Topic 3

How many parents does sexual reproduction require?

2 parents

How many parents does asexual reproduction require?

1 parent

Does sexual reproduction require the fusion of gametes?

Yes

Does asexual reproduction require the fusion of gametes?

No

Does sexual reproduction create identical or non - identical gametes?

Non - identical

Does asexual reproduction create identical or non - identical gametes?

Identical

How many chromosomes does the zygote receive from each parent during sexual reproduction?

23 chromosomes

In sexual reproduction, does the zygote receive 50% or 100% of DNA from each parent?

50%

In asexual reproduction, does the zygote receive 50% or 100% of DNA from each parent?

100%

Does sexual or asexual reproduction mix different DNA from each parent?

Sexual

Does sexual or asexual create variation within a species?

Sexual

Name 2 advantages of sexual reproduction

• Creates genetic variation meaning there is an increased chance of survival when adapting to new environments/foreign disease as natural selection can take place.

• Selective breeding to breed for desired characteristics.

Name 3 disadvantages of sexual reproduction

• Requires more time/energy.

• Less offspring produced.

• 2 parents required meaning organisms must find a mate which uses energy + is slower.

Name 3 advantages of asexual reproduction

• Produces lots of offspring very fast.

• 1 parents required meaning there’s no need to find a mate which is fast + uses less energy.

• Requires less time/energy.

Name 1 disadvantage of sexual reproduction

No genetic variation as they are all clones. This means there is less chance of survival if environment changes or a new disease is introduced.

Is the egg cell haploid or diploid?

Haploid

Is the sperm cell haploid or diploid?

Haploid

How many chromosomes does a gamete have?

1 set of chromosomes / 23 chromosomes

What is a fertilised egg cell?

Zygote

What is a zygote?

Fertilised egg cell

Is a zygote diploid or haploid?

Diploid

How many chromosomes does a zygote have?

2 sets of chromosomes / 46 chromosomes

How does a zygote form an embryo?

Mitosis

Describe what happens during fertilisation

The nucleus of a sperm (male gamete) and egg cell (female gamete) fuse together to form a zygote.

Explain how fertilisation and meiosis lead to the formation of a foetus

• During fertilisation, the nucleus of a haploid sperm (male gamete) and haploid egg cell (female gamete) fuse together to form a diploid zygote.

• This gives the zygote 46 chromosomes in total; 23 from each parent.

• Mitosis then allows the single cell to multiply and divide and continuously increase the cell number.

• Differentiation then produces all of the specialised cells.

What is meiosis?

A type of cell division that produces haploid gametes.

Does meiosis begin with a diploid or haploid cell?

Diploid (4 chromosomes)

What happens first in meiosis?

• DNA replicates (4 to 8 chromosomes).

• Chromosomes form an x shape, becoming 2 armed chromosomes.

• Chromosomes line up along the middle.

How many cell divisions does meiosis include?

2

Explain the full process of meiosis

• DNA replicates (4 to 8 chromosomes)

• Chromosomes form an x shape, becoming 2 armed chromosomes.

• Chromosomes line up along the middle.

• The cell divides but not fully. The pairs are also pulled apart, leaving 4 chromosomes one each cell.

• The cell divided fully and cells become 1 armed, instead of 2 armed.

• Cells divide again, leaving 4 genetically different haploid gametes. 2 chromosomes each.

Describe the cells produced at the end of meiosis

• Genetically different to each other and parents.

• Haploid gametes.

• 4 cells produced.

• 2 chrosmomes.

Explain the difference between meiosis and mitosis

Mitosis

• Genetically identical .

• Diploid body cells produced.

• 2 cells produced.

• 1 cell division.

Meiosis

• Genetically different.

• Haploid gametes produced.

• 4 cells produced.

• 2 cell divisions.

Describe the structure of DNA

• Double helix structure.

• DNA backbone made of phosphate and sugar.

• Many nucleotide which are made of a phosphate bonded to a sugar bonded to a base.

• Bases are cytosine, guanine, thymine and adenine. C pairs with G. A pairs with T.

• Bases pair via weak hydrogen bonds.

How is DNA arranged?

Double helix structure.

What shape does DNA have?

Double helix structure.

What do nucleotides consist of?

Sugar, phosphate, base.

Which molecules make up the DNA’s backbone?

Sugar and phosphate.

Name the four DNA bases

Adenine, Cytosine, Guanine, Thymine.

How are DNA bases bonded?

Weak hydrogen bonds.

What type of bond bonds DNA bases together?

