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Biology > TH- Chromosomal basis of inheritance > Flashcards

TH- Chromosomal basis of inheritance Flashcards

1
Q

Describe Law of segragation

A

alleles for each gene separate during gamete formation, so each gamete formed will only have one allele from the gene

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2
Q

Describe Law of Independent Assortment

A

genes for different traits assort independently of each other during gamete formation

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3
Q

Which structure undergoes the segregation and assortment?

A

chromosomes

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4
Q

explain alleles vs genes

A

-genes are segments of DNA and each gene has 2 alleles

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5
Q

What are the 2 advantages of working with fruit flies?

A
  • a single mating produces hundreds of offsprings so a new generation can be bred every 2 weeks
  • they only have 4 chromosomes
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6
Q

What is wild type?

A

a phenotype for a character most commonly observed in the natural population

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7
Q

What are mutant phenotypes?

A

traits that are different from the wild type

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8
Q

what mutation did morgan observe after mating his flies for many months and how did he symbolize the alleles?

A
  • white eyes

- w^+ = red eyes, w = white

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9
Q

which eye colour allele was dominant and which was ressesive for the fruit flies?

A
  • red was dominant

- white reccessive

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10
Q

why did morgan conclude that eye colour was a sex-linked gene?

A

because only males had white eyes in the F1 generation

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11
Q

why did the white eyes show up in males whose mother was heterozygous and father had red eyes?

A
  • the eye colour was on the X chromosome and males only have 1 X chromosome so one copy of the recessive w allele turned their eyes red
  • whereas the females have 2 X chromosomes so they inherited the dominant and recessive genes causing them to have red eyes
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12
Q

If X and Y chromosomes are different how are they able to behave as homologs?

A

Y chromosone has short segment at either ends that are homologous to the X chromosome hence allowing them to pair up

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13
Q

what gene is required for the development of testes, where is it found and what happens if it is absent?

A
  • SRY gene on Y chromosomes

- if absend then ovaries will form even with XY chromosomes

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14
Q

What is a sex-linked gene? and specific names when its on X and Y

A
  • a gene located on the sex chromosomes
  • X = X-linked genes
  • Y = Y-linked genes
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15
Q

Why the amount of disorders that can be passed from a Y chromosome much less than X?

A

because there are only a few genes on the Y chromosome and most of them code for proteins that help in the functioning of the testes

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16
Q

What gene is required for the development of female gonads, where is it found and what happens if an embryo with XY has extra copies of the gene?

A
  • the gene WNT4 makes a protein that promotes ovary development
  • it is found on chromosome 1, an autosome
  • if a XY embryo has extra copies of WNT4 it can develop female gonads
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17
Q

what is hemizygous?

A

an individual who has only one member of a chromosome pair or chromosome segment rather than the usual two.

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18
Q

If an X-linked trait is due to a recessive allele, a female will express the phenotype only if …? and why is that?

A
  • only if she is homozygous for the allele

- because males are hemizygous

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19
Q

what does Duchenne muscular dystrophy do to the body, name of protein missing and which type of linked disorder is this?

A
  • progressive weakening of the muscles and loss of coordination due to absence of a key muscle protein called dystrophin
  • X-linked disorder
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20
Q

what does Hemophilia do to the body and which type of linked disorder is this?

A
  • Hemophilia is caused by the absence of one or more of the proteins required for blood clotting.
  • When a person with hemophilia is injured they clot much slower
  • X-linked disorder
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21
Q

What is Barr body?

A

Inactive X in each cell of a female

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22
Q

Why do females not have twice the amount of proteins if they have 2 X chromosomes?

A
  • due to the fact that 1 X chromosome is inactivated forming a Barr body during early embryonic
  • development hence that X is not expressed
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23
Q

where is Barr body found?

A

lies along the inside of the nucleus envelope

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24
Q

where are Barr body chromosomes reactivated?

A
  • in cells that make eggs

- so every gamete has an active X chromosome after meiosis

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25
Q

What is mosaicism and how does it affect female cells?

A
  • being composed of cells of two genetically different types.
  • some cells have an active X from the father and some from mother
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26
Q

explain how the X chromosome inactivated and mention the gene involved

A
  • attachment of methyl groups (—CH3) to DNA nucleotides causing DNA methylation
  • two regions, one on each X chromosome, associate briefly with each other in each cell
  • one of the genes, called XIST (for X-inactive specific transcript), becomes active only on the chromosome that will become the Barr body
  • Multiple copies of the RNA product of this gene attach to the X chromosome on which they are made eventually almost covering it.
  • Interaction of this RNA with the chromosome initiates X inactivation
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27
Q

What are linked genes?

A

2 or more genes on the same chromosomes inherited together

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28
Q

What is genetic recombination?

A

production of offspring with combinations of traits that differ from those found in either P generation parent.

29
Q

What are parental types?

A

offspring that inherits a phenotype that matches either of the parents

30
Q

What is crossing over?

A

two homologous non-sister chromatids (1 maternal and 1 paternal) pair up with each other and exchange different segments of genetic material to form two recombinant chromosome sister chromatids.

31
Q

What is a genetic map ?

A

-an ordered list of the genetic loci along a particular chromosome.

32
Q

what is recombination frequency?

A

% of recombinant offsprings

33
Q

what did Sturtevant predict about crossing over?

A
  • the farther apart two genes are, the higher the probability that a crossover will occur between them
  • hence higher the recombination frequency.
34
Q

what is a linkage map?

