Genetics Continued

Human Karyotype: 23 pairs of chromosomes.

Recap

• Genes are units of DNA located at particular regions of a particular chromosome….usually coding for a particular protein.

• In most cases we have two copies of each genes, one from our mother and one from our father. So when considering heredity, you have to look at what one has inherited from each parent.

Gene-Interaction

• Some alleles are dominant or recessive in relationship to other alleles. When you have one copy of a dominant allele, it may cover up the expression of a recessive allele.

• Remember: genotype = the genes you have phenotype = particular trait

• Some alleles dominant are recessive in relationship to other alleles. When you have one copy of a dominant allele, it may cover up the expression of a recessive allele.

• Remember: genotype = the genes you have

phenotype = particular trait

Eye Color: an Exercise

Genotype PhenotypeBB brown eyesBb brown eyesbb blue eyes

Locus of Genes on Chromsomes

Mutations

• Mutations are random changes in genetic material: they are what allow for variation in genes such as alleles.

• Mutations can also result in the duplication or deletion of large portions of a chromosome.

Down’s Syndrome KarotypeTrisomy 21

Sex-Linked Traits

• Females have matched sex chromosomes (XX) and males have UN-matched sex chromosomes (XY).

• This means that males only have one copy of a particular set of genes. Where females have two copies of these same genes.

Sex-Linked Traits

• Genes that are located on the X-Chromosome are inherited differently in males and females.

• For example, if a gene is recessive, a male would only need one copy of that gene to express (show) that trait. Where a female would need TWO copies of the same recessive gene.

Hemophilia Genetics

• There is a particular gene responsible for the clotting mechanism in blood. The gene is located on the X-Chromosome and has two alleles:

• N = Normal blood• h = Blood lacking the clothing Mechanism

Genotype/Phenotype

Genotype Phenotype NN Normal Blood N h Normal Blood (carrier) hh Hemophiliac

Hemophilia

• If a mother was a carrier (Nh) and Dad has Normal Blood (N), daughters would have one of two to genotypes.

• They would either inherit an N from both Mom and Dad (NN: normal blood) or an N or h from mom and a N from Dad (Nh: Normal blood but a carrier.)

Hemophilia

Mom: (Nh) Dad: (N)

• Sons are going to inherit only one copy of this gene beause they inherit the Y –Chromomoe from their father.

• This means that sons are either going to be N, with normal blood or h and be hemophiliacs.

Hemophilia

Sickle Cell

• There is a gene on an autosome (non-sex chromosome) responsible for blood cell shape. It has two alleles: N for normal and S for sickle shaped. N and S are co-dominant: They display incomplete domination.

• NN = Normal Blood• SS = Sickle Cell Anemia• NS = Sickle Cell Trait