Genetics II

1. Genetics Continued

2. Human Karyotype: 23 pairs of
chromosomes.

3. Recap
• Genes are units of DNA located at particular
regions of a particular chromosome….usually
coding for a particular protein.
• In most cases we inherit one copy of a gene
from mom and one from dad.

4. 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

5. Eye Color: an Exercise
Genotype Phenotype
BB brown eyes
Bb brown eyes
bb blue eyes

6. Locus of Genes on Chromsomes

7. 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.

8. Down’s Syndrome Karotype
Trisomy 21

9. 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.

10. 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.

11. 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

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

13. 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.)

14. 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.

15. Hemophilia

16. 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