Post on 30-Dec-2015
transcript
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
2. 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
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.youtu
be.com/watch?v=8Aaivktz8G0
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