GeneticsGenetics& &

HeredityHeredity

Who was Gregor Mendel?

• Austrian monk who studied mathematics and science

• As a boy he could predict the possible types of flowers and fruits that would result from crossbreeding two plants in his father’s garden

Who was Gregor Mendel?

• Curiosity about the connection between the color of a pea flower and the type of seed that same plant produced inspired him to begin experimenting with garden peas in 1856.

• Made careful use of scientific methods, which resulted in the first recorded study of how traits pass from one generation to the next.

What is GENETICS?

The study of how traits are inherited through the interactions of genes.

What is a GENE?

• The material that controls which traits are expressed in an organism

• Genes come in pairs and offspring inherit one copy of each gene from each parent

Define HEREDITY

The passing of traits from parent to offspring

Define ALLELE

• The different forms of a trait that a gene may have

• One form of a gene

Genes are made of DNA. Genes help us to make proteins (e.g. muscle

protein, hormones, enzymes, antibodies, skin collagen, hair keratin)

that will determine certain characteristics we inherit.

Define ALLELE

For a specific characteristic (e.g. eye colour), there may be one or more types

(e.g. blue, brown) that may be determined by slightly different variations of the DNA in the gene. These are called alleles. For

example, in eye colour, there may be brown eye colour determined by a gene

orallele B, or for blue eye colour, it is determined by a slightly different gene

or allele b.

Define TRAIT

• Ways of looking, thinking, or being

• Traits that are genetic are passed down through the genes from parents to offspring

Describe RECESSIVE

• A trait that is covered over, or dominated, by another form of that trait and seems to disappear

• Hidden when the other copy of the gene contains the dominant allele.

• A recessive allele shows up only when there is no dominant allele present

• Shown with a lower-case letter

What is HOMOZYGOUS?

• Both alleles [forms of the gene] are the same

• When offspring inherit two dominant genes, (one dominant gene from each parent) they are said to be homozygous dominant

• When offspring inherit two recessive genes, (one recessive gene from each parent) they are said to be homozygous recessive

What is HETEROZYGOUS?

• When alleles occur in different forms

• When offspring inherit one dominant gene and one recessive gene, they are said to be heterozygous

• Since the dominant gene will be expressed, they are said to be heterozygous dominant

Describe CO-DOMINANCE

• When an organism has two different alleles for a gene that does not follow the dominant/recessive pattern

• The organism shows a trait that is a blend of the traits represented by the two alleles

• Also called INCOMPLETE DOMINANCE

Describe CO-DOMINANCE

For example:

The gene for the color of some flowers has one allele for red and one for white. When both alleles are present, neither is dominant, and the flower color is pink

Describe DOMINANT

• A trait that covers over, or dominates, another form of that trait

• Trait that always shows up, even when only one of the two alleles is in the dominant form

• Shown by a capital letter

GENOTYPES AND PHENOTYPES

• Each characteristic (e.g. eye color) is determined by a pair of genes/alleles. One of those genes came from the father via sperm, and the other came from the mother via egg.

• Genotype is the pair of genes/alleles written in letter form (e.g. BB).

• Phenotype is the characteristic that appears as a result of that genotype (e.g. brown eyes).

Example 1 - Eye Color in Humans

GENOTYPE PHENOTYPE

BB Brown-eyed person

Bb Brown-eyed person

bb Blue-eyed person

Example 2 - Height in Pea Plants

GENOTYPE PHENOTYPE

TT Tall pea plant

Tt Tall pea plant

tt Short pea plant

GENOTYPE

An organism's genetic makeup

Define PHENOTYPE

Outward physical appearance and behavior of an organism

What is a PUNNETT SQUARE?

• A tool to predict the probability of certain traits in offspring that shows the different ways alleles can combine

• A way to show phenotype & genotype

• A chart that shows all the possible combinations of alleles that can result when genes are crossed

What is a PUNNETT SQUARE?

• Letters stand for dominant and recessive alleles

• An uppercase letter stands for a dominant allele

• Lowercase letters stand for recessive alleles

Punnett Square• The Punnett Square below shows

the possible eye colors inherited by the children.

•  Possible genotypes of children = all Bb• Possible phenotypes of children = all brown-

eyed children

B B

b Bb Bb

b Bb bb

List the 3 Principles of Heredity

• Traits are controlled by alleles on chromosomes

• An allele’s effect is dominant or recessive

• When a pair of chromosomes separate during meiosis the different alleles for a trait move into separate sex cells

What is meant by MULTIPLE ALLELES?

• A trait that is controlled by more than two alleles is said to be controlled by multiple alleles

• Traits controlled by multiple alleles produce more than three phenotypes of that trait

What is meant by MULTIPLE ALLELES?

For Example:

The alleles for blood types in humans are called A, B, and O

The O allele is recessive to both the A and B alleles

What is meant by MULTIPLE ALLELES?

When a person inherits one A allele and one B allele for blood type, both alleles are expressed

The person has the blood phenotype AB

What is meant by MULTIPLE ALLELES?

A person with phenotype A blood inherited an A and an O allele (AO)

~OR~

an A and an A allele (AA)

What is meant by MULTIPLE ALLELES?

Someone with phenotype B blood has the genotype BB or BO

This person inherited either a B and an O allele

~OR~ Two B alleles

What is meant by MULTIPLE ALLELES?

A person with phenotype O blood has the genotype OO

What is POLYGENIC INHERITANCE?

• Occurs when a group of gene pairs acts together to produce a trait

• The effects of many alleles produces a wide variety of phenotypes