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

2 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.

3 Karyotyping

4 Important terms and concepts A diploid cell has two sets of homologous chromosomes and two alleles of each gene

5 Important terms and concepts A gamete is haploid and has one of each of the homologous chromosomes and one allele of a specific gene

6 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 own set of chromosomes genes and alleles

7 Sex chromosomes In humans: Two sex chromosomes the X chromosome and the Y chromosome XY XX Y X

8 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

9 ABO blood groups The ABO blood groups are an example of codominance and multiple alleles There are three alleles I I i AB I & I are dominate i is recessive Note that i = O blood type AB

10 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 A A A A B B B B A A B B

11 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.

12 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.

13 Important terms and concepts Pedigrees – The study of family trees to look for a pattern of inheritance MaleFemale

14 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.

15 Linkage maps Linkage groups Genes are located on a chromosome that are inherited as a group. Un-linked or non-linked genes Genes are located on different chromosomes. This can also apply to genes on the same chromosome if they are far apart.

16 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

17 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.