Why are Identical Twins Rare?

Why are Identical Twins Rare?

by Ms. Poliseri

Multiple Choice

What is responsible for holding the instructions in a cell (also known as the control center)?

• Nucleus

• Envelope

• Ribosomes

• genes

Multiple Choice

What is another name for the instructions for building proteins?

• Nucleus

• genes

• heredity

• r

Multiple Choice

What is the name for the piece of a cell that builds proteins?

• Nucleus

• genes

• Ribosomes

• DNA

​Why are identical twins rare?

• ​What do you know about twins so far?

Multiple Choice

Finish the sentence: Everyone is different. We have different hair colors, eye colors, and combinations of traits. All of these differences are called ___________.

• Cells

• Genes

• Changes

• Variation

​

• ​Identical means "exactly the same"

• ​Same proteins

• ​Same genes

​How do we get our genes?

• ​From our biological parents

• ​Each parent has complete set of genes

• ​Genes are on chromosomes with two copies of each gene

​How do genes pass on?

• ​One gene copy from each parent gets passed on to the offspring

• ​Every person is unique!

• ​Also why siblings can look so different!

​Fertilization

• ​When one copy of a gene is given from the mother and one copy is given from the father

• ​RANDOM

• ​many combinations-variation

Multiple Choice

How many copies of a gene do parents pass on to their offspring?

• 0

• 1

• 2

• 3

Multiple Choice

How many copies of a gene does each person have? (also called alleles or gene versions)

• 0

• 1

• 2

• 3

​Fraternal Twins

• ​Fertilization happens twice

• ​​​One copy from mom, one copy from dad in BOTH

• ​Two separate chances for variation

​Identical Twins

• ​Fertilization happens ONCE

• ​One copy from mom, one copy from dad & split

• ​No chance for genetic variation

Open Ended

How are identical twins and fraternal twins different?