Biology Revision.

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*14.1 meiosis, Medelian inheritance

*14.2 variation

*14.3 population genetics

*14.4 classification

*14.5 ecosystems

*14.6 photosynthesis

*14.7 food chains and webs

*14.8 respiration

*14.9 carbon and nitrogen cycles

*14.10 deforestation

Medelian Experiment

He noticed pea plants were either full sized (tall) or very short (dwarf)

He used self fertilisation to find PURE BREEDING PLANTS

Then produced offspring by FERTILISATION

All plants grew tall

So he took the offspring and crossed them with each other.

The offspring were ¾ Tall and ¼ Dwarf


Each plant has 2 genes

Genes give instructions to organisms-'grow tall' 'grow short'

If a plant has both type of gene the GROW TALL gene is DOMINANT the GROW SHORT is RECESSIVE

To show crosses we use symbols P-parents T-grow tall t-grow short

GAMETES: T & T x t & t

F1: Tt all offspring are TALL

2nd cross Tt x Tt

GAMETES: T t x T t

F2: TT, Tt, Tt, tt ¼ will be DWARF

Punnett squares/diagrams

1.Mendel's experiment (second part) using PUNNETT SQUARES

2.Showing CODOMINANCE-Feather colour in chickens is controlled by CODOMINANT ALLELES C -allele for white feather C -allele for black

3.Showing MULTIPLE ALLELES-Blood group is controlled by a gene which has 3 alleles- I & I are co dominant and I is recessive

4.SEX LINKAGE- X chromosomes are LARGE, y chromosomes are SMALL-Male humans XY Women XX

5.DIHYBRID INHERITANCE-All previous examples dealt with the inheritance of a single characteristic e.g. MONOHYBRID INHERITANCE-With DIHYBRID INHERITANCE we are looking at the inheritance of a pair of characteristics.



Illustration of the process by which a single parent diploid cell (Both homologous chromosomes) divides to produce four daughter haploids cells (One homologous chromosome of the pair).

Meiosis is the type of cell division by which germ cells (eggs and...