Sexual Reproduction Increases Variation: DNA & Inheritance Sexual Reproduction Increases Variation: We Are All Unique The Happy Families Game can easily be slotted in alongside basic sex education. There is no reference to how sex is carried out here so it is possible to use this activity with pupils who have been withdrawn. The focus here is on genetics and the fact that you inherit half of your DNA, so half of your genes from your mum and half from your dad. One of the evolutionary advantages of sexual reproduction is that it increases variation. As a consequence of this variation we are all unique, with the exception of identical twins Dr Gail Davies

So in terms of inheriting our DNA/genes from our parents this is where the egg and sperm come in. Half of our DNA is in the egg and half our DNA is in the sperm. How this actually works is that as humans we have 46 chromosomes arranged in 23 pairs (no.s 1-22 and the sex chromosomes XX girl, XY boy). To be able to maintain this chromosome number a process of meiosis (special form of cell division) has to take place when the sperm and the egg are formed. Effectively they each contain one half of the 23 pairs, so when they fuse together to make a baby we get 46 chromosomes, arranged in their 23 pairs The cartoon shown here is not an accurate depiction of what happens at the DNA level but gives a broad concept of inheriting DNA from both Mum and Dad.

This cartoon illustrates DNA as a set of instructions, which is written in a very precise code. Within this code there are specific recognisable sections of instructions that are genes. We often talk of genes coding for certain characteristics. This cartoon uses one of the characteristics that you can see which is a widow’s peak hairline. Other examples can include attached or detached ear lobes and cleft chin.

Inheritance of Characteristics: Distinctive Ears We can often see characteristics that are passed down in a family, this is in turn showing us that DNA, genes for that characteristic, are being passed down. So by looking at an observable characteristic that is inherited we are indirectly looking at DNA and genes that are being inherited. See next slide This illustration is showing us how a set of distinctive ears are inherited in a family. I always discuss this as my family, you may wish to discuss it as a family you know or change the slide to fit a characteristic in your family. Dad, his Dad (grandad) and Grandad (great grandad) all have the rather large distinctive ears, but only one son James has them while Charlie does not.

Family Tree This is a family tree. Squares are males, circles are females. Lines joining means they are married or partners and their children are represented by the lines coming down. Family trees are drawn so that geneticists can look at inheritance. In this family shown on the previous slide we saw that the paternal great grandad, the paternal grandad, dad and James had the distinctive ears. They clearly have the DNA instructions for this characteristic and we have coloured their “squares” in blue to show they have that gene. No other member of the family has these ears, so they do not have that gene and their symbols remain uncoloured in the diagram. It is now easy to see from the family tree how genes/characteristics are passed down, inherited.

Happy Families Simple inheritance game. It shows how children receive characteristics from their parents. Will they get their mum’s blue eyes or their dad’s brown eyes? Will they be tall like their dad? Have they got their mum’s nose? Can you tell who the parents are of a child from their features? Introduction to Happy Families Game. See Teachers’ notes

Features Zac (Dad) Zoe (Mum) Jenny (Child) Kevin Eyes Green Brown Hair Black & Curly Brown & Curly Nose Small Large Lips Full Height Tall Medium Brain Power 2 Not so Bright (Dim) 4 Very Bright 3 4+2=6 6 divided by 2 =3 This slide illustrates the simple rules of inheritance used in the game. This is the same as the Worked example in the game templates The first five characteristics are inherited on an equal chance basis, 50:50, so the child can get either the mum’s or the dad’s characteristic. The final one Brain Power has been used as a numerical value so that the child receives the average of the parents’ values. This is in no way meant to represent how intelligence is inherited. You will now need the templates and cards together with the instructions to play.

Hello Good Looking You could finish with the Happy Families Game, however if you wish you can continue and introduce the Hello Good Looking with DNA codes here. This nicely finishes using DNA as a code for inheriting characteristics.