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Biology > Chapter 15 - The Chromosomal Basis of Inheritance > Flashcards

Chapter 15 - The Chromosomal Basis of Inheritance Flashcards

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1
Q

What is the chromosome theory of inheritance?

A

Developed by Walter S. Sutton, Theodor Boveri; according to this theory, Mendelian genes have specific loci (positions) along chromosomes, and it is the chromosomes that undergo segregation and independent assortment

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2
Q

What is Mendelian inheritance based on?

A

Chromosome behavior;

  • Chromosomes and genes are both present in pairs in diploid cells
  • Homologous chromosomes separate and alleles segregate during meiosis
  • Fertilization restores the paired condition for both chromosomes and genes
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3
Q

What is the wild type?

A

The phenotype for a character most commonly observed in natural populations

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4
Q

What are mutant phenotypes?

A

Traits that are alternatives to the wild type; due to alleles assumed to have originated as changes, or mutations

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5
Q

What is a sex linked gene?

A

A gene located on either sex chromosome

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6
Q

What are Y-linked genes?

A

Sex chromosomes located on the Y chromosome

  • Most Y linked genes are related to sex determination
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7
Q

What are X-linked genes?

A

The human X chromosome contains approximately 1,100 genes

  • X chromosomes have genes for many characters unrelated to sex
  • X linked genes follow specific patterns of inheritance
  • For a recessive X linked gene to be expressed, a female needs two copies of the allele (homozygous) and a male needs only one copy of the allele (hemizygous)

*X linked recessive disorders are much more common in males than in females, i.e. color blindness

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8
Q

What is hemizygous?

A

Used to describe males who have only one locus for the x-linked allele

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9
Q

What is a Barr body?

A

The inactive X in each cell of a female condenses into a compact object called a Barr body, which lies along the inside of the nuclear envelope; most of the genes of the X chromosome that forms the Barr body are not expressed; in the ovaries however, Barr body chromosomes are reactivated in the cells that give rise to eggs, such that following meiosis, every female gamete has an active X

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10
Q

What are linked genes?

A

Genes located near each other on the same chromosome tend to be inherited together in genetic crosses; such genes are said to be genetically linked

Each chromosome has hundreds of thousands of genes

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11
Q

What is genetic recombination?

A

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

  • Genes that are far apart on the same chromosome have a recombination frequency of about 50%
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12
Q

What are parental types?

A

Offspring with a phenotype matching one of the parental phenotypes

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13
Q

What are recombinant types?

A
  • Recombinants; offspring with non-parental phenotypes (new combinations of traits)
  • A 50% frequency of recombination is observed for any two genes in different chromosomes
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14
Q

What process must occasionally break the physical connection between specific alleles of genes on the same chromosome?

A

The crossing over of homologous chromosomes; accounts for the recombination of linked genes

  • Morgan discovered that genes can be linked, but the linkage was incomplete because some recombinant phenotypes were observed
  • Recombinant chromosomes bring alleles together in new combinations of gametes
  • Random fertilization increases even further the number of variant combinations that can be produced
  • This abundance of genetic variation is the raw material upon which natural selection works
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15
Q

What is a genetic map?

A

An ordered list of the genetic loci along a particular chromosome

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16
Q

What is a linkage map?

A

A genetic map based on recombination frequencies

17
Q

What is a nondisjunction?

A

An occasional mishap in which the members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separated during meiosis II; as a result, one gamete receives two of the same type of chromosome and another gamete receives no copy

18
Q

What is aneuploidy?

A

Results from the fertilization of gametes in which nondisjunction occurred; offspring of this type have an abnormal number of a particular chromosome

19
Q

What is a monosomic zygote?

A

Has only one copy of a particular chromosome

20
Q

What is a trisomic zygote?

A

Has three copies of a particular chromosome

21
Q

What is polyploidy?

A

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

  • Triploidy (3n) is three sets of chromosomes
  • Tetraploidy (4n) is four sets of chromosomes
  • Polyploidy is common in plants, but not in animals
  • Polyploids are more normal in appearance than aneuploids
22
Q

What are the four types of changes that occur because of the breakage of a chromosome?

A
  • Deletion; occurs when a chromosomal fragment is lost
  • Duplication; repeats a segment
  • Inversion; reverses orientation of a segment within a chromosome
  • Translocation; moves a segment from one location to another
23
Q

What is Down Syndrome a result of?

A

An aneuploid condition that results from three copies of chromosome 21 (affects 1 out of ever 700 children born in the US)

24
Q

What are the two normal exceptions to Mendelian genetics?

A

One exception involves genes located in the nucleus and the other exception involves genes located outside the nucleus

In both cases, the sex of the parent contributing an allele is a factor in the pattern of inheritance

25
Q

What is genomic imprinting?

A

For a few mammalian traits, the phenotype depends on which parent passed along the alleles for those traits; genomic imprinting involves the silencing of certain genes depending on which parent passes them on

  • It appears that imprinting is the result of methylation of cysteine nucleotides
  • Genomic imprinting is thought to affect only a small fraction of mammalian genes
  • Most imprinted genes are are critical for embryonic development
26
Q

What type of genes are found in organelles in the cytoplasm?

A

Extracellular genes or cytoplasmic genes

  • Mitochondria, chloroplasts, and other plant plastids carry small circular DNA molecules
  • Extracellular genes are inherited maternally because the zygotes cytoplasm comes from the egg
27
Q

What are the characteristics that make Drosophila melanogaster (fruit flies) a convenient organism for genetic studies?

A
  • Produce many offspring
  • A generation can be bred every two weeks
  • Have only four pairs of chromosomes
28
Q

What contribution did Morgan bring to understanding Mendelian inheritance?

A

Morgan’s experiments provided convincing evidence that chromosomes are the location of Mendel’s heritable factors (genes)

  • Chromosomes and genes are both present in pairs in diploid cells
  • Homologous chromosomes separate and alleles segregate during meiosis
  • Fertilization restores the paired condition for both chromosomes and genes
29
Q

Explain how crossing over can unlink genes?

A
  • Morgan discovered that genes can be linked, but the linkage was incomplete, because some recombinant phenotypes were observed
  • He proposed that some process must occasionally break the physical connection between genes on the same chromosome
  • That mechanism was the crossing over of homologous chromosomes
30
Q

How is sex genetically determined in humans?

A

Chromosomal system for determining sex in mammals is X-Y;

XX - female
XY - male

A gene on the Y chromosome called SRY (sex determining region on the Y) is responsible for development of the testes in an embryo

31
Q

Explain why sex-linked diseases are more common in males.

A

For a recessive x-linked trait to be expressed, a female needs to copies of the allele while a male needs only one copy of the allele

Some disorders caused by the recessive alleles on the X chromosome in humans

  • Color blindness (mostly X-linked)
  • Duchenne muscular dystrophy
  • Hemophilia
32
Q

Describe the process of X inactivation in female mammals. Explain how this phenomenon produces the tortoiseshell coloration in cats.

A

In mammalian females, one of the two X chromosomes in each cell is randomly inactivated during embryonic development;

The inactive X condenses into a Barr Body

If a female is heterozygous for a particular gene located on the X chromosome, she will be a mosaic for that character

33
Q

Explain how genetic maps are constructed for genes located far apart on a chromosome.

A

Genetic maps are constructed to predict a recombination frequency;

Genes that are far apart on the same chromosome can have a recombination frequency near 50%

Biology (24 decks)

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