3 b) inheritance

Question 1

3.9 understand that the nucleus of a cell contains chromosomes on which genes are located

Answer 1

In the nucleus of a cell there are chromosomes; these are long sections of tangled DNA, sections of which are different genes.

Question 2

3.10 understand that a gene is a section of a molecule of DNA and that a gene codes for a specific protein

Answer 2

Different genes code different proteins. Genes are sections of your DNA.

Question 3

3.11 describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G)

Answer 3

DNA resembles a ladder (that has been twisted,) on either side of each rung will be a base- they are a base pair: either adenine (A) with thymine (T) or cytosine (C) with guanine (G).

Question 4

3.12 understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics

Answer 4

Genes (sections of DNA coding for different proteins) come in a variety of forms: for example the gene that codes for hair can come in many different colours. These different forms are different alleles, having these differences is where you vary in inherited characteristics (If there was only one allele for hair we would all have exactly the same hair.)

Question 5

3.14 describe patterns of monohybrid inheritance using a genetic diagram

Answer 5

Monohybrid inheritance is the inheritance of one gene.
A genetic diagram consists of the parents gamets (according to their genotype) and their possible offspring:
(B and b represent an allele for a gene)
http://scienceaid.co.uk/biology/genetics/images/mono.png

Question 6

3.15 understand how to interpret family pedigrees

Answer 6

A pedigree diagram shows a specific gene in a family. It will have a key but most often: a circle represents a female and a square represents a male; often coloured in represents one allele and blank another (but sometimes they are different colours.)

In this diagram, the mother and two sons have a different genes to the others:

http://www.sads.org/SADS/media/images/figure_2.jpg

Question 7

3.16 predict probabilities of outcomes from monohybrid crosses

Answer 7

From mono-hybrid cross diagrams there are four outcomes, some times some of the out comes are the same.
To work out the probability of a child inheriting a genotype, you see how many times it comes up and divide it by 4 then times by 100 for a percent.
To work out phenotype probability you work out how many times they will express a characteristic and divide it by four then times by 100 for a percent.

If we say in this diagram the B represents brown hair and b represents red hair
(The capital letter is always dominant)

http://scienceaid.co.uk/biology/genetics/images/mono.png

The likely hood of the chlid carrying one allele for brown and one for red (Bb) is two out of four:
2/4= 0.5
x100= 50%
The likely hood of the child having red hair (red hair is recessive so they both have to be red (bb)) is two out of four: also 50%

Question 8

3.17 understand that the sex of a person is controlled by one pair of chromosomes, XX in a female and XY in a male

Answer 8

One pair of chromosomes (out of 23 pairs) controls the gender of a person. XX is female; XY is male.

Question 9

3.18 describe the determination of the sex of offspring at fertilisation, using a genetic diagram

Answer 9

Genetic diagrams work the same as mono-hybrid inheritance diagrams: showing the mothers and fathers and then the different out comes. The only difference is, they will always be the same because one parent is always male and one parent is always female:

http://www.bbc.co.uk/schools/gcsebitesize/science/images/ocr_bio_gender.jpg

Question 10

3.19 understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes

Answer 10

Mitosis is when a cell replicates it self to make an identical copy.
A diploid cell is one with 23 pairs of chromosomes.
(you don’t need to know the stage names, but its useful to know how mitosis happens.)

Question 11

3.20 understand that mitosis occurs during growth, repair, cloning and asexual reproduction

Answer 11

Mitosis cell division is the type that occurs in growth, repair cloning and asexual reproduction.

Question 12

3.21 understand that division of a cell by meiosis produces four cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes

Answer 12

Meiosis is when a cell splits in half, creating two copies, and then splits in half again to create four cells each with half the genetic information of a normal cell (haploid 23 chromosomes.)
This is how gametes are made.

Question 13

3.22 understand that random fertilisation produces genetic variation of offspring

Answer 13

Because gametes contain a random selection of genetic information from each parent, the fertilised egg will be a mix of different genotypes which is why offspring are genetically different to their parents.

Question 14

3.23 know that in human cells the diploid number of chromosomes is 46 and the haploid number is 23

Answer 14

The diploid number is how many chromosomes each cell is meant to have: 46 in humans (23 pairs).
The haploid number is half of the diploid number: so 23.

Question 15

3.24 understand that variation within a species can be genetic, environmental, or a combination of both

Answer 15

Variation in a species is the differences between the members of a species.
Genetic is caused by what genes are inhereted.
Environmental is caused by some action after birth (e.g the sun giving you a tan.)
Some variation is a bit of both…

Question 16

3.25 understand that mutation is a rare, random change in genetic material that can be inherited

Answer 16

A mutation is when a gene is copied incorrectly, this gene can be passed down. It doesn’t happen very often or on purpose.

Question 17

3.26 describe the process of evolution by means of natural selection

Answer 17

Evolution is a change in species over a very long time (sometimes into different species.)
Natural selection is survival of the fittest.
What happens is:

• A mutation occurs
• If the mutation is beneficial, the animal will survive longer and reproduce more
• Some of its offspring will inherit the mutation
• These offspring will also have better chance of survival, meaning they live longer and reproduce more
• Over a long period of time this process is repeated and gradually the mutation becomes a common gene in a species and those with the mutation become the only ones, as those without cannot compete with those expressing the mutated gene

Question 18

3.27 understand that many mutations are harmful but some are neutral and a few are beneficial

Answer 18

A lot of mutations are harmful, like genetic diseases; cystic fibrosis.
Some don’t change the chances of survival: like having a different colour hair.
There are a few mutations which are beneficial, for example a insect pollinated plant becoming brighter.

Question 19

3.28 understand that resistance to antibiotics can increase in bacterial populations, and appreciate how such an increase can lead to infections being difficult to control.

Answer 19

Bacteria experience mutations (the reproduce very frequently so it is not rare.) These mutations can mean that they are no longer affected by a certain antibiotic, this makes it easier for them to survive. If bacteria evolve to be resistant to drugs we are treating them with then they are difficult to control; sometimes they can be stopped using a different antibiotic, but some are becoming resistant to all the drugs that we know of…