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My ESA1 > MGD S4 - Inheritance of Genes > Flashcards

MGD S4 - Inheritance of Genes Flashcards

1
Q

Outline the cell cycle

A

See diagram

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2
Q

Give a brief overview of DNA replication

A

Double helix separates and each strand is a template for the new copy. Catalysed by DNA polymerase. Extend 3’ end of existing DNA. (dNMP)n primer strand + dNTP nucleotide ➡️ (dNMP)n+1 + PPi - Stepwise reaction driven by pyrophosphate hydrolysis - Chain growth is directional, from 5’ to 3’

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3
Q

Briefly outline the stages of DNA replication in prokaryotes

A

Circular “naked” chromosome: - Initiation - Elongation - Termination

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4
Q

Describe the process of initiation in prokaryotic DNA replication

A
  • Recognition of origin of replication - Requires recruitment of DNA polymerase plus other specific proteins - Requires a “kick-start” by primase (2/3 RNA nucleotides) as DNA polymerase can only extend a 3’ end - Template 3’ to 5’ to extend 5’ to 3’. DNA polymerase reads in opposite direction
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5
Q

Describe the process of elongation in prokaryotic DNA replication

A
  • Moving replication forks - Helicase unwinds double helix bit by bit - DNA polymerase extends 3’ ends only: leading to leading strand (continuous), lagging strand (discontinuous) and Okazaki fragments - DNA ligament joins fragments
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6
Q

What is the difference between the leading and lagging strands?

A
  • Lagging strand: made in small parts (discontinuous) - Leading strand: made continuously
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7
Q

Describe the process of termination in prokaryotic DNA replication

A
  • When 2 facing replication forks meet and DNA ligase joins final fragments - Chromosome number stays the same - One replicated chromosome consists of two sister chromatids (maternal copy - non-sister chromatids from paternal copy)

SECOND DIAGRAM - see slide 18

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8
Q

What is the product of DNA replication in prokaryotes?

A

2 new double stranded antiparallel DNA molecules

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9
Q

Describe some features of DNA replication in eukaryotes

A
  • Double stranded so 5’ and 3’ on both ends - Can start at different positions - DNA replication forks in both directions - One chromosome = one DNA molecule - After replication: one replicated chromosome = 2 identical DNA molecules (2 chromatids) - Takes human cell ~8 hours to replicate all DNA
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10
Q

Describe chromosome structure

A

The classical X-shape is a replicated chromosome containing two identical DNA molecules

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11
Q

Give an overview of mitosis

A
  • Cell division for somatic cells - Production of two identical daughter cells (with same chromosome content as parental cell) - ~50 mitotic rounds during development - Mitotic growth necessary for some tissue (epidermis, mucosae, bone marrow, spermatogonia)
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12
Q

Describe prophase

A
  • Spindle fibres appear - Chromosomes condense - Nuclear membrane disintegrates
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13
Q

Describe prometaphase

A
  • Spindle fibres attach to chromosome - Chromosomes condense - Spindle fibres connected to centromere by kinetochore
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14
Q

Describe metaphase

A
  • Chromosomes align - Chromosomes line up randomly in middle of cell (at metaphase plate)
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15
Q

Describe anaphase

A
  • Centromeres divide - Chromosomes split - Sister chromatids move to opposite poles
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16
Q

Describe telophase

A
  • Nuclear membrane reforms - Chromosomes decondense - Spindle fibres disappear
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17
Q

Describe cytokinesis

A
  • Cytoplasm divides - Parent cell becomes two daughter cells with identical genetic information
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18
Q

Give an overview of meiosis

A
  • Special division for germ line cells - Production of four non-identical cells (gametes) with half chromosome content of parental cell - One round of replication followed by two rounds of division: meiosis I and II - Diploid (2n: 46 chromosomes) reduced to haploid (n: 23 chromosomes) - Production of eggs and sperm

Image=meiosis I

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19
Q

Describe prophase I

A

Disintegration of nuclear membrane

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20
Q

Describe metaphase I

A
  • Chromosomes line up in pairs on metaphase plate - Crossing over occurs
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21
Q

Describe crossing over

A
  • If it doesn’t occur meiosis goes wrong - Occurs between sister chromatids too but has no effect as they’re identical - 1 complete form of each maternal and paternal chromosome
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22
Q

Describe anaphase I

A

Each replicated chromosome goes to either end of the cell. Still random lining up: random assortment of chromosomes. Whole replicated chromosome of each goes into daughter cell

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23
Q

Describe telophase I

A

Nuclear membrane reforms

24
Q

Describe cytokinesis I

A

Cell divides into two daughter cells

25
Q

Which stage of meiosis is similar to mitosis?