A

a genetic map based on recombination frequencies

35
Q

what are map units?

A

distances between the genes

36
Q

What is nondisjunction and how does it affect amount of chromosomes in a gamete?

A
  • it is when a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis II
  • out of 4 gametes 2 are normal but one gamete receives two of the same type of chromosome and another gamete receives no copy.
37
Q

what is aneuploidy?

A

when a zygote has an abnormal number of chromosomes.

38
Q

when is a aneuploid zygote is said to be monosomic? and provide n expression

A

when it has only 1 copy of chromosomes instead of the 2 found in diploid cells. (2n-1)

39
Q

when is a aneuploid zygote is said to be trisomic? and provide n expression

A

when it has three copies of a chromosome instead of two. (2n+1)

40
Q

What is polyploidy?

A

condition in which an organism has more than two complete sets of chromosomes

41
Q

State the 2 types of polyploidy

A

Triploidy (3n) and Tetraploidy (4n), there are more…

42
Q

How can a triploidy form?

A

fertilization of an abnormal diploid egg produced by nondisjunction of all its chromosomes.

43
Q

How can a tetraploidy form?

A

Failure of a 2n zygote to divide after replicating its chromosomes, resulting later on in a 4n embryo.

44
Q

What 4 types of changes can occur due to breakage of a chromosome?

A
  • deletion
  • duplication
  • inversion
  • translocation
45
Q

What is deletion in terms of breakage of chromosome?

A

removes a chromosomal segment causing certain genes to be missing

46
Q

What is duplication in terms of breakage of chromosome?

A

repeats a segment

47
Q

What is inversion in terms of breakage of chromosome?

A

reverses a segment within a chromosome (changes orientation of the segment)

48
Q

What is translocation in terms of breakage of chromosome?

A

moves a segment from one chromosome to another non homologous chromosome

49
Q

Is down syndrome a polyploidy or aneuploidy condition?

A

aneuploidy

50
Q

Why do people get down syndrome?

A

Because the cells are trisomic for chromosome 21

51
Q

Why do Aneuploid conditions involving sex chromosomes appear to upset the genetic balance less than those involving autosomes?

A
  • Y chromosome carries relatively few genes

- extra copies of the X chromosome become inactivated as Barr bodies.

52
Q

Describe Klinefelter syndrome by saying what is different compared to normal and symptoms

A
  • when a male has an extra X chromosome forming XXY
  • have male sex organs, but the testes are abnormally small
  • man is sterile
  • even though extra X is inactivated there may be some breast enlargement and feminine characteristics
  • may have subnormal intelligence
53
Q

What happens to males born with an extra Y chromosome?

A

undergo normal sexual development and do not exhibit any well-defined syndrome, but tend to be taller than average.

54
Q

What happens to females born with extra X chromosome?

A
  • are healthy and have no unusual physical features other than being slightly taller than average.
  • are at risk for learning disabilities
  • are fertile.
55
Q

Describe Turner syndrome by saying what is different compared to normal, symptoms and what is given to them that helps them form secondary sex characteristics?

A
  • Monosomy X
  • they are sterile because their sex organs do not mature.
  • when provided with estrogen replacement therapy girls develop secondary sex characteristics
56
Q

Describe cri du chat (“cry of the cat”) by saying what is different compared to normal and symptoms?

A
  • due to deletion in chromosome 5
  • severely intellectually disabled, has a small head with unusual facial features, and has a cry that sounds like the mewing of a distressed cat
  • usually die early
57
Q

Describe how chronic myelogenous leukemia (CML) develops and what it leads to

A
  • translocation happens during mitosis of cells that are precursors of white blood cells
  • Philadelphia chromosomes form due to exchange of a large portion of chromosome 22 with a small fragment from a tip of chromosome 9 produces a shortened, easily recognized chromosome 22,
  • causes cancer by creating a new “fused” gene that leads to uncontrolled cell cycle progression.
58
Q

what is genomic imprinting?

A

is when expression of certain genes depend on whether they were inherited from the male or female parent

59
Q

what does genomic imprinting do to an allele?

A

either silencing an allele in one type of gamete (egg or sperm) or activating it in the other

60
Q

How does genomic imprinting silence or activate alleles?

A

-imprint seems to consist of methyl (—CH3) groups that
are added to cytosine nucleotides of one of the alleles.
-Such methylation may silence the allele,
- However, for a few genes, methylation has been shown to activate expression of the allele.

61
Q

What are cytoplasmic/ extranuclear genes?

A

genes located on organelles in the cytoplasm

62
Q

who are extranuclear genes inherited from?

A

they are inherited maternally because the zygote’s cytoplasm comes from the egg

63
Q

what do products of mitochondrial genes help make?

A

protein complexes of the electron transport chain and ATP synthase

64
Q

what happens if there is a defect in one of these proteins made by mitochondrial genes?

A

-reduce the amount of ATP the cell can make and cause a number of human disorders

65
Q

which parts of the body are more susceptible to energy deprivation?

A

muscles and nervous system.

66
Q

State 2 mitochondrial diseases

A

mitochondrial myopathy and Leber’s hereditary optic neuropathy

67
Q

what does Leber’s hereditary optic neuropathy cause?

A

produce sudden blindness in people

68
Q

what does mitochondrial myopathy cause?

A

weakness, intolerance of exercise, and muscle deterioration.

69
Q

Which parent is mitochondrial disorders inherited from and why?

A

mother because we receive our mitochondria from her

Biology (15 decks)

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