Transcript Human Genetics - Biology Department

BSC 2010L

Humans
Haploid # of
chromosomes:
23
 Diploid #: 46

 Remember:
 Have 23 pairs
 1 of each
pair came
from mom
 1 of each
pair came
from dad

Each pair of chromosomes is referred to as
HOMOLOGOUS CHROMOSOMES

Have the same genes
 For each gene there can be 2 alleles (different
forms)
 Look at picture below:
 B = brown eyes
 b = blue eyes
 Brown is dominant so this person’s phenotype would be
brown eyes

Incomplete Dominance

Form of inheritance where heterozygous alleles
are both expressed, combined phenotype
 Example: a plant with white flowers and plant with
red flowers has offspring with pink flowers

Codominant

Both alleles are expressed
 Example: Blood types in humans
 If a person has the A allele and the B allele, then both
A and B are expressed on the surface of the red
blood cell

Some Dominant Traits in Humans



Widow’s peak
Unattached earlobes
Freckles

Down Syndrome (Trisomy 21)


3 #21 chromosomes
Sex Chromosomal Abnormalities
 Turner Syndrome – XO
 Never reaches puberty
 Poly-X Syndrome (XXX)
 Tend to have learning disabilities
 Klinefelter Syndrome (XXY)
 Testes underdeveloped, long limbs, poor muscle
growth
 Jacob Syndrome (XYY)
 Taller, speech and reading problems

Genes located on the sex
chromosomes (23rd pair in
humans)

Examples:
 Color-blindness
 Hemophilia

Males only need 1 gene on X
chromosome to have trait –
look at boy on far right

Method that allows tracking of a genetic
disorder within a family
Circles – Females
 Squares – Males
 Affected individuals – filled in
 Carriers – half filled in

http://www.sciencegeek.net/Biology/review/Sem1Review.htm

Patterns of inheritance

Autosomal Dominant – many children affected
Autosomal Recessive – few children affected
 X-linked recessive – mostly males affected


Patterns of inheritance
 Autosomal Dominant – many children affected
 Autosomal Recessive – few children affected
 X-linked recessive – mostly males affected

Patterns of inheritance
 Autosomal Dominant – many children affected
 Autosomal Recessive – few children affected
 X-linked recessive – mostly males affected