Heredity Basics

1. HEREDITY
Chapter 5

2. • Heredity is the passing of traits from parent to
offspring
• Genetics is the science that studies how traits are
inherited
• Alleles are the different forms of a trait that a gene
may have.
– alleles determine traits
– A gene is a section of DNA on a chromosome

3. • Gregor Mendel is known
as the father of genetics
– in 1856, Mendel
experimented with
pea plants using the
scientific method
– he traced one trait of the plants through
several generations

5. • An organism that always produces the same traits
generation after generation is called a purebred.
• A hybrid receives different information (different
alleles) for a trait from each parent

6. B
Purebred Labrador Retrievers Purebred Standard Poodles
<- < Hybrid Labradoodles

7. DOMINANT AND RECESSIVE ALLELES:
• A dominant trait covers over (or dominates)
another form of the trait
• Recessive describes a trait that is covered over, or
dominated, by another form of the trait
- a recessive trait seems to disappear in an
organism

9. • A Punnett Square is a tool used to predict results in
genetics.
- In a Punnett Square, letters represent dominant
and recessive alleles
- Capital letters represent dominant alleles;
lowercase letters represent recessive alleles
• The letters in a Punnet Square are a form of code
- they show the genotype, or genetic makeup of
an organism

10. This Punnet Square shows the genotype for the height
of an organism

11. This Punnett Square shows the genotype for eye color

12. • A phenotype is the outward appearance and
behavior of an organism as a result of its
genotype.
- for example, if you have blue eyes, the
phenotype for your eye color is blue

13. https://www.23andme.com/gen101/phenotype/

14. • An organism with two alleles that are the same is
homozygous.
- on a P.Sq, they are represented with the same
form of the same letter. Ex: TT or tt
• An organism that has two different alleles for a
trait is called heterozygous
- represented using different forms of the
letter on a P.Sq. EX: Tt

15. MENDEL’S PRINCIPLES OF HEREDITY:
1. Traits are controlled by alleles on chromosomes
2. An allele’s effect is either dominant or recessive
3. When a pair of chromosomes separates during
meiosis, the different alleles for a trait move into
separate sex cells

16. • Incomplete dominance refers to the production of
a phenotype that is intermediate (“mid-way”)
between two homozygous parents. The dominant
trait is then incomplete.
- For example, if crossing a red flower and a white
flower produces a pink flower, the red trait is
present, but does not completely dominate

18. • Polygenic inheritance occurs when a group of gene
pairs acts together to produce a trait
- In humans, eye color, skin shade, hair color, height,
etc… all are results of polygenic inheritance
Punnett Square for possible skin shades

21. • Environmental factors that effect genes may be
internal or external
- Internal influences include chemicals in the body
- External influences include the living conditions
and habits of the organism (smoking, diet, etc)

23. • A mutation is a permanent change in a gene or
chromosome
• Mutations are a result of errors in copying DNA
• One common chromosome disorder in humans
is Down Syndrome
• Down syndrome results when three copies of
chromosome #21 are made, instead of two
copies

25. • A recessive genetic disorder is caused by a
recessive gene
- This means that the parent who carries the gene
for the disorder does not have the disorder, but
can pass it on to their offspring
- Cystic fibrosis is a common recessive genetic
disorder

26. • Some inherited conditions are linked with the X and
Y chromosomes, which determine gender of
offspring
• These are called sex-linked disorders, because they
are caused by sex-linked genes.
• Color blindness is a sex-linked disorder

27. • A tool used for tracing a trait through the
generations of a family is called a pedigree
• Pedigree is used to determine patterns of
inheritance
• This helps geneticists to predict the probability
that a baby may be born with a specific trait
– Diseases and disorders; traits in animal
breeding