Inheritance

1
Inheritance

• Why are you unique?

2
Inheritance

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

3
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4
What is Variation?

• Individuals within a species have different
  characteristics
• Variation ensures survival

5
Two types of variation 1. discontinuous

• A characteristic you either have or you dont!

6
Two types of variation 2. Continuous

• Produces a range of differences for a single
  characteristic within a population
• Variation in height is an example of this

7
Does variation always happen?

• Sexual reproduction

• Asexual reproduction
• needs only one parent
• produces identical offspring called clones

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

8
What can you remember so far?

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• Or go back to the start again if you need to look
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9
About cells

• Dividing and growing!

10
Cell division

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

11
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

12
Cell division by meiosis

• Meiosis produces sex cells or gametes
• Sex cells have half, the haploid number, of
  chromosomes

13
How many chromosomes?

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

14
Whats the point?

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

15
What can you remember so far?

• Click the brain box picture to check your
  knowledge and understanding
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• Or back to the main menu

16
Boys or girls?

• What will your baby be?

17
What are little girls made of?

• XX

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What are little boys made of?

• XY

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Predicting the chances

• Will it be a boy?
• Will it be a girl?
• We can work out the chances.

20
Mums and Dads!
Now work it out!

• Mums produce only and chromosomes
• Dads produce or chromosomes

x
x
x
x
x
x
x
x
x
x
Y
Y
Y
x
x
Y
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and the babies?

• Half will be girls
• Half will be boys!
• 50 of each sex

22
What can you remember?

• Try out the worksheet exercise
• Or go back to review what you have learnt
• Or return to the main menu

23
Why am I unique?

• Its down to your genes!

24
Its all down to your parents!

• At fertilisation two gametes join
• A gamete has half a set of instructions the
  haploid number
• A zygote is a fertilised egg cell
• It has has a full set of instructions - the
  diploid number

25
What causes variation?
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What is a gene?
Adenine Thymine Guanine Cytosine

• Genes are short sections of chromosomes
• Genes are groups of bases on DNA molecules
• All genes are made of just 4 bases

27
Pairs of bases!

• The four bases are arranged in pairs on
  chromosomes
• A always pairs with T
• C always pairs with G

A T G C T A C - G
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Amazing spirals

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

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So why do you look like that??
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Phenotype

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

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Genotype

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

32
What have you learnt from this section?

• Test yourself here
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33
So how do your genes work?
34
Gene competitions?

• This rabbits genotype is BB the black fur gene
  is dominant

This rabbits genotype is bb the white fur gene
is recessive
35
How do the genes work?
Homozygous - two genes the same Heterozygous -
two different alleles Homozygous
BB? Bb? bb?
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How do they work?

• Dominant genes are stronger
• They are written as capital letters -B
• Recessive genes are weaker
• They are written as small letters b

This rabbit may have a genotype of either Bb or BB
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Genes in conflict?

• B B BB
• B b Bb
• b b bb

Phenotype - Black fur
Genotype BB
Phenotype - Black fur
Genotype - Bb
Phenotype - White fur
Genotype - bb
38
Now work it out..
B
B
B
B
B
B
parent
B
b
b
B
b
b
b
parent
b
b
B
b
B
b
b
gametes
offspring
39
What are the off spring like?

• All the offspring have the same genotype
• They all have one dominant gene
• They all have one recessive gene
• The dominant gene wins so the offspring all
  have black fur!

B
b
B
b
40
What is their genotype?

• Offspring have a mixture of their parents genes
• They are heterozygous
• They each have one allele for white fur and one
  allele for black fur

B
b
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What about the next generation?
B
B
b
b
b
B
B
B
B
B
b
B
B
b
B
b
b
b
b
b
parents
gametes
3 1
offspring
42
What are their genotypes?
heterozygous
B
b
B
B
homozygous
b
b
homozygous
43
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