Weak hydrogen bonds

Are the hydrogen bonds between bases strong or weak?

Weak

Which DNA bases complementary base pairs with T?

Adenine

Which DNA bases complementary base pairs with A?

Thymine

Which DNA bases complementary base pairs with C?

Guanine

Which DNA bases complementary base pairs with G?

Guanine

If a sample contains 30% adenine, what percentage of cytosine would be in the same sample of DNA?

20%

If a sample contains 40% guanine, what percentage of thymine would be in the same sample of DNA?

10%

What does a sequence of the three bases code for?

Amino Acid

Define: Chromosomes

Long, coiled molecules of DNA found in the nucleus of eukaryotic cells.

Where are chromosomes found?

Nucleus

Define: Gene

Section of DNA on a chromosome that codes for a protein.

Define: Genome

All of an organisms DNA.

Explain the full method for the DNA Extraction practical

1. Crush fruit using pestle and mortar

2. Add detergent

3. Add salt

4. Add protease

5. Filter mixture

6. Add ethanol

Why do we crush the fruit during DNA extraction?

To break down the cell wall.

Why do we add detergent during DNA extraction?

Break down the cell membrane/nucleus to release DNA.

Why do we add salt during DNA extraction?

To clump DNA.

Why do we add protease during DNA extraction?

To break down the enzymes that would usually break down DNA.

Why do we filter the mixture during DNA extraction?

To remove large pieces of insoluble fruit.

Why do we add ethanol DNA extraction?

To precipitate DNA.

How does the DNA appear at the end of the DNA extraction practical? How can it be extracted?

Appears as a stringy white precipitate; can be fished using a glass rod.

Define: Allele

A different version of the same gene

What is the difference between a genotype and phenotype?

Genotypes are the alleles someone has whilst the phenotypes are the physical characteristics someone has a result of their alleles.

Define: Heterozygous

Alleles are different e.g. Aa

Define: Homozygous

Alleles are different e.g. AA

Name the 3 genotypes

• Homozygous recessive

• Homozygous dominant

• Heterozygous

Define: Dominant Allele

Alleles that will always be expressed in the phenotype as only 1 is needed to be expressed. Always overrules the recessive allele.

Define: Recessive Allele

Alleles that will only effect the phenotype if the other allele is the same. Will always be overruled by the dominant allele.

In a recessive linked disease, how many alleles are needed for someone to have the disease?

2

In a dominant linked disease, how many alleles are needed for someone to have the disease?

1

How many pairs of chromosomes are there in the human body?

23

Haw many pairs of body chromosomes and sex chromosomes are there in the human body?

22 Body Chromosomes + 1 Sex Chromosomes

Which chromosomes do males have?

XY

Which chromosomes do females have?

XX

What is the chance of a couple having a baby girl?

50%

What is the chance of a couple having a baby boy?

50%

Does the male or female determine the babies gender? Why?

Males as they can pass on X or Y chromosomes whilst females can only pass on X chromosomes.

Is the Y chromosome smaller or bigger than the X chromosome?

Smaller

Does the Y chromosome carry more or less genes than the X chromosome? Why?

Carries less genes as it’s smaller.

What does a family pedigree chart show?

The occurrence of different phenotypes in a family tree.

Name the 4 blood groups

A, B, AB and O

Why can different blood groups not be mixed?

It can cause clotting

Which blood type can be given to anyone?

O

Which blood type can receive any blood type?

AB

Which blood group alleles are codominant?

I^A and I^B

Which blood group alleles are recessive?

I^O

Which genotype would give the blood group A?

I^A I^A or I^A I^O

If someone has the genotype I^A I^A, what blood group will the person be?

A

If someone has the genotype I^A I^O, what blood group will the person be?

A

Which genotype would give the blood group B?

I^B I^B or I^B I^O

If someone has the genotype I^B I^B, what blood group will the person be?

B

If someone has the genotype I^B I^O, what blood group will the person be?

B

Which genotype would give the blood group AB?

I^A I^B

If someone has the genotype I^A I^B, what blood group will the person be?

AB

Which genotype would give the blood group O?

I^O I^O

If someone has the genotype I^O I^O, what blood group will the person be?

O

Which 2 factors can effect variation?

Genetics + Environment

Give examples of variation caused by genetics

• Eye colour

• Blood type

• Natural hair

Give examples of variation caused by environment

• Piercinhs

• Religion

• Scars

• Language

Give examples of variation caused by both genetics + environment

• Height

• Body Mass

• Flexibility

How many genes were located and sequence during the Human Genome Project?

Over 20,000 genes.