Reproduction (X and Y chromosomes) Noadswood Science, 2016

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

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)

Size Order the following in terms of their size: -

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

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)

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

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

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

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

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)

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

Variation

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

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