19/04/23

Inheritance and Inheritance and variation#variation#

ReproductionReproduction

19/04/23

VariationVariationVariation is a name given to differences in a species, e.g. dogs:

Variation is due to each animal having different GENETIC INFORMATION in their cells.

AQA Science © Nelson Thornes Ltd

2006  3VariationsVariations

There are variations between members of the same species. Because of these variations, some individuals are more successful than others. In harsh conditions, the fittest survive.

humans have human genes

Genes are the units of inheritance. Organisms differ because they have different genes.

What makes organisms What makes organisms different?different?

gerbils have gerbil genes

bananas have (yes, you’ve guessed it) banana genes!

Sexual reproductionSexual reproduction

In sexual reproduction, genetic information from two parents is mixed to make a new

plan for the offspring. This leads to variation between members of a species.

19/04/23

Fertilisation in HumansFertilisation in HumansTo put it simply, it’s an “egg and sperm race”…

Egg

Sperm

FertilisationFertilisation

In sexual reproduction, fertilisation happens when a male and a female sex cell join together.

19/04/23

Eggs and spermEggs and spermThe female egg cell and the male sperm cell are examples of ____________ cells:

The egg cell is basically an enlarged cell with massive _____ reserves

The ______ cell is specialised in two ways:

Words – food, swimming, sperm, specialised, digest

Head packed with “enzymes” to ______ its way through the egg

Strong tail for ________

Nucleus

19/04/23

Sexual reproductionSexual reproductionSexual reproduction involves two organisms of the same species. Each organism produces a GAMETE.

For example, in animals the gametes are the egg and the sperm:

When the sperm penetrates the egg the egg is fertilised and cells start to reproduce to form a new individual:

ReproductionReproduction

1.After sexual intercourse, one sperm may fertilise an egg. This produces a zygote

2.The zygote forms an embryo and the embryo embeds itself in the uterus lining

3.The embryo grow into a foetus and then a baby

19/04/23

FertilisationFertilisationFertilisationFertilisation

FertilisationFertilisation

Male reproductive organsMale reproductive organsMale reproductive organsMale reproductive organs

Male reproductive Male reproductive organsorgans

Female reproductive organsFemale reproductive organsFemale reproductive organsFemale reproductive organs

Femal reproductive Femal reproductive organsorgans

FertilisationFertilisationFertilisationFertilisation

FertilisationFertilisation

In all living things, characteristics are passed on in the chromosomes that offspring inherit from their parents.

Passing on characteristicsPassing on characteristicsWhat makes this baby human? What determines its gender?

This means that all human characteristics must be something to do with chromosomes. Where are chromosomes found?

19/04/23Where is this information Where is this information stored?stored?

Section of a chromosome:

Genes for eye colour

Genes for hair

colour

Genes for blood group:

Different species have different numbers of chromosomes. Humans have 46 (23 pairs) in every cell.

Genetic information is stored by genes which are arranged on chromosomes:

Chromosomes and their genes are made of a molecule called DNA.

DNA molecules carry the code that controls what cells are made of and what they do.

DNA stands for deoxyribonucleic

acid.

Each chromosome is a very long molecule

of tightly coiled DNA.

Which part of a DNA molecule holds this information?

What is DNA?What is DNA?

19/04/23

Sexual reproductionSexual reproductionIn plants, the gametes are the egg and pollen:

Any type of sexual reproduction helps a species to become more varied because the offspring inherit characteristics from both parents.

Fertilisation

ReproductionReproduction

1.Asexual reproduction can be achieved by plants, bacteria and fungi. It produces clones.

2.Sexual reproduction can be achieved by flowering plants and animals. It produces offspring with varied characteristics.

19/04/23

Asexual & Sexual ReproductionAsexual & Sexual ReproductionAsexual & Sexual ReproductionAsexual & Sexual Reproduction

Asexual & Sexual ReproductionAsexual & Sexual Reproduction

FertilisationFertilisationFertilisationFertilisation

FertilisationFertilisation

19/04/23

Environmental differencesEnvironmental differencesClearly, not all differences are due to just our genes…

Variation due to inheritance only

Variation due to environment only

Variation due to a bit of both