Transcript Chapter 14

Biology
Ch. 14
Human Heredity
I. Human Chromosomes
- heredity in humans is the same as in
other organisms
- most genetic diseases are recessive
and rare
A. Karyotype
- A chart showing a complete diploid set
of paired homologous chromosomes
1. Sex Chromosomes
- pair of chromosomes that determine
an individual’s sex
XX - female
XY – male
- other sex determination systems exist
2. Autosomes
- the other chromosome pairs except
the sex chromosomes
- Humans have _____ autosomes.
B. Inheritance of Human Traits
1.Dominant and Recessive Alleles
- Many human traits are controlled by
dominant and recessives alleles.
- Ex. MC1R gene helps determine skin
and hair color.
Red hair results from being
homozygous recessive for
the MC1R gene.
2. Codominance
- Both alleles are expressed in heterozygotes.
- Ex. Type AB blood express IA and IB alleles.
Type A
Type AB
Type B
Type O
3. Sex-linked Traits
- Traits controlled by genes located
on the X sex chromosome.
- Ex. Red-green colorblindness
What People with
Regular Vision See
What Red-Green
Colorblind People See
3. Sex-linked Traits
- Traits controlled by genes located
on the X sex chromosome.
- Ex. Red-green colorblindness
- Ex. Hemophilia
Queen Victoria’s Family
Pedigree of Europe’s Royal Families
4. X-Chromosome Inactivation
- In females, 1 X chromosome is inactivated
resulting in a mosaic of gene expression in
heterozygotes
- Ex. Calico cat
4. X-Chromosome Inactivation
- In females, 1 X chromosome is inactivated
resulting in a mosaic of gene expression in
heterozygotes
- Ex. Sweat gland mosaic
Fertilized Egg
Maternal X
Paternal X
Early Cell Division
X Chromosome Inactivation
Barr
Body
Mitosis
Skin lacking
sweat glands
Normal skin
C. Pedigrees
- A chart used to show inheritance patterns
Pedigree chart of
Queen Victoria’s
family showing
the inheritance
of hemophilia.
II. Human Genetic Disorders
- A mutation in DNA’s base sequence
changes a protein’s structure by
changing the sequence of amino acids.
A single
amino acid
substitution
in a protein
causes
sickle-cell
disease.
A. Genetic Disorders Caused
by Single Genes
1. Sickle-Cell Disease
- affects hemoglobin, the protein that
carries O2 in red blood cells
- causes blood blockages, pain, tissue
and organ damage
- most common in sub-Saharan Africa.
- 1 out of 10 African-Americans are carriers.
- Heterozygous advantage: carriers are resistant
to malaria.
Malaria
HbS Alelle
Frequency(%)
0-2.5
2.5-5.0
5.0-7.5
7.5-10
10-12.5
> 12.5
2. Cystic Fibrosis (CF)
- affects CFTR, a transport protein in the
cell membrane
- causes excessive production of thick
mucus in lungs and digestive system
3. Huntington’s Disease
- rare, dominant, nervous system disorder
- symptoms (uncontrollable movements,
mental deterioration) appear late in life
Woody Guthrie
Huntington’s Disease
B. Chromosomal Disorders
Nondisjunction:
- a failure of homologous chromosomes
to separate during meiosis
- results in gametes with missing or
extra chromosomes
B. Chromosomal Disorders
Nondisjunction:
Down Syndrome (Trisomy 21)
Incidence of Down Syndrome
Number per 1000 Births
400
300
200
100
0
10
20
30
40
Age of Mother (years)
50
Turner’s Syndrome (Monosomy X)
XYY Syndrome
Trisomy X (XXX)
Klinefelter’s Syndrome (XXY)
Down Syndrome (Trisomy 21)
Normal Female
Edward’s Syndrome (Trisomy 18)
III. Selective Breeding
- Humans have used selective breeding for
thousands of years to
produce new varieties
of crops and
domestic animals.
Maize was domesticated
from its wild grass ancestor
more than 8,700 years ago.
III. Selective Breeding
- Humans have used selective breeding for
thousands of years to
produce new varieties
of crops and
domestic animals.
The dog was
domesticated
from the grey
wolf over than
14,700 years ago.
A. Hybridization
Nondisjunction:
- a failure of homologous chromosomes
to separate during meiosis
- results in gametes with missing or
extra chromosomes
B. Inbreeding
Nondisjunction:
- a failure of homologous chromosomes
to separate during meiosis
- results in gametes with missing or
extra chromosomes
C. Polyploidy
Nondisjunction:
- a failure of homologous chromosomes
to separate during meiosis
- results in gametes with missing or
extra chromosomes
The
End
Human Chromosomes
(23 homologous pairs)
Epistasis: Black, Chocolate, and
Golden Labrador Retrievers