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BIOL226 > Topic 2 > Flashcards

Topic 2 Flashcards

1
Q

What is the chromosome theory of inheritance?

A

A cytological explanation to Mendel’s ratios and the physical ‘basis’ for the laws. The pattern of gene transmission reflects the chromosome’s behaviour during meiosis and introduces the concept of sex determination (sex linkage; sex as a phenotype inseparable from chromosome). Genes are not inherited in isolation but as aprt of larger structural units (chromosomes) shared with other genes with which they segregate.
This marks the birth of cytogenetics.

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2
Q

What biological processes explain Mendelian laws?

A

First Law:
Alleles of a single gene segregate independently from each other because of meiosis
Second Law:
Alleles of different genes segregate independently from each other because of meiosis

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3
Q

Compare mitosis and meiosis.

A

Mitosis: Replication in Interphase and Prophase, segregation in metaphase, anaphase, and telophase, resulting in 2 diploid daughter cells

Meiosis: Interphase, Prophase I, Metaphase I, Anaphase I, Telophase I
Then the two new diploid cells undergo Prophase II, Metaphase II, Anaphase II, Telophase II, resulting in 4 haploid gamete cells

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4
Q

What is a chromosome?

A

A single strand of DNA in the nucleus that duplicates into 2 chromatids attached at the centromere making an x-shape

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5
Q

Compare chromatids and homologs.

A

Sister chromatids have identical copies: same genes and alleles in the same order.

Homologous chromosomes are the same chromosome from different parents/ Same genes in the same order. If they have the same alleles they’re homozygous. If they have different alleles they’re heterozygous.

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6
Q

What is the chromosomal basis for Mendel’s first law?

A

Different alleles of the same gene segregate independently when homologous chromosomes separate in Meiosis I

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7
Q

What is the chromosomal basis for Mendel’s second law?

A

Different genes segregate independently when different chromosomes separate in Meiosis I (4 possible gametes)

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8
Q

What is the chromosomal basis for Mendel’s frequencies in regards to the first law?

A

In meiosis the each allele will double creating 2 chromatids of each allele

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9
Q

What is the chromosomal basis for Mendel’s frequencies in regards to the second law?

A

The chance of each of the several orientation outcomes is random

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10
Q

In sex-linked genes, hemizygous (male) genotype in the F1 will show which phenotype?

A

recessive

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11
Q

Describe how co-segregating genes defy Mendel’s laws.

A

When the inheritance of the traits are dependent, it is because the two genes are one the same chromosome.
Ex) Sex-linked

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12
Q

What is the unit of segregation?

A

chromosomes, which carry genes

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13
Q

Human are a heterogametic species. What does this mean?

A

Females: XX
Males: XY

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14
Q

What is the function of the SRY gene?

A

Sex determining:
Activates other genes (some autosomal) through a transcripting factor that is required for embryonic gonad to develop into testes.

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15
Q

What happens in the human body without the SRY gene?

A

Because it is required for male reproductive development, without the SRY gene (XX or XO), female reproductive development is the default.

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16
Q

What is XX male syndrome?

A

If XX embryos have a piece SRY due to cross-over they will develop physically as males. Can have full male genitalia or appear intersex.

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17
Q

What is androgen insensitivity syndrome?

A

Dominant X-linked gene that causes dysfunctional androgen receptor (the cells cannot respond to androgens, either complete or partial). Affected XY people may have female external genitalia or present as intersex. XX people are carriers with generally no phenotype.

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18
Q

Describe non-disjunction in sex linked genes of fruit flies.

A

Non-disjunction of the X chromosomes produces rare white-eyed females (XXY) in F1, where normally only males (XY) should carry the white mutation.
At the same time, rare viable red eye makes (X0) that lack the Y chromosome can appear (in flies, it is the dosage of X chromosome in the genotype, not the presence of the Y, that determines sex) because of X nondisjunction

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19
Q

Describe three patterns of x-linked recessive inheritance.

A

(1) Rare, skips generations (probably recessive)
(2) only males affected (probably sex-linked)
(3) Only females are carriers

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20
Q

In rare cases, do we assume unrelated individuals are homozygous wildtype or heterozygous?

A

homozygous wildtype

21
Q

Describe the inheritance of sex-linked dominance in humans.

A

Affected males transmit the trait to all of their daughters but to none of their sons
Affected heterozygous females transmit the trait to 1/2 of their children, regardless of sex (like autosomal dominant).
Affected homozygous females transmit the trait to all their children.
Because females can be heterozygous or homozygous, more females have the trait than males.

22
Q

Name the types of chromosomal changes.

A

Loss of genetic material: deletion and missing chromosomes
Gain of genetic materials: extra chromosomes and duplication
Relocation of genetic materials: translocation (from another chromosome) and inversion

23
Q

What is the major difference between gene mutation and chromosome mutation?

A

Gene mutation typically affects one gene, while large-scale chromosome mutations affect many genes

24
Q

Define diploid, monoploid, haploid, euploid, polyploid

A

Diploid: normal for most eukaryotes (2n)
Monoploid: the number of unique chromosomes in a set (1n)
Haploid: only 1 set of chromosomes–no homologous chromosomes (male bees, gametes)
Euploid: having a ‘normal’ number of each chromosome
Polyploid: extra copies of each chromosome (triploid, tetraploid)

25
Q

Describe polyploid organisms.

A

Most common in plants: possibly because relative gene dosage is preserved. The plants look the same but polyploids are typically bigger because cells are larger.
In animals, often related to asexual or hybrid species

26
Q

What are three advantages to polyploidy?

