Bio: Unit 2: GENETICS

Why are cells small?

• Helps materials move in and out efficiently.

What happens when a cell gets larger?

• Volume increases faster than surface area.

• Surface area-to-volume ratio decreases.

Why is cell division important?

• Growth, repair, and replacing cells.

 What is the cell cycle?

• The process of a cell growing and dividing.

• The cell spends most of its life in interphase

What are the 3 stages of interphase?

• G1, S, G2

 What happens in G1?

• Cell grows and carries out normal functions.

• Makes proteins and organelles.

• Checks that the cell is big enough, has enough energy, and is ready to copy DNA.

 What happens in S phase?

• Cell duplicates its DNA.

• Each chromosome gets two identical copies.

• Checks that DNA was copied correctly.

What happens in G2?

• Cell continues to grow.

• Makes molecules needed for cell division.

• Checks for DNA damage.

• Finds and repairs DNA damage before mitosis.

What are the two parts of M phase?

• Mitosis

• Cytokinesis

What are the 4 stages of mitosis?

• Prophase → Metaphase → Anaphase → Telophase

 What happens in prophase?

• Chromosomes become visible.

• Nuclear envelope breaks down.

• Spindle fibres begin to form.

What is a centromere?

• The point where sister chromatids are attached.

What happens in metaphase?

• Chromosomes line up in the middle.

• Spindle fibres attach to the centromeres.

• Chrom lines up so each daughter cell gets the same genetic information.

What happens in anaphase?

• Sister chromatids separate.

• They move to opposite sides of the cell. Called individual chromosomes

 What happens during telophase?

• Chromosomes reach opposite ends.

• Spindle fibres disappear.

• Nuclear membranes reform.

• DNA becomes chromatin again.

 What is cytokinesis?

• Cytoplasm divides.

• Two daughter cells are formed.

How is cytokinesis different in plants and animals?

• Animal: membrane pinches inward.

• Plant: cell plate forms.

What are the DNA base pairs?

• A–T

• G–C

What is a gene? Give an example.

• A part of DNA that helps determine a trait. Ex: eye color

What is a genome?

• The entire DNA sequence of an organism.

• About 3 billion base pairs in human genome

What is a somatic cell?

• A body cell that is not a reproductive cell.

• 46 chromosomes in human somatic cells

What is a chromosome?

• Condensed DNA wrapped around proteins.

 What is chromatin?

• Uncondensed DNA that can be read and copied.

What is sexual reproduction?

• Reproduction that uses two parents

• Each parent contributes a sex cell (gamete)

What are gametes?

• Sex cells used in sexual reproduction

• Sperm and egg cells

 What happens when a sperm fertilizes an egg?

• They fuse together

• Form a zygote

What is fertilization?

• When a sperm and egg cell fuse together

• Forms a zygote

What happens when sperm and egg join?

• 23 + 23 = 46 chromosomes

• The zygote is diploid

• 23 human egg and sperm cells

What is a zygote?

• The first cell of a new individual

• It is diploid (2n)

What is meiosis? whats the purpose?

• A two-stage cell division

• Produces gametes

• Makes cells with half the chromosomes

Purpose:

• To make sex cells

• Gives them half the normal number of chromosomes

How many chromosomes are in a human cell before and after meiosis?

Before: 46 chromosomes

After: 23 chromosomes

How many cells are produced at the end of meiosis?

4 genetically different cells

What is the main difference between mitosis and meiosis?

Mitosis	Meiosis
Makes 2 cells	Makes 4 cells
Genetically identical	Genetically different
Used for growth and repair	Makes gametes
Same chromosome number	Half the chromosome number

What does haploid (n) and diploid (2n)

haploid (n):

• One set of chromosomes

• Humans have 23

diploid (2n):

• Two sets of chromosomes

• Humans have 46

Gametes and zygote. Which is haploid or diploid?

• Gametes are haploid

• Zygotes are diploid

What are homologous chromosomes? What do they carry?

• Chromosome pairs that contain the same types of genes

• One comes from each parent(mom and dad)

What they carry:

• Genes for traits such as:

  • Eye colour

  • Hair colour

What happens during Interphase before meiosis?

• DNA copies itself

• The cell prepares for division

What happens during Prophase I?

• Chromosomes become visible

• Nuclear membrane breaks down

• Spindle fibres form

• Homologous chromosomes pair up

What is a tetrad?

• A pair of homologous chromosomes

• 4 chromatids total

What is synapsis?

When homologous chromosomes pair up

What is crossing over? why is it important

• Chromosomes exchange pieces of DNA

• Creates new genetic combinations

Significance:

• Creates genetic variation

• Helps make individuals genetically different

What happens during Metaphase I?

• Tetrads line up in the middle of the cell

What happens during Anaphase I?

• Homologous chromosomes move to opposite sides

• One chromosome from each pair goes to each cell

Why is Anaphase I called the “reduction” stage?

The chromosome number is reduced by half

What happens during Telophase I?

• Nuclear membranes begin to form

• 2 haploid cells are formed

How many chromosomes does each cell have after Meiosis I in humans?

• 23 chromosomes

• They are haploid

What happens at the beginning of Meiosis II?

• The two haploid cells begin dividing again

• DNA does NOT copy again

What happens during Prophase II?

• Nuclear membrane breaks down

• Spindle fibres form

What happens during Metaphase II?

Chromosomes line up in the middle

What happens during Anaphase II?

• Sister chromatids separate

• They move to opposite sides

What happens during Telophase II?

• Nuclear membranes form

• Cell division is completed

What is produced at the end of Meiosis II?

• 4 haploid cells

• Each has 23 chromosomes

• They are genetically different

What is gametogenesis? Where does it happen?

The formation of haploid sex cells

Where it Occurs:

• Testes

• Ovaries

What is spermatogenesis and oogenesis?

Spermatogenesis: Production of sperm cells

oogenesis: Production of egg cells

Difference between egg and sperm production.

• Sperm cells are produced by equal division

• Egg production has unequal division

What happens during oogenesis?

• One large egg cell is produced

• Smaller cells called polar bodies are also formed

What is a polar body?

• A small cell produced during egg formation

• Has little cytoplasm

Why is the egg cell large and the sperm cell small?

Egg cell:

• It needs more nutrients

• It does not need to swim

Sperm cell:

• They need to swim

• Smaller cells can move more easily

How many eggs does a female typically produce in her lifetime?

About 400–500

What is a karyotype?

• An organized picture of a person's chromosomes

• Chromosomes are arranged into pairs

• They’re arranged by size and shape

Significance:

• They allow scientists to study chromosomes

• They can help identify chromosome differences

What are sex chromosomes?

Chromosomes that help determine biological sex

What are autosomes?

All the chromosomes that are not sex chromosomes

What is the XX/XY system?

XX- Female chromosomes

XY- Male chromosomes

Which parent determines whether the child receives an X or Y chromosome?

• The father

• Sperm can carry X or Y

• The egg carries X