Let’s think about it…
1. What are autosomes?
2. What are sex chromosomes?
3. What are the human autosomes and sex
chromosomes?
4. What are the chances of two parents
conceiving a boy? A girl?
Ch 12
Inheritance patterns
and Human Genetics
Human chromosome review
• 23 pairs
• 1-22 = autosomes
• 23rd pair = sex chromosome
• What are they two sex chromosomes?
• Female: XX
• Male: XY
• Y chromosome contains SRY gene
• SRY: Sex determining Region Y- gene coding
for production of male gonads (testes)
Sex-linked genes and traits
• Sex-linked traits: trait coded for by alleles
on a sex chromosome
• X chromosome much larger = many more
gene than Y
• Examples:
• SRY (Y-linked)
• Color blindness (X-linked)
• Hemophilia (x-linked)
Linked genes
• Linked genes: pairs of
genes that tend to be
inherited together
• Genes close to each other
on chromosome
• Example
• If crossing over occurs,
A & B are likely to be
inherited together
• A & E less likely
Mutations
• Change in nucleotide base sequence
• Germ cell mutation: in gametes
• does not affect organism
• can be passed down to offspring
• Somatic cell mutation: in body cells
• Can affect organism
• Lethal mutations: can cause death (usually
before birth)
Mutations
• Chromosomes can be:
• Deleted
• Flipped around (inverted)
• Moved to the wrong chromosome
• DNA bases (& sequences) can be:
• Deleted
• Inserted
• Substituted
• Etc.
Mutations
• Two main categories:
1. Chromosomal (affect chromosome)
• Nondisjunction: chromosomes fail to separate
during meiosis
• Down Syndrome
Gene (affect DNA sequence)
• Frameshift: affects one codon and as a
result, all codons downstream are changed
(shifts the reading frame
• ATC/GTA/GCT/GCT/ATT
• ATC/GTT/AGC/TGC/TAT/T
2.
Chromosomal
• Nondisjunction video
Gene
12-2 Human genetics
• Pedigree: diagram that shows how a trait is
inherited over several generations
Pedigrees used to:
1. See patterns of
inheritance
2. See if trait is
autosomal or
sex-linked
3. Dominant or
recessive
Genetic Disorders and Diseases
• http://www.youtube.com/watch?v=8s4he3wLgkM
Genetic traits and disorders
• Some traits have a single gene with two or more
alleles
• Blood type
• Cystic fibrosis
• Most human traits are polygenic: characters
influenced by several genes
• Skin color; 3-6 genes
Genetic traits and disorders
• Complex characters: influenced by environment
and genes
• Skin color exposed to sunlight
• Height
• Breast cancer
• Diabetes
• Heart disease
Multiple alleles
• Genes have more than three alleles
• ABO blood type
Incomplete dominance
• Heterozygote is an intermediate phenotype
X-linked traits
• More common in
males (x-linked
recessive)
• Males inherit X from
mom and no other
• No possibility of
heterozygous
• Colorblindness
• http://www.youtube
.com/watch?v=8Aai
vktz8G0
Single allele traits
• Single allele of a gene
controls these traits
• <200 human traits
• Huntington’s Disease
• Autosomal dominant
• Symptoms @30-40 y. o.
Detecting genetic disease
• Genetic screening: examination of a person’s genetic
information
• Need DNA from embryo
• Amniocentesis: removal of amniotic fluid surrounding
fetus
• 14th-15th week
• Chorionic villi sampling: sample of chorion villi (tissue
surrounding developing embry)
• 8th-10th week
Open text to page 246
• Copy table in your notes
• You only need the disorder, pattern of
inheritance, and brief description of symptoms