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BIO 1210 > Sex Linkage (Genetics) > Flashcards

Sex Linkage (Genetics) Flashcards

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1
Q

Who is the famous scientist for determining sex linkages in the 1900s?

A

Thomas Morgan

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2
Q

What organisms were used in experiments for sex linkage?

A

Fruit flies

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3
Q

What is the wild type allele for the fruit fly?

A

red eyes

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4
Q

What is the mutant allele for the fruit fly?

A

white eyes

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5
Q

T or F: the mutant allele was found in both female and male offspring

A

FALSE. Only F2 generation MALES

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6
Q

What phenotype did the F1 offspring have when a female fruit fly with red eyes was crossed with a male fruit fly with white eyes?

A

All had red eyes

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7
Q

When the F1 of the fruit flies were crossed, what phenotypes were present? and in which ratio?

A

3 red eyes: 1 white eye but the only ones with white eyes were the males

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8
Q

Which allele was dominant and which was recessive in Morgan’s experiments?

A

Red eyes dominant

White eyes recessive

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9
Q

Define sex chromosome

A

chromosomes involved in determining if an organism is male or female (X or Y)

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10
Q

In humans and fruit flies, what is the typical genotype for biological males?

A

XY

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11
Q

In humans and fruit flies, what is the typical genotype for biological females?

A

XX

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12
Q

Where did Morgan determine the gene for eye colour is? Why did he decide this?

A

On the X chromosome because males have only ONE X chromosome so they have to display whichever genes they get on the X.

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13
Q

How come the females didn’t show the white eyed phenotype?

A

Because females have two X chromosomes, so they would only show the white eyes if they had two white-eye alleles (one on each X)

So females will show the red eye phenotype if they are hetero- or homozygous for red

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14
Q

Define reciprocal crosses

A

A pair of matings where the phenotypes of the males and females are different (parents are true bred)

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15
Q

What are reciprocal crosses used for? What do the results show?

A

Testing for sex linkage

If the results are different, the condition is SEX LINKED

if the results are the same, it’s autosomal

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16
Q

Which sex chromosome is much shorter than the other?

A

the Y is much shorter than the X

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17
Q

During meiosis in the testes and ovaries, what occurs to the X and Y chromosomes?

A

They segregate

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18
Q

Which chromosome(s) can females produce in gametes?

A

Only the X

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19
Q

Which chromosome(s) can males produce in gametes?

A

50% X and 50% Y

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20
Q

What biological sex will result if a sperm containing a Y chromosome fertilizes an egg?

A

A male offspring

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21
Q

What biological sex will result if a sperm containing an X chromosome fertilizes an egg?

A

A female offspring

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22
Q

How do alternatives of sex chromosome numbers and/or pairs occur?

A

Due to incorrect separation of chromosomes during meiosis

23
Q

Describe the syndrome related to having only an X chromosome

A

Turner Syndrome

Occurs in females, usually shorter in height and infertile

24
Q

Describe the syndrome related to having XXX chromosomes

A

Trisomy X

2 Xs are inactivated so mild or no symptoms occur but can be taller

25
Q

Describe the syndrome related to having only a Y chromosome

A

Not viable, organisms need an X to survive

26
Q

Describe the syndrome related to having XXY chromosomes

A

Klinefelter Syndrom

Usually lower in testosterone, fertility is usually impacted

27
Q

Describe the syndrome related to having XYY chromosomes

A

XYY Syndrome

Usually taller, no symptoms, and testosterone is normal

28
Q

When do sexual differences begin to occur in human embryos?

A

around 2 months

29
Q

Which sex chromosome determines sex? How?

A

Y

A gene on the Y chromosome is responsible for the development of testes (SRY)

If there is no SRY present, the embryo will develop ovaries

30
Q

Define a sex-linked gene

A

A gene located on an X or Y chromosome

31
Q

About how many genes does a Y chromosome have?

A

~78

32
Q

About how many genes does a X chromosome have?

A

~1100

33
Q

T or F: There are more X-linked disorders than Y-linked?

A

TRUE

34
Q

T or F: Fathers pass their X-linked alleles to their daughters, but not their sons

A

TRUE

35
Q

T or F: Mothers pass their X-linked alleles to their sons, but not their daughters

A

FALSE. Mothers pass their X-linked alleles to BOTH daughters and sons

36
Q

When will a female offspring express a recessive X linked trait?

A

Only if they are homozygous for that trait

37
Q

Will a female express a recessive X linked trait if they are heterozygous for that trait?

A

Unlikely

38
Q

Define carrier

A

An organism that often doesn’t display the phenotype of the recessive trait but can transmit that allele to their offspring

39
Q

Can males be carriers?

A

NO because they only have one copy

40
Q

What are the symbols for the genotype of an unaffected female?

A

XNXN

N is superscript

41
Q

What are the symbols for the genotype of a phenotypically unaffected but carrier female?

A

XNXn

N and n is superscript

42
Q

What are the symbols for the genotype of an affected female?

A

XnXn

n is superscript

43
Q

What are the symbols for the genotype of an unaffected male?

A

XNY

N is superscript

44
Q

What are the symbols for the genotype of an affected male?

A

XnY

n is superscript

45
Q

How are the results of a Punnet Square reported?

A

Unaffected females: carrier females: unaffected males: affected males

X is always listed before Y

46
Q

Give 3 examples of X-linked disorders

A
  1. Colour blindness (recessive)
  2. Muscular dystrophy (recessive)
  3. Hemophilia (recessive)
47
Q

Define Barr Body

A

Occurs in females when 1 of the 2 X chromosomes is randomly chosen to be inactivated during embryonic development

48
Q

Where is the Barr Body located?

A

Inside the nuclear envelope

49
Q

T or F: most of the genes on the Barr Body are not expressed

A

True

50
Q

When are the Barr Body’s reactivated?

A

In female gametes

51
Q

Give an example of a heterozygous female for an X-linked trait with half the cells expressing each allele

A

Calico cats

52
Q

Define pedigree

A

A family tree with the history of a particular trait

53
Q

What is the purpose of a pedigree?

A

A way to study human genetics and lineage by analyzing matings that have already occurred to look at the transmission of certain traits

54
Q

When examining a pedigree, how can you tell if a condition is sex linked or autosomal?

A

If only the male offspring are affected it is sex linked

If both male and female offspring are affected equally, it is autosomal

BIO 1210 (16 decks)

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