Inheritance 3.26 - 3.39

Question 1

What is sex determined by?

Answer 1

By an entire chromosome pair (as opposed to most other characteristics that are just determined by one or a number of genes).

Question 2

What are the female sex chromosomes?

Answer 2

XX

Question 3

What are the male sex chromosomes?

Answer 3

XY

Question 4

What is the definition of mitosis?

Answer 4

Nuclear division giving rise to genetically identical cells.

Question 5

What is mitosis used for?

Answer 5

growth, repair of damaged tissues, replacement of cells and asexual reproduction.

Question 6

How many copies of each chromosome do most body cells have?

Answer 6

Most body cells have two copies.

Question 7

What are these cells with two copies of each chromosome called?

Answer 7

Diploid. When cells divide their chromosomes double beforehand. This ensures that when the cell splits in two, each new cell still has two copies of each chromosome.

Question 8

What is the importance of mitosis?

Answer 8

All cells in the body (excluding gametes) are produced by mitosis of the zygote.
Mitosis is important for replacing cells e.g, skin cells, red blood cells and for allowing growth (production of new cells e.g. when a zygote divides to form an embryo).

Question 9

Where does mitosis occur?

Answer 9

In growth - mitosis produces new cells.
In repair - to replace damaged or dead cells.
In asexual reproduction - mitosis produces offspring that are genetically identical to the parent.

Question 10

What is the definition of meiosis?

Answer 10

The process in eukaryotic, sexually-reproducing animals where a cell replicates DNA once but divides twice, producing four cells that have half the genetic information of the original cell. It is the cell division that reduces the chromosome number by half leading to the formation of four non-identical daughter cells.

Question 11

What is meiosis used for?

Answer 11

it produces the gametes (sex cells).

Question 12

Describe the process of meiosis?

Answer 12

Meiosis is a type of nuclear division that gives rise to cells that are genetically different
It is used to produce the gametes (sex cells)
The number of chromosomes must be halved when the gametes (sex cells) are formed
Otherwise there would be double the number of chromosomes after they join at fertilisation in the zygote (fertilized egg)
This halving occurs during meiosis, and so it is described as a reduction division in which the chromosome number is halved from diploid to haploid, resulting in genetically different cells
It starts with chromosomes doubling themselves as in mitosis and lining up in the centre of the cell
After this has happened the cells divide twice so that only one copy of each chromosome passes to each gamete
We describe gametes as being haploid - having half the normal number of chromosomes
Because of this double division, meiosis produces four haploid cells.

Question 13

What is the importance of meiosis?

Answer 13

Production of gametes e.g. sperm cells and egg cells, pollen grains and ovum
Increases genetic variation of offspring
Meiosis produces variation by forming new combinations of maternal and paternal chromosomes every time a gamete is made, meaning that when gametes fuse randomly at fertilisation, each offspring will be different from any others.

Question 14

Phenotypic variation can be caused in which two main ways?

Answer 14

It can be genetic - controlled entirely by genes.
Or it can be environmental - caused entirely by the environment in which the organism lives.

Question 15

What is genetic variation?

Answer 15

Meiosis creates genetic variation between the gametes produced by an individual.
This means each gamete carries substantially different alleles.
During fertilization, any male gamete can fuse with any female gamete to form a zygote.
This random fusion of gametes at fertilization creates genetic variation between zygotes as each will have a unique combination of alleles.
Zygotes eventually grow and develop into adults.

Question 16

What are examples of genetic variation in humans?

Answer 16

Blood group
Eye colour
Gender
Ability to roll tongue
Whether ear lobes are free or fixed

Question 17

What is environmental variation?

Answer 17

Characteristics of all species can be affected by environmental factors such as climate, diet, accidents, culture and lifestyle.
In this instance ‘environmental’ simply means ‘outside of the organism’ and so can include factors like climate, diet, culture, lifestyle and accidents during lifetime.

Question 18

What are examples of environmental variation?

Answer 18

An accident may lead to scarring on the body.
Eating too much and not leading an active lifestyle will cause weight gain.
Being raised in a certain country will cause you to speak a certain language with a certain accent.
A plant in the shade of a big tree will grow taller to reach more light.

Question 19

What is a diploid cell?

Answer 19

A diploid cell is a cell that contains two complete sets of chromosomes (2n).
These chromosomes contain the DNA necessary for protein synthesis and cell function.
Nearly all cells in the human body are diploid with 23 pairs (46) of chromosomes in their nucleus.

Question 20

What is a haploid cell?

Answer 20

Haploid cells contain one complete set of chromosomes (n).
In other words they have half the number of chromosomes compared to diploid cells.
Humans have haploid cells that contain 23 chromosomes in their nucleus.
These haploid cells are called gametes and they are involved in sexual reproduction.
For humans they are the female egg and the male sperm.

Question 21

What is the definition of variation?

Answer 21

Differences between individuals of the same species.

Question 22

What are mutations?

Answer 22

Mutations are rare, random changes that occur in the sequence of DNA bases in a gene or a chromosome. They occur continuously.

Question 23

What was Charles Darwin’s theory?

Answer 23

The theory of evolution by natural selection.

Question 24

What is the definition of evolution?

Answer 24

The change in the frequency of a phenotype in a population over many generations.

Question 25

What is in Darwin’s theory?

Answer 25

Individuals in a species show a wide range of variation caused by differences in genes.
Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce.
Therefore these characteristics are passed to their offspring at a higher rate than those with characteristics less suited to survival.
Over many generations, these beneficial characteristics become more common in the population and the species changes (the species evolves).
This idea of natural selection became known as ‘survival of the fittest’.
Darwin published his ideas in his famous book, On the Origin of Species (1859).

Question 26

What are antibiotics?

Answer 26

Chemical substances made by certain fungi or bacteria that affect the working of bacterial cells, either by disrupting their structure or function or by preventing them from reproducing.

Question 27

What are antibiotics effective against?

Answer 27

Antibiotics are effective against bacteria but not against viruses.

Question 28

What is the cause of antibiotics having been overused?

Answer 28

Antibiotic resistance has developed in many different types of bacterial species.

Question 29

Describe the process of a bacteria becoming antibiotic resistant.

Answer 29

Bacteria, like all organisms, have random mutations in their DNA.
One of these mutations may give them resistance to an antibiotic.
If an organism is infected with bacteria and some of them have resistance, they are likely to survive treatment with antibiotics.
The population of the resistant bacteria will increase.
If the resistant strain is causing a serious infection then another antibiotic will be needed.

Question 30

Why do antibiotics not affect viruses?

Answer 30

Because antibiotics work by disrupting cell functions such as respiration, or breaking down the structure of the cell in some way.
However, viruses do not carry out any cell functions and do not have cell walls, cell membranes or any cell organelles as viruses infect and utilise the machinery of animal cells to reproduce, which are not affected by antibiotics.