Unit 2b human diversity change
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Unit 2B Human Diversity & Change. Inheritance Pedigrees. Symbols used in simple pedigrees. Male. Female. Mating. Unaffected individuals. Affected individuals. Offspring. Twins. I. 2. 1. Identical. Non-identical. II. Deceased individuals. 1. 3. 2.

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Unit 2b human diversity change

Unit 2BHuman Diversity & Change

Inheritance

Pedigrees


Symbols used in simple pedigrees
Symbols used in simple pedigrees

Male

Female

Mating

Unaffected individuals

Affected individuals

Offspring

Twins

I

2

1

Identical

Non-identical

II

Deceased individuals

1

3

2

A pedigree is a diagram recording the ancestry of an individual


Autosomal pedigrees dominant or recessive
Autosomal pedigreesdominant or recessive?

Aa

Aa

If two parents of similar appearance have an offspring who is different, the parents must have the dominant trait.The non-look-alike offspring is recessive.

aa

Aa

Aa

aa


Only a recessive trait can skip a generation
Only a recessive trait can skip a generation

aa

Aa

Aa

Aa

aa

If neither of these events occurs in a pedigree then either trait could be dominant.


Aa

Aa

Aa

Aa

?

aa

?

?

Aa or AA?

It is sometimes impossible to tell whether a dominant phenotype is homozygous or heterozygous.


Sex linked pedigrees dominant or recessive
Sex linked pedigreesdominant or recessive?

XAXa

XAy

Notice that this is not the case with a female offspring.

Males:Xay

XAXa

XAy

If two parents of similar appearance have a male offspring who is different, the parents must have the dominant trait.The non-look-alike male offspring is recessive.

Females:XAXA or XAXa

Males:Xay or XAy


Is it sex linked or autosomal
Is it sex linked or autosomal?

XAXa

Xay

XAy

XAXa

Xay

If only males inherit the trait it may be X-linked recessive.N.B. X-linked dominant pedigrees look very much like autosomal pedigrees.


Things that cannot happen in an x linked pedigree
Things that cannot happen in an X-linked pedigree

A man with a dominant trait cannot have a daughter with the recessive trait.

All his daughters will inherit his dominant gene.

XAy

XAX?

XAX?

XaXa

A woman with a recessive trait cannot have a son with the dominant trait.

All her sons will inherit her recessive gene.

Xay

Xay

XAXA or XAXa

XAy

Two parents with the same trait cannot have a daughter with a different trait.

XAXA or XAXa


Working out an x linked pedigree
Working out an X-linked pedigree

XX

Xy

XX

Xy

XX

Xy

Xy

XX

1. Apply the X and Y chromosomes


Working out an x linked pedigree1
Working out an X-linked pedigree

XX

XAy

XX

XAy

XX

XAy

Xay

XX

2. Complete the male genotypesMales have only one gene so their phenotype is the same as their genotype


Working out an x linked pedigree2
Working out an X-linked pedigree

XAX

XAy

XAX

XAX

XAy

XAy

Xay

XAX

3. Every female displays the dominant trait and must carry at least one dominant gene


Working out an x linked pedigree3
Working out an X-linked pedigree

XAXa

XAy

XAXa

XAX?

XAy

XAy

Xay

XAX?

4. Deduce the genotypes of the femalesRemember, in some cases it will not be possible


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