GENES
genome- complete set of genes
genes- short stretches of DNA that code for a characteristic, located on chromosomes
q- long part
p- short part
Humans have 46 chromosomes
23 from each parent
You get a copy from each parent
Alleles- different forms of genes that are different by only a few bases, only two can be at
each locus (one from mom and one from dad)
Homozygous- if the alleles are the same
Heterozygous- if alleles are different
They both are located in the same locus
Mutations
When the daughter cell is different from the parent cell as a result of an error
Incorrect base can be used because of the speed and amount of process
Exposure to radiation or chemicals (mutagens)
If mutagens cause tumors, they are called carcinogens
Human Genome Project- determining sequence of human genome and identifying genes in
it.
Sickle cell anemia
Caused by a base change in the gene for beta globin chain of haemoglobin
Occurs in 6th codon GAG : GLUTAMIC ACID
mutation changes codon to GTG: VALINE
Base change alters tertiary structure of haemoglobin and causes hemoglobin molecules to
stick to low oxygen concentration. The molecules can’t carry oxygen adequately, making
hemoglobin molecules deformed
One HbS is good for resistance to malaria
But two HbS causes anemia
Eukaryotes have 2 copies
Prokaryotes only have 1
Prokaryotic chromosome is linear and contains only the DNA that it needs to carry out the
basic functions
They also have plasmids- circular DNA that contains antibiotic properties
Eukaryotic chromosomes, histones are basic (alkaline) proteins. during interphase histones
give a bead like appearance
Each chromosome pair (from each parent) is called homologous pair
XX- female
XY - male
One is called the sex chromosomes- gametes
22 others are called autosomes
1 is largest- 22 is smallest
carry less genes- carry more genes
Eukaryotic chromosomes are linear DNA molecules associated with histone proteins
There are different chromosomes that carry different genes
Homologous carry the same sequence but not necessarily the same alleles
It is important to note that the genome size may sometimes be misleading. An organism with
a huge genome does not necessarily have a very high number of genes. The main reason is
that the genome size includes both the protein-coding genes and non-coding DNA of the
organism.
Diploidy Haploidy
Haploid nuclei- sex cells
ova and sperm cells can only have one set of chromosomes, 23
when sex cells fuse to form a zygote, an embryo develops with 46 chromosomes in each
pair
Zygote contains two pairs- diploid
mitotic division will give rise to diploid daughter cells
●
●
●
●
●
●
IA IA
IB IB
ii
IA IB
IA i
IBi