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Chapter 4 Section 1Human Inheritance
Friday, January 28, 2011
Traits Controlled by A Single Pair of Alleles
Many Human traits are controlled by single genes with one dominant and one recessive alleles.
Either you have the trait or you don’t.
Examples are Widows Peak and Dimples
Friday, January 28, 2011
Multiple Alleles
Human traits can be controlled with a single gene that has more than two alleles.
An example of multiple alleles controlling a trait is blood type.
Punnett squares can predict the possible outcomes for the blood type of the offspring.
What would be the phenotype of the offspring if you crossed a an A blood type with an AB blood type?
Friday, January 28, 2011
Traits Controlled by Many Genes.
Some human traits that show a large number of phenotypes are controlled by many genes that act as a group to produce a single trait.
Examples are height and skin color.
Friday, January 28, 2011
Effects of the Environment
The effects of genes can be altered by environmental surroundings.
Examples: poor diet, medical care and living conditions.
Friday, January 28, 2011
Sperm and Egg. The sex of the offspring is determined by the males.
Females eggs are always an “X” Chromosome.
Men produce both “X” and “Y” sperm.
If an “X” sperm fertilizes an “X” egg an female is produced. (Female : XX)
If a “Y” sperm fertilizes an “X” egg an male is produced. (male : XY)
Friday, January 28, 2011
Sex Linked Genes Some human traits occur more in one
sex than the other and are usually carried on the sex chromosomes “X” and “Y”.
Traits controlled by sex-linked genes are called sex-linked traits.
Because males have only one “X” chromosome they are more likely to have sex-linked traits.
Females have a second “X” chromosome which can hide or mask the trait. Males do not have a matching chromosome.
An example is red-green colorblindness.
Friday, January 28, 2011
PedigreesA tool that geneticists use to trace inheritance is
called a pedigree.
A pedigree or “family tree” tracks family members and how traits are passed on from generation to generation.
Circles represent Females. Squares represent males.
A horizontal line that connect males and females shows marriage.
A vertical line and bracket connects parents to their children.
Half shaded shows a carrier for a trait. Fully shaded indicates the person has the trait.
A non-shaded circle or square means the person is neither a carrier nor has the trait.
Friday, January 28, 2011
Friday, January 28, 2011
