1. Reproduction (X and Y chromosomes)
Noadswood Science, 2016

2. Reproduction (X and Y chromosomes)
Saturday, April 14, 2018
Reproduction (X and Y chromosomes)
To understand the mechanisms of reproduction

3. Precise Learning
Sexual reproduction involves the joining (fusion) of male and female gametes:
sperm and egg cells in animals
pollen and egg cells in flowering plants.
In sexual reproduction there is mixing of genetic information which leads to variety in the offspring. The formation of gametes involves meiosis.
Asexual reproduction involves only one parent and no fusion of gametes. There is no mixing of genetic information. This leads to genetically identical offspring (clones). Only mitosis is involved.
When a cell divides to form gametes:
copies of the genetic information are made
the cell divides twice to form four gametes, each with a single set of chromosomes
all gametes are genetically different from each other.
22 pairs control characteristics only, but one of the pairs carries the genes that determine sex:
In females the sex chromosomes are the same (XX)
In males the chromosomes are different (XY)

4. Size
Order the following in terms of their size: -

5. Reproduction
During reproduction genetic information is passed from parents to their offspring
There are two distinct methods for this to occur: -
Asexual reproduction
Sexual reproduction

6. Asexual reproduction
Asexual reproduction only needs one parent, unlike sexual reproduction, which needs two parent
Since there is only one parent, there is no fusion of gametes and no mixing of genetic information – as a result, the offspring are genetically identical to the parent and to each other (clones)
Some plants produce side branches with plantlets on them (e.g. Busy Lizzy)
Other plants produce runners with plantlets on them (e.g. strawberries)

7. Plants – asexual reproduction
Asexual reproduction in plants can take a number of forms
Many plants develop underground food storage organs that later develop into the following year’s plants (e.g. potato plants and daffodil plants)
Daffodil bulb at start of season
Daffodil bulb at end of season

8. Sexual Reproduction
Sexual reproduction happens when a male gamete and a female gamete join - this fusion of gametes is called fertilisation
Sexual reproduction allows some of the genetic information from each parent to mix, producing offspring that resemble their parents, but are not identical to them
In this way, sexual reproduction leads to variety in the offspring

9. Sexual reproduction
Each pair of genes affects a different characteristic – the genes in the pair can come in different forms
These different versions of the same gene are called alleles
Offspring inherit a random mixture of thousands of alleles from their parents, which is why offspring do not look exactly like either parent

10. Why Sexual
Why have sexual reproduction – surely it is easier to simply have asexual reproduction?!
Sexual reproduction leads to variety – this is critical for a species survival as the greater the variety within the individuals the more likely that at least a few of them will have the ability to survive difficult conditions

11. Variation
Young plants and animals resemble their parents, showing similar characteristics
However, young plants and animals can also differ from their parents and each other – these similarities and differences lead to variation within the same species
There are two causes of variation: -
Genetic variation (slightly different genes)
Environmental variation (upbringing)

12. Variation in Plants
Environmental variation in plants is much greater, as they are strongly affected by: -
Temperature
Sunlight
Moisture levels
Soil composition

13. Variation

14. Practice Questions Name the male and female gametes in humans
How many parents are there in asexual reproduction?

15. Answers Name the male and female gametes in humans – sperm and egg
How many parents are there in asexual reproduction – 1