Chapter 5

Heredity

Ch 5.1 - Genetics

A. Heredity – the passing of traits from parents to offspring

1. Genes on chromosomes control the traits that show up in an organism

2. The different forms of a trait a gene may have are alleles

The Human Genome(Project 1990-2003)

3. Each sex cell contains one allele for that trait

4. The study of how traits are inherited is genetics

B. Gregor Mendel – “Father of Genetcs”

1. Mendel was the first to use mathematics of probability to explain heredity and to trace one trait for several generations

2. Allele – the different variations of a trait that genes carry

a) Dominant allele – covers up or dominates the other trait

b) Recessive allele – the trait that doesn’t show up or seems to disappear

c) Hybrid – receives different genetic information for a trait from each parent

3. Probability – helps predict what an

offspring will inherit

4. Punnett square – tool to help predict what an offspring will inherit

a) Uppercase letters stand for dominant alleles

b) Lowercase letters stand for recessive alleles

5. Genotype – the genetic makeup of an organism (represented by the letters)

a) Homozygous – an organism with 2 alleles for one trait that are the same

(TT or tt)

b) Heterozygous – an organism with 2 alleles for one trait that are different

(Tt)

6. Phenotype – the way an organism looks or behaves as a result of its genotype

Example:

In peas, the color yellow is dominat (Y) to

the color green which is recessive (y)

Find the probabilities of what genes the

offspring of 2 heterozygous parent plants

would inherit

Genotype:

Phenotype:

Ch 5.2 – Genetics Since Mendel

A. Incomplete Dominance

1. Neither allele is dominant for a trait

2.The phenotype produced is intermediate between the 2 inherited traits

Ex: four o’clocks

red flowers x white flowers = pink

B. Multiple Alleles

1. More than 2 alleles control a trait

2. Can produce 3 or more phenotypes

Ex: Blood types

Alleles – A,B, and O

Phenotypes – Type A, Type B,

Type AB and Type O

C. Polygenic Inheritance

1. A group of genes act together to produce a trait which creates a great variety of phenotypes

2. Many human traits are controlled in this way

Ex: hair color, eye color, skin color, height

D. Mutations – genes that are copied incorrectly

1. Can be harmful, beneficial or have no effect

2. Chromosome disorders – caused by inheriting too many or too few chromosomes

Ex: Down(‘s) Syndrome – extra copy of chromosome 21

E. Recessive Genetic Disorders

1. If both parents have a recessive allele for a disorder they can pass it on to their child

2. Because the parents are heterozygous they show no symptoms themselves

Ex: Cystic Fibrosis

C c

C

c

CC Cc

Cc cc25% chance child could inherit this disease

C = no cystic fibrosis

c = has cystic fibrosis

F. Sex Determination

1. One pair of chromosomes (called X and Y chrom’s) are responsible for the sex of an organism

2. Female egg cells- carry X chromosomes

Male sperm cells- half have X & half have Y

3. If two X’s are inherited:

XX = female

If one X and one Y are inherited:

XY = male

X

X

X

Y

XX

XX

XY

XY50% chance

boy

50% chance girl

G. Sex-linked Disorders – disorders that can be inherited by genes on the X or Y chromosomes

Ex: color blindness

Ch 5.3 – Advances in Genetics

A. Genetic Engineering – changing the arrangement of DNA that makes up a gene

1. Recombinant DNA

a) inserts useful DNA segment into bacteria cell

b) Insulin for diabetic patients is produced in this way

2. Gene Therapy

a) Inserts normal DNA into a virus which can then infect human cells and reproduce more copies of it

b) Also done in plants by inserting genes with desired traits

B. Pedigree – a tool used to show patterns of genetic inheritance and follow traits through a family

Affected Male

Unaffected Male

Affected Female

Unaffected Female