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

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.youtub

e.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

Let’s think about it…

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