Human Genome
Biology Ch 14
Chromosomes
Carries genetic information
from parents to offspring
Karyotype – picture of all
chromosomes grouped in pairs
Autosomes – chromosomes paired
together by size, shape, content (22
pairs)
Sex Chromosomes – one pair of
chromosomes that determine gender
(one pair)
Sex Chromosomes
XX = Female
XY = Male
Pedigree
Can use genetic information to develop a pedigree – a chart
that shows traits as passed from generation to generation
P = Parent generation
F1 = First offspring
generation
F2 = next generation
offspring
Pedigree Problem
Imagine that you are a genetic counselor. The pedigree shown on
the next slide illustrates the inheritance of albinism in three
generations of a family. A couple from the family have come to
you to ask for advice about how the trait is inherited.
*Your task is to determine whether the allele for albinism is
dominant or recessive.*
Pedigree Problem
Answer on a separate piece of paper:
1.
2.
3.
By remembering the previous
slide, restate the problem that
must be solved.
Copy this pedigree on to the
paper. Label each person on
the pedigree with his or her
phenotype: normal (N) or
albino (A).
Write down HOW you would
analyze the pattern of
inheritance of the albinism
trait and describe how you
will use your analysis to infer
the genotype of as many
individuals as possible.
Trait Control
Most human traits are NOT controlled by a single gene
Other controls:
• Multiple genes – polygenic
• Environmental
influence
Single gene
trait
Multiple Controls
Blood type = CoDominance & Multiple Alleles
Alleles =
IA, IB, I
IA and IB are Co-dominant
AND are BOTH dominant
over the recessive i
Genotype(s) IAIA , IA i
IBIB, IBi
I AI B
ii
Polygenic trait distribution
Single gene trait distribution graph:
Autosomal Chromosome disorders
Mutations found ONLY on the autosomes (chromosomes 1 through 22)
Can be single gene mutation or polygenic mutation)
Autosomal Dominant Genetic Disorders:
These disorders are caused when an individual has inherited the defective
allele from a single parent. Ex: Aa or AA (Dwarfism, Huntington disease)
Autosomal Recessive Genetic Disorders:
Such disorders manifest only when an individual has got two defective alleles
of the same gene, one from each parent. Ex: aa (Albinism, Cvstic fibrosis)
Co-dominant alleles:
Disorder manifested when two dominant alleles are inherited. Ex: AB (Sickle
cell disease)
Multi-factorial Genetic Disorders:
Such disorders are the result of genetic as well as environmental factors.
(Alzheimer’s disease?, dementia?)
Sex linked genes
 Genes found X or Y chromosomes
 X chromosome has approx 1000
genes – Many life functions
 Y chromosome have approx 150
genes – SRY region determines male
characteristics
Sex-linked traits:
• Colorblindness
•Hemophilia
•Duchenne Muscular Dystrophy
Autosome Chromosome Disorders
Non-disjunction – results in abnormal number of
chromosomes in gametes (Down Syndrome)
Sex Chromosome Disorders