Inheritance

What are gametes?

Sex cells → sperm/eggs in humans or pollen/eggs in plants

Why does asexual reproduction produce genetically identical clones?

There is no fusion of gametes so genetic material dosen't mix

What process is involved in asexual reproduction?

Mitosis

What is fertilisation

The fusion of the nucleus of male and female gametes to form a zygote

What process is involved in sexual reproduction?

Mitosis AND meiosis

How are gametes formed?

During meiosis

What are the stages of meiosis?

1. DNA duplicate

2. The chromosomes line up at the equator in pairs

3. The cell undergoes meiosis 1 → the pairs of chromosomes are pulled apart

4. Some of the mother's and some of the father's chromosomes go into new cells → genetic variation

5. Chromosomes line up at the equator in both cells

6. The cell undergoes meiosis 2 → chromosomes are pulled apart

7. 4 gametes are formed → each have 23 chromosomes

Where does meiosis occur?

In the testes and ovaries

How many chromosomes do we have?

46 → 23 pairs

Define zygote

A fertilised egg cell

What are the advantages of sexual reproduction?

• Variation in offspring

• Species can adapt to new environments

• Disease is less likely to affect all individuals in a population

What are the advantages of asexual reproduction?

• Population can increase rapidly when the conditions are favourable

• Only one parent is needed

• More time /energy efficient as you don't need a mate

• Faster than sexual reproduction

What are the disadvantages to sexual reproduction?

• Time and energy are needed to find a mate

• Not possible for an isolated individual (incells)

What are the disadvantages of asexual reproduction

• no variation in a population

• Species may only be suited to one habitat

• Disease may affect all the individuals in a population

What is the structure of DNA?

A polymer made from 4 different nucleotides, shaped like a double helix

What does a nucleotide consist of?

• Sugar

• Phosphate group

• 1/4 bases

How does each base complimentary pair with eachother?

C and G

ConGregATe

A and T

Define genetic code

The code formed by the order of the bases in DNA that determines an organism's characteristics

What are chromosomes?

Long threads of DNA made up of many genes

Define gene

A small section of DNA in a chromosome

What do genes do?

They code for a particular sequence of amino acids to make a specific protein

How do malarial parasites reproduce?

Asexually in a human host but sexually in the mosquito

How do fungi reproduce?

Asexually by spores but also sexually to give variation

Define genome

The entire genetic material of an organism

How has the study of the human genome improved medicine?

We can:

• Search for genes linked to different types of diseases

• Understand inherited disorders and their treatments

• Trace human migration patterns

What is a triplet code?

A sequence of 3 bases which codes for a particular amino acid

Define protein synthesis

The production of proteins from amino acids

What is mRNA?

The short section of DNA needed to form a protein

Define mutation

A change in a gene or chromosome

name the different types of mutations

• Insertion

• Deletion

• Substitution

• Inversion

What happens during substitution?

One base takes the place of another → different amino acid will be synthesised

What happens during insertion?

An extra base will be added

What happens during deletion?

A base is removed

What happens during inversion?

The order of the bases change

What can mutations of DNA do?

• Change the activity of a protein

• Change the phenotype → genetic diseases

Define alleles

Different versions of the same gene

What is the difference between genotypes and phenotypes?

Phenotypes → physical characteristics

Genotypes → The allele which gives an organism their characteristics

What are the sex chromosmes for males?

XY chromosome

What are the sex chromosomes for females?

XX chromosomes

What does cystic fibrosis affecr?

• Lungs

• Digestive system

What happens to the lungs of a patient with cystic fibrosis?

They become clogged with thick, sticky mucus because too much is produced which causes respiratory problems as they become very damaged

What causes cystic fibrosis?

2 faulty recessive alleles → inherited disorder

What is the condition called which causes a person to have extra fingers or toes?

Polydactyly

What causes polydactyly?

A dominant allele → inherited disease

What is the difference between a recessive and dominant allele?

Recessive → both alleles must be present to express the trait → weaker

Dominant → Only one allele is needed to show the trait → stronger

How can genetic disorders be screened?

• PGD → used when genetic disorders are linked to the baby's sex

• CVS → A sample taken out of the placenta 10-12 weeks into the pregnancy

• Amniocentesis → testing amniotic fluid

What are the problems with genetic testing?

• Not available for every inherited disorder

• Unreliable → false positive/negatives