InheritanceInheritance

Why are you unique?Why are you unique?

InheritanceInheritance

• What we are like What we are like depends on the depends on the genesgenes we inherit we inherit from our parentsfrom our parents

• The study of The study of inheriting inheriting characteristics is characteristics is called called geneticsgenetics

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How genes work

About genes Boys and girls

About cells

About variation

Start at the top Start at the top andand work round clockwise! work round clockwise!

What is Variation?What is Variation?

• Individuals Individuals within a within a speciesspecies have different have different characteristicscharacteristics

• VariationVariation ensures ensures survivalsurvival

Two types of variation Two types of variation 1. 1. discontinuousdiscontinuous

• A A characteristicharacteristic you either c you either have or you have or you don’t!don’t!

Tongue rolling ability

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100

1 2

number who cannot or can roll their tongue

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ople

Two types of variationTwo types of variation 2. Continuous 2. Continuous

• Produces a range Produces a range of differences for a of differences for a single single characteristic characteristic within a within a populationpopulation

• Variation in height Variation in height is an example of is an example of this…this…

Does variation always Does variation always happen?happen?• Sexual Sexual reproductionreproduction • Asexual Asexual

reproductionreproduction

• needs only one needs only one parentparent

• produces identical produces identical offspring called offspring called clonesclones

• needs two parents• produces offspring with a mixture of their characteristics

What can you remember so What can you remember so far?far?• Click the brain box Click the brain box

picture to check picture to check your knowledge your knowledge and understandingand understanding

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About cellsAbout cells

• Dividing and growing!Dividing and growing!

Cell divisionCell division

• Cells divide to make new cellsCells divide to make new cells

• Cells divide when we are Cells divide when we are growinggrowing

• Cells divide during Cells divide during repairrepair of the body of the body

• Cells divide to make Cells divide to make eggs eggs andand sperms sperms

Cell division by mitosisCell 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 meiosisCell division by meiosis

• Meiosis Meiosis produces produces sex sex cells cells oror gametes gametes

• Sex cells have Sex cells have half, the half, the haploid haploid number, of number, of chromosomeschromosomes

How many chromosomes?How many chromosomes?

• Humans have Humans have 23 pairs23 pairs of of chromosomes like thesechromosomes like these

• The The diploiddiploid number of number of chromosomes is chromosomes is

23x2 = 23x2 = 4646

• Sex cells (gametes) have Sex cells (gametes) have 23 single23 single chromosomes - chromosomes - the the haploidhaploid (half) (half) numbernumber

What’s the point?What’s the point?

• An egg cell has 23 chromosomesAn egg cell has 23 chromosomes

• A sperm cell has 23 chromosomesA sperm cell has 23 chromosomes

• When they join at When they join at fertilisationfertilisation there are 46 chromosomesthere are 46 chromosomes

• This makes a This makes a full set of full set of instructionsinstructions to make a to make a new human new human beingbeing!!

What can you remember so What can you remember so far?far?• Click the brain box picture Click the brain box picture

to check your knowledge to check your knowledge and understandingand understanding

• Click here to do a worksheetClick here to do a worksheet

• Click here to try another Click here to try another worksheetworksheet

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Boys or girls?Boys or girls?

• What will your baby be?What will your baby be?

What are little girls made What are little girls made of?of?

•XXXX

What are little boys made What are little boys made of?of?

•XYXY

Predicting the chances: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 We can work out the out the chances….chances….

Mums and Dads!Mums and Dads!

•Mums produce Mums produce only and only and chromosomeschromosomes

•Dads produce Dads produce or or chromosomeschromosomes

Now work it out!

……and the babies?and the babies?

•Half will be Half will be girlsgirls

•Half will be Half will be boys!boys!

•50% of each 50% of each sexsex

What can you remember?What can you remember?

• Try out the Try out the worksheet exercise…worksheet exercise…

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Why am I unique?Why am I unique?

• It’s down to your genes!It’s down to your genes!

It’s all down to your It’s all down to your parents!parents!

• At fertilisation two At fertilisation two gametesgametes join join

• A gamete has A gamete has halfhalf a a set of instructions – set of instructions – the the haploidhaploid number number

• A A zygotezygote is a is a fertilised egg cellfertilised egg cell

• It has has a It has has a fullfull set of set of instructions - the instructions - the diploiddiploid number number

What causes What causes variationvariation??

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?What is a gene?

• GenesGenes are short are short sections of sections of chromosomeschromosomes

• Genes are groups Genes are groups of of basesbases on on DNADNA moleculesmolecules

• All genes are made All genes are made of just of just 44 bases bases

Adenine

Thymine

Guanine

Cytosine

Pairs of bases!Pairs of bases!

•The fourThe four bases bases are are arranged in pairs on arranged in pairs on chromosomeschromosomes

•A A always pairs withalways pairs with T T

•C C always pairs withalways pairs with G G

A – T

G – C

T – A

C - G

Amazing spiralsAmazing spirals

•The The arrangement of arrangement of bases forms a bases forms a double helixdouble helix shape – like a shape – like a twisted ladder!twisted ladder!

•This is a This is a chromosomechromosome

So why do you look like So why do you look like that??that??

PhenotypePhenotype

• The The physical physical appearanceappearance of of individuals within a individuals within a species variesspecies varies

• The genes that are The genes that are inherited from inherited from parents control the parents control the phenotypephenotype of each of each individualindividual

GenotypeGenotype

• The different genes The different genes that each individual that each individual has is their has is their genotypegenotype

• Every body cell Every body cell carries carries pairspairs of of genesgenes on the paired on the paired chromosomeschromosomes

• Genes can be Genes can be dominantdominant or or recessiverecessive

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• Test yourself here Test yourself here

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So how do your genes work?So how do your genes work?

Gene competitions?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?How do the genes work?

BB?BB?

Bb?Bb?

bb?bb?

Homozygous - Homozygous - two genes the two genes the samesame

Heterozygous - Heterozygous - two different two different allelesalleles

HomozygousHomozygous

How do they work?How do they work?

• Dominant genes Dominant genes are ‘are ‘stronger’stronger’

• They are written as They are written as capital letters -‘capital letters -‘B’B’

• Recessive genes Recessive genes are ‘are ‘weaker’weaker’

• They are written as They are written as small letters – ‘small letters – ‘b’b’ This rabbit may have a

genotype of either Bb or BB

Genes in conflict?Genes in conflict?

•B + B =BBB + B =BB

•B + b = BbB + b = Bb

•b + b = bbb + b = bb

Phenotype - Black fur

Phenotype - Black fur

Phenotype - WhiteWhite fur

Genotype BB

Genotype - Bb

Genotype - bb

Now work it out…..Now work it out…..

parent

parent

gametes offspring

What are the off spring like?What are the off spring like?

• All the offspring have the same All the offspring have the same genotypegenotype

• They all have one dominant gene They all have one dominant gene

• They all have one recessive geneThey all have one recessive gene

• The dominant gene ‘wins’ so the The dominant gene ‘wins’ so the offspring all have black fur!offspring all have black fur!

What is their genotype?What is their genotype?

• Offspring have a mixture of their Offspring have a mixture of their parents’ genes:parents’ genes:

• They are They are heterozygousheterozygous

• They each have one allele for white They each have one allele for white fur and one allele for black furfur and one allele for black fur

What about the next What about the next generation?generation?

parents

gametes

offspring

3 : 1

What are their genotypes?What are their genotypes?

heterozygousheterozygous

homozygoushomozygous

homozygoushomozygous

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