A

Meiosis II

26
Q

Describe prophase II

A

Nuclear membrane disintegrates

27
Q

Describe metaphase II

A

(Still crossed over) random line up

28
Q

Describe anaphase II

A

Chromosomes split

29
Q

Describe telophase II

A

Nuclear membrane reforms

30
Q

Describe cytokinesis II

A

Cells divide into 4 haploid daughter cells

31
Q

What is the difference between meiosis I and meiosis II?

A
  • Meiosis I: homologous pairs line up and chromosomes separate - Meiosis II: chromosomes line up and chromatids separate. As soon as chromatids separate, they’re called chromosomes again
32
Q

What are the consequences of meiosis?

A
  • Maintaining constant chromosome number from generation to generation - Generation of genetic diversity: 1. Random assortment of chromosome 2. Crossing over of genetic material
33
Q

What is spermatogenesis?

A
  • Cell division to produce male gametes - 1 spermatocyte (2n) ➡️ 4 sperm (n) - Length of spermatogenesis is ~48 days
34
Q

What is oogenesis?

A
  • Cell division to produce female gametes - 1 oocyte (2n) ➡️ 1 egg (n) + 3 polar bodies (discarded) - Length of oogenesis is 12-50 years - All oocytes already in foetus, arrested in meiosis I - Period - 1 oocyte goes through meiosis to metaphase II - Old mothers: DNA can be damaged - Meiosis only complete at fertilisation
35
Q

What happens if crossing over does not occur?

A

See image

36
Q

Describe mistakes in meiosis and their consequences

A
  • Humans are not very good at meiosis. Missegregation: 30 in 100 - Consequences: a third of all identified (they are many more) miscarriages, infertility, leading cause of mental retardation
37
Q

Contrast mitosis and meiosis

A

See image

38
Q

What are the environmental factors that affect genotype and phenotype?

A
  • Radiation - Mutagens - Chemicals that affect cell growth - Diet - Lifestyle - etc
39
Q

What creates genetic variation?

A

Mutation Meiosis: - Independent assortment of chromosomes (2^n possibilities, n is the number of chromosome pairs) - Crossing-over of genetic material

40
Q

Give a brief overview of inheritance

A
  • Each human has 25,000 genes - Each individual has 2 copies of each gene - Each individual has 2 alleles of a gene - There are many alleles of a gene within a population
41
Q

Define homozygous

A

Two alleles of a gene are different Individual is a homozygote

42
Q

Define heterozygous

A

Two alleles of a gene are different Individual is a heterozygote

43
Q

Define hemizygous

A

Only one alleles of a gene on the X chromosome - males only

44
Q

Define dominant

A

The dominant allele in a heterozygote determines the phenotype

45
Q

Define recessive

A

The non-dominant allele in a heterozygote

46
Q

Give a flow diagram to help identify type of inheritance

A

See image

47
Q

What are the different symbols used when drawing a pedigree?

A

See image

48
Q

Describe autosomal recessive diseases

A
  • Heterozygotes unaffected - Males and females equally affected - Two heterozygotes have 25% chance of having affected offspring - Two homozygous individuals will have affected offspring only - Disease seems to come out of nowhere; can skip generations - Both parents of affected individual must be at least heterozygous carriers - For example: Cystic Fibrosis
49
Q

Describe autosomal dominant diseases

A
  • Heterozygotes affected - Males and females equally affected - Disease rarely found in homozygous state - Every affected individual has 50% chance of having affected offspring - Every affected individual will have at least one affected parent - Disease cannot skip generations - For example: Huntington’s disease
50
Q

Describe X-linked recessive diseases

A
  • Hemizygous males and homozygous females affected - Disease more common in males - Heterozygous female carrier had 50% chance of having affected sons - Affected males cannot give trait to son - Daughters of affected males are heterozygous - Every affected male will have at least a heterozygous carrier mother - Every affected female will have at least a carrier mother and an affected father - For example: Haemophilia A
51
Q

Give an example of codominance

A

Human ABO blood groups - Human isoglutamin gene codes for glycoproteins on the surface of red blood cells - Gene I: 3 alleles A, B, O or Ia, Ib, Io - Alleles A and B are dominant over allele O - Neither A or B is dominant over the other; they are codominant - Blood Group A: IaIa/IaIo - Blood Group B: IbIb/IbIo - Blood Group AB: IaIb - Blood Group O: IoIo

52
Q

Give an example of complementation

A

Albinism Recessive Two genes: A1 and A2 Alleles: A1, a1 and A2, a2

53
Q

Why does complementation occur?

A

More than one gene can be involved in producing a phenotype

54
Q

Describe linkage and recombination

A
  • Genes on the same chromosome are “linked” - Genes on different chromosomes are “not linked” - Linked genes do not show independent assortment at meiosis - Recombination frequency between two linked genes is dependent on the distance between the genes - Genes close together are “tightly linked” - Genes far apart on the same chromosome almost behave as unlinked genes
55
Q

Give an overview of meiosis II

A

See image

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