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Science of Reproduction > Chromosomes and Gametes > Flashcards

Chromosomes and Gametes Flashcards

1
Q

What are the fundamental principles of evolution?

A
  • The ability to reproduce
  • Variation

Each new generation in turn reproduces or dies out – selection of the fittest

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2
Q

What is a karyotype?

A

The number and appearance of human chromosomes

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3
Q

Describe the structure of a chromosome

A

Each chromosome has a constriction point called the centrosome

Divides chromosome into 2 sections / “arms” – short (p) and long (q)

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4
Q

What is the significance of the centromere location?

A

Gives a chromosome its characteristic shape

- used to describe location of the gene

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5
Q

What are the 3 roles of functional DNA?

A
  • replicate
  • separate its 2 copies at mitosis
  • maintain itself between generations
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6
Q

What are the DNA requirements for sexual reproduction?

A

Each parent passes on one allele to each offspring

If alleles are heterozygous, trait phenotype either dominant / recessive

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7
Q

When do copy number variants occur?

A

Copy number variants (CNV) occur if more than one, three or more copies of alleles

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8
Q

Briefly outline transcription and translation if a gene

A
  1. Promoter + coding seq. transcribed into gene product
  2. Introns removed from exon by splicing
  3. mRNA exported out of nucleus
  4. Translated into proteins in ribosomes by complexes of tRNA & proteins
  5. Proteins folded into unique 3D structure - determines function
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9
Q

How can a single gene become tissue specific?

A

Same gene can be tissue specific by having alternative promoters

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10
Q

Give an example of a tissue specific gene

A

CYP19A1 (encodes aromatase)

uses different promoters in breast, ovary and brain

Aromatase converts androgens into oestrogen

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11
Q

What is the role of some non-coding regions in genes?

A

Most genes contain non-coding regions that regulate gene expression

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12
Q

How does one gene produce multiple gene products?

A

Via Alternative splicing of exons

- Products are known as Isoforms

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13
Q

How can a protein be modified after production?

A

Post-translational modification - e.g phosphorylation

Glycosylation

  • adding on carbohydrates to protein
  • making protein more stable and soluble
  • LH/FSH is modified like this
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14
Q

How are hormones modified for action?

A

Often secreted as “prohormones” and are enzymatically processed to form active hormones
eg. prepro GnRH

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15
Q

Give an example of alternative splicing producing isoforms

A

3 alternatively spliced variants of human FSHR found in testicular tissue
– possible association with spermatogenic defects

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16
Q

What is the purpose of LH/FSH glycosylation?

A

Different no. of glycosylated elements added on to gonadotropins to form variations of the hormones.

Different glycosylated elements have different activities and will form different isoforms throughout reproductive life.

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17
Q

What is the significance of DNA in reproduction?

A

DNA needs to be able to be passed through generations

18
Q

How do most cells in the body reproduce?

A

Most cells and many organisms replicate by doubling DNA and dividing to give 2 identical progeny or clones - asexual reproduction

19
Q

What is the process by which human cells reproduce?

A

Mitosis:
Fusion of haploid cells (gametes) to create unique progeny.
Uniqueness brought about by crossing over and independent sorting of chromosomes

20
Q

Describe the asexual mitosis of somatic cells

A
  1. Homologous chromosomes
  2. DNA replicated
  3. Sister chromatids form
  4. BIvalent chromosomes line up between 2 mitotic
    spindles
  5. Undergo two cell divisions
  6. gametes formed
21
Q

What is the product of somatic cell division?

A

Somatic / diploid cells replicate by simple cell division

  • give identical progeny
  • limited no. of divisions,
    e. g hepatocytes, pancreas, skin cells
22
Q

What are the advantages of diploidy?

A

Prevents accumulation of genetic mutations

Increased genetic diversity

Maintenance occurs due to advantage of genetic variability

Variation in off-spring → survival of the fittest? More able to evolve + adapt to changing environment

23
Q

Why is allelic variation not always bad?

A

Mitosis can cause allelic variation - but just as many good as bad

If 2 good ones occurred then both would proliferate
- out-survive others

24
Q

Where are X and Y chromosomes thought to originate from?

A

Differentiated from pair of identical chromosomes (autosomes) ~300 million years ago

Ancestral mammals developed variation which made it male - gradually becoming Y and the other the X (sex locus (Y) = male)

25
Q

How many working genes are found on each X and Y chromosome?

A

X chromosome → 1000 working genes

Y chromosome → 86 working genes

26
Q

What is a gamete?

A

A haploid cell specialised for sexual fusion (egg + sperm)

27
Q

How many chromosomes in a haploid cell?

A

23 in total

28
Q

How do gametes reproduce?

A

Unlike other cells gametes go through cycles of diploidy & haploidy

Undergo cycles of mitosis to increase numbers
Then undergo meiosis
Then combine at fertilisation

29
Q

How are gametes formed?

A

From germ line cells: primordial germ cells that migrate into gonad and differentiate to either male or female gametes

30
Q

What is the process producing oocytes?

A

oogenesis (incorporated as part of folliculogenesis)

31
Q

What is the process producing sperm?

A

spermatogenesis

32
Q

Which phase of the cell cycle do chromsosomes duplicate?

A

Chromosomes replicate during S-phase of cell cycle

- still attached at centromere

33
Q

What is a chromatid?

A

Each copy of replicated chromososme

‘sister’ as they’re identical

34
Q

What is interphase?

A

Period of cell cycle between cell divisions - Not a “resting period”

35
Q

What processes occurs during interphase?

A

Cell carries out functions and grows

DNA and organelles duplicate

36
Q

Describe the structure of genetic material during interphase

A

Genetic material in long, thin threads called chromatin.

Twist randomly around one another like tangled strands of yarn.

37
Q

What are the 4 stages of mitosis?

A

Prophase; Metaphase, Anaphase & Telophase

38
Q

What occurs during prophase of the cell cycle?

A

nuclear & cytoplasmic changes.

39
Q

Outline the nuclear changes that occur in prophase

A

Chromatin condenses
Forms chromosomes - DNA wraps around histones

DNA loops + twists to form tightly compacted structure

Condensed DNA can’t replicate - gene activity shut down

Sister chromatids easier to separate without breaking

Nuclear membrane also begins to break down.

40
Q

What are the cytoplasmic changes of prophase?

A

Mitotic spindle forms - made of microtubules associated with centrioles

Centrioles duplicated during interphase, move away from each other toward opposite poles in prophase

Science of Reproduction (32 decks)

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