A

(1) Lowers chance of inbreeding risk (buffered against deleterious alleles)
(2) Lessen selection on individual gene copies (gene function diversification)
(3) Associated with asexual reproduction (mechanism unclear)

27
Q

What are some agricultural advantages of polyploids?

A

Alloploidy– mixing two uneven genomes via hybridization
Combinations of allopolyploidy and chromosome of loss or gain creates new species

Autoploidy– multiplication of chromosomes from the same organism
1) Bigger plants
2) seedless plants

28
Q

How are autopolyploids generated naturally and artificially?

A

Naturally: mistakes during meiosis
Artificial: treating meiotic or mitotic cells with microtubule inhibitor to arrest cells in metaphase

29
Q

How are allopolyploids generates naturally and artificially?

A

Naturally or induced: formed by hybridization: crosses between two related species
Note: usually sterile; number and type of chromosomes matter
Ex) Mules

30
Q

Why are polyploid tissues important for normal physiology?

A

In some tissues, cells replicate the DNA (s-Phase) but do not divide (polyploid tissue in an otherwise euploid organism).
Polyploidy can be a mechanism of selectivity increasing cell volume and/or cell metabolism.

31
Q

What are the agricultural advantages of monoploid generation?

A

Monoploid organisms can be used in research for screening genotypes for useful mutations
- no heterozygosity to hide genes
- recessive mutations show their phenotype
- screening for resistance to chemicals

32
Q

Compare aneoploidy, monosomy, and trisomy.

A

Aneuploid: abnormal number of one or more chromosomes, but not all.
Monosomic: one missing chromosome
Trisomic: one extra chromosome compared to wildtype

33
Q

What are two types of X non-disjunction?

A

Turner Syndrome (XO) and Klinefelter syndrome (XXY)

34
Q

Why do trisomies increase in frequency with increased maternal age?

A

All oocytes are present at the mother’s birth and arrest in Meiosis I, aging in the ovaries. During aging, the association between homologs weakens increasing the chance of non-disjunction with age.

35
Q

Trisomies for other chromosomes are often incompatible with development and lead to miscarriages. Why?

A

Other chromosomes have too many critical genes.

36
Q

True or false? Nondisjunction can happen at the first OR second division in meiosis.

A

True

37
Q

Why are trisomies and monosomies so harmful?

A

The amount of gene product is (in part) dependent on how many copies of the gene there are.
The products of genes typically do not work in isolation (interact with other genes, likely on other chromosomes).
Gene imbalance is often not enough to be lethal, but the combination of many pathways perturbed (when a whole chromosome is duplicated or missing) is often lethal.

Too much transcription (trisomies) as well as too little (monosomies) are equally problematic, as they disturb the relative amounts of protein needed to correctly perform a given function.

38
Q

What effect does larger chromosome size have on trisomies?

A

Larger chromosomes generally have more genes and therefore, a greater chance of imbalance that is essential for embryonic development.

Note: in humans the only viable form of trisomy is downs syndrome

39
Q

Why are trisomies for sex chromosomes less deleterious compared to trisomies of autosomes?

A

Imbalance of the Y chromosome will have an effect restricted to fertility since this chromosome encodes mostly for genes involved in sex determination and function.
Imbalance of X chromosome will have a minor effect since the X chromosome has naturally evolved to be dosage compensated between the two sexes.

40
Q

What are two causes of chromosomal arrangements (deletion, inversion, translocation, duplication)?

A

(1) Repair errors after breakage
- caused by DNA damage
- 2+ DNA strand breaks
- repaired incorrectly

(2) Errors during crossing over
- caused by recombination ‘mistakes’
- crossover between repeated sequences that are not homologous

41
Q

What are three types of rearrangements?

Hint: even if chromosomal rearrangements can maintain gene dosage, they still often disrupt meiosis and therefore reduce fertility

A

(1) Non-viable: too damaged that it lacks correct number of centromeres and cant separate properly, lack correct arrangement of telomeres so that terminal genes are eroded in further rounds of mitosis, or loss of required genes or severe impairment of gene function
(2) Unbalanced rearrangements: changes gene number, deletions and duplications involving at least one gene
(3) Balanced rearrangements: no change in gene and centromere number, inversions and reciprocal translocations that change gene order

42
Q

Why are chromosomal translocations often silent?

A

If no gene is affected by the breakpoint and a centromere is not part of the translocation, it can be homozygous viable and undetected (reciprocal).

43
Q

What is Williams syndrome?

A

Phenotype:
- developmental delays and learning disabilities
- distinct facial features
- highly social personalities, musical talent, and strong language skills

Genotype:
- deletion of ~27 genes on chromosome 7
- deleted section flanked by 2 repeats, increasing the likelihood of mismatch during crossover

44
Q

Inversions may affect gene function. In what ways and why?

A

Effect depends on breakpoint of the inverted section:
(1) disrupting gene sequences
(2) modifying gene expression
(3) creating new genes
Could possibly have no effect, the genes could be shortened or new genes could be created

45
Q

Inversions disrupt chromosome pairing in meiosis. How?

A

Homologous regions need to line up for meiosis. Inversion loop creates messy gametes.

46
Q

True or false? A small fraction of Down Syndrome cases are caused by a translocation.

A

True; caused by a translocation between chromosome 21 and 14 which effectively creates a trisomy of 21

47
Q

Define chromatin.

A

Chromatin refers to a mixture of DNA and proteins that form the chromosomes found in the cells of humans and other higher organisms.

48
Q

What does hemizygous mean?

A

The meaning of HEMIZYGOUS is having or characterized by one or more genes (as in a genetic deficiency or in an X chromosome paired with a Y chromosome)

BIOL226 (10 decks)

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