Inheritance

Question 1

Inheritance definition

Answer 1

hetransmission of genetic information from generation to generation

Question 2

Gene definition

Answer 2

A length of DNA that codes for a protein

Question 3

Allele definition

Answer 3

An alternative form of a gene (Alleles give all organisms their characteristics)

Question 4

Chromosomes

Answer 4

Chromosomes are made of DNA which contains genetic information in the form of genes. They are located in the nucleus

Question 5

How is the sex of the child decided

Answer 5

• Females have the sex chromosomes XX
• Males have the sex chromosomes XY

This means that when eggs (the female gamete) are formed, the only sex chromosome they can have is X, so all eggs have the X chromosome. When sperm are formed, however, they have a 50/50 chance of getting either the X chromosome or the Y chromosome.
Therefore, the male decides the sex of the child as only the male can pass on the Y chromosome

Question 6

What does the sequences of bases in a gene decide?

Answer 6

The sequence of bases in a gene determines the sequence of amino acids used to make a specific protein

• Different proteins are made of different combinations of amino acids. The sequence of amino acids in the chain determines how the chain will fold up to make the protein, so different proteins have different three-dimensional shapes. The three-dimensional shape of a protein determines its function.

Question 7

How does DNA control cell function?

Answer 7

DNA controls cell function by controlling the production of proteins, including enzymes, membrane carriers and receptors for neurotransmitters

• Proteins are involved in nearly every aspect of cell activity and any change in the DNA sequence (a mutation) can alter the structure and function of the resulting protein.

Question 8

Stages of protein synthesis

Answer 8

• Transcription(rewriting the base code of DNA into bases of RNA)
• Translation(using RNA base sequence to build amino acids into a sequence in a protein)

the gene coding for the protein remains in
the nucleus
* messenger RNA (mRNA) is a copy of a gene
* mRNA molecules are made in the nucleus
and move to the cytoplasm
* the mRNA passes through ribosomes
* the ribosome assembles amino acids into
protein molecules
* the specific sequence of amino acids is
determined by the sequence of bases in the
mRNA

Question 9

How are genes expressed?

Answer 9

Most body cells in an organism contain the same set of genes within their DNA, but not all of these genes are actively expressed in every cell. Expression**of a gene means whether that gene is transcribed and translated in a particular cell or not. In each type of cell, only a specific subset of genes is expressed, which means only certain proteins are produced. This selective expression of genes allows cells to perform their specialized functions and conserves energy and other resources.

• For example, muscle cells express genes that produce proteins involved in contraction, while nerve cells express genes for proteins that transmit nerve signals.

Question 10

What is a haploid nucleus?

Answer 10

A nucleus containing a single set of chromosomes (In humans: 23, only gametes)

Question 11

What is a diploid nucleus?

Answer 11

A nucleus containing two sets of chromosomes (In humans: 46, every other cell in body except gametes)

Question 12

What is in a diploid and haploid nucleus?

Answer 12

In a diploid cell, there is a pair of each type of chromosome and in a human diploid cell there are 23 pairs

Question 13

Mitosis definition

Answer 13

nuclear division giving rise to genetically identical cells

Question 14

Roles of mitosis

Answer 14

Since mitosis gives rise to genetically identical daughter cells, mitosis is useful when we need more of the same type of cells

Mitosis is used in:

• Growth
  
  • In growth, body cells divide to form more of the same type of body cells
• Repair of damaged tissues
• Replacement of cells
• Asexual reproduction
  
  • Asexual reproduction relies on mitosis too, because this type of reproduction does not rely on the fusion of gamete nuclei, so mitosis ensures that chromosome number is maintained.

Question 15

Process of mitosis

Answer 15

1. Just before mitosis, each chromosome in the nucleus copies itself exactly (forms x - shaped chromosomes)
2. Chromosomes line up along the centre of the cell where the copies of chromosomes separate, maintaining the chromosome number in each daughter cell

Question 16

Stem cell definition

Answer 16

Unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions

Question 17

Meiosis definition

Answer 17

A reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells (Meiosis is involved in the production of gametes)

Question 18

How does genetic variation occur in meiosis?

Answer 18

This means that when meiosis occurs, and the chromosomes are split between the daughter cells, some daughter cells will get one of the alleles and the other daughter cells will get the other allele. Therefore, the daughter cells are not genetically identical and there is genetic variation.

Question 19

Process of meiosis

Answer 19

The number of chromosomes must behalvedwhen thegametes(sex cells) are formed. Otherwise there would be double the number of chromosomes after they join at fertilisation in the zygote (fertilized egg)

1. Each chromosome makes identical copies of itself (forming X-shaped chromosomes)
2. First division: chromosomes pair up along the centre of the cell, recombination occurs and then cell fibres will pull the pairs apart, each new cell will have one of each recombinant chromosome pair
3. Second division: chromosomes will line up along the centre of the cell, cell fibres will pull them apart (as with mitosis)
4. A total of four haploid daughter cells will be produced

Question 20

Differences between mitosis and meiosis

Answer 20

• Mitosis two daughter cells are produced and in meiosis four daughter cells are produced
• In mitosis daughter cells are diploid and is meiosis daughter cells are haploid
• In mitosis daughter cells are genetically identical and in meiosis the daughter cells are genetically different
• In mitosis only one cell division occurs while in meiosis two cell divisions occur

Question 21

Inheritance definition

Answer 21

the transmission of genetic information from generation to generation

Question 22

Genotype definition

Answer 22

the genetic make-up of an organism and in terms of the alleles present

Question 23

Phenotype definition

Answer 23

the observable features of an organism

Question 24

Homozygous definition

Answer 24

having two identical alleles of a particular gene
- two identical homozygous individuals that breed together will be pure-breeding

Question 25

Heterozygous definition

Answer 25

having two different alleles of a particular gene - a heterozygous individual will not be pure-breeding

Question 26

Dominant allele definition

Answer 26

an allele that is expressed if it is present in the genotype

Question 27

Recessive allele definition

Answer 27

an allele that is only expressed when there is no dominant allele of the gene present in the genotype

Question 28

Codominance definition

Answer 28

a situation in which both alleles in heterozygous organisms contribute to the phenotype

Question 29

Sex linked characteristic definition

Answer 29

a feature in which the gene responsible is located on a sex chromosome and that this makes the characteristic more common in one sex than in the other

Question 30

What are pedigree diagrams?

Answer 30

Pedigree diagrams trace the inheritance pattern of a specific characteristic (usually a disease) through generations of a family using symbols - They can be used to predict the probability of someone in the family inheriting a particular trait or genetic disorder

Question 31

What are the symbols of pedigree diagrams?

Answer 31

Square is male Circle is female Shaded means has trait Not shaded means doesn’t have trait Half shaded means carrier of trait Horizontal line means marriage Vertical line connects parents to children 🌟 Children are listed from left to right from oldest to youngest

Question 32

What is monohybrid inheritance?

Answer 32

Monohybrid inheritance is the inheritance of characteristics controlled by a single gene

Question 33

What is a punnett square diagram?

Answer 33

A Punnett square diagram shows the possible combinations of alleles that could be produced in the offspring, from this the ratio of these combinations can be worked out

Question 34

How are the dominant and recessive alleles shown in punnett square?

Answer 34

The dominant allele is shown using a capital letter and the recessive allele is shown using the same letter but lower case

Question 35

How to construct punnett squares?

Answer 35

- Determine the parental genotypes - Select a letter that has a clearly different lower case, for example: Aa, Bb, Dd - Split the alleles for each parent and add them to the Punnett square around the outside - Fill in the middle four squares of the Punnett square to work out the possible genetic combinations in the offspring - You may be asked to comment on the ratio of different allele combinations in the offspring, calculate a percentage chance of offspring showing a specific characteristic or just determine the phenotypes of the offspring - Completing a Punnett square allows you to predict the probability of different outcomes from monohybrid crosses

Question 36

What is test cross and what does it involve?

Answer 36

Breeders can use a test cross to find out the genotype of an organism showing the dominant phenotype - This involves crossing the unknown individual with an individual showing the recessive phenotype - By looking at the ratio of phenotypes in the offspring, we can tell whether the unknown individual is homozygous dominant or heterozygous

Question 37

Inheritance of blood groups rules

Answer 37

There are three alleles of the gene governing this instead of the usual two - Alleles IA and IB are codominant, but both are dominant to IO - I represents the gene and the superscript A, B and O represent the alleles

Question 38

Why are males more likely to have sex linked characteristics?

Answer 38

In almost all cases, there are only alleles on the X chromosome as the Y chromosome is much smaller - Because males only have one X chromosome, they are much more likely to show sex-linked recessive conditions like colourblindness and haemophilia - Females, having two copies of the X chromosome, are likely to inherit one dominant allele that masks the effect of the recessive allele - A female with one recessive allele masked in this way is known as a carrier; she doesn’t have the disease, but she has a 50% chance of passing it on to her offspring