q

Why do sex-linked disorders occur more commonly in males than in females?

A

Sex-linked disorders occur more commonly in males than in females because sex-linked genes are carried on the X chromosome and males only have one X chromosome, and therefore only one copy of the gene.

42
Q

How would a female be affected by a sex-linked characteristic?

A

In order for a female to be affected by a sex-linked characteristic, she would have to inherit 2 copies of the recessive gene: her mother would have to be a carrier of the sex-linked characteristic and her father would have to have the sex-linked condition.

43
Q

When is a mendelian ratio of 9:3:3:1 produced in a dihybrid cross

A

When both parents are heterozygous for both characteristics

44
Q

Do linked genes follow mendel’s law of independant assortment?

A

No, linked genes do not follow mendel’s law of independant assortment.

45
Q

What can separate linked genes?

A

Crossing over (which occurs during meiosis) can separate linked genes.

46
Q

Why does the male determine the sex of the offspring?

A

The male determines the sex of the offspring as 50% of the male gametes carry an X chromosome and 50% carry a Y chromosome. Females produce gametes that carry an X chromosome.

47
Q

Give an example of an X-linked gene

A

White eyed fruit flies are an example of an X-linked gene.

48
Q

What is a very rare sex-linked characteristic in Holstein Cattle? How is it likely to happen?

A

Male calves can be born with very little hair and no incisors. This sex-linked characteristic is more likely to happen if closely related animals are crossed.

49
Q

What are the advantages of using fruit flies when studying genetics

A

These are the advantages of using fruit flies when studying genetics:

  • Fruit flies are easy to keep
  • They produce a large number of offspring, which is good for statistical analysis.
  • They produce a new generation every two weeks.
  • They only have four pairs of chromosomes
  • They have well documented mutations, e.g. inheritance of white eyes in male fruit flies.
50
Q

What is a mutation

A

A Mutation is a permanent change in the DNA sequence of a gene.

51
Q

What are mutations in genes a source of and what can they lead to?

A

Mutations in genes are a source of new alleles and can lead to variations.

52
Q

Give an example of something that was caused by a mutation.

A

The appearance of the white-eye allele in fruit flies was caused by a mutation in the gene for eye colour.

53
Q

Are mutations rare and random events?

A

Yes, mutations are rare and random events.

54
Q

Give a well-known example of a mutation

A

A well-known example of a mutation is sickle-cell anaemia.

55
Q

Describe how sickle cell is formed.

A

The mutation occurs in the gene for the production of the haemoglobin molecule in red blood cells. This produces red blood cells that are an abnormal, rigid sickle shape.

56
Q

What can mutations also lead to?

A

Mutations can also lead to changes in chromosome numbers, and result in the formation of cells that are polyploidy.

57
Q

What are factors that cause mutations known as?

A

Factors that cause mutations are known as mutagens.

58
Q

What do mutagens do?

A

Mutagens interact with the DNA and cause changes to the DNA sequence.

59
Q

Name 5 factors that cause mutations.

A

X-Rays, UV Light, Radiation, radon and colchicine are all factors that cause mutations.

60
Q

Define Mutagen and give 5 examples of a mutagen.

A

Mutagen is an agent that can bring about a genetic mutation. Examples are X-Rays, Radon, Colchicine and UV Light.

Agricultural Science - Leaving Cert 2018 (10 decks)

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