A complete set of notes on the Genetics Section of the IEB Matric / Grade 11 Syllabus for Life Sciences [Biology]. These notes helped me to achieve a distinction for my Life Science Prelim. These notes include an in-depth analysis of the following sub-sections:
Genetics
Inheritance and Variatio...
Genetics & Inheritance:
- Hereditary:
• The tendency for the characteristics of parents to be passed to their offspring
• There are also differences between parents & offspring
- Science of genetics studies how similarities & differences happen
Genes: Dominant, Recessive & Alleles
- Homologous chromosomes are the same & have same number and sequence of
genes
- GENES:
• Basic unit of inheritance
• Region of the chromosome / certain short section of the DNA molecule
• Carries instructions on how to make a specific protein
- Humans are diploid: inherit 2 genes for each characteristic
• 1 from mother
• 1 from father
• These genes are at same locus [position] on homologous chromosomes
- An allele is two or more alternative forms of a gene or genes at same locus on
homologous chromosomes
• Homozygous alleles are both the same
• Heterozygous alleles are two different alleles
- Genotype: shows the alleles for the characteristics that we are interested in and is
thus the genetic makeup
• Symbols such as: BB, Bb or bb
- Phenotype: a description of the condition produced by the alleles
,- Dominant allele:
• One that shows in the phenotype when it occurs in a homozygous or heterozygous
condition
• Capital letter
- Recessive allele:
• One that is not shown in the phenotype when it occurs in a heterozygous condition
• Only expressed if both alleles are recessive
• Lower case
- One can determine the genotype of an organism with two recessive alleles because
recessive alleles will then be visible in the phenotype
CHARACTERISTIC DOMINANT RECESSIVE
Eye colour Brown Blue
Hair colour Brown Blond
Hairline shape Widow’s peak Smooth
Lip width Thick Thin
Ear lobe attachment Freely hanging Attached
Tongue rolling ability Roll Can’t roll
MENDEL: FATHER OF GENETICS
- Austrian Monk [Gregor Mendel] in the middle of 19th century
- Mendel made first breakthrough in understanding how characteristics were inherited
- Studied the inheritance of some characteristics of the vegetable pea
- His investigations & conclusions made were the start if genetics
How he did it:
- Selected 7 pairs of contrasting characteristics in peas for study
- Started with pure breeding plants [homozygous]
• Offspring of these plants that were identical to them for one characteristic he was
interested in
, - Cross-pollinated plants breeding true for one characteristic with pure-breeding plants
with the contrasting characteristic
• Crossed two sets of homozygous plants
- Self-pollinated first generation to get the second generation
- Hybrid:
• Offspring that results from cross between two breeding parents that are
genetically different
- Mendel studied inheritance of one pair of contrasting characteristics at a time: he
studied monohybrid intelligence
- First filial generation or F1 generation
• first group of offspring
- Second filial generation or F2 generation
• Generation that comes from F1
Results of Mendel’s Monohybrid cross:
Note: he crossed tall pure breeding plants with short pure breeding plants
- Neither in F1 or F2 generations were there medium-sized plants
- F1 was only tall plants
- Short plants appeared in F2
- Ratio of tall plants to short plants in F2 generation was 3:1
Conclusion: [of 7 different investigations]
- Process didn’t involve blending: separate factors present
- One factor for each pair of characteristics was hidden if the other factor was present
• Hidden: recessive
• Present: dominant
- Pure bred parents had 2 of the same factors
- Parent plants pass 1 of their 2 factors to any offspring
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