Class notes

All lecture notes of BIOL113 Genetics module

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Course
BIOL113: Genetics

Institution
Lancaster University (LU)

23 pages covering all 12 lecture on this module. Includes definitions and specific examples used in the modules lectures/exams. Covers things such as Inheritance, DNA structure, mutations, gene/chromosomal abnormalities and disorders, gene transduction in bacteria, Homoetic genes ect. (I achieve...

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Uploaded on September 5, 2023
Number of pages 23
Written in 2022/2023
Type Class notes
Professor(s) Dr andrew fielding
Contains All classes

mendel
inheritance
chromosome
chromosomal abnormalities
protein synthesis
mutation
bacteria
genetics
gene disorders
gene expression
meiosis
dna repair
mutagen

Institution
Lancaster University (LU)
Education Unknown
Course
BIOL113: Genetics

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1

Biol113 – Genetics
ALL NOTES

Chapter 1 Contents
L1 – Mendelian Inheritance + role of meiosis in determining inheritance patterns .............................. 2
L2 – Linkage, Recombination + Deviation from Mendelian Ratios ......................................................... 3
L3 – Chromosomal Abnormalities ........................................................................................................... 4
L4 – The Molecular Basis of Inheritance ................................................................................................. 6
L5 – Frome Gene to Protein .................................................................................................................... 9
L6 – The Mechanism of Protein Synthesis ............................................................................................ 10
L7 – Mutation, mutagens + DNA repair ................................................................................................ 12
L8 – Single Gene Disorders.................................................................................................................... 13
L10 – Bacterial Genetics ........................................................................................................................ 15
L11 – Gene Expression in Eukaryotes ................................................................................................... 18
L12 – Genetics of Development ............................................................................................................ 21

, 2

L1 – Mendelian Inheritance + role of meiosis in determining
inheritance patterns

Gregor Mendel 1st Law of Segregation: 2 forms of a gene present in each parent segregate
independently
Offspring receives 1 allele from 1 gamete from each parent
Monohybrid cross results:
1. 2 true breeding individuals with differing phenotype bred together
2. F1 gen = all hybrids express dominant allele
3. F2 gen = 3:1 ratio of dominant:recessive
Mendel’s Model:
• Alleles cause variation in inherited characteristics
• Offspring inherits 2 alleles, 1 from each parent for each character
• the dominant allele determines the phenotype if the allele differs
• alleles are discrete + do not blend
• 2 alleles segregate during gamete formation

Mendel’s Law of Independent Assortment: different genes get assorted independently of each
other
• Looks at pairs of alleles -> dihybrid cross:
1. 2 trur breeding individuals with differing phenotypes bred together YYRR x yyrr
2. F1 gen = all offspring YR phenotype
3. F2 gen = 2 old phenotypes – YR, yr = parental
2 new phenotypes = Yr, yR = recombinants
If no independent assortment:
1. YR + yr are linked
2. Only YR and yr gametes
3. F1 gen = YR
4. F2 gen = YR and yr offspring in 3:1 ratio as no recombinant phenotypes

The Chromosome Theory of Inheritance (Walter Sutton): pairs of chromosomes separate during
meiosis
• Heritable factors at loci on chromosomes
• Chromosomes undergo segregation + independent assortment
Somatic cell: any cell in organisms except reproductive cells
Homologous pair: 2 chromosomes inherited from each parent
Chromatid: 1 of 2 identical strands of newly replicated chromosome
Sister chromatids: 2 identical chromatids help together by a common centromere

, 3

Meiosis = only occurs in non-somatic cells, consists of interphase 1 + 2 cell divisions, 4 non-identical
haploid cells produced, synapsis only in meiosis
Meiosis 1 = homologous chromosome separate
Meiosis 2 = sister chromatids separate
Observations:
• Chromosomes in pair in non-somatic cells
• Chromosome pairs segregate equally
• Different chromosome pairs assort independently
Genetic Variation: mutations, independent assortment, crossing
over, random fertilisation

L2 – Linkage, Recombination + Deviation from Mendelian Ratios

Crossing over:
Crossing-over: the process of genetic recombination that gives rise to new combinations of linked
genes
- Occurs during pachytene phase of prophase 1
Pachytene: chromosomes are zipped up + look like thick thread
1. Synapsis: pairing of homologous chromosomes
2. Formation of synaptonemal complex: holds homologous chromosomes together in tetrad
3. Genes cross over at chiasms producing recombinant chromosomes with new combinations
of linked genes

Recombinants:
Recombinant phenotype: combination of phenotype differs from parents (always lowest frequency)
- Due to independent assortment for genes on different chromosomes + crossing-over for
genes on the same chromosome
Recombinant Frequency: percentage of progeny that inherit a combination of alleles that differs
from either parent RF = total no. of recombinants x 100/ total no. of progeny RF < 50%
- Depends on whether the genes are on the same or different chromosomes
- When genes on the same chromosome, recombinants only due to crossing-over
+ = wild gene
Percentages won’t add up due to multiple crossing over events

Coupling vs Repulsion heterozygote:
Coupling heterozygote: wild genes on same chromosome, mutants on other
Repulsion heterozygote: 1 wild gene + 1 mutant on each chromosome
Largest phenotype frequency = parental
Chromosome linkage maps:
1% RF = 1cM
Genes further apart = more likely to stay together during crossing over

Deviations from Mendelian ratios:
- Sex-linkage
- Incomplete dominance: dominant allele does not completely mask the effect of a recessive
allele at the same locus

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