Inheritance Why are you unique?

Inheritance What we are like depends on the genes we inherit from our parents What we are like depends on the genes we inherit from our parents The study of inheriting characteristics is called genetics The study of inheriting characteristics is called genetics

Menu page choose the section you want to work on from this page Start at the top and work round clockwise! About variation About cells Boys and girls About genes How genes work

What is Variation? Individuals within a species have different characteristics Individuals within a species have different characteristics Variation ensures survival Variation ensures survival

Two types of variation 1. discontinuous A characteristic you either have or you don’t! A characteristic you either have or you don’t!

Two types of variation 2. Continuous Produces a range of differences for a single characteristic within a population Produces a range of differences for a single characteristic within a population Variation in height is an example of this… Variation in height is an example of this…

Does variation always happen? Sexual reproduction Sexual reproduction Asexual reproduction Asexual reproduction needs only one parent needs only one parent produces identical offspring called clones produces identical offspring called clones needs two parents produces offspring with a mixture of their characteristics

What can you remember so far? Click the brain box picture to check your knowledge and understanding Click the brain box picture to check your knowledge and understanding Or go back to the start again if you need to look at the information again …… Or go back to the start again if you need to look at the information again ……

About cells Dividing and growing! Dividing and growing!

Cell division Cells divide to make new cells Cells divide to make new cells Cells divide when we are growing Cells divide when we are growing Cells divide during repair of the body Cells divide during repair of the body Cells divide to make eggs and sperms Cells divide to make eggs and sperms

Cell division by mitosis Mitosis is cell division of body cells Mitosis produces 4 exact copies of the parent cell The new daughter cells have the diploid number of chromosomes

Cell division by meiosis Meiosis produces sex cells or gametes Meiosis produces sex cells or gametes Sex cells have half, the haploid number, of chromosomes Sex cells have half, the haploid number, of chromosomes

How many chromosomes? Humans have 23 pairs of chromosomes like these Humans have 23 pairs of chromosomes like these The diploid number of chromosomes is The diploid number of chromosomes is 23x2 = 46 23x2 = 46 Sex cells (gametes) have 23 single chromosomes - the haploid (half) number Sex cells (gametes) have 23 single chromosomes - the haploid (half) number

What’s the point? An egg cell has 23 chromosomes An egg cell has 23 chromosomes A sperm cell has 23 chromosomes A sperm cell has 23 chromosomes When they join at fertilisation there are 46 chromosomes When they join at fertilisation there are 46 chromosomes This makes a full set of instructions to make a new human being! This makes a full set of instructions to make a new human being!

What can you remember so far? Click the brain box picture to check your knowledge and understanding Click the brain box picture to check your knowledge and understanding Click here to do a worksheet Click here to do a worksheet Click here to try another worksheet Click here to try another worksheet Or go back to the start again if you need to look at this information again …… Or go back to the start again if you need to look at this information again …… Or back to the main menu Or back to the main menumain menumain menu

Boys or girls? What will your baby be? What will your baby be?

What are little girls made of? XX XX

What are little boys made of? XY XY

Predicting the chances: Will it be a boy? Will it be a boy? Will it be a girl? Will it be a girl? We can work out the chances…. We can work out the chances….

Mums and Dads! Mums produce only and chromosomes Mums produce only and chromosomes Dads produce or chromosomes Dads produce or chromosomes Now work it out!

…and the babies? Half will be girls Half will be girls Half will be boys! Half will be boys! 50% of each sex 50% of each sex

What can you remember? Try out the worksheet exercise… Try out the worksheet exercise… Or go back to review what you have learnt Or go back to review what you have learntgo back go back Or return to the main menu Or return to the main menumain menumain menu

Why am I unique? It’s down to your genes! It’s down to your genes!

It’s all down to your parents! At fertilisation two gametes join At fertilisation two gametes join A gamete has half a set of instructions – the haploid number A gamete has half a set of instructions – the haploid number A zygote is a fertilised egg cell A zygote is a fertilised egg cell It has has a full set of instructions - the diploid number It has has a full set of instructions - the diploid number

What causes variation ? All living cells contain a complex protein called DNA Long strands of DNA forms chromosomes inside cells Chromosomes are long strings of genes

What is a gene? Genes are short sections of chromosomes Genes are short sections of chromosomes Genes are groups of bases on DNA molecules Genes are groups of bases on DNA molecules All genes are made of just 4 bases All genes are made of just 4 bases Adenine Thymine Guanine Cytosine

Pairs of bases! The four bases are arranged in pairs on chromosomes The four bases are arranged in pairs on chromosomes A always pairs with T A always pairs with T C always pairs with G C always pairs with G A – T G – C T – A C - G

Amazing spirals The arrangement of bases forms a double helix shape – like a twisted ladder! The arrangement of bases forms a double helix shape – like a twisted ladder! This is a chromosome This is a chromosome

So why do you look like that??

Phenotype The physical appearance of individuals within a species varies The physical appearance of individuals within a species varies The genes that are inherited from parents control the phenotype of each individual The genes that are inherited from parents control the phenotype of each individual

Genotype The different genes that each individual has is their genotype The different genes that each individual has is their genotype Every body cell carries pairs of genes on the paired chromosomes Every body cell carries pairs of genes on the paired chromosomes Genes can be dominant or recessive Genes can be dominant or recessive

What have you learnt from this section? Test yourself here Test yourself here Or go back and look at this section again Or go back and look at this section againgo back go back Or select a new topic from the menu Or select a new topic from the menumenu

So how do your genes work?

Gene competitions? This rabbit’s genotype is BB – the black fur gene is dominant This rabbit’s genotype is bb – the white fur gene is recessive

How do the genes work? BB?Bb?bb? Homozygous - two genes the same Heterozygous - two different alleles Homozygous

How do they work? Dominant genes are ‘stronger’ Dominant genes are ‘stronger’ They are written as capital letters -‘B’ They are written as capital letters -‘B’ Recessive genes are ‘weaker’ Recessive genes are ‘weaker’ They are written as small letters – ‘b’ They are written as small letters – ‘b’ This rabbit may have a genotype of either Bb or BB

Genes in conflict? B + B =BB B + B =BB B + b = Bb B + b = Bb b + b = bb b + b = bb Phenotype - Black fur White Phenotype - White fur Genotype BB Genotype - Bb Genotype - bb

Now work it out….. parent gametes offspring

What are the off spring like? All the offspring have the same genotype All the offspring have the same genotype They all have one dominant gene They all have one dominant gene They all have one recessive gene They all have one recessive gene The dominant gene ‘wins’ so the offspring all have black fur! The dominant gene ‘wins’ so the offspring all have black fur!

What is their genotype? Offspring have a mixture of their parents’ genes: Offspring have a mixture of their parents’ genes: They are heterozygous They are heterozygous They each have one allele for white fur and one allele for black fur They each have one allele for white fur and one allele for black fur

What about the next generation? parents gametes offspring 3 : 1

What are their genotypes? heterozygous homozygous homozygous

Got it? Test your self here Or go back and have another look at the facts first!go back Or back to the main menu.main menu. Teachers can use the extra resource Punnet Squares on an IWBPunnet Squares but you may need to download Smartbook software [free of charge] to use the file –Smartbook software