Essential Question:

How are traits passed on from the parents to their offspring?

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Chromosomes• A eukaryote chromosome is made of DNA and

protein.• Chromosomes can be stained to show

banding.• The chromosome structure and banding can

be used to arrange the chromosomes in pairs.• This is called karyotyping.• One application of karyotyping is to identify

non-disjunction in a fetus – thus alerting the parents of any possible genetic problems.

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Karyotyping

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Important terms and concepts

• A diploid cell has two sets of homologous chromosomes and two alleles of each gene

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Important terms and concepts

• A gamete is haploid and has one of each of the homologous chromosomes and one allele of a specific gene

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Important terms and concepts

• A fertilised egg gets one chromosome from each parent, and becomes diploid again with two alleles of each gene

• The gamete from the other parent

will bring its ownset of chromosomesgenes andalleles

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Sex chromosomes In humans: Two sex chromosomes

the X chromosome and the Y chromosome

XY XX Y X

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Important terms and concepts

• Carriers: heterozygous individuals that carry a recessive gene to the next generation

• Multiple alleles: when there are more than two types of alleles for a given trait

• Codominance: when both phenotypes of an allele in an heterozygous individual are expressed or dominate as in blood types (ABO) – neither dominates over the other and can have a blending

phenotypic affect – meaning that both will express.– in multiple alleles many alleles can be codominant with respect

to each other

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ABO blood groups• The ABO blood groups are an example of

codominance and multiple alleles

• There are three alleles

I I iA B

I & I are dominate

i is recessive

Note that i = O blood type

A B

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ABO blood groups

The genes I and I code for two forms of red

blood cell surface antigens while the recessive

allele i codes for no antigen on the cell surface.

A B

AA

A A

B

B

B

B

A

A

B

B

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ABO blood groups• How many genotypes are possible?

• What are the possible phenotypes?

• Each Antigen provokes the production of an Antibody that recognises it.

• Anti- A and Anti-B.

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Important terms and concepts

• Linkage: all genes on one chromosome are linked, (those that are farthest apart separate and act as if they are unlinked)

• Sex linkage: genes that are located on the sex chromosomes are called sex linked

Traits associated with sex chromosomes follow a particular pattern of

inheritance

Ex: hemophilia, colour blindness, etc.

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Important terms and concepts

• Pedigrees– The study of family trees to look for a pattern of

inheritance

Male Female

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Linkage maps• Recombination

The formation of new gene combinations.

It is accomplished by re-assortment of chromosomes during meiosis and by crossing over.

Draw the picture of crossing over found on page 276.

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Linkage maps• Linkage groups

Genes are located on a chromosome that are inherited as a group.

• Un-linked or non-linked genesGenes are located on different chromosomes.

This can also apply to genes on the same chromosome if they are far apart.

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Polygenic inheritance• Polygenic inheritance is when a character

is controlled by more than one gene.– human skin colour• seems to be controlled by 3 or 4 genes

– human height

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Polygenic inheritance• Continuous variation:– individuals show a range of phenotypes with a

smooth graduation from one extreme to another and is denoted by a bell shape curve.