This document covers everything that you need to cover for Life Sciences Paper 1. It dies touch up on Meiosis as it is sometimes assessed in some exams. This document consist of answers from past memos. It also follows the exam marking guidelines
Answer: - Allows for a bigger brain
- Development of speech/ communication - Higher intelligence
- Complex behaviour
- Quick processing of information
- Process large amounts of information
2.
ADVANTAGES OF BIPEDALISM???
Answer: - Frees the arms so that they could carry offspring/ tools / food / manipulate things - Allows ability to see furtherto spot danger/ food
- Exposes a large surface area for thermoregulation
- Reduces the surface area exposed to the sun so less
heat is absorbed/ less heat lost/thermoregulation
- Expose the genitalsto attract opposite sex
- Efficient locomotionallows traveling over longer distances
3.
What are the sources of stem cells?
Answer: ➢ Umbilical cord
➢ Embryos
➢ Bone marrow
4.
WHAT IS MENDEL’S LAW OF INDEPENDENT ASSORTMENT?
Answer: -The various genes are separate entities and do not influence each other in any way. They sort themselves out independentlyduring gamete formation
since homologous chromosomes arrange themselves randomly along the equator
during metaphase I
5.
USES OF DNA PROFILING / ANALYSIS
Answer: - To investigate crimes/ resolve disputes
- To identify organisms from their remains
- To identify family relationships other than paternity e.g. siblings or cousins
- To test for the presence of specific alleles / genes that cause a genetic disorder - To establish matching tissues for organ transplants
Content preview
LIFE SCIENCES GRADE 12 - PAPER 1
(Answers from past Assessment Guidelines)
MEIOSIS
Where in animals and plants?
Where in the cell?
Events of Interphase + 4 cell division phases
Importance
Abnormal meiosis
DIFFERENCES BETWEEN MITOSIS AND MEIOSIS
MEIOSIS MITOSIS
• Meiosis involves 2 cell divisions • Mitosis involves 1 cell division
• Meiosis gives rise to sex cells • Gives rise to somatic cells
• Cells produced are haploid • Cells produced are diploid
• Differs according to gender • Has no gender specification
• 2 phases • 1 phase
• 4 daughter cells formed • 2 daughter cells
• Half the number of chromosomes to the • Same number of chromosomes formed
parent cell as in parent cell
• All cells formed are genetically • Genetically identical to each
different to each other and parent cell other and parent cell
• Cells responsible for genetic • Cells responsible for growth and
variation in reproduction (gametes) repair (somatic cells)
DIFFERENCES BETWEEN MEIOSIS I AND MEIOSIS II
MEIOSIS I MEIOSIS II
• Crossing over occurs in prophase 1 • No crossing over occurs
• Chromosomes arranged at the • Chromosomes arranged singly at
equator in homologous pairs in the equator in metaphase 2
metaphase 1
• Homologous chromosome pairs • Sister chromatids separate
separate
• Whole chromosomes are pulled to • Chromatids are pulled to opposite
opposite poles in anaphase 1 poles in anaphase 2
• 2 diploid daughter cells produced • 4 haploid daughter cells produced
THE IMPORTANCE OF MEIOSIS
• Production of haploid gametes
• The halving effect of meiosis overcomes the doubling effect of fertilisation, thus
maintaining a constant chromosome number from one generation to the next
• Mechanism to introduce genetic variation through:
- Crossing over
- The random arrangement of chromosomes at the equator
1
,ABNORMAL MEIOSIS
Non-disjunction and its consequences
• Non-disjunction of chromosome pair 21
during Anaphase in humans to form
abnormal gametes with an extra copy of
chromosome 21
• The fusion between an abnormal gamete
(24 chromosomes) and a normal gamete (23
chromosomes) may lead to Down syndrome
STRUCTURE AND ARRANGEMENT OF CHROMOSOMES IN A NORMAL HUMAN
KARYOTYPE
- Each chromosome comprises two chromatids
- held together by a centromere
- There are 23 pairs/46 chromosomes in
- human somatic cells/body cells
- which are arranged into homologous pairs
- that are similar in length
- carry genes for the same characteristics
- have alleles of a particular gene at the same lociand
- have the same centromere position
- Each somatic cell has 22 pairs/44 autosomesand
- a pair/2 gonosomes/sex chromosomes/X and Y chromosomes
- Autosomes are arranged in pairs from largest to smallest in a karyotype
- Males have XY chromosomes
- Females have XX chromosomes
- The X chromosome is larger than the Y chromosome
BEHAVIOUR OF THE CHROMOSOMES DURING THE DIFFERENT PHASES OF
MEIOSIS I
- During prophase I
- chromosomes pairup/homologous pairs form
- Crossing overexchange of genetic material occurs
- between chromatids/adjacent chromosome pairs
- During metaphase I of meiosis
- homologous chromosomes/chromosome pairs are arranged
- at the equatorof the cell
- in a random way
- with the chromosome attached to the spindle fibre
- During anaphase I
- chromosome pairs separate/chromosomes move to opposite poles
- During telophase I
- the chromosomes reach the poles of the cell
2
, EVENTS THAT LEAD TO DOWN SYNDROME
- Non-disjunction occurred/A homologous pair of chromosomes
- at position 21
- failed to separate
- during anaphase
- resulting in one gamete with 24 chromosomes / an extra Chromosome /
2 chromosomes at position 21
- The fertilisation of this gamete with a normal gamete/gamete
with 23 chromosomes /1 chromosome at position 21
- results in a zygote with 47 chromosomes
- There are 3 chromosomes /an extra chromosome at position 21/ this is Trisomy 21
HOW MEIOSIS CONTRIBUTES TO GENETIC VARIATION
Crossing over
- Occurs during prophase I
- Chromatids of homologous chromosomes overlap
- at points called chiasma/ chiasmata
- Genetic material is exchanged
- resulting in new combinations of genetic material from both parents
Random arrangement of chromosomes
- Occurs during metaphase I / II
- Each pair of homologous chromosomes /each chromosome
- may line up in different ways on the equator of the spindle
- allowing the gametes to have different combinations of maternal and paternal
chromosomes
- so that they separate in a random/ independent manner
- resulting in new combinations of genetic material
3
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