Biology - Inheritance, variation and evolution

What is asexual reproduction?

Reproduction that only requires one parent. The offspring are genetically identical to the parent (clones). There is no variation in offspring.

What are the advantages of asexual reproduction?

- only one parent needed

- faster than sexual reproduction

- large numbers of offspring can be produced

-useful when conditions are stable and favourable

What are the disadvantages of asexual reproduction?

-no genetic variation

-if the environment changes (e.g, disease, climate), they all could be wiped out

Examples of organisms that reproduce asexually?

Bacteria (binary fission)

-Some plants (strawberry runners, potato tubers)

-Some animals (starfish can regenerate)

Does mitosis produce haploid or diploid cells?

diploid cells

What are diploid cells?

• a cell that contains two complete sets of chromosomes (2n)

• one set inherited from each biological parent

What are haploid cells?

A cell that contains a single set of unpaired chromosomes (n)

How do cells divide in asexual reproduction?

mitosis

What is sexual reproduction?

Reproduction involving 2 parent organisms combining gametes to create a genetically different offspring.

What are gametes?

sex cells

How are gametes made?

through meiosis

What is a zygote?

fertilized egg cell

What are the gametes in human cells?

Sperm and egg cells

What are the gametes in plant cells?

egg cells and pollen

What is a flower?

The flower is the reproductive organ of a plant.

What is the stamen of a flower?

Male part of the flower

What is the anther of a flower?

produces pollen

What is a pollen grain of a flower?

male gamete of a plant

What is a filament of a flower?

stalk that supports the anther

What is the carpel/pistil of a flower?

The female reproductive part of a flower

What is the stigma of a flower?

The part of the pistil where pollen is collected

What is the style of a flower?

connects stigma to ovary

What is the ovary of a flower?

This is the inner part of the flower that contains the ovules.

What are the ovules of a flower?

female gametes of a plant

What are haploid cells?

Cells with a single set of chromosomes. (gametes)

What are diploid cells?

Cells that have two sets of chromosomes. Human body cells are diploid.

How are plants made?

1. Pollen is transferred from the anther to the stigma

2. A pollen tube grows down the style to the ovary

3. the male nucleus travels down the tube and fuses with the female nucleus

4. This produces a zygote which develops into a seed. The ovary becomes a fruit to protect the seed

5. When the conditions are right the seed germinates and a new plant is made

What is pollination?

transfer of pollen from anther to stigma

What are the two ways of pollination?

insect pollination - insects carry pollen between flowers

Wind pollination - pollen is blown by the wind

What is fertilisation in plants?

When pollen fuses with the egg in the ovary

This produces a zygote, which develops into a seed. The ovary becomes a fruit that protects the seed.

What is germination?

the process by which a plant grows from a seed

How do plants reproduce asexually?

-Runners (e.g. strawberry plants): side shoots grow from the parent and develop roots.

-Bulbs (e.g. onions, daffodils): underground storage organs that produce new shoots.

-Cuttings (used in horticulture): humans can grow new plants from parts of existing ones.

How do fungi commonly reproduce?

asexually

How do fungi reproduce asexually?

By spores: Most fungi produce spores — tiny cells that can grow into a new fungus.These spores are often made in structures like sporangia. Spores can be spread by the wind, water, or animals, and when they land in a suitable place, they germinate and grow new hyphae.

What is budding?

Some fungi, like yeast, reproduce by budding.

-A small bump (called a bud) forms on the parent cell, the nucleus divides, and one nucleus moves into the bud.The bud then breaks off to form a new, identical cell.

How do fungi reproduce sexually?

This happens when conditions are less favourable (for example, when food or water is scarce)

Two different hyphae (from different fungi of the same species) join together.

The nuclei fuse to make a zygospore (a thick-walled spore).

When conditions become better, the zygospore germinates and grows a new fungus.

How does malaria reproduce asexually?

Inside the human body:

1. The parasites travel to the liver, where they reproduce asexually — meaning they make identical copies of themselves.

2. After multiplying, they leave the liver and infect red blood cells.

3. Inside the red blood cells, they reproduce asexually again until the cells burst, releasing more parasites into the blood.

This bursting causes the fever and chills typical of malaria.

How does malaria reproduce sexually?

The mosquito picks up male and female forms of the parasite from the person's blood.

Inside the mosquito's gut, these parasites join together and reproduce sexually.

The new parasites then move to the mosquito's salivary glands, ready to infect the next person the mosquito bites.

Are gametes haploid or diploid?

Haploid- they only have one chromosome of each type.

How are gametes made?

through meiosis

What are the advantages of sexual reproduction?

-produces variation in the population

-some offspring may survive better if the environment changes

-species can adapt and evolve overtime

What are the disadvantages of sexual reproduction?

- Requires two parents

- slower then asexual reproduction

- Can prevent favourable genes from being passed onto offspring

- Fewer offspring than asexual reproduction.

What is meiosis?

a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.

How does meiosis work?

1. DNA replicates - each chromosome makes a copy

2. First division - chromosomes line up in pairs.

-They swap sections of DNA, introducing variation

-pairs are separated, the cell divides, 2 cells are formed

3. Second division - chromosomes in each of the cells line up again

-the chromatids are pulled apart

-each cell divides again, 4 diploid cells are produced which are all genetically different from the others

What is fertilisation?

fusion of male and female gametes to form a zygote.

What happens to the zygote after fertilisation?

divides by mitosis to increase the number of cells, cells differentiate as embryo develops

What does DNA stand for?

deoxyribonucleic acid

What is DNA?

The molecule that carries genetic information

What is genetic information?

The instructions that your genes carry that control your characteristics

What is the structure of DNA?

-Double-helix, "twisted ladder"

-The two sides of the "ladder"(strands) are made of sugar and phophate molecules

-The rungs of the "ladder" are made of base pairs

How are base pairs bonded?

hydrogen bonds

What are the 4 base pairs?

Adenine, Thymine, Cytosine, Guanine

(A, T, C, G)

How do bases pair up?

A-T

G-C

What is a nucleotide?

the combination of a sugar, a phosphate and a nitrogenous base

What is a gene?

A segment of DNA that codes for a specific protein, which controls characteristics

What are examples of proteins?

enzymes, pigments (like melanin), hormones, structural proteins

What is the function of genes?

-to code for a particular combination of amino acids which make a specific protein

-This determines characteristics like hair and eye colour

What are chromosomes?

Coiled up lengths of DNA molecules that are found in the nuclei

Where are chromosomes found?

nucleus

How many chromosomes do humans have?

46 (23 pairs)

How many chromosomes do zygotes have?

46

How many chromosomes do gametes have?

23

Where are chromosomes inherited from?

Half from your mother, half from your father

What is a genome?

The entire genetic material of an organism

What is the purpose of the Human Genome Project?

to identify the DNA sequence of every gene in the human genome to help them understand diseases and make new medicines

How many base pairs are there in the human genome?

3 billion

What is protein synthesis?

the process of making proteins by using the information present in the DNA

What are the two stages in protein synthesis?

1. Transcription

2. Translation

How does protein synthesis work?

Transcription

-The cells make a copy of the gene because the DNA is too large to leave the cell

-The copied molecule is called mRNA

-It carried the code from the DNA to the ribosomes

Translation

-the ribosome reads the code in groups of three (codons)

-Each codon codes for a specific amino acid

-tRNA molecules bring the correct amino acid to the ribosome

-The ribosome joins the amino acids together in the right order to form a protein chain (polypeptide)

After the polypeptide is made, it folds into a specific shape. The shape determines the function of the protein

Summary of protein synthesis?

1. DNA holds the code for proteins

2. the code is copied into mRNA

3. mRNA travels to the ribosome

4. tRNA brings amino acids according to the the code

5. A protein is formed and folded into it’s final shape

What is a polypeptide?

long chain of amino acids

What does tRNA stand for?

transfer RNA

What does mRNA stand for?

messenger RNA

What is mRNA?

a single-stranded copy of the gene carrying instructions to make proteins

What is gene expression?

controls which proteins are made by switching on or off genes

Why do we need gene expression?

because each cell in the body has the same DNA, but different cells express different genes. This is why different cells make different proteins

How does gene expression work?

1. a gene in the DNA is transcribed into mRNA

2. the mRNA is then translated into a protein at the ribosome

3. If a gene is switched on, its protien is made, and if it’s switched off it isn’t made

How can environmental factors affect gene expression?

factors such as temperature, diet or chemicals can influence gene expresion. (epigenetics)

What is a mutation?

A random change in the DNA sequence

What does mutation mean?

That one or more of the bases (T,A,G,C) have been changed

What are the types of mutation

substitution, insertion, deletion

What is substitution?

When one base is replaced for another

What is insertion?

When an extra base is inserted

What is deletion?

when a base is removed

What are the effects of mutation?

it might change the amino acid sequence of the protein and might cause it to fold differently

What would happen if the amino acid sequence of a protein changed?

-Most mutations would have no effect

-The protein might fold differently

-So the active site of an enzyme might not fit the substrate

-or a structural protein might lose its strength or stop working altogether

Or it might give the organism an advantage

-It might produce a more efficient enzyme or a stronger structural protein

What is an example of mutation?

If the gene for making insulin is mutated, the body might not make working insulin, leading to diabetes

What is inheritance?

The process by which genetic information is passed from parents to offspring.

What does inheritance explain?

It explains why children look similar to their parents

What is an allele

Different versions of the same gene, found at the same locus on a chromosome.

How many alleles do you have for each gene?

two (one from each parent)

What is a dominant allele?

The allele that is always expressed, even if there is only one copy of the gene

What is a recessive allele?

An allele that is masked when a dominant allele is present. It is only expressed if two copies are present

What does homozygous mean?

A genotype where both alleles for a gene are the same. (either both dominant or recessive)

What does heterozygous mean?

A genotype where the two alleles are different

What is a genotype?

genetic makeup of an individual/the alleles they have

What is a phenotype?

physical characteristics of an organism

What are the chromosomes for a female?

XX

What are the chromosomes for a male?

XY

How is sex determined by chromosomes?

Each parent gives a chromosome

-The mother always gives an X

-The father either gives an X or a Y

The chance of having a boy or a girl is roughly 50:50