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Reproduction and Inheritance
DNA, Genes and Chromosomes:

Genes:
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DNA is a long list pf instruction on how to put an organism together
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Proteins are important because they control most processes in the body
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By controlling the production of proteins, genes also control our inherited
characteristics
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The different versions of the same gene are called alleles
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The two strands are held together by chemical called bases
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The bases are paired, and they always pair up the same way – A-T and C-G
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DNA is a type of nucleic acid
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Both new cells are
genetically identical to the original cell
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This type of cell division is known as mitosis
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This is known as asexual
reproduction
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Asexual Reproduction – Involves only one parent
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Mitosis – When a cell reproduces itself by splitting to form two cells with identical
sets of chromosomes
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Mitosis isn’t just used during asexual reproduction – it is how all plants and animals
grow and repair damaged tissue
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Sexual Reproduction and Meiosis:
Sexual Reproduction:
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Where genetic information from two organisms is combined to produce offspring
which are genetically different to either parent
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Gametes are
sperm cells and egg cells
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At fertilisation, a male gamete fuses with a female gamete to form a zygote
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The zygote then undergoes cell division and develops into an embryo
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The fertilisation of gametes is random – this produced genetic variation in the
offspring
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Meiosis:

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Meiosis is another type of cell division
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In humans, meiosis only happens in the reproductive organs
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Sexual Reproduction in Plants:
Flowers:
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Stamen:
o The stamen is the male
reproductive part
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o The anther contains pollen
grains – these produce the
male gametes
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Carpel:
o The carpel is the female reproductive part
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o The stigma is the end bit that pollen grains attach to
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o The ovary contains the female gametes inside ovules
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Cross-Pollination – A type of sexual reproduction where pollen is transferred from
the anther of one plant to the stigma of another
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Adaptations:
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Here’s how some plants have adapted for pollination by insects:
o Have brightly coloured petals to attract insect
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o They make big, sticky pollen grains – the grains stick to insects as they go
from plant to plant
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Here’s how some plant have adapted for pollination by wind:
o Small, dull petals on the flower
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o They make a lot of pollen grains – they're small and light so that they can
easily be carried by the wind
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o A large and feathery stigma to catch pollen as it’s carried past by the wind
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Fertilisation in Plants:
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A pollen grain lands on the stigma of
a flower, usually with help from
insects or the wind
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A nucleus from the male gamete
moves down the tube to join with a
female gamete in the ovule
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This divides by mitosis to form an embryo
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The ovary develops into a fruit around
the seed

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