genetics & heredity

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


• 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?

What is GENETICS?

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

What is a GENE?

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 the following terms:

• Heredity• Allele• Trait

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

Define TRAIT

• Ways of looking, thinking, or being

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

Describe RECESSIVE

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?

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?

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


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

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

Define GENOTYPE

Define GENOTYPE

An organism's genetic makeup

Define PHENOTYPE

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


• Letters stand for dominant and recessive alleles

• An uppercase letter stands for a dominant allele

• Lowercase letters stand for recessive alleles

Read More About Punnett Squares Here:

http://www.borg.com/~lubehawk/psquare.htm



List the 3 Principles of Heredity

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


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


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


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

~OR~

an A and an A allele (AA)


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


A person with phenotype O blood has the genotype OO

What is POLYGENIC INHERITANCE?

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

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