Let’s think about it… 1.What are autosomes? 2.What are sex chromosomes? 3.What are the human...

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

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.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