Topic 13 Triple Reproduction, DNA and Genetics

Question 1

Sexual reproduction involves the joining (fusion) of male and female gametes:

Answer 1

• sperm and egg cells in animals
• pollen and egg cells in flowering plants

Question 2

Asexual reproduction involves only one parent and no fusion of gametes so:

Answer 2

There is no mixing of genetic information. This leads to genetically identical offspring (clones). Only mitosis is involved

Question 3

In sexual reproduction there is mixing of

which leads to

The formation of gametes involves

Answer 3

genetic information

variety in the offspring

meiosis

Question 4

Meiosis

fertilisation

Answer 4

halves the number of chromosomes

restores the full number of chromosomes

Question 5

Cells in reproductive organs divide by meiosis to form gametes.
When a cell divides to form gametes:

Answer 5

copies of the genetic information are made
* the cell divides twice to form four gametes, each with a single set of chromosomes
* all gametes are genetically different from each other

Question 6

Gametes join at

The new cell divides by

. The number of cells

As the embryo develops cells

Answer 6

fertilisation to restore the normal number of chromosomes.

mitosis.

increases

differentiate

Question 7

Advantages of sexual reproduction:

Answer 7

produces variation in the offspring
* if the environment changes variation gives a survival advantage by natural selection
* natural selection can be speeded up by humans in selective breeding to increase food production

Question 8

Advantages of asexual reproduction

Answer 8

• only one parent needed
• more time and energy efficient as do not need to find a mate
• faster than sexual reproduction
• many identical offspring can be produced when conditions are favourable

Question 9

Some organisms reproduce by both methods depending on the circumstances. e.g

Answer 9

• Malarial parasites reproduce asexually in the human host, but sexually in the mosquito.
• Many fungi reproduce asexually by spores but also reproduce sexually to give variation.
  *Many plants produce seeds sexually, but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils.

Question 10

that the genetic material in the nucleus of a cell is composed of

Answer 10

a chemical called DNA.

Question 11

DNA

Answer 11

a polymer of two strands forming a double helix, contained in structures called chromosomes.

Question 12

a gene

Answer 12

as a small section of DNA on a chromosome, coding for a particular sequence of amino acids, to make a specific protein.

Question 13

Define a genome as the

Answer 13

entire genetic material of an organism.

Question 14

Describe basic structure of a nucleotide:

Answer 14

consists of a common sugar, a phosphate group and one DNA base (A, C, G or T)

Question 15

The DNA polymer is made up of

Answer 15

repeating nucleotide units.

Question 16

In the complementary strands a C is always
on the opposite strand,
and a T

Answer 16

linked to a G

to an A.

Question 17

mutations may occur

Most do not

or alter it only slightly so that

Answer 17

spontaneously

alter the protein

its appearance or function is not changed.

Question 18

Ordinary human body cells contain - pairs of chromosomes.

Answer 18

23 pairs of chromosomes.

Question 19

Gamete

Answer 19

a reproductive cell of an animal or plant

Question 20

Chromosome

Answer 20

A structure found inside the nucleus of a cell. A chromosome is made up of proteins and DNA organized into genes

Question 21

Gene

Answer 21

a small section of DNA on a chromosome, that code for a particular sequence of amino acids, to make a specific protein.

Question 22

Allele

Answer 22

each of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Question 23

Dominant allele

Answer 23

A dominant. allele is always expressed, even if one copy is present. Dominant alleles are represented by a capital letter, for example, A

Question 24

recessive allele

Answer 24

A recessive allele is only expressed if the individual has two copies and does not have the dominant allele of that gene.

Question 25

Homozygous

Answer 25

alleles are both identical for the same characteristic, for example AA or aa.

Question 26

Heterozygous

Answer 26

A homozygote is an individual who has identical alleles for a particular gene. Heterozygous. alleles are both different for the same characteristic, for example Aa.

Question 27

Genotype

Answer 27

the combination of alleles an organism has

Question 28

Phenotype

Answer 28

The observable characteristics of an organism (seen just by looking - like eye colour, or found – like blood type)

Question 29

some disorders are caused by inheritance of certain alleles:

Answer 29

Cystic fibrosis (a disorder of cell membranes) is caused by a recessive allele Polydactyly (extra fingers or toes) is caused by a dominant allele

Question 30

Variation definition

Answer 30

differences in the characteristics of individuals in a population

Question 31

Variation may be due to differences in:

Answer 31

The genes they have inherited (genetic causes) The conditions in which they have developed (environmental causes) A combination of genes and the environment

Question 32

There is usually extensive genetic variation within a population of a species Variants arise from:

Answer 32

mutations

Question 33

Mutations how much they occur? how they affect phenotype?

Answer 33

occur continuously: most mutations have no effect on the phenotype, some influence phenotype, very few determine phenotype Very rarely a mutation will lead to a new phenotype. If the new phenotype is suited to an environmental change it can lead to a relatively rapid change in the species

Question 34

each nucleotide consists of

Answer 34

one sugar molecule, one phosphate molecule and one 'base'

Question 35

its the order of ------- in a gene that devices the order of ----------- in a protein

Answer 35

bases amino acids

Question 36

each amino acid is coded for by a sequence of

Answer 36

three bases in the gene

Question 37

the amino acids are joined together to make

Answer 37

various proteins

Question 38

There are parts of DNA that don't code for proteins instead these parts:

Answer 38

are non-coding and switch genes on or off so they control whether a gene is expressed or not

Question 39

A gene codes for a : DNA is made up of: mRNA carries the:

Answer 39

specific protein nucleotides code to the ribosomes

Question 40

Proteins are made in To make proteins But....

Answer 40

the cell cytoplasm on tiny structure called ribosomes ribosomes use the code in the DNA DNA is found in the cell nucleus and can't move out of it because it's really big. So the cell needs to get the code from the DNA to the ribosome which is done by mRNA made by copying the code from DNA. The mRNA acts as a messenger carries code between DNA and ribosome.

Question 41

3 different types of proteins

Answer 41

enzymes hormones structural proteins which are physically strong e.g collagen strengthens connective tissue

Question 42

Mendel reached 3 important conclusions

Answer 42

characteristics in plants are determined by 'hereditary units' hereditary units are passed on to offspring unchanged from both parents, one unit from each parent Hereditary units can be dominant or recessive- if an individual has both the dominant and recessive unit for a characteristic- the dominant characteristic will be expressed