WHAT WE KNOW:

1.) For every trait, an organism has at least

2 genes that code for it

2.) Each parent contributes 1 gene/trait to

their offspring

3.) Some genes are dominant and some

genes are recessive

WE CAN PREDICT HOW TRAITS CAN BE PASSED ON FROM PARENTS TO OFFSPRING WITH A PUNNETT SQUARE

Rules:

1.) Dominant genes are represented by a capital letter.

2.) Recessive genes are represented by a lower case letter.

3.) Punnett Squares predict the probability that something

will happen, not what actually WILL happen!

DadMom

H h

Entry #

Entry # continued

I. Multiple Alleles and Human GeneticsA. Incomplete Dominance

1. Mendel’s ideas about Dominant and Recessive genes does not always hold true.

2. Some gene pairs in living things show incomplete dominance – where neither gene can hide the other. Instead, they create a blending of genes.

ex. In Four O’clock Flowers,

Purebred Red flowers X

Purebred White flowers=

Pink flowers (neither gene is dominant)

ex. We also can see this in the inheritance of human hair type

Curly CCWavy CcStraight cc

B. Multiple Alleles (Co-Dominance)1. In human beings, some traits are determined by a blending of more that one set of homologs, which means that more than two alleles can code for a trait

ex. Skin color - four pairs of genes blend (8 alleles)

Hair color - four pairs of genes blend (8 alleles)

Eye color - three/four pairs of genes blend (6-8 alleles)

2. The four major human blood groups are also determined by

multiple alleles. These groups are called A, B, AB, and O.a. Both the allele for group A blood and that for

group B blood are dominant. If an A allele and a B

allele are inherited, the child will have AB blood. The

O allele is recessive.

C. Inherited Diseases1. Sometimes the structure of an inherited gene contains an error. If the gene controls the production of an important protein inside the cell, the cell and therefore the organism will not be able to function properly.2. Many inherited diseases can be treated, but not cured. Much of today’s research involves “fixing” the gene while the organism is in utero.ex. Sickle-cell anemia, juvenile diabetes, Alzheimer's

Disease,

D. Sex-Linked traits

1. The X and Y chromosomes (homologs 23) are the sex

chromosomes. Females carry XX and males carry XY

2. The X chromosome carries genes for traits other that just

gender. But the Y chromosome carries few, if any other traits

than those for maleness.

3. Therefore, any gene, even a recessive gene, carried on the X

chromosome will produce a trait in a male who inherits the

gene. This is because there is no matching gene on the Y

chromosome to mask it.

4. These traits are called sex-linked because they are passed

from parent to offspring on the sex chromosomes, and there

are more males who present with these traits than females.

Human Genetics Practice

Blood Groups

Genotypes for Blood Groups

A AA or AO

B BB or BO

AB AB

O OO

1.) Cross a hybrid Blood Group A with a Group O. Use a Punnett Square.

2.) In a hospital, Mrs. Light and Mrs. Bright shared a room when they were both having a baby. When they and their babies were allowed to go home, Mrs. Bright thought that she was given the wrong baby. The hospital told her that she was crazy. Blood tests on all involved showed the following data:

Mrs. Light: A Mr. Light: A Baby at their house: A Mrs. Bright: AB Mr. Bright: O Baby at their house: O