What is genetics? The study of how traits are inherited and passed from parents to children

Genetics 101

What is genetics?

The study of how traits are inherited and passed from parents to children

ObjectivesBy the end of this lesson, you will be able to answer the following

questions. How do twins happen?

How is the sex of a baby determined?

What determines the traits or characteristics of a child? What are recessive and dominant genes?

How do I read a Punnett Square and predict heritability?

Genetics is what has created…

This…

this

and this

Gregor Mendel Between 1856 and 1863 Mendel patiently cultivated and tested at least 28,000 pea plants, carefully analyzing seven pairs of seeds for comparison, such as shape of seed, color of seed, tall stemmed and short stemmed and tall plants and short plants.

Mendel is seen as the father of genetics. It wasn’t until the early 1900’s that Mendel’s work was taken seriously.

In 1944, Oswald Avery, Colin Macleod, and Maclyn McCarty theorized that a substance called deoxyribonucleic acid, or DNA for short, was the actual genetic material found in chromosomes.

Since then, we have made great leaps and bounds in genetics which has allowed us to clone animals, do DNA testing, and further increase our food supply.

TwinsThere are two types of twins: They are Identical

and Fraternal

What’s the difference??

Identical TwinsIf one egg is fertilized and splits

into two embryos, the resulting children are called

Identical twins.

They are exactly alike genetically. They will always be the same sex.

Fraternal TwinsWhen two eggs are fertilized and develop into twins they

are called Fraternal

They are only as closely related as any brothers and sisters.

They can be the same sex or different sexes.

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Conjoined TwinsSometimes the egg does not completely split and

conjoined twins result.

A Child’s Sex:

Every person has chromosomes, which carry the genes, that determine who we are. Our parents give these genes to us. Two (one pair) of these chromosomes are sex genes.

Each egg carries a female chromosome. Each sperm carries either a male or female chromosome

The female is labeled the _____ chromosome .The male is labeled the ____ chromosome.

X

Y

Millions of sperm swim towards the same egg, but only one can fertilize it.

The eggs carry only the X chromosome. The sperm carry either the X or the Y chromosome.

Y

x

XX

Females are XX (both parents contributed a female chromosome)

Males are XY (the mother contributed an X and the father contributed a Y)

It depends on which sperm from the father fertilizes the egg. The father determines the sex of the child.

Our traits and the traits of our childrenIn the same way, our traits are carried through our

parents’ genes to us. Humans have 23 pairs of chromosomes (including the sex

determining ones). For each pair, one gene is contributed from the father and one from the mother. Our traits are determined by which genes our parents gave us.

Eye ColorWe use letters to represent the genetic make-up of an organism.

Capital letters are used for _______________________.

Lower case letters are used for ______________________

What color is dominant? What color is recessive? B= Brown gene b= blue gene When a dominant and a recessive gene occur together, the

dominant gene takes over and “shows”. A dominant gene over rides the effects of the recessive genes.

Dominant

Recessive

If a blue eyed man has children with a brown eyed woman and the genes look like Bb, the person will be carrying the blue eyed gene, but will have brown eyes.

Brown eyes can be either BB, or Bb. When the genes are

different (Bb), they are called _______________

Blue eyes will always be bb. Why? ________________________________________

Hybrid

Only the recessive gene is present. If the dominant brown was present, the eyes would LOOK brown.

How can we predict heredity?A man with brown eyes (BB) has children with a blue eyed (bb)

woman. B B b

b

______ chance brown eyes _____ chance blue eyes

___________ is the genetic makeup of the person’s trait (e.g. hybrid brown)

__________ is how the person looks. (e.g. brown eyes).

If your eyes are brown, your Genotype is either BB or Bb.

If your eyes are brown, your Phenotype brown.

Phenotype

Genotype

What if a blue eyed man has children with a hybrid brown eyed woman?

______ chance blue eyed children

_____ chance brown eyed children

What about two blue eyed parents?

_______ Chance of blue eyes

_______ Chance of brown eyes

Cross two brown eyed hybrid parents:

_______ Chance of blue eyes

_______ Chance of brown eyes

Cross two dominant brown eyed parents:

_______ Chance of blue eyes

_______ Chance of brown eyes

Cross a Hybrid brown x blue eyed person:

_______ Chance of blue eyes

_______ Chance of brown eyes

How has the study of genetics affected our lives? Improved our Food Supply:

Scientists have helped to select for crops that provide more food and are resistant to insects, for cows that give more milk, for beef and chickens that grows faster, etc.

DNA Testing: Determining paternity, and eliminating people accused of crimes.

Medical AdvancesScientists have created drugs ( eg. insulin), vaccines, and linked

some genes to disease which have all had large impacts on our health.

Cloning: Scientists have cloned many animals. What’s next?

What’s next?

Human cloning?

Curing diseases?

Selecting the traits of our children?

??????????? The potential is endless!

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