Aqa Igcse Biology. Key Facts Chapter 10

Front 1

What does the nucleus of a cell contain?

Back 1

Chromosomes

Front 2

What do chromosomes do?

Back 2

Carry genes

Front 3

How many sets of genes do the nuclei of males and female sex cells contain?

Back 3

One

Front 4

How many sets of gens do offspring cells contain?

Back 4

Two

Front 5

What are the two main causes of variation between individuals of the same kind of organism?

Back 5

Genetic causes

environmental causes

Front 6

Put these things into size order from largest to smallest: Genes, DNA and chromosomes

Back 6

One chromosome --> many genes --> lots of DNA

Front 7

What are the features and characteristics of asexual reproduction?

Back 7

Does not involve the fusion of gametes.

All genetic information from one parent.

All offspring genetically identical to parent.

Little variation.

Identical copies produced by asexual reproduction are clones.

Front 8

What are the features and characteristics of sexual reproduction?

Back 8

Involves the fusion of gametes.

There is mixing of genetic information.

Offspring show variation.

In animals the sex cells are egg and sperm.

Off spring are similar to both parents but not identical.

Combination of two sets of genes.

Front 9

Why is variation important to survival?

Back 9

Some characteristics may have a better chance of surviving than others.

Front 10

How many pairs of chromosomes do humans have?

Back 10

23

Front 11

What chromosomes do human females have which make them female?

Back 11

Two X chromosomes (XX)

Front 12

What chromosomes do human males have which make them male?

Back 12

An X and a Y chromosome (XY)

Front 13

What are alleles?

Back 13

A different form of a gene

Front 14

What is the phenotype?

Back 14

Physical appearance of the characteristic (e.g. dimples or no dimples)

Front 15

What is the genotype?

Back 15

The genetic make up (e.g. DD, Dd or dd)

Front 16

What is meant when two alleles are homozygous?

Back 16

Both alleles are the same.

DD = homozygous dominant

dd = homozygous recessive

Front 17

What is meant when two alleles are heterozygous?

Back 17

The two alleles are different (Dd)

Front 18

What is monohybrid inheritance?

Back 18

The inheritance of a single characteristic controlled by a pair of alleles

Front 19

What did Gregor Mendel do?

Back 19

Observed patterns of inheritance in pea plants before chromosomes were discovered. Mendel realised that there are separate units of inheritance.

Front 20

What are chromosomes made of?

Back 20

DNA

Front 21

What is DNA made up of?

Back 21

Stands which are twisted into a double helix structure.

DNA contains four compounds called bases.

Front 22

What are genes?

Back 22

Short sections of DNA with a large number of bases, grouped into threes.

A sequence of three bases is the code for a particular amino acid.

The order of the bases controls the order of the amino acids in the protein.

Front 23

Is polydactyly dominant or recessive?

Back 23

Dominant

Front 24

Is cystic fibrosis caused by the dominant or recessive allele?

Back 24

Recessive

Front 25

What does cystic fibrosis do?

Back 25

The allele affects cell membranes and causes the production of thick sticky mucus.

Front 26

Is sickle-cell anaemia caused by the dominant or recessive allele?

Back 26

Recessive

Front 27

What does sickle-cell anaemia do?

Back 27

Affects the shape of red blood cells so they cannot carry oxygen efficiently, they may also block small blood vessels and cause pain.

people who are homozygous recessive normally do not survive.

Front 28

What happens if you are heterozygous for the sickle-cell anaemia allele?

Back 28

The person has some sickle blood cells and this gives them protection from the malaria parasite.

Front 29

How is Down's syndrome caused?

Back 29

the presence of extra chromosome 21

(A mistake during meiosis could lead to a cell with too many or too few chromosomes)

Front 30

What are the results and problems that arise from screening embryos?

Back 30

Results of the test may give parents choices.

In IVF the embryos are screened and only healthy babies are inplanted.

some people may think that it is unethical to destroy unhealthy embryos.

Front 31

How do gene probes work?

Back 31

DNA is isolated from the embryo cells.

A gene probe that will bind onto the gene for a specific disorder is produced.

The gene probe has a fluorescent chemical attached to it.

The probe is added to a mixture containing the DNA sample.

UV light is used to detect the probe.

If the probes have attached to the faulty allele and fluoresce, the embryo or foetus is affected by the condition.

Front 32

What are the concerns about embryo screening?

Back 32

Risk or miscarriage.

The reliability of the information of the screening process.

Decisions about terminating the pregnancy.