Chapter 5 Notes
5-1 What Is Genetics?
Vocabulary:
Heredity: Passing of traits from parent to offspring.
Allele: The different forms of a trait that a gene may have.
Genetics: The study of how traits are inherited.
Dominant: Factor (trait) that dominates or covers up another factor (trait). Ex. B =
brown hair
Recessive: Factor (trait) that disappears if a dominant trait is present. Ex. b = blond hair
Punnett Square: A tool used to predict the number of times certain traits will occur.
Genotype: Genetic make up of an organism. Ex. BB, bb, Bb
Homozygous: An organism that has two alleles that are the same for a trait. (BB, bb)
B=hair color B = Brown…b = blond
Heterozygous: An organism that has two different alleles for a trait. (Bb)
Phenotype: The way an organism looks and behaves as a result of its genotype
5-1 cont……
How traits are inherited






Genes are made of DNA
Genes control all traits of an organism (trait is physical feature you see on an
individual ex. Freckles)
Genes are found on chromosomes
When cells split during meiosis, chromosomes separate = genes separate = sex
cell
Genes for eye color , hair color etc are found in genes found on chromosomes in
each sex cell.
Different sperm in a man will have different genes for the same trait.(ex. one
sperm will code for a straight hairline, while another codes for a widows peak.)
Alleles are specific genes for a specific trait found on a DNA strand.
 Genetics
Def…Alleles: are specific genes for a specific trait found on a DNA strand.
Def…Genetics: is the study of how these traits above are inherited
The Father of Genetics:


Gregor Mendel was the first known scientist to have record of studying genetics.
Mendel studied garden peas in 1856.
Why was Mendel called the Father of Genetics?
Answer…
Mendel’s Garden:
Def…Purebred: an organism that produces the same traits in its offspring. TT =
purbred for tall, tt = purebred for short.
Dominant and Recessive Factors:

Mendel discovered that one allele can dominate another allele causing the
dominate allele to mask the recessive allele.
Dominant Factor: masks recessive allele/trait… ex. T (tall) dominates t (short) in
pea plants. T = dominate allele for height
Recessive Factor: is masked by dominate allele or trait. t = recessive allele (is
masked by T allele)
Probability: (coin activity) See pages 126-127


Can be used to predict the outcome of an event.
Mendel realized that he could predict the probability of getting a tall plant when
one parent pea plant was short and one was tall.

Probability is measured through the use of ratios (ex… 3:1 = of 4 plants 3 will be
tall and 1 will be short.)
Using math to calculate probability. (pg 127)
Ans…
What is the probability of getting heads - vs- tails when flipping a coin?
Ans…
Using a Punnett Square:


A punnett square is used to predict the probability of having a certain
characteristic in offspring based on the genes of the parents during sexual
reproduction.
The paired alleles TT, Tt, or tt represent genotype (shows the organisms genetic
makeup for that trait (ex..height TT =purebred dominate)
Practice Punetts
Alleles Determine Traits:




Every cell in your body has two alleles for every trait.
Alleles that are the same for the same trait are called homozygous (ex… TT or tt
for height)
Two different alleles for the same trait is called heterozygous (ex. Tt )
Physical trait that is seen due to a particular genotype is called a phenotype.
Determining Genotypes and Phenotypes:
Phenotype Ratio:
Genotype Ratio:
Phenotype Percentage:
Genotype Percentage:
Practice Determining Genotypes and Phenotypes:
Section 5-2
Genetics Since Mendel
Vocabulary:
Incomplete Dominance: intermediate phenotype when organism is
heterozygous
Multiple Alleles: a trait controlled by more than two alleles
Polygenic Inheritance: a group of gene pairs act together to produce a
trait
Sex Linked Gene: an allele inherited on sex chomosome
Concepts:
Incomplete Dominance:
 A good example of this is four O’clock flours
 Alleles are not completely dominate = intermediate color, black =
white = gray
Punnnett Square Example:
Multiple Alleles:
 Blood type is a good example of multiple alleles
 The alleles found in blood type A, B, AB and O;
A = AA, or AO
B = BB or BO
AB = AB
O=O
 Type AB is the universal recipient
 Type O is the universal donor
Multiple Genes:
 Polygenic is when a group of gene pairs act together to produce a
single trait ex.. eye, skin and hair color, height, weight, body build,
shapes of eyes, ears and lips.
 Finger prints are also a good example
Q: What type of finger print do you have?
Ans…
Q: Which parent do you think you received your finger print from?
Ans…
D. Mutations—genes that are altered or copied incorrectly
1. A mutation can be harmful, beneficial, or have no effect
2. Chromosome disorders—caused by more or fewer chromosomes than
normal
3. Down’s syndrome—caused by an extra copy of chromosome 21
E. Recessive genetic disorders
1. Both parents have a recessive allele responsible for the disorder and pass
it to their child.
2. Because the parents are heterozygous, they don’t show any symptoms.
3. Cystic fibrosis is a homozygous recessive disorder
F. Sex Determination
1. Chromosomes that determine the sex of an organism are XX in females
and XY in males.
2. Females produce eggs with an X chromosome only. Males produce sperm
with either an X or a Y chromosome.
G. Sex-linked disorders
1. An allele inherited on an X or Y chromosome is a sex-linked gene.
2. Color blindness is a sex-linked disorder caused by a recessive allele on the
X chromosome.
3. A pedigree follows a trait through generations of a family.
Section 5-3 Advances in Genetics:
I. Vocabulary:
Genetic Engineering: Biological and chemical methods to change the
arrangement of DNA that makes up a gene.
II. Concepts:
Sex Determination:
 Sex chromosomes first discovered in fruit flies.
 Two types of sex chromosomes X and Y
 Each human has a pair of sex chromosomes
 Males have a X and Y combination
 Females have an X and X combination
 Egg cells contain X chromosomes only
 Sperm cells contain X and Y chromosomes = males determine sex of
baby.
Why is genetics important?
 Knowing how genes are inherited has led to couples seeking the
advice of genetic counselors before having children.
 Couples with bad genes have elected to adopt healthy children.
Genetic Engineering:
 Has developed medicine like insulin
 Used to improve crop production
 Desirable traits from one plants genes can be inserted into another
plant.
 Research has gone into controlling the height of grass so it doesn’t
need to be cut.
3 Types of Genetic Engineering:
1. Recombinant DNA
 Recombinant DNA procedure involves the placement of a
section of DNA in a piece of bacteria where it can grow and
multiply.
 This procedure is used to produce large amounts of insulin of
diabetic patients
 Recombinant DNA is also used to manufacture growth
hormone to treat dwarfism and chemicals to treat cancer
2. Gene Therapy:
 Used to replace abnormal alleles
 How is it done?
1. Virus DNA is removed
2. Normal allele is placed in the virus
3. Virus delivers normal allele to target cell
4. Normal allele replaces abnormal allele
 Used to cure specific type of cystic fibrosis..uses cold virus
3. Genetically Engineered Plants:
 Desired traits of one plant are removed to be added to a plant that
lack that trait.
 Example..potato plants have a natural resistance to insects. These
genes are being placed into other plants to increase their resistance to
moth larvae and beetles